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The incidence of diabetes is increasing at an alarming rate, and regular glucose monitoring is critical in order to manage diabetes. Currently, glucose in the body is measured by an invasive method of blood sugar testing. Blood glucose (BG) monitoring devices measure the amount of sugar in a small sample of blood, usually drawn from pricking the fingertip, and placed on a disposable test strip. Therefore, there is a need for non-invasive continuous glucose monitoring, which is possible using a sweat sensor-based approach. As sweat sensors have garnered much interest in recent years, this study attempts to summarize recent developments in non-invasive continuous glucose monitoring using sweat sensors based on different approaches with an emphasis on the devices that can potentially be integrated into a wearable platform. Numerous research entities have been developing wearable sensors for continuous blood glucose monitoring, however, there are no commercially viable, non-invasive glucose monitors on the market at the moment. This review article provides the state-of-the-art in sweat glucose monitoring, particularly keeping in sight the prospect of its commercialization. The challenges relating to sweat collection, sweat sample degradation, person to person sweat amount variation, various detection methods, and their glucose detection sensitivity, and also the commercial viability are thoroughly covered.

Monitoring sweat loss is an effective method for evaluating dehydration during body thermoregulation. However, current wearable microfluidic sweat sensors often face limitations in terms of breathability and heat dissipation, and textile‐based sweat sensors cannot achieve the accurate control and detection of sweat volume. Herein, we report a textile patch with an unprecedented layer‐by‐layer isovolumetric water transport (IVWT) ability for sweat loss monitoring. The patch features an all‐porous laminated fabric with multiple IVWT units and conductive nonwoven fabric sensing units, enabling controllable and quantitative sweat penetration similar to dam‐transporting ships. Each layer of the IVWT unit could accurately and stably transport 6.29 ± 0.10 μL of sweat across all tests. This design allows the identification of sweat volume by increasing stepwise jumps in the conductance signals. The dam‐inspired textile patch not only provides sweat volume measurements that are highly consistent with those obtained using the absorbent pad method but also offers superior air permeability ( 98% of the clothing), excellent heat dissipation ( 79% of the uncovered skin), and excellent compatibility, which facilitates seamless integration into various types of wearable garments. A fully integrated wireless transmission device with the textile patch provided a validated predictive model for estimating whole‐body sweat loss during dehydration monitoring. A dam‐inspired textile patch for controllable and quantitative sweat transport (as in dams transporting ships) and sweat loss monitoring. Unlike the conventional Janus‐structured textile of directional water transport model, this textile patch features a multi‐laminated all‐porous fabric structure with an unprecedented layer‐by‐layer isovolumetric water transport ability.

Wearable devices have received tremendous interests in human sweat analysis in the past few years. However, the widely used polymeric substrates and the layer-by-layer stacking structures greatly influence the cost-efficiency, conformability and breathability of the devices, further hindering their practical applications. Herein, we report a facile and low-cost strategy for the fabrication of a skin-friendly thread/paper-based wearable system consisting of a sweat reservoir and a multi-sensing component for simultaneous in situ analysis of sweat pH and lactate. In the system, hydrophilic silk thread serves as the micro-channel to guide the liquid flow. Filter papers were functionalized to prepare colorimetric sensors for lactate and pH. The smartphone-based quantitative analysis shows that the sensors are sensitive and reliable. Although pH may interfere the lactate detection, the pH detected simultaneously could be employed to correct the measured data for the achievement of a precise lactate level. After being integrated with a hydrophobic arm guard, the system was successfully used for the on-body measurement of pH and lactate in the sweats secreted from the volunteers. This low-cost, easy-to-fabricate, light-weight and flexible thread/paper-based microfluidic sensing device may hold great potentials as a wearable system in human sweat analysis and point-of-care diagnostics.

Simultaneous detection of correlated multi-biomarkers on a single low-cost platform in ultra-low fluid volumes with robustness is in growing demand for the development of wearable diagnostics. A non-faradaic biosensor for the simultaneous detection of alcohol, glucose, and lactate utilizing low volumes (1–5 μL) of sweat is demonstrated. Biosensing is implemented using nanotextured ZnO films integrated on a flexible porous membrane to achieve enhanced sensor performance. The ZnO sensing region is functionalized with enzymes specific for the detection of alcohol, glucose, and lactate in the ranges encompassing their physiologically relevant levels. A non-faradaic chronoamperometry technique is used to measure the current changes associated with interactions of the target biomarkers with their specific enzyme. The specificity performance of the biosensing platform was established in the presence of cortisol as the non-specific molecule. Biosensing performance of the platform in a continuous mode performed over a 1.5-h duration showed a stable current response to cumulative lifestyle biomarker concentrations with capability to distinguish reliably between low, mid, and high concentration ranges of alcohol (0.1, 25, 100 mg/dL), glucose (0.1, 10, 50 mg/dL), and lactate (1, 50, 100 mM). The low detection limits and a broader dynamic range for the lifestyle biomarker detection are quantified in this research demonstrating its suitability for translation into a wearable device.