Communicating Supraparticles to Enable Perceptual, Information‐Providing Matter

Materials are the fundament of the physical world, whereas information and its exchange are the centerpieces of the digital world. Their fruitful synergy offers countless opportunities for realizing desired digital transformation processes in the physical world of materials. Yet, to date, a perfect connection between these worlds is missing. From the perspective, this can be achieved by overcoming the paradigm of considering materials as passive objects and turning them into perceptual, information‐providing matter. This matter is capable of communicating associated digitally stored information, for example, its origin, fate, and material type as well as its intactness on demand. Herein, the concept of realizing perceptual, information‐providing matter by integrating customizable (sub‐)micrometer‐sized communicating supraparticles (CSPs) is presented. They are assembled from individual nanoparticulate and/or (macro)molecular building blocks with spectrally differentiable signals that are either robust or stimuli‐susceptible. Their combination yields functional signal characteristics that provide an identification signature and one or multiple stimuli‐recorder features. This enables CSPs to communicate associated digital information on the tagged material and its encountered stimuli histories upon signal readout anywhere across its life cycle. Ultimately, CSPs link the materials and digital worlds with numerous use cases thereof, in particular fostering the transition into an age of sustainability.


Introduction
The possibility of transmitting information digitally in milliseconds around the globe, the ever-increasing data storage DOI: 10.1002/adma.202306728capacity, and powerful computation methods lead to the digitization of many processes in our daily life with a fundamental impact on our society, culture, and economy.Nowadays, digitization is also envisioned to become a key enabler for guiding our use of (natural) resources into a more sustainable future.Many innovative concepts that aim to combat current challenges in the physical world of materials are envisaged to be realized with digital assistance, for instance: i. fighting resource scarcity and environmental pollution by closing material loops in a circular economy via highly autonomous sorting and recycling processes; [1,2,[3][4][5] ii.reducing technical breakdowns of products by making predictive maintenance for components down to the micrometer scale possible and preventing the disposal of entire devices by implementing assisted repair measures with subcomponent resolution; [6,7] iii.reducing overproduction, energy consumption, and waste in product manufacturing via autonomous production facilities based on the Internet of Things (IoT); [8,9,10] iv.combating counterfeiting and reducing damage during manufacturing and shipment of (semifinished) products by implementing responsive material passports that trace their entire trade routes and indicate harmful conditions across their life cycle. [11,12,13]e realization of these visionary concepts requires direct, automatable, on-demand detection of information on the type, origin, fate, and intactness of materials at any scale, anywhere, and anytime.Despite the tremendous progress in manufacturing materials with specific target properties and advanced characterization methods, [14] the intrinsic physicochemical properties of materials lack distinct information-providing features for the aboveoutlined demand, to date.
The rapid progress in storing, computing, and exchanging information digitally gave rise to an alternative route for achieving materials with the desired capability.This route is based on equipping materials with aids that act as synergistic connectors between physical materials and digitally stored information.Upon interrogation by a corresponding readout device, these aids provide associated information on their hosting material from digital databases.Barcodes, quick response (QR) codes, and radio-frequency identifiers (RFIDs) present ubiquitous examples of such aids.The readout and subsequent verification of their physical identification (ID) code unlocks access to digital databases and enables previously acquired information on the tagged object to be obtained on demand anywhere and anytime.
If such aids can be sufficiently small to be integrated into materials at any scale and provide materials with information on their type, origin, fate, and intactness, they would shift the paradigm of considering materials as passive objects toward esteeming them as perceptual, information-providing matter and foster the realization of the aforementioned concepts (i-iv).
Classical barcodes, QR codes, and RFIDs can provide information on the type, origin, and fate of a tagged object via the interrogation of their ID signal and an associated digital database.They are however prone to counterfeiting, difficult to miniaturize while maintaining easily detectable, and cannot offer information on the intactness of their host. [15,16,17]o overcome these limitations, miniaturized ID codes that enable even tiny objects to be distinguished, [15,[18][19][20][21][22][23][24][25][26][27][28][29][30][31] ID codes with physical unclonable functions (PUFs) that aim to erase the concerns of counterfeiting, [32,33,34,35] responsive ID codes, [36][37][38][39][40][41] and wireless identification and sensing platforms (WISPs) [42] were introduced.Responsive ID codes and WISPs augment the ID signal of QR codes and RFIDs with real-time information from their physical environment, respectively.Responsive QR codes exploit the environmentally sensitive optical signal of their graphical encoding elements, i.e., the ink, to report not only an ID signature but also for example the current temperature [38] or the presence of specific gases. [37]Similarly, WISPs enrich the ID code of RFIDs with information on temperature, [43] humidity, [44] mechanical stress, [45] or other stimuli [46] via circuit-connected, (micro-)electrical capacitive or resistive sensors.
The harvested real-time information on the physical surrounding of tagged objects is relevant for many scenarios, but it provides limited information on the intactness of a material.The intactness of materials is rather determined by threshold-exceeding events of harmful stimuli exposure across their elapsed history, for instance, temporary mechanical or thermal impact.Registering these events via reversible, real-time sensors of responsive QR codes, or WISPs would require either permanent signal readout and subsequent digital data storage or internal data storage on a memory device.WISPs with active RFIDs can provide either permanent information exchange with high data rates and long readout ranges (>10 m) [47] or store sensor information on an integrated memory chip for a readout on demand. [48]However, these types of WISPs require a constant power supply from an integrated battery or ambient power scavengers, for instance, a solar cell. [47,49]This requirement causes higher costs, larger size, increased weight, and a limited lifetime, which impedes their integration options into objects and their mass deployment. [42,49,50]s in the aforementioned visionary concepts (i-iv) neither permanent signal readout nor constant power supply can be guaranteed, their realization demands alternative approaches.
Herein, we thus puts the spotlight on another promising approach to enable perceptual, information-providing matter via the integration of small-scaled aids, so-called communicating supraparticles (CSPs).This recently introduced approach [6] has by far not reached its true potential yet and seeks interdisciplinary collaborations to achieve the required advances in many research fields to be developed.
CSPs are built up from different types of nanoparticles (NPs) and optionally functional molecules with adequately discriminative spectral signals.To achieve advanced properties, these building blocks are assembled in defined ratios via toolbox-like manufacturing processes into (sub-)micrometer-sized particulate entities with a more complex structure. [51]The cooperative interplay of the individual signals from their different building blocks equips CSPs with specifically designed physical signal characteristics that contain two essential features: an infinitely variable and environmentally robust ID signature, and one or multiple tunable, stimulus-selective recorder feature(s) (Figure 1a1).Deciphering the signal of CSPs thus not only enables a tagged material to be actively linked with countless digitally stored information via an ID signature but provides additional information about its intactness via recorder feature(s) for harmful impact of environmental stimuli.CSPs thus enhance the information capacity of miniaturized ID tags [11,21,25,29,30,52] and stimuli recorders [53][54][55] by joining their functionalities in one entity.
With respect to nomenclature, we propose to categorize information-providing particles as either: a) particles with signal characteristics that enable their differentiation and identification upon signal readout, i.e., ID particles or ID tags, or b) particles with (ir)reversibly responsive signal characteristics that upon signal readout, enable to monitor changes in their surrounding in real-time, i.e., sensor particles, or trace elapsed thresholdexceeding stimuli impact, i.e., recorder particles.
Communicating (supra)particles (CSPs) are the next level, i.e., a combination of (a) and (b), and carry signal characteristics that convey both an ID signature and one or multiple recorder functionalities upon signal readout.
The purely materials-based approach of CSPs aims to eliminate the need for a circuit connection on a solid dielectric substrate and a constant power supply of WISPs with active RFIDs.CSPs are self-consistent, particulate entities with sufficiently small dimensions and tunable surface properties that come in the form of powder and operate autonomously without a constant power supply.They can thus be processed as an additive.This allows their flexible integration via customized integration procedures into materials at any point in their entire life cycle-from raw materials to intermediates and final product. [29]Thereby, CSPs become an integral part of the hosting material, which hampers the removal of the information provider and thus a loss of the desired information, for instance, when cutting the QR code or RFID label from an object.
In sum, CSPs present a platform system to customize miniaturized information providers and their respective readout methods for tagging diverse materials with different target applications.CSPs are therefore considered as the enabling technology to turn passive materials into perceptual, information-providing matter via the integration of (sub-)micrometer-sized particles (Figure 1a2).functional signal characteristics that comprise an ID signature and recorder features for environmental stimuli impact.Detecting these signal features grants access to associated, digitally stored information.Integrating CSPs into "passive" materials turns them into perceptual, information-providing matter.b) Customized CSPs can be integrated into materials at desired locations in their life cycle followed by a readout for initial calibration (b1).The CSP signal is thereby digitized, which enables associating digital information to the hosting material.Subsequently, identification and status acquisition of the material are possible via interrogating the CSP anywhere in the life cycle of the tagged material (b2).Associated digital information is transmitted back to the physical world.An exposure to threshold-exceeding environmental stimuli causes irreversible signal changes in the recorder features upon readout, leading to appropriate action in the physical world of materials.
After the incorporation of CSPs into a target material, an initial calibration is performed by detecting their signal characteristics (Figure 1b1).The ID signature and the pristine state of the recorder(s) are thereby digitized to create a kind of digital twin of the tagged physical material. [56]The ID signal is henceforth associated with this physical material and enables linking unlimited digital information to it, for instance, the material type, origin, and fate.In addition, the recorder feature(s) are activated by registering their pristine state and matching them with the individual limitations of the tagged material.Subsequently, anywhere across the life cycle of the tagged material, upon interrogation of the CSP, the environmentally robust, unchanged ID signature identifies the physical material and enables conveying the digitally linked information back to a connected device in the physical world, for example, the readout device (Figure 1b2).Simultaneously, the signal of the associated recorder features is evaluated in comparison to their pristine state using dig-itally stored calibration.These recorders memorize elapsed harmful or desired exposures to target stimuli across the entire history of the tagged material via irreversible spectral changes (Figure 1b3).The obtained signal information of the recorders enables appropriate actions in the physical world to be taken, for example, inducing repair measures.The irreversible changes of recorder features can be designed in two ways: they can either quantitatively record the maximum impact of an experienced target stimulus or the integrated exposure to a target stimulus as a function of time.To give practical examples, spoilage of food products, such as dairy products, fish, or meat correlates not only with the temperature but also the duration of storage. [57]herefore, monitoring the intactness of these products requires time-temperature integrating (TTI) recorders integrated into food packaging that change their signal with the temporal accumulation of experienced temperature events. [53,58,59]In contrast thereto, the verification of processes that require a specific threshold temperature such as sterilization or (de)bonding demands maximum-temperature recorders.Their signal change correlates with the highest experienced temperature. [6,54,60,61]ereafter, we describes the emerging, modular concept of CSPs that are envisioned to enable perceptual, information providing matter to be realized.We exploit the initially outlined visionary, yet highly relevant use cases for CSPs (i-iv) to derive requirements for the four essential steps of the CSP concept.Starting from the requirements for the individual steps of the CSP concept, we describe how the toolbox-like manufacturing process of CSPs is envisioned to overcome many of the challenges arising from the outlined use cases.Finally, we discuss current hurdles for the implementation of CSPs and provide an outlook on their potential contribution to the transition of the world of physical materials into an age of sustainability by fostering the realization of innovative concepts.

Realization of Sustainable Concepts with Perceptual, Information-Providing Matter Enabled by Integrated Communicating Supraparticles (CSPs)
We envision that CSPs become one of the key enabling technologies for realizing innovative concepts that require a synergistic connection between physical materials and digital information and aim to guide our use of (natural) resources into a more sustainable future.
In a circular economy, materials, for instance, polymers or battery materials, will be collected, fragmented, sorted, recycled, and reused to close material loops (i).For efficient recycling processes and high-quality recyclates, not only a high purity of materials but also a verification of the intactness of their properties are demanded.Perceptual, information-providing matter enabled by homogeneously integrating CSPs into the polymer melt of thermoplastics could fulfill this demand.]62] Simultaneously, the recorder functionality of CSPs will report elapsed, threshold-exceeding stimuli exposure, e.g., thermal degradation of polymer chains, and thus allow the material-specific evaluation of the intactness of the material properties.This evaluation can either approve the direct recycling and reuse of the material or indicate the need for additional processing before it can be reused as feedstock.
For electronic products, the integration of CSPs in subcomponents, for example, the housing of capacitors, could make predictive maintenance and assisted repair measures with subcomponent resolution possible (ii).Frequent, automated status acquisition processes could trace malfunctioning subcomponents, for example, caused by elapsed thermal hotspots.The ID signature of CSPs would allow the subcomponent to be identified and the altered signal of the temperature recorder to be associated with the intrinsic limitations of their host.The experienced thermal hotspot could thus be precisely evaluated with the respective calibration to indicate potential malfunctions of single subcomponents.
Complementary to WISPs, particularly for small objects, CSPs could also foster the transformation of (semifinished) products into cyber-physical systems [63] and thereby, contribute to the realization of the next anticipated industrial revolution, the so-called Industry 4.0 (iii). [8,9]This revolution is based on products that control their own manufacturing by communicating information among each other via the Internet of Things (IoT), triggering actions, and monitoring changes.Integrated CSPs could provide information on individual processing steps by associating them digitally to the tagged object via automated detection of their ID signature.The recorder features could verify successful processes, for example, mechanical processing, or report any occurred damage due to threshold-exceeding impact and thus, enable the intactness of the object to be evaluated before the next process step.
Even before materials or (semifinished) products enter a factory, the integration of CSPs could allow for creating a material or product passport via their ID signature to track the origin and processing steps of their hosting objects (iv). [13,52]The stimuli recorders would make uncovering, locating, and eliminating harmful conditions, for example, extreme humidity or temperatures, during the manufacturing, shipment, and use of products, possible.
To sum these use cases up, it seems almost impossible to find one information-providing particle type for all imaginable scenarios with their highly specific requirements.Hence, the modular concept of CSPs with versatile options to customize their functional signal characteristics as well as their integration and readout processes is beneficial to meet highly specific requirements for many target applications.

Concept of Communicating Supraparticles (CSPs)
We propose four essential steps for turning passive materials into perceptual, information-providing matter via CSPs (Figure 2): synthesis and selection of suitable signal-carrying building blocks (a); assembly of these building blocks to CSPs (b) yielding a flexibly applicable powder additive; integration of CSPs into target materials (c); and information acquisition via CSP signal readout and processing (d).
In industrial scenarios, however, these subsequently conducted steps affect each other.To give one illustrative example, it is a challenge to integrate CSPs into the existing material processing steps (c) while ensuring meaningful signal readout of integrated CSPs (d), despite potentially interfering physicochemical material properties, such as their color.Additionally, these challenges will also affect the selection of signal-carrying building blocks (a) and their assembly to CSPs (b) and thus limit design freedom.Therefore, every step must be carefully evaluated not only for the final endeavor but also regarding the execution and limitations of its effects for the other three steps.
In the following, we define a catalog of requirements for each of the four essential steps of CSPs by exploiting the aboveoutlined use cases (Section 2) and thereby aim to inspire a variety of different scientific communities.We present approaches and design principles on how these requirements can be met based on state-of-the-art technology and describe current challenges, which require further improvement to succeed in creating perceptual, information-providing matter via CSPs.

Signal-Carrying Building Blocks
Signal-carrying building blocks form the foundation for the functional signal characteristic of the envisaged CSPs.Thus, the first and fundamental step of the CSP concept is the synthesis and selection of suitable signal-carrying building blocks.This step benefits from the established library of NPs [64,[65][66][67][68] and (macro-)molecules, for example, functional dyes [69] or polymers, [70] with precisely tunable properties and signal characteristics that can be utilized as a toolbox for the manufacturing of CSPs.The spectral signal features of the selected building blocks define the communication pathway and majorly also the information capacity of CSPs.The communication pathway refers to the type of signal and the corresponding readout method used to convey the information.The information capacity of CSPs describes the variety of distinguishable ID codes as well as the type and number of integrated recorders for environmental stimuli.

Requirements
Ideal signal-carrying building blocks for CSPs are inexpensive, producible from mostly abundant precursors on a large scale, and nontoxic (Figure 3a1).The use of nontoxic signal carriers is important to not only achieve consumer acceptance but also to remove legislative and ecological hurdles for the implementation of CSPs in diverse applications.If toxic building blocks cannot be replaced to achieve a CSP with specific functionality, examples showed that encapsulation of these elements into biocompatible materials can increase their safety and reduce health concerns. [71]he use of edible signal carriers could even expand the application area of CSPs from technical materials to food products, pharmaceuticals, and cosmetics. [34]esides these basic requirements, suitable signal-carrying building blocks enable CSPs to possess a functional signal characteristic with a high encoding capacity, that is, the number of distinguishable ID codes to identify and uniquely differentiate many different objects.The signal of these building blocks should be robust to the impact of environmental stimuli in order to provide an unchanged ID signature across the entire life cycle of the CSPhosting material (Figure 3a2).The resistance of the ID signature to environmental changes is of particular importance, since it is not only required for associating the digitally stored information of the tagged material but also for linking the recorder signals to their digitally stored calibration.Additionally, signal carriers with environmentally sensitive signal features are demanded that equip CSPs with recorders for environmental stimuli impact to ultimately create a signal characteristic that provides information on the intactness of very different materials and objects (Figure 3a3).Therefore, signal carriers with recorder functionalities for many different harmful or desired environmental stimuli events, for example, thermal stress, mechanical impact, humid atmospheres, exposure to chemical gases, and others are desired.Their sensitivity toward target stimuli events must be flexibly adaptable to the specific limitations of the CSP-hosting material, which can be very different.Importantly, the recorder building blocks should possess a negligible susceptibility toward nontargeted environmental stimuli impact.Thereby, undesired irreversible signal changes due to oxidation, photobleaching, thermal degradation, chemical gases, humid atmospheres, etc., are prevented yielding highly selective stimuli-recorders.

Suitable Communication Pathway for CSPs
Every potential use case for CSPs predetermines which material should be analyzed at which state.Thus, typically the communication pathway determines the selection of signal-carrying building blocks and not vice versa.[75] These are hereafter briefly discussed regarding their applicability to CSPs.Signal encoding strategies based on characteristic physical properties of NPs or other nanomaterials, such as size, [76] shape, [77] magnetism, [78] and phase change, [79,80] or particularly the sequence of chemical subunits in macromolecules, for example, monomers in polymers [81] or nucleotides in DNA, [82] have a great potential for the storage and exchange of information.For an interrogation, however, these information providers need to be (destructively) extracted from the tagged material and afterward analyzed with costly, bulky analytics often by trained personnel, which all together hampers their easily conducted detection at any point of care. [29,30,83]Moreover, they hardly provide options to augment the ID signal with distinct stimuli-recorder features making them not ideally suitable as a primary communication pathway for the envisaged CSPs.
[41] However, their integration option into materials is restricted due to the anisotropic signal nature and its accessibility for optical readout, making them unsuitable to become an integral part of the hosting material.Graphical encoding is therefore not considered as a primary but an additional communicating pathway for CSPs when increased information capacity or security is demanded and line-of-sight labelling of the hosting material is possible (detailed discussion provided later).
Optically and magnetically excited signal responses are used as their communicating pathway, respectively.This signal encoding scheme relies on uniting a multitude of different NP or molecular building blocks owing distinct signal features in a defined ratio into one entity.It is thereby essential that the signal features of the selected building blocks are adequately discriminated by their corresponding readout method, typically via a spectrometer. Persistent environmentally robust spectral signals can serve as fingerprint features for ID tagging (Figure 3b1).In contrast, spectral recording of stimuli events that exceed specific thresholds is facilitated by exploiting defined irreversible changes in specific spectral ranges, for instance, via changes in the intensity, spectral position, band shape, bandwidth, or lifetime (Figure 3b2).
From our perspective, spectrally resolved optically or magnetically excited signal responses are the best suitable communication pathways for CSPs.They can be detected contactless from a certain distance. [54,94,96]Their isotropic signal character facilitates detecting the information of an information provider nearly independent of its orientation, which grants the desired flexibility for their incorporation as a powder. [19]In combination with their tunable physicochemical surface properties, [97] this flexibility ultimately allows CSPs to become an integral part of the tagged material.Moreover, spectrally resolved signal responses enhance reliability as they are built from many data points and do not only consist of single values.Multiple different pieces of information stemming from different signal carriers within the same CSP can in principle be harvested by single detection of one spectrum and can be separately analyzed afterward.Furthermore, ratiometric detection of the signal response is possible, that is, the detection of relative intensities in distinct spectral ranges using an internal reference. [74,95,98,99]This method achieves obtaining reliable signal information independent of external factors, such as the CSP concentration or the measurement setup, for instance, the excitation power or the distance between the tagged object and the detector. [74,100]pectral Optical Communication Pathway: Building blocks with a spectral optical communication pathway can be divided based on the nature of their optical signal into luminescencebased and nonluminescent systems. [30]The signal of luminescent building blocks can be decoded in the spectral, time, and frequency domains based on their emission color, [88] lifetime, [101] and phase angle, [102] respectively.Luminescent species thus offer even more options for implementing ID and recorder features than other optical building blocks. [74,102,103]Nonluminescent building blocks with a spectral optical communication pathway rely on either distinguishable infrared (IR) signals [104] or Raman signals. [105,106]Photonic balls, [107][108][109][110][111] i.e., nanoarchitectures with spectrally discriminable optical reflectivity, so-called structural colors, represent yet another option for spectral optical signal encoding.Their optical signal is not prone to any molecular degradation processes, e.g., photobleaching, which is attractive for many applications.
Spectral Magnetic Communication Pathway: A thereto very different and rather new spectrally encoded communication pathway for miniaturized information providers is the detection of magnetically excited signal responses of magnetic particles via magnetic particle spectroscopy (MPS). [112]MPS spectra describe the nonlinear magnetic behavior of analyzed samples in the form of harmonic amplitudes as a function of higher harmonics.A vast variety of superparamagnetic NPs [113] as well as factors that alter their MPS response have been reported.Different material compositions, [94,95] sizes, surface properties, [114] and agglomeration states, [94,95,115] and combinations thereof [116] significantly alter their magnetic response, which opens up the possibility to synthetically design NPs with optimized properties for ID and recorder features when aiming for CSPs.

Current Challenges and Potential Future Directions
The established toolbox of signal-carrying NPs with different spectral optical properties is broad, yet some general selection criteria reduce the number of relevant building blocks for CSPs and present challenges that should be overcome by further research in this field.
For the envisaged mass deployment of CSPs, advances in the reproducible, large-scale, and economically feasible fabrication of NPs and functional molecules are desired.
A promising approach is, for example, robotic synthesis [117] which can be combined with automated materials characterization and machine-learning optimization. [65,118]Other interesting approaches are the development of microfluidic technologies for continuous flow synthesis of nanomaterials with in-flow quality control [119] or scalable (semi-)continuous synthesis approaches of NPs. [120]However, these approaches are still in their infancy and require further optimization to achieve commercial viability.
The key to achieving a spectral CSP signal characteristic with a large information capacity, that is, a high encoding capacity or a large number of different recorder features, is a maximumachievable number of spectrally distinguishable signal carriers with the same communication pathway.Thus, for all optical signal carriers, narrow spectral line widths (full width at half maximum, FWHM) [121] and for magnetic building blocks, a characteristic MPS fingerprint region (i.e., characteristic intensities at different harmonic ranges) are of paramount importance.These yield a reduced spectral signal overlap, improved discrimination of signals stemming from different building blocks, and thereby enhanced signal quantity and transmittable information capacity. [18]Furthermore, a broad excitation range is desired, which enables the simultaneous excitation of all signal carriers within one CSP ideally with one excitation source, for example, light with a single wavelength [6,89] or one electromagnetic frequency. [94,95,114]This makes ratiometric signal detection possible and eases the complexity as well as the costs of the readout process. [122]oncerning the aforementioned selection criteria of CSPs, luminescent QDs, [18,88,123] CDs, [124] lanthanide-doped NPs, [89,93,125] or UCNPs [25,100,126] outperform many organic fluorescent molecules by providing improved resistance to photobleaching, [127] spectrally tunable emissions with small FWHM, [128] limited crosstalk, as well as large Stokes or anti-Stokes shifts that enable single-wavelength excitation.Furthermore, nontoxic alternatives for toxic QDs [129] were developed. [130]For SERS-based CSPs, a large library of Ramanactive reporters with narrow fingerprint bands is essential.This toolbox gets frequently expanded. [87,106]Besides these reporters, advanced plasmonic-active Au and Ag nanomaterials with well-defined, tunable plasmon modes [67,131,132] and increased SERS enhancement performance are required, for example, nanocubes, nanostars, or hybrid nanostructures. [67,133]The combination of plasmonic nanomaterials and Raman-active reporters into larger entities [132,134] as well as encapsulation techniques for Raman reporters [67,87,135] yield systems with huge potential for ID tags, stimuli recorders, and thus the concept of CSPs.Current challenges in this field are the stability of Raman reporters, the development of stimuli-selective recorders, and the improvement of signal intensity in complex environments.In the field of photonic balls, recent progress in optimizing the structural periods and refractive indices led to materials with narrow, adjustable reflective peaks in the entire range of visible light range. [108,136,137,138]These can be exploited for creating ID tags [27,137] or label-free stimuli-responsive photonic balls and nanostructures for diverse environmental stimuli. [53,107,111,139,140]ompared to the building blocks for the different spectral optical communication pathways, the MPS signal of magnetic signal carriers is less intensively studied, to date, albeit the available library is large.Therefore, a combination of environmental testing and analysis of their (altered) magnetic properties will enable the discrimination of robust or susceptible magnetic NPs suitable for ID and recorder features, respectively.If cross-sensitivities to specific triggers are revealed, the established synthetic know-how in the large magnetic NP community will be able to develop strategies to tailor these, e.g., by creating protective coatings around magnetic NPs.
Considering the established library of building blocks with spectral optical or magnetic signal features, one of the major future directives is to supply CSPs with recorder building blocks that possess a high selectivity and flexibly adjustable detection range for many different environmental stimuli.While for all aforementioned spectral optical communication pathways, an enormous variety of reversible sensors for real-time sensing of diverse stimuli was established, [73,74,141] the library of irreversible recorders that memorize the history of a specific stimulus is more narrow.Detected irreversible signal changes in the development of sensor probes, so far mostly undesired, shall in future be particularly exploited for establishing a vast library of recorder building blocks for CSPs.Established examples of spectral recorder building blocks are a TTI recorder based on Au/Ag nanorods [58] or a humidity recorder based on cholesteric liquid crystals [142] both indicating exposure to the target stimulus via an irreversible color change.Other examples are threshold temperature indicators with a turn-on luminescence response [61] or metal-organic frameworks (MOFs) for recording exposure to gaseous species. [75,143]

Assembly of Signal-Carrying Building Blocks to CSPs
In many future application scenarios for perceptual, informationproviding matter, the functional signal characteristics of individual signal carriers cannot achieve the demanded information capacity.They provide either environmentally robust or sensitive signal features and thus lack options for providing both, an ID signature and (multiple) recorder features.
Therefore, in the second step toward perceptual, informationproviding matter, suitable signal-carrying building blocks are united into defined CSP entities.The cooperative interplay of the selected spectrally distinguishable signal carriers with robust and environmentally sensitive signals, respectively, is envisaged to enable CSPs to achieve the desired information capacity: an appropriate ID variety as well as an application-specific number of recorder features for different stimuli impact as the intactness of materials is harmed by more than one stimulus.
Uniting different spectrally distinguishable signal carriers into one entity, for example, a CSP provides a striking advantage.All individual building blocks of a CSP that use the same signal encoding can be detected simultaneously and with relative intensities to each other.[100] Building blocks that provide environmentally robust signal features are particularly suitable as internal references.We envision that the manufacturing of CSPs from signal-carrying building blocks is predominantly based on the assembly of NPs and benefits from the huge variety of established NP assembly methods of which many allow for precise control of NP connectivity, distribution, and (exotic) compositional combination. [51,144]The integration of molecular signal carriers can be facilitated, for instance, by chemically linking them into or onto suitable carrier NPs, [30] which makes them more resilient and prevents undesired leaching into their surroundings. [29]147]

Requirements
Well-suitable NP assembly methods for the concept of CSPs have to fulfill various requirements (Figure 4a1).Accuracy and reproducibility facilitate obtaining CSPs with reliable, tailor-made functional signal characteristics for diverse applications.Particularly, achieving a high spectral encoding capacity depends on a precise stoichiometry of the assembled building blocks. [84,86]oreover, assembly methods for CSPs should be easily scalable to reduce their manufacturing costs and allow for their mass deployment.CSPs shall come in the form of a powder additive with defined processing options and adjustable surface properties to make their flexible integration into diverse materials possible (see Section 3.3).To avoid the leaching of individual building blocks from CSPs into surrounding material, appropriate mechanical cohesion between the assembled NPs is desired.
Additionally, suitable assembly methods should enable the variation of utilized types of signal-carrying building blocks (Figure 4a2).This is required to tune the communication pathway and information capacity of CSPs toward different properties of their respective hosting material, for instance, different optical absorption, geometries, and intrinsic limitations.
Importantly, upon colocalization of different signal carriers into the confined space of (sub-)micrometer-sized SPs, the individual signals of different building blocks often do not simply add up, but (un)desired interaction phenomena occur. [51,148]hese phenomena are either coupling effects, i.e., interference of signals stemming from different components, or emergence effects that yield entirely new functionalities by the interplay of neighboring building blocks.The degree of building block interaction within the confined space of the resulting CSP entity thus has to be controlled to eventually obtain the desired functional signal characteristics of CSPs (Figure 4a3).

Configuration of the Information Capacity of CSPs via Assembly of Signal Carriers
Taking the presented vision to the extremes, every type and batch of any material should be distinguishable via a unique ID signal.Additionally, all histories of environmental stimuli, which affect this material, should be sensitively, selectively, and simultaneously recorded to make the striven on-demand status acquisition possible.
One concept for different spectral ID signatures is based on spectral ratiometric coding.This strategy relies on differentiable relative intensity ratios of spectrally distinguishable building blocks within the same optical [88] or magnetically excited spectrum. [94]To give an illustrative example, uniting NPs with distinguishable luminescence emission colors in different number ratios into one polymer bead [149] or supraparticle [89] yields (sub-)micrometer-sized entities with luminescent spectra related to the chosen number ratio (Figure 4b1).Such entities consisting of different building block ratios are thus spectrally distinguishable and identifiable.Thereby, they facilitate a significantly higher ID variety compared to their individual constituting building blocks.The number of achievable fingerprint spectra via ratiometric coding depends on the number of adequately distinguishable signal carriers and the number of differentiable relative intensity levels. [25,30,121]Additionally, such robust spectral signatures can be used as internal references for ratiometric readout of spectrally distinguishable recorder features. [6]Environmentally triggered irreversible spectral changes, for example, in intensity, spectral position, or harmonic amplitude can thus be quantitatively determined (Figure 4b1).
The main limitation for configuring the information capacity of CSPs is the number of distinguishable spectra, which are defined by the ratio of signal-carrying building blocks and their spectral properties.Spectral signal overlap of the available build-ing blocks should thus be minimized.Vice versa, enhancing the spectral range that can be accurately excited and detected by the respective readout devices enhances the number of distinguishable spectra. [86]owever, the number of distinguishable ID signatures and different stimuli-recorder features, respectively, obtained from a CSP, will never be infinite. [25,88]The assembly method will influence the design possibilities of a CSP and should offer flexibility to achieve the best possible information content for every application scenario.When high encoding capacity is demanded, a greater share of environmentally robust, spectrally distinguishable signal carriers can be selected and assembled in various ratios to CSPs yielding a large number of differentiable ID signatures.This leaves however only a limited spectral range for adding recorder features. [15]Contrarily, the share of robust signal carrier types can be reduced if a high number of different recorder features is desired to monitor the history of multiple environmental stimuli.In this case, the number of achievable ID signatures is smaller.
Hybrid signal encoding can overcome these spectral limitations (Figure 4b2). [30,80,116]This approach is based on detecting signal features with different signal encoding schemes out of one entity.Thereby, the number of distinguishable codes and detectable environmental stimuli can be significantly increased, respectively.A frequently exploited hybrid encoding approach is the combination of spectral and graphical signal encoding, [16,92,150,151,152] with all the benefits and drawbacks of graphically encoded signals (see Section 1).
Alternatively, CSPs can exploit hybrid spectral signal encoding.This strategy is based on combining two or more groups of spectrally distinguishable signal carriers that can be excited and detected separately into one entity.Pioneering examples for dual-spectrally encoded miniaturized information providers, mostly advanced ID tags, include combinations of individually excited downconverting fluorophores, [15] down-and upconverting fluorophores, [91,152] fluorophores and SERS-reporters, [153,154] plasmonic and SERS species, [155] as well as fluorescent and magnetic NPs. [95,156]Depending on the utilized combination of signal elements, one or multiple excitation sources are required to harvest the entire signal information of the tag via multiple spectrometers.These separate pieces of information are digitized, joined, and computed to increase the information capacity of CSPs, that is, either a larger number of ID signatures and/or more stimuli-recorder features.It is however important to note that using CSPs with multiple signal encoding schemes increases the complexity and operation costs of the signal decoding process. [30]

Achieving Envisaged Information Capacity by Controlling the Interaction of Signal-Carrying Building Blocks
From our perspective, NP assembly methods at the liquidliquid or air-liquid interface are the most promising to meet the above-described requirements.Many of them are scalable, [144,157] precise, [109,157,158,159] and allow for flexibly interchanging the combined building blocks. [51,157]Among these methods, we recognize three general strategies to achieve the requirements of assembly techniques for CSPs.One strategy aims to adapt and optimize Figure 5. Designing suitable CSP architectures toward achieving the envisaged information capacity: a) Options for adjusting the degree of signal carrier interaction by variation of their distribution within intermixed (a1), core-shell (a2), Janus-like (a3), spacer NP-based (a4), or multihierarchical CSP architectures (a5).b) Identifying suitable CSP architectures for forcing or reducing the interaction of selected signal carriers: an intermixed CSP architecture is suitable to achieve desired interaction between optical signal carriers (b1).A core-shell architecture is suitable for hybrid-encoded CSPs with reduced signal interference of optical signal carriers due to magnetic building blocks (b2).A multihierarchical CSP architecture is suitable to reduce the interaction among all incorporated signal carriers (b3).
industrially well-established techniques, such as spray-drying, to the precise and reproducible assembly of NP and molecular building blocks into SP structures. [6,51,55,94,107,160,161,162]Another strategy is the transfer of highly accurate NP assembly methods, such as emulsion [138,159,163] or microfluidic methods, [163,164] from the lab-to pilot-and industrial scale.A third strategy aims to explore and establish new NP assembly methods that fulfill many requirements. [157,165]One example, is the universal in-fiber fabrication of polymer composite SPs with tunable sizes and compositions via fiber drawing and exploiting their Plateau-Rayleigh instability. [157]nce accurate, scalable, and flexibly adjustable NP assembly methods are realized, the interaction of colocalized signal carriers within CSP entities must be controlled to achieve the envisaged information capacity.We hypothesize that designing appropriate CSP architectures can be a key to success in this endeavor.These architectures can, for instance, focus on controlling the distribution of signal carriers to adjust the degree of building block inter-action (Figure 5a), because the arising coupling and emergence effects are often strongly distance-dependent. [54,166]Different particle architectures such as intermixed NPs (Figure 5a1), [51,89] core-shell (Figure 5a2), [167,168] or Janus-like CSP architectures (Figure 5a3) enable to tune the distance between the signal carriers and the degree of their interaction. [169]These architectures can be created, for instance, via the addition of structure-directing agents or multiple consecutive assembly steps.Alternatively, the distribution of signal carriers can be altered by the addition of nonsignal-carrying, environmentally robust, NPs, e.g., SiO 2 NPs, and their utilization as spacers (Figure 5a4). [54,114,170,171]Such an architecture reduces the interplay between interacting species by increasing their distances.Another strategy to reduce the interaction of all signal-carrying building blocks is the encapsulation of individual or soft-agglomerated signal carrier types into, for instance, polymer NPs and their subsequent assembly into multihierarchical SP architectures (Figure 5a5). [94,95]Due to the spacing by the inert matrix material, the interaction of signal carriers is diminished compared to directly assembled ones.A further option for fine-tuning signal carrier interactions could be achieved by exploiting surface ligands with specific steric [172] and electrostatic properties, respectively, or different polarity.They are expected to influence the CSP structure formation and the resulting confinement of signal-carrying building blocks within the CSP.
The relevance of identifying an appropriate CSP architecture for achieving the envisaged information capacity can be highlighted based on the following examples (Figure 5b).In an intermixed SP architecture, signal carriers are densely packed which offers a huge interaction potential.Luminescent species are wellknown for their strongly distance-dependent energy transfer interactions, for example, via dipole-dipole coupling (Förster resonance energy transfer) or photon reabsorption. [173]Therefore, an intermixed CSP architecture might be suitable to specifically exploit cascade energy transfer interactions to achieve single wavelength excitation for multiple different luminescent species that would not be simultaneously excitable without their interaction (Figure 5b1). [128,174] core-shell architecture can be the structural motif of choice if reduced interaction between two different signal carrier types within a CSP is desired.This can be of particular interest for hybrid-encoded CSPs using magnetic and optical signal-carrying building blocks.It is well-known that magnetic materials absorb light over a large spectral range and are, e.g., strong luminescence quenchers. [95,175]The interference of optical signals by magnetic signal carriers in a hybrid-encoded CSP could thus be significantly reduced by positioning the magnetic building blocks in the core of the CSP and surrounding them with optical building blocks in a core-shell CSP architecture (Figure 5b2).The detection of magnetic signals is possible irrespective of the surrounding shell.If any interaction between signal-carrying building blocks is detrimental to achieving the desired information capacity of a CSP, a multihierarchical architecture is considered suitable as distance-dependent interaction phenomena might be even better controlled (Figure 5b3).This could be of relevance when both the interaction among magnetic signal carriers and the interaction between optical species need to be reduced to achieve the envisaged information capacity for a hybrid-encoded CSP. [95]t this point, we would like to stress that the precise architectural design of CSPs can not only be used to control the interaction between the assembled signal carriers but be exploited for creating stimuli-recorder functionalities.One example is a maximum-temperature recorder based on irreversible changes in the spectral magnetic signature of SPs that consist of robust iron oxide NPs and a temperature-sensitive polymer. [54]Another example is a luminescent color-change indicator SP for shear stress impact with a specifically designed core-shell structure each hosting luminescent species with a different emission color. [167]Hence, another future directive toward creating recorder functionalities can be exploiting exotic combinations of building blocks.Such specifically designed SP architectures that offer stimuli-induced irreversible changes could yield, for instance, altered building block interactions.
Additionally, the porosity of CSPs that is characterized by the interstitial pores between assembled NPs can be utilized to achieve specific stimuli-recorder functionalities.These voids can be customized in size and shape via the selection of NPs of different sizes and geometries. [51,66,161,176]Functional molecular signal carriers can exploit these pores as channels that provide them with freedom for action and motion.Pioneering examples include recorders for gaseous species based on the molecular mobility of dye molecules in the pores of SPs granted by capillary condensation of solvent vapors. [55,147]This freedom for action and motion is likely not achievable upon direct chemical integration of interactive molecules into matrices and highlights the potential of exploiting the configurable porosity of CSPs for the incorporation of interactive molecules into hosting materials.Additionally, the configurable porosity of CSPs provides a large, defined interaction area with the surrounding atmosphere, which can itself be exploited to create stimuli-responsive functionalities. [107,145]n sum, the established variety of NP assembly and structure manipulation methods provides multiple options to design CSP architectures toward exploiting beneficial or circumventing interfering signal interplay of the selected building blocks.It is therefore essential to match the NP assembly method with the selected signal carriers and control their potential interaction by designing appropriate CSP architectures to ultimately achieve their envisaged functional signal characteristics.

Current Challenges and Potential Future Directions
While NP assembly methods at the liquid-liquid or air-liquid interface are the most promising for creating CSPs, many of these methods are either not yet scalable or not precise enough to meet the demanded accuracy.Besides intrinsic kinetic restrictions, [177] in many cases, this can be rationalized by a lack of detailed mechanistic understanding of many assembly processes.This knowledge gap can likely be closed by collaborative research efforts of SP and computer scientists aiming toward gaining more mechanistic insights into diverse NP assembly methods via calculations and theoretical simulations.Such a collaboration could enable CSP architectures and respective functional signal characteristics to be predicted and maybe even reliably tuned via internal or external assembly parameters. [178]Furthermore, we want to motivate the SP community to explore the fabrication of larger batch sizes and establish protocols for quality control.We believe that further innovation cycles will be required to be able to synthesize readily customized CSPs with the desired precision and at scale.
Pioneering examples showed that it is likely possible to control the interaction of signal carriers by assembling them into appropriate SP architectures. [54,94,95,170,173]Whether this level of interaction control can also be achieved for CSPs is, however, an open research question, which requires an in-depth investigation.If an all-rounder method to assemble all selected building blocks into CSPs with an appropriate architecture cannot be identified, combinations of different, consecutively conducted assembly methods could be exploited.
Another open challenge is the creation of homogeneous protective shells around particles in the lower micrometer size range.Such a shell could not only avoid the leaching of individual building blocks from CSPs into surrounding material but also increase the selectivity of certain recorder features by blocking out specific other triggers, for example, gaseous species that may cause unintended signal alterations.
Albeit the huge application potential of CSPs, to the best of our knowledge, examples of complex-structured particles that follow our herein-presented definition and provide both, an ID signature and one or multiple stimuli-recorder features, are rarely reported, to date.One exemplary CSP type exploits three types of luminescent particles united in desired ratios in a core-satellite structure. [6]The luminescent signal of the CSP provides a tunable ID signature and an adjustable maximum temperature recorder.These two separate pieces of information can be detected ratiometrically via fluorescence spectroscopy using a single excitation wavelength.Another CSP type utilizes hybrid signal encoding by combining luminescent and magnetic NPs assembled in a core-shell architecture hosting magnetic NPs in the core and luminescent NPs in the shell. [156]The signal characteristics of this CSP provide a magnetic ID signature that can be obtained via MPS and a luminescent turn-off recorder for experienced shear stress detectable via fluorescence spectroscopy.With these two pioneering examples, however, the true potential of CSPs has by far not been unlocked, yet.
To approach this goal, we want to encourage the SP community to identify suitable signal carriers for creating CSPs with different spectral encoding schemes, for instance, SERS, MPS, etc., that combine both, an ID signature and recorder features, in their spectral signal characteristics.Based on these advances, the next step should be to exploit hybrid spectrally encoded CSPs with an even greater information capacity.It is however important to note that interference by spectrally overlapping (optical) signals must be considered and avoided. [30,154,179]

Integration of CSPs into Materials
The next step to realize the initially outlined application scenarios (i-iv) with perceptual, information-providing matter is the integration of CSPs into materials and objects, for instance, thermoplastic polymers or the housing of capacitors.We envision that the integration of CSPs into materials can be facilitated by the incorporation of CSPs as a powder additive.Compared to the addition of a particle suspension, the solvent-free application of a dry powder additive cuts the need to match the compatibility of the used solvent with the respective hosting material.Additionally, many materials in our everyday life are composites that already contain powder-based additives.Thus, diverse material processing techniques to integrate such additives are already industrially well-established.
At this point, it is important to mention that one of the main hazards of all engineered nanomaterials, besides direct cytotoxicity, [180] is their inhalation and subsequent damage to the respiratory system. [181]This risk is particularly relevant for dry (nano-)powders used in the manufacturing industry as they easily form aerosols.Upon assembly of NPs to SPs, however, the risk of forming respirable aerosols is reduced due to the lower fraction of respirable airborne particles [182] and the elimination of micrometer-sized particles in the deeper lungs by alveoli macrophage is possible, [183] which improves the safety during the handling and processing of CSPs.Additionally, their micrometer dimension makes CSPs unlikely to cross most biological barriers and thus reduce their health hazards. [184] should be noted that the focus of this section is put on the properties of CSPs to cope with the integration into diverse matrices and respective integration methods.Furthermore, we discuss how material processing steps can influence the desired functionality of CSPs and how CSPs may overcome resulting difficulties.As the variety of materials and potential integration methods for CSPs is vast, we do not aim to suggest one specific approach but rather describe general selection and quality criteria.Our critical assessment shall be used as a guideline to identify suitable processes for individual application scenarios.

Requirements
The main objectives for the integration of CSPs into materials are minimal interference with the functional properties of the hosting material (Figure 6a1) and ideally no alteration of the previously used material processing steps (Figure 6a2).Importantly, such integration processes must conserve the functional signal characteristics of CSPs (Figure 6a3) and enable their signal to be detected afterward (Figure 6a4).This, in turn, demands high flexibility to adjust CSPs to different integration processes and hosting materials and vice versa.CSPs with different communication pathways and respective readout methods have different intrinsic limitations, such as their transmission through different materials, their limit of detection (LoD), or interfering material properties, such as the autofluorescence that increase the noise of the detection process. [5]These factors must also be considered for hybrid-encoded CSPs.
Additionally, different application scenarios have different areas of interest in which the identity and intactness of materials shall be evaluated.For instance, when the intactness of a material is harmed by exposure to gaseous species, harvesting the information from the surface of a material is relevant.In another scenario, even the smallest fragments of materials must be identifiable and reviewable which demands a homogeneous incorporation of CSPs into the bulk of a material.
From the above-outlined objectives, we deduce the following requirements for the design of CSPs: Flexibly adjustable physical and chemical surface properties, that is, the polarity, wettability, etc., to enable their incorporation into various hosting materials (Figure 6b1).Furthermore, CSPs should owe resilience against thermal (melting), chemical, and mechanical impact (agitation) to cope with many of the established processing techniques for integrating powder additives (Figure 6b2).Importantly, if these stimuli, e.g., temperature or mechanical shear stress are targeted for the respective CSP application, an integration during the material processing seems very challenging.

Integration of CSPs with Different Communication Pathways
The identification of suitable integration of CSPs into materials largely depends on the physical nature of their communication pathway.Optically excited signal responses are mainly impaired by any parameter that disrupts the optical path between a CSP and the excitation source or a CSP and the detector.One major interference factor is the intrinsic optical absorption of the tagged material and other incorporated additives, e.g., conventional dyes or pigments. [4,114]Strong optical absorption limits the light penetration into the bulk and thus restricts the application of CSPs with an optical communication pathway to (near-)surface levels (Figure 6c1).Other disruptive factors are the geometry, surface roughness of the object (scattering), or coverage with foreign material.The modular approach of CSPs allows matching the utilized optical building blocks and their excitation to cope with some of these challenges.For instance, material-specific optical windows with low absorption in certain spectral ranges can be exploited for excitation and signal detection. [185]This however drastically limits the achievable information capacity due to the reduced spectral range to convey information.
As an alternative communication pathway, CSPs can utilize the detection of magnetically excited signal responses of magnetic NPs via MPS. [54,114]The communication pathway is by nature independent of the optical absorption of the hosting material.This allows the integration of these CSPs into the bulk of materials even they exhibit a strong optical absorption (Figure 6c2).Magnetically excited signals may however be impaired by magnetically interfering components, for instance, ferromagnetic pigments in the direct surrounding of a CSP.Therefore, an allrounder communication pathway for all imaginable scenarios is not feasible, to date.
The excitation and detection of optical signals, in turn, are, besides their light absorption properties, not interfered by surrounding magnetic matter.Materials that hamper both, optical and magnetically excited signal responses, are rarely encountered.Thus, CSPs that are built up from both, optical and magnetic building blocks, and provide the same type of information via both communication pathways may even cope with very chal-lenging material properties (Figure 6c3). [95]Such hybrid-encoded CSPs can thereby expand the applicability of conventional miniaturized information providers.It is however important to note that in such a scenario the achievable information capacity of hybrid-encoded CSPs is reduced.

Current Challenges and Potential Future Directions
The integration of SPs and thus also CSPs into materials is not yet well explored.Pioneering examples include the creation of SP-based coatings via doctor blade coating, [145,146,156,167,168,186] spray-coating, [187] or low-tech alternatives using acrylate- [188] or polysilazane-based lacquers. [151,171]Such SP coatings could be suitable for CSPS with an optical communication pathway and allow optically transmitted information to be detected if transparent coating materials are used. [151,156,167,168]Other studies showed that magnetic SPs can be embedded into agar, [189] adhesives, [54] or polymers via melt-blending. [114]These are the first examples of integrating (C)SPs into the bulk of materials while their magnetically excited signal response remains readily detectable via MPS.Also, the first examples of applying SPs via additive manufacturing processes were achieved. [160,190]Comparing these few examples with the variety of established methods for integrating powder-based additives into diverse materials, one can state that the integration of CSPs is still in its infancy.Therefore, we want to encourage the SP, material science, and chemical engineering communities to study the incorporation of SPs and in particular CSPs into materials with the ultimate goal to achieve the initially outlined objectives (Figure 6a).
If the incorporation of CSPs into materials harms the material properties of their host, a lower concentration threshold that mitigates such negative influences shall be explored.Once this threshold concentration is found, it must be matched with the LoD of the respectively used CSPs, their communication pathways, and corresponding readout methods.At this point, it is important to note that CSPs with a low LoD can be homogeneously distributed throughout the hosting material.CSPs with a high LoD will have to be integrated at a higher concentration at specific locations in the tagged material to cope with requirements regarding price and unaffected material properties (Figure 6d). [29]Furthermore, signal interfering interactions between CSPs and other additives, for instance, dyes, flame retardants, and UV protectors, or with CSPs themselves in, e.g., a polymer master batch must be identified and minimized.Another important future research area is if and how CSPs can be integrated into the established processing steps of diverse materials.

Information Acquisition via CSP Signal Readout and Processing
The last and final step toward achieving perceptual, informationproviding matter is information acquisition via CSP signal readout and processing.It is important to mention that this step is highly interconnected with all aforementioned steps, that is, the chosen communication pathway or the integration site of the CSPs.In the following, we therefore mostly focus on aspects that can uniquely be associated with the readout process, instruments, and signal processing.

Requirements
Suitable readout processes for CSPs must be fast [(milli-) seconds], nondestructive, contactless, automatable, adjustable to various geometries of the analyzed object, and feasible in complex environments (Figure 7a).To realize the desired point-ofcare information acquisition, readout instruments should be transformed into handheld devices while remaining inexpensive and accurate (Figure 7b1).Suitable processing software shall allow untrained personnel to easily operate these devices and thereby, obtain the desired information (Figure 7b2).Ideally, the readout instrument is equipped with a permanent (wireless) connection to digital databases like a smartphone (Figure 7b3).Thereby, these devices will present the interface between the physical and digital worlds.They harvest the signal characteristics of the CSPs within the tagged material, which is subsequently digitized, computed, and synchronized with the digital databases.The digitally stored information is thereby obtained, transferred back to the readout device, and exploited to take appropriate actions in the physical world.
For real-world applications of CSPs, two further key characteristics have to be considered for the information acquisition process.Generally, it is desired to incorporate CSPs in the lowest possible concentration to minimize additional costs and alterations in the properties of the hosting material.It was suggested by others that additives for ID tagging shall achieve a LoD in the parts per billion range. [29]This LoD is thus a well-suitable goal also for CSPs (Figure 7c1).For industrial application however, a worse LoD might be justified by a significantly reduced price of the readout devices.The second essential characteristic to harvest a huge information capacity is the discrimination of signals provided by different signal carrier types within the functional signal characteristics of CSPs.Besides having advanced signal carriers at hand, offering optical signals with narrow FWHM or spectral magnetic signals with narrow fingerprint areas, the spectral resolution and accuracy of the readout instrument are decisive (Figure 7c2).To exploit all the benefits of hybrid-encoded CSPs, readout instruments are required that combine multiple readout techniques in a simple, cost-effective manner, ideally within one handheld device.

Status Quo, Current Challenges, and Potential Future Directions
The suggested spectral communication pathways via optically or magnetically excited signal responses, i.e., fluorescence, Raman, IR, UV-vis spectroscopy, or MPS, fulfill all of the aforementioned basic requirements and are thus suitable for the concept of CSPs (Figure 7a).
Additionally, great progress in creating miniaturized, portable, cost-effective, and accurate spectrometers as well as smartphonebased signal decoding techniques was achieved recently.]139,193] Many of these devices can be operated by untrained personnel and provide the option to be connected to digital databases for automated signal correlation.Establishing such advanced readout instruments for sensitive and accurate point-of-care detection of the signal of incorporated CSPs with many different signal encoding methods will however require enormous research efforts of physicists and (electrical) engineers in the upcoming years, which we want to fuel herein.
Regarding the envisaged LoD for CSPs in the ppb range, several signal carriers and their respective readout techniques come already close or have even achieved it. [1,5,194]These systems have been investigated for many years, which makes us confident that rather new technologies catch up shortly. [114,195]To transfer the achieved LoD from laboratory measurements to real-world applications and to obtain the desired signal quality at this low concentration, CSPs with enhanced signal intensities, powerful excitation sources, and highly sensitive detectors with improved signalto-noise ratios have to be developed.It is important to mention that the development of advanced readout instruments for hybrid-encoded CSPs will of course be an even greater challenge due to the increased complexity and thus be likely to cause higher operation costs and several more years to be implemented. [30]dvanced signal processing methods will be another cornerstone for achieving the striven LoD, reducing the interference from spectral signal overlap, and minimizing detection errors.Therefore, powerful artificial intelligence (AI) or algorithmassisted methods for signal processing must be established, which is however already an active research field.Pioneering examples include (deep-learning-assisted) deconvolution algorithms for the spectral discrimination of fluorophores [122,196] or Raman signals, [179,197] as well as machine learning or softwareassisted recognition of graphical and optical patterns. [32,198]We expect that physicists and computer scientists will collaboratively work toward achieving the highest possible sensitivity, spectral resolution, and accuracy and thereby, contribute to realizing the concept of perceptual, information-providing matter via the integration of CSPs.

Envisaged Impact of Perceptual Information-Providing Matter via CSPs
Once many of these challenges have been met, from our perspective, the technological implementation of CSPs can be realized.It is however expected that regulative hurdles, consumer acceptance, and technology transfer will pose additional barriers before CSPs will ultimately be commonly accepted in the market.Yet, it is assumed that upcoming legislative regulations will aim toward traceability and quality assessment along the supply chains as well as more sustainable manufacturing and use of products. [13,199]Once coming into force, they will create a technology pull, which could foster the implementation of CSPs in the market.
The integration of nontoxic, economically feasible (added value to cost ratio), and highly potent CSPs into a wide range of materials and thus the realization of perceptual, informationproviding matter is envisioned to create not only technological but also economic and social impact.
With significant progress in the different contributing disciplines, we envision that even the following future scenarios for CSPs can become a reality.At the beginning of the implementation of CSPs, the selection of their communication pathway, the design of their functional signal characteristics, and the customization of their chemical properties toward a specific target material and application will be carried out by experts.The rapid progress in materials informatics and AI-assisted fabrication technologies points toward the implementation of AI-based manufacturing of customized CSPs with desired properties for specific demands. [14,65,68,200]This includes the synthesis and selection of suitable building blocks, deciding on an appropriate ratio of ID and recorder building blocks, choosing an ideal assembly method, and finding the best incorporation procedure.AIbased manufacturing of CSPs could therefore not only reduce the manufacturing costs for new types of CSPs but also contribute to optimizing their performance.
In our vision, CSPs become an integral part of the hosting material in many scenarios.Once a circular economy is established, this raises the question about postlife scenarios for the tagged material.The demanded information, which shall be conveyed by the integrated CSP, as well as the application and readout environment of the material may be very different between the initial and the second use.Therefore, strategies to either recover, reprogram and reactive, or deactivate CSPs are demanded.Their recovery from a tagged material may be achieved by exploiting the modular approach to configure the physicochemical properties of CSPs.The surface chemistry of CSPs could be designed in a way that upon a certain external trigger, their extraction and separation from the hosting material by chemical and/or physical means is possible.As another option, some pioneering strategies to reprogram the ID signature of a tag using external triggers without the need to extract the integrated CSPs have been described. [151,170]To realize this vision in its entirety, including the reactivation of the recorder features, however, many additional innovation cycles are required.If CSPs can neither be recovered nor reprogrammed, they should be deactivated upon exposure to specific external triggers to thereby pave the way toward fresh tagging with customized CSPs for the second use of the material.In contrast, if CSP can be recovered, their reuse and recycling after their application should be explored.

Conclusion
CSPs present an emerging platform system to create miniaturized information-providing additives.The functional signal characteristics of CSPs convey an ID signature and one or multiple recorder features for harmful or desired environmental stimuli.After integrating CSPs as an integral part of materials, associated, digitally stored information on their hosting material is obtained upon detection of their signal on demand anywhere and anytime across the life cycle of their host.Information can include the material type, origin, and fate as well as the intactness of the tagged material.
The flexible toolbox-like assembly approach of CSPs from NP and molecular signal carriers into hierarchical SP architectures provides a plethora of options for customizing their functional signal characteristics and the utilized communication pathway to cope with many challenges arising from tagging very different materials with various target applications.
The realization and widespread implementation of CSPs present an interdisciplinary challenge and require the contribution of many different disciplines.Most important are chemists to synthesize advanced signal carriers and manufacture highly potent CSPs, chemical engineers for establishing appropriate implementation procedures, physicists and electronic engineers to develop advanced readout instruments, and computer scientists for enabling reliable, automated detection and computing processes.
Compared to other small-scaled aids, for example, WISPs that aim to achieve information-providing objects, CSPs benefit from flexible integration into materials at all scales, reduced demand for scarce resources, and easy synthesis requiring only a few chemical processing steps.CSPs are therefore envisioned to become a complementary key contributor to guide the use of (natural) resources by humankind into a more sustainable future via the realization of perceptual information-providing matter and creating a synergistic connection between the digital and physical worlds.

Figure 1 .
Figure1.a) (Sub-)micrometer-sized CSPs possess functional signal characteristics that comprise an ID signature and recorder features for environmental stimuli impact.Detecting these signal features grants access to associated, digitally stored information.Integrating CSPs into "passive" materials turns them into perceptual, information-providing matter.b) Customized CSPs can be integrated into materials at desired locations in their life cycle followed by a readout for initial calibration (b1).The CSP signal is thereby digitized, which enables associating digital information to the hosting material.Subsequently, identification and status acquisition of the material are possible via interrogating the CSP anywhere in the life cycle of the tagged material (b2).Associated digital information is transmitted back to the physical world.An exposure to threshold-exceeding environmental stimuli causes irreversible signal changes in the recorder features upon readout, leading to appropriate action in the physical world of materials.

Figure 2 .
Figure 2. Essential steps toward achieving perceptual, information-providing matter enabled by CSPs: a) Synthesis and selection of suitable signalcarrying building blocks.b) Assembly of these building blocks to CSPs in the form of a powder additive.c) Integration of CSPs into target materials.d) Information acquisition via CSP signal readout and processing.

Figure 3 .
Figure 3. a) Requirements and general selection criteria of signal-carrying building blocks suitable for assembly to CSPs (a1-a3).b) Signal carriers with spectral communication pathways for CSPs with environmentally robust (b1) and sensitive (b2), respectively.

Figure 4 .
Figure 4. a) Requirements and general selection criteria of suitable NP assembly methods to obtain CSPs with the desired information capacity.b) Configuration of the information capacity of CSPs via assembly of signal-carrying building blocks using ratiometric spectral coding and recording (1) and hybrid spectral coding and recording, respectively (2).

Figure 6 .
Figure 6.a) Objectives for the integration of CSPs into materials (a1-a4) and b) resulting requirements for the design of CSPs (b1,b2).c) Exemplary integration options for CSPs with spectral optical (c1), spectral magnetic (c2), and hybrid-encoded communication pathway (c3), as well as for CSPs with a high limit of detection (c4).

Figure 7 .
Figure 7. a) General selection criteria for suitable CSP signal readout technique.b) Requirements for point-of-care information acquisition from integration CSPs (b1-b3).Demanded key characteristics of suitable readout techniques for real-world application of CSPs, i.e., a low limit of detection (c1) as well as high spectral resolution and accuracy (c2).