Wearable sweat sensors have the potential to provide clinically meaningful information associated with the health and disease states of individuals. Current sensors mainly rely on enzymes and antibodies as biorecognition elements to achieve specific quantification of metabolite and stress biomarkers in sweat. However, enzymes and antibodies are prone to degrade over time, compromising the sensor performance. Here, we introduce a wearable plasmonic paper–based microfluidic system for continuous and simultaneous quantitative analysis of sweat loss, sweat rate, and metabolites in sweat. Plasmonic sensors based on label-free surface-enhanced Raman spectroscopy (SERS) can provide chemical “fingerprint” information for analyte identification. We demonstrate the sensitive detection and quantification of uric acid in sweat at physiological and pathological concentrations. The well-defined flow characteristics of paper microfluidic devices enable accurate quantification of sweat loss and sweat rate. The wearable plasmonic device is soft, flexible, and stretchable, which can robustly interface with the skin without inducing chemical or physical irritation.

Point-of-care biosensors are critically important for early disease diagnosis and timely clinical intervention in resource-limited settings. The real-world application of these biosensors requires the use of stable biological reagents and cost-effective fabrication approaches. To meet these stringent requirements, we introduce a generic encapsulation strategy to realize ultrastable plasmonic bioink by encapsulating antibodies with an organosiloxane polymer through in situ polymerization. Plasmonic nanostructures serve as sensitive nanotransducers, allowing for label-free biochemical detection. The plasmonic bioink with encapsulated antibodies exhibits excellent thermal, biological, and colloidal stabilities making it compatible with printing process. As a proof-of-concept, we demonstrate the printability of the ultrastable plasmonic bioinks on different types of substrates with direct writing techniques. The organosiloxane polymer preserves the biorecognition capabilities of the biosensors under harsh conditions, including elevated temperature, exposure to chemical/biological denaturants, and ultrasonic agitation. Plasmonic biochips fabricated with the ultrastable ink exhibit superior stability compared to the biochips with unencapsulated antibodies.

Preserving the functionality of nanosensors is critical for their reliable performance under harsh environmental conditions. Biofunctionalized plasmonic nanostructures are an important class of bionanoconjugates for biosensing, bioimaging and nanotherapeutics. Plasmonic nanostructures and biomolecules exhibit poor thermal stability over time. Here, we report a class of metal organic framework, zeolitic imidazolate framework-8 (ZIF-8), as a protective coating for preserving plasmonic nanostructures and plasmonic bionanoconjugates at elevated temperature. Gold nanobipyramids (AuNBPs) with sharp tips are attractive plasmonic nanotransducers with high sensitivity but are prone to structural change and loss of sensitivity. This work reports the first observation that ZIF-8 can preserve the structure of AuNBPs, and corresponding strong electromagnetic field enhancement and high refractive index sensitivity. In addition, ZIF-8 coating enables nearly 100% retention of biorecognition capability of antibodies immobilized on the AuNBP surface after exposure to 60°C for 48 hours. The efficacy, versatility, and facile implementation of ZIF-8 coating offer great promise for the preservation of nanosensors.

Skin-inspired soft and stretchable electronic devices based on functional nanomaterials have broad applications such as health monitoring, human–machine interface, and the Internet of things. Solution-processed conductive nanocomposites have shown great promise as a building block of soft and stretchable electronic devices. However, realizing conductive nanocomposites with high conductivity, electromechanical stability, and low modulus over a large area at sub-100 μm resolution remains challenging. Here, we report a moldable, transferrable, high-performance conductive nanocomposite comprised of an interpenetrating network of silver nanowires and poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate). The stacked structure of the nanocomposite synergistically integrates the complementary electrical and mechanical properties of the individual components. We patterned the nanocomposite via a simple, low-cost micromolding process and then transferred the patterned large-area electrodes onto various substrates to realize soft, skin-interfaced electrophysiological sensors. Electrophysiological signals measured using the nanocomposite electrodes exhibit a higher signal-to-noise ratio than standard gel electrodes. The nanocomposite design and fabrication approach presented here can be broadly employed for soft and stretchable electronic devices.

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