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The cover picture shows a process used to fabricate carbon nanotubes (CNTs) by chemical vapor deposition (CVD). This process is enabled by patterning catalyst ink directly on silicon substrates with nanometer-scale precision using dip-pen nanolithography. A multipen writing method is employed to increase the patterning rate. The development of new molecular inks for the deposition of the precursor catalyst results in a high yield of isolated CNTs, ideal for subsequent device fabrication. The work demonstrates advantages of the new method for producing high-quality isolated CNTs in scalable array geometries. The image is a graphical representation of the patterning process. Arrays of dots are written with catalyst ink on the substrate at predefined locations marked by fiducial markers, which are alphabetical pairs of letters. After patterning, the CVD process facilitates synthesis of CNTs at the catalyst sites on the substrate. The arrows denote the final result-isolated CNTs grown from nanocatalyst clusters. For more information, please read the Communication “Controllable Patterning and CVD Growth of Isolated Carbon Nanotubes with Direct Parallel Writing of Catalyst Using Dip-Pen Nanolithography” by I. Kuljanishvili, V. Chandrasekhar, et al., beginning on page 2523.

The cover picture illustrates how gold nanoparticles (AuNPs) can dynamically modulate the activity of DNA polymerases and realize hot-start (HS)-like effects in polymerase chain reactions (PCR). In particular, when a high-fidelity Pfu DNA polymerase is combined with AuNPs it becomes a HS version of Pfu with high fidelity and high specificity. That is, AuNPs inactivate the polymerase activity of Pfu at low temperature, resembling an antibody-based HS PCR, which largely suppresses non-specific amplification at temperatures between 30 °C and 60 °C, leading to highly specific and sensitive PCR amplification with Pfu. More importantly, the fidelity of Pfu is not sacrificed in the presence of AuNPs. This AuNP-based HS strategy provides a straightforward and potentially versatile approach to realize high-performance PCR amplification. For more information, please read the Full Paper “Modulation of DNA Polymerases with Gold Nanoparticles and Their Application in Hot-Start PCR” by C. Fan, J. Hu, et al., beginning on page 2597.

This Review highlights the most significant achievements and challenges related to an application of the quantitative structure–activity relationship (QSAR) approach in the risk assessment of nanoscience.

Under similar electrodeposition conditions the unique surface properties of pyrolyzed photoresist films result in smaller gold nanoparticles with a higher density when compared to other common electrode materials. Reactive ion etching of such surfaces results in the formation of unique AuNP-capped pyramidal carbon structures (see image).

Miniaturized DNA arrays are obtained by using elastic deformation in conjunction with conventional pin spotting. The process takes advantage of elastomers that offer high mechanical flexibility, which makes it possible to achieve substantial miniaturization in a single step (see image).

Aptamers conjugated with quantum dots (QDs) bind to target molecules on the cellular membrane of cancer cells. QDs with a carboxyl terminal are conjugated with three types of tumor-targeting aptamer (see picture). Various types of cancer cell are simultaneously targeted with QD-TTA1 (605nm, light green), QD-AS1411 (655nm, red), and QD-MUC-1 (705nm, violet).

Carbon nanotubes are fabricated using chemical vapor deposition at predetermined locations by patterning catalyst directly on a substrate with nanometer-scale precision using dip-pen nanolithography with multipen cantilevers (see image). The development of new molecular inks for the deposition of the precursor catalyst results in a high yield of isolated carbon nanotubes, ideal for subsequent device fabrication.

Sensors made from single carbon nanotubes have great potential to function as nanometer-scale electrical probes for single-cell studies (see image). A nanotube is used both as an amperometric and a transistor sensor and signals are correlated with the activity of a macrophage cell located on the device. In addition, the stability and sensitivity issues are highlighted and ways to enhance nanotube sensors are demonstrated.

Highly anisotropic rods containing anionic magnetic nanoparticles and organic fluorescent nanospheres (see image) are synthesized using an electrostatic co-assembly strategy in the presence of cationic polyelectrolytes. The hybrid elongated architectures maintain the superparamagnetic properties of the -Fe₂O₃ constituents, as evidenced by their in-phase response to an external rotating magnetic field.

On-wire lithography is used to synthesize a new nanostructure composed of a goldpolypyrrole segment and gold nanodisk pairs for parallel electrical and spectroscopic readout (see image). As proof-of-concept, the binding of telomerase to surface-functionalized oligonucleotide receptors and subsequent elongation of the oligonucleotides are demonstrated by parallel electrical and spectroscopic measurements.

Fabrication of clean nanogaps is achieved using combined electrochemical/chemical etching of microfabricated gold wires in an iodine-based solution. In contrast to simple chemical etching, all visible spurious metal grains are removed while the gap is forming (see image). Obtained gaps have a controlled size between 1 and 10nm, which is suitable to connect small molecules or nanoparticles.

Surface-immobilized nanoscale reactors utilizing membrane protein channels are used to generate precisely patterned chemically and biologically active surfaces (see image). The enzymatic conversion of a fluorogenic substrate in the cavity of immobilized nanoreactors is a model reaction demonstrating future potential application of the system in sensors, analytics, microfluidics, and single-molecule spectroscopy.

Photothermal control of the enzymatic activity of horseradish peroxidase (HRP) bound to the surface of gold nanoparticles (AuNPs) is demonstrated. Laser light is absorbed by the AuNPs and transformed into heat, which dissipates into the environment of each nanoparticle. This heat influences the enzymatic conversion of ABTS and H₂O₂ to ABTS⁺ and H₂O, respectively (see image).

The frontispiece shows magnetofluorescent nanoparticles penetrating the external wall of a MCF-7 adenocarcinoma cell in an orderly way. The background is derived from a TEM image of an ultrathin section of fixed cells after treatment with nanoparticles. The nanoparticles consist of a small cluster of iron oxide nanocrystals encapsulated in a thick silica shell containing organic dye molecules. Several properties of the newly synthesized bifunctional nanoparticles including size, surface charge, presence or absence of oligoethylene glycol coating, and intensity of fluorescent and magnetic signals are evaluated according to their in vitro toxicity, capability of internalizing within the cell cytoplasm, and intracellular fate. For more information, please read the Full Paper “Towards Ideal Magnetofluorescent Nanoparticles for Bimodal Detection of Breast Cancer Cells” by E. Clementi, D. Prosperi, et al., beginning on page 2555.

Uptake, intracellular fate, and toxicity of unconjugated anionic magnetofluorescent nanoparticles within MCF-7 cells are investigated (see image), demonstrating that these particles are safe and follow physiological pathways of endocytosis and degradation, and that they can be developed as an effective nanodiagnostic tool for the study of breast-cancer cells.

The biodistribution and retention time of nanoparticles (<20nm) in the bloodstream constitutes a crucial issue for in vivo applications (imaging and therapy). Besides improvement of the colloidal stability and increase of the hydrophilic character, PEGylation exerts a strong influence on the biodistribution of the nanoparticles, which depends on the nature of the end group and the length of the polyethylene glycol chains (see image).

Ion-beam irradiation can be utilized to bend and realign semiconductor nanowires towards a different direction after they have been grown (see image). Experimental observations and computer simulations show that defects created during irradiation play a critical role in the alignment process.

Nanobarriers and nanocarriers: The ability to finely tune the emission wavelengths of quantum dots (QDs) by changing their diameter allows the use of QDs as nanoprobes for subcellular barriers. An automated high content imaging approach (see image) shows that cellular compartmentalization of QDs within the cells depends not only on the particle size but also on individual cell type.

Micrometer-sized particles dispersed in nematic liquid crystals (LCs) form microstructured LC gels composed of LC-rich microdomains (bright and colorful in the image) stabilized mechanically by particle networks. Thin films of the microstructured gels supported on chemically functionalized surfaces are shown to undergo ordering transitions, which lead to changes in optical appearance, upon exposure to specific chemical environments.

Hot stuff! Gold nanoparticles add a hot-start property to a high-fidelity DNA polymerase, Pfu, which significantly increases the sensitivity and specificity of polymerase chain reactions (PCRs, see picture). The strategy prevents unwanted nonspecific amplification and improves the performance of PCR systems.

Polymer-hydrogel capsules are stabilized via disulfide linkages whereby crosslinking relies on the thiol–disulfide exchange without the use of oxidizing agents (see image). The method permits the formation of hollow capsules as well as functional capsosomes, hydrogel capsules subcompartmentalized with enzyme-loaded liposomes, without the loss of activity of liposome-encapsulated enzymes.

Making sense: Carboxylic acid-functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires (NWs; see image) are directly synthesized onto biosensor devices across the electrode junction by using a simple electrochemical approach. The devices show typical properties of depletion-mode p-type field-effect transistors. The detection of label-free protein is demonstrated.

A nose for disease: An array of gold-nanoparticle sensors can distinguish between the odor prints of non-small-cell lung cancer (NSCLC) and negative controls with 100 accuracy, by detecting volatile organic compounds in exhaled breath. Principal component analysis gives well-defined clusters for both states (see picture), thus providing a tool for lung cancer screening and diagnosis.