Multifunctional Wearable Sensing Devices Based on Functionalized Graphene Films for Simultaneous Monitoring of Physiological Signals and Volatile Organic Compound Biomarkers.

In this study, a multifunctional wearable sensing device based on two different graphene films is fabricated and can achieve the simultaneous detection of physiological signals and volatile organic compound (VOC) biomarkers without mutual signal interference. The wearable device was designed with two sensing components: on the upper layer of the device, four kinds of porphyrin-modified reduced graphene oxide (rGO) films were prepared and used for a sensor array that could sufficiently react with VOC vapors to achieve highly sensitive detection. A porous rGO film was designed on the underlayer of the device and used as a strain-sensing matrix, which could be closely attached to the skin to achieve a highly sensitive detection of the physiological signal. A polyimide film between the two sensing components was used not only as a flexible substrate, but also as a protective layer to avoid the porous rGO film's response to VOC molecules. Investigation of the detection ability showed that the porous rGO strain-sensing matrix can achieve a higher gauge factor (282.28) than the unstructured rGO counterpart (8.96) and is more desirable for the detection of physiological motion. In contrast, the porphyrin-modified rGO sensor array displayed a superior response to VOC vapors, and eight different VOC biomarkers could be detected and discriminated using the as-prepared sensor array together with a pattern recognition approach. The multifunctional sensing devices displayed excellent ability for the detection of a variety of human physiological signals, such as pulse and respiration rates. Simultaneous analysis of simulated diabetic breath samples, simulated nephrotic breath samples, and breath samples exhaled by healthy individuals using our wearable device exhibited clear identification and discrimination. Our study provides new insights into fabrication and design of multifunctional sensing devices without signal interference, and the application of the proposed devices are promising in preventive medicine and health care.

A multifunctional wearable sensor based on a graphene/inverse opal cellulose film for simultaneous, in situ monitoring of human motion and sweat.

A multifunctional, wearable sensor based on a reduced oxide graphene (rGO) film onto a porous inverse opal acetylcellulose (IOAC) film has been developed and can perform simultaneous, in situ monitoring of various human motions and ion concentrations in sweat. The rGO film is used as a strain-sensing layer for monitoring human motion via its resistance change, whereas the porous IOAC film is used as a flexible microstructured substrate not only for high sensitive motion sensing, but also for collection and analysis of ion concentrations in sweat by its simple colorimetric changes or reflection-peak shifts. Studies on humans demonstrated that the devices have excellent capability for monitoring various human motions, such as finger bending motion, wrist bending motion, head rotation motion and various small-scale motions of the throat. Simultaneous, in situ analysis of the ion concentration in sweat during these motions shows that the IOAC substrate can detect a wide range of NaCl concentrations in sweat from normal 30 to 680 mM under the conditions of severe dehydration. This investigation provides new horizons toward the design and fabrication of multifunctional, wearable health monitoring devices and the proposed wearable sensor shows promising applications in healthcare and preventive medicine.

Spherical porphyrin sensor array based on encoded colloidal crystal beads for VOC vapor detection.

A spherical porphyrin sensor array using colloidal crystal beads (CCBs) as the encoding microcarriers has been developed for VOC vapor detection. Six different porphyrins were coated onto the CCBs with distinctive encoded reflection peaks via physical adsorption and the sensor array was fabricated by placing the prepared porphyrin-modified CCBs together. The change in fluorescence color of the porphyrin-modified CCBs array serves as the detection signal for discriminating between different VOC vapors and the reflection peak of the CCBs serves as the encoding signal to distinguish between different sensors. It was demonstrated that the VOC vapors detection using the prepared sensor array showed excellent discrimination: not only could the compounds from the different chemical classes be easily differentiated (e.g., alcohol vs acids vs ketones) but similar compounds from the same chemical family (e.g., methanol vs ethanol) and the same compound with different concentration ((e.g., Sat. ethanol vs 60 ppm ethanol vs 10 ppm ethanol) could also be distinguished. The detection reproducibility and the humidity effect were also investigated. The present spherical sensor array, with its simple preparation, rapid response, high sensitivity, reproducibility, and humidity insensitivity, and especially with stable and high-throughput encoding, is promising for real applications in artificial olfactory systems.

Colorimetric photonic hydrogel aptasensor for the screening of heavy metal ions.

We have developed a robust method for the visual detection of heavy metal ions (such as Hg(2+) and Pb(2+)) by using aptamer-functionalized colloidal photonic crystal hydrogel (CPCH) films. The CPCHs were derived from a colloidal crystal array of monodisperse silica nanoparticles, which were polymerized within the polyacrylamide hydrogel. The heavy metal ion-responsive aptamers were then cross-linked in the hydrogel network. During detection, the specific binding of heavy metal ions and cross-linked single-stranded aptamers in the hydrogel network caused the hydrogel to shrink, which was detected as a corresponding blue shift in the Bragg diffraction peak position of the CPCHs. The shift value could be used to estimate, quantitatively, the amount of the target ion. It was demonstrated that our CPCH aptasensor could screen a wide concentration range of heavy metal ions with high selectivity and reversibility. In addition, these aptasensors could be rehydrated from dried gels for storage and aptamer protection. It is anticipated that our technology may also be used in the screening of a broad range of metal ions in food, drugs and the environment.

Quantum-dot-coated encoded silica colloidal crystals beads for multiplex coding.

Multiplex optical coding carriers for biological assays have been achieved by coating silica colloidal crystals beads with quantum dots, which provided high stability, large capacity and simplicity for practical application.