Biosensor systems for wearable continuous monitoring are desired to be developed into conformal patch platforms. However, developing such patches is very challenging owing to the difficulty of imparting materials and components with both high stretchability and high performance. Herein, we report a fully stretchable microfluidics-integrated glucose sensor patch comprised of an omnidirectionally stretchable nanoporous gold (NPG) electrochemical biosensor and a stretchable passive microfluidic device. A highly electrocatalytic NPG electrode was formed on a stress-absorbing 3D micropatterned polydimethylsiloxane (PDMS) substrate to confer mechanical stretchability, high sensitivity, and durability in non-enzymatic glucose detection. A thin, stretchable, and tough microfluidic device was made by embedding stretchable cotton fabric as a capillary into a thin polyurethane nanofiber-reinforced PDMS channel, enabling collection and passive, accurate delivery of sweat from skin to the electrode surface, with excellent replacement capability. The integrated glucose sensor patch demonstrated excellent ability to continuously and accurately monitor the sweat glucose level.

A conformal patch biosensor that can detect biomolecules is one promising technology for wearable sweat glucose self-monitoring. However, developing such a patch is challenging because conferring stretchability to its components is difficult. Herein, we demonstrate a platform for a nonenzymatic, electrochemical sensor patch: a wrinkled, stretchable, nanohybrid fiber (WSNF) in which Au nanowrinkles partially cover the reduced graphene oxide (rGO)/polyurethane composite fiber. The WSNF has high electrocatalytic activity because of synergetic effects between the Au nanowrinkles and the oxygen-containing functional groups on the rGO-supporting matrix which promote the dehydrogenation step in glucose oxidation. The WSNF offers stretchability, high sensitivity, low detection limit, high selectivity against interferents, and high ambient-condition stability, and it can detect glucose in neutral conditions. If this WSNF sensor patch were sewn onto a stretchable fabric and attached to the human body, it could continuously measure glucose levels in sweat to accurately reflect blood glucose levels.

In particular, the measurement of metabolites, such as sweat glucose, has been extensively investigated for diabetes management and glucose metabolism monitoring. [7,8] The key requirements to realizing a wearable biosensing system capable of high-accuracy, continuous measurement of glucose include device stability during operation, stretchability for conformal contact to the human body, capability of handling sweat samples accurately and minimization of power consumption.A significant hurdle for wearable electronics is the prolonged operation of the sensor, which necessitates a suitable power source that therein affects the miniaturization, form factor in design and stretchability. For the purpose of monitoring, wearable sensor systems based on the transduction principles of colorimetric, [9][10][11][12][13][14] electrochemical, [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] or biofuel cell-based [32][33][34][35][36][37] sensors with deformability are often integrated with a microfluidic device for fluid handling. Specifically, biofuel cell-based metabolite sensors have low energy consumption because they are self-powered. For enzymatic biofuel cell-based biosensors, enzymes have been used in the bioanodes of biofuel cells for the oxidation of metabolites such as glucose [34,35] or lactate. [34,36,37] The use of enzymes in the bioanodes of enzymatic biofuel cells as the catalyst complicates the device fabrication because of the complex immobilization process and enzymes instability by environmental degradation over time. [38,39] The enzymes denature very easily when changes to the surrounding thermal and chemical environment occur, and they lose their reactivity. Moreover, this denaturation is irreversible, and the reactivity is not restored, even if the measurement environment returns to the normal range. To overcome this limitation, a self-powered fuel cell-based sensor system employing catalytic inorganic nanomaterials as electrodes of the fuel cell is of great interest because nanomaterials are less sensitive to environmental changes than enzymes and they have reversible degradation properties. [28,29,38,39] Therefore, the catalytic effect of nanomaterials is expected to be recovered when the detection environment returns to the normal range. Furthermore, nanostructured metal electrodes during glucose sensing provided selectivity toward other interferents such as ascorbic acid and uric acid while lactate is difficult to be oxidized by them. [38,39] Our previous studies Wearable sensor patches for continuous or intermittent monitoring of biomolecules from body fluids are highly desired as a stretchable integrated platform conformable and attachable to the human body. However, realizing such integrated sensor patches is very challenging because of the difficulty of achieving full stretchability, controlling transport of the body fluid, and minimizing power consumption. In this study, a stretchable and self-powered microfluidic-integrated sensor patch comprising a stretchable non-e...