A Wearable Healthcare Platform Integrated with Biomimetical Ions Conducted Metal–Organic Framework Composites for Gas and Strain Sensing in Non‐Overlapping Mode

Abstract Intelligent wearable devices are essential for telemedicine healthcare as they enable real‐time monitoring of physiological information. Elaborately constructing synapse‐inspired materials provides a crucial guidance for designing high‐performance sensors toward multiplex stimuli response. However, a realistic mimesis both in the “structure and sense” of biological synapses to obtain advanced multi‐functions is still challenging but essential for simplifying subsequent circuit and logic programs. Herein, an ionic artificial synapse integrated with Ti3CNT x nanosheets in situ grown with zeolitic imidazolate framework flowers (ZIF‐L@Ti3CNT x composite) is constructed to concurrently mimic the structure and working mechanism of the synapse. The flexible sensor of the bio‐inspired ZIF‐L@Ti3CNT x composite exhibits excellent dual‐mode dimethylamine (DMA) and strain‐sensitive response with non‐overlapping resistance variations. The specific ions conduction working principle triggered by DMA gas or strain with the assistance of humidity is confirmed by the density functional theory simulation. Last, an intelligent wearable system is self‐developed by integrating the dual‐mode sensor into flexible printed circuits. This device is successfully applied in pluralistic monitoring of abnormal physiological signals of Parkinson's sufferers, including real‐time and accurate assessment of simulated DMA expiration and kinematic tremor signals. This work provides a feasible routine to develop intelligent multifunctional devices for upsurging telemedicine diagnosis.


Nonoverlapping Mode
Qingqing Zhou a , Zixun Geng a , Long Yang a , Bo Shen a , Zitong Kan a , Yu Qi a , Songtao      vapor concentration in the range of 80-400 ppm at RT (including the ZIF-L 1/2 @Ti 3 CNT x , ZIF-L 1/4 @Ti 3 CNT x , ZIF-L 1/8 @Ti 3 CNT x and ZIF-L 1/16 @Ti 3 CNT x , respectively).  (including the ceramic tube electrodes, ceramic planer   interdigital electrodes, PI substrate with Au electrodes, butter paper and TPU substrates with Cu electrodes) to 55 ppm DMA gas.                     Table S1. The binding energy (BE) and proportion of the Ti element in the Ti 3 CNT x , and ZIF-L @Ti 3 CNT x composites sensing materials. Table S2. A comparison of the sensing properties of recently reported MXene and ZIF-based sensors with the as-prepared ZIF-L@Ti 3 CNT x sensor in this work.

Synthesis of the Ti 3 CNT x nanosheets
To chemically exfoliate the bulk Ti 3 AlCN, 2 g of LiF powder was firstly immersed into 20 mL of HCl (9 M) and stirred for 15 min at 35°C in a water bath.
Then, 1 g of Ti 3 AlCN chunk was slowly added into the above solution and kept stirring for 24 h. After the etching procedure, HCl and LiF residuals in the supernatant were removed and the precipitates were purified and washed with deionized (DI) water by repetitive centrifugation (3500 rpm for 10 mins) until the pH value of the solution approached to 6. To obtain monolayer Ti 3 CNT x nanosheets, the above-washed precipitates were immersed in 200 mL of DI water and sonicated for 1 h at 18°C. Finally, after centrifugation (3500 rpm) for 30 mins, the upper suspension was collected as the delaminated Ti 3 CNT x nanosheets and the resultant sediment was collected as multilayered Ti 3 CNT x nanosheets. 6

Modification of Ti 3 CNT x MXene
Firstly, LiOH powder (45 wt%) was dispersed in the delaminated Ti 3 CNT x (30ml, 2.5 mg/mL) solution and stirred for 6 h at room temperature. Then, the mixture was collected after washed repeatedly with DI water by centrifugation to obtain Ti 3 CNT OH nanosheets.
Noticeably, the ZIF-L 1/4 @Ti 3 CNT x composites has the optimal sensing performance after a series of gas sensing tests, so it is mainly discussed and further abbreviated as ZIF-L@Ti 3 CNT x composites. In comparison, similar experimental treatment were utilized to fabricate the pristine flower-like ZIF-L particles by dissolving Zn(NO 3 ) 2 ·6H 2 O and 2-MeIM (mole ratio was1:4) into 15 mL of DI water without the delaminated Ti 3 CNT x nanosheets. In addition, the ZIF-L@Ti 3 CNT OH was fabricated by the procedure similar to that of ZIF-L@Ti 3 CNT x , except for changing Ti 3 CNT x to Ti 3 CNT OH .

Synthesis of flexible TPU nanofibers substrate
Firstly, the electrospinning precursor solution was fabricated by dissolving 6.0 g of TPU powder in 20 mL of DMF/THF (3:1, v/v) solvent, followed by stirring for 5 h at RT. Subsequently, single-spinneret electrospinning was performed at a DC voltage of 15 kV, a receiving distance of 15cm and the feed rate of 20 µL min −1 , respectively.

Characterizations of various ZIF-L@Ti 3 CNT x composites
The biomimetic synaptic architecture of ZIF-L@Ti 3 CNT x composites were MHz at AC amplitude of 10 mV.

Fabrication and measurement of various vapor sensors
To fabricate the gas sensors, 60 μL of fresh Ti 3 CNT x , ZIF-L and ZIF-L@Ti 3 CNT x composites solution (5 mg/mL) were directly dripped onto the rigid ceramic tube and alumina flat-based substrates, or onto flexible commercial polyimide (PI), as-spinning TPU and transparent sulfate paper-based substrates.
Herein, different types of substrates are used to illustrate the superior compatibility of the prepared sensing materials which can be flexibly applied to various practical scenarios. The chemiresistive response value of all sensors is defined as R a /R g , where

Proton Conductivity Evaluation
Before measurement, the ZIF-L@Ti 3 CNT x solution was dropped to a finger electrode (1×1 cm 2 ). The proton conductivity was determined by equation (2): [2] where R f is the resistance (Ω), d is the space between the electrode teeth (50 μm), l is the length of the teeth (7000 μm), N is the number of electrodes (20), t is the thickness of the samples (1-2 μm).
The activation energy (E a ) was calculated by equation (3): where σ 0 is the pre-exponential factor, k B is the Boltzmann constant, T is the temperature in Kelvin.

Preparation of the flexible strain Sensor
The ZIF-L@Ti 3 CNT x solution was filtrated onto the electrospun TPU membrane, and then, Cu tape electrode was adhered to both side of the TPU substrate to construct the flexible strain sensor, where length, width and thickness of the substrate is 2, 0.5 and 0.13 mm, respectively.

Computational Details
Density functional theory (DFT) calculations were performed using the Vienna Ab 9 initio Simulation Package (VASP) based on the pseudopotential plane wave (PPW) method. [3] The perdew-Bueke-Ernzerhof (PBE) functional was used to describe exchange-correlation effects of electrons. [4] The projected augmented wave (PAW) potentials were chosen to describe the ionic cores and took valence electrons into account using a plane wave basis set with a kinetic energy cutoff of 500 eV. [5] In order to simulate the proton transfer under humid and dry environment, hydrogen network built by water molecules and imidazole molecules were modelled. The DMA/ZIF-L system is placed with 12 water molecules to simulate high humidity environment, and with 1 water molecules is to simulate the dry environment. All structures were first optimized to reach their most stable configuration. During the geometry optimizations, all the atom positions were allowed to relax. In this work, the Brillouin-zone sampling were conducted using Monkhorst-Pack (MP) grids of special points with the separation of 0.04 Å -1 . [6] The convergence criterion for the electronic self-consistent field (SCF) loop was set to 1×10 -5 eV/atom. The atomic structures were optimized until the residual forces were below 0.05 eVÅ -1 . The barrier of proton transport within hydrogen network was calculated by CI-NEB method. [7]

Development of flexible intelligent wearable systems
To be specific, the ESP32 chip is performed in this device, which is integrated with Wi-Fi connectivity developed by Espressif Systems (Shanghai) Co., Ltd. In addition, an integrated electric circuit (ESP32 module) is designed to read the resistance data of the flexible sensor and upload it to the cloud by using a divider    Figure S3. A partial magnification of (002) diffraction peak of Ti 3 CNT x nanosheets and ZIF-L@Ti 3 CNT x composites.