The paper argues for the need for a healthcare system that provides proactive health monitoring and treatment before the onset of diseases. This is in contrast to the current reactive system where patients seek medical attention after developing symptoms. Wearable biosensors, particularly those that analyze sweat, offer a promising solution for continuous, non-invasive, real-time physiological monitoring. Sweat, unlike other biofluids like blood, urine, tears, saliva, or tissue fluids, offers several advantages for wearable sensing due to its accessibility, non-invasive nature, and rich content of biomarkers reflecting the body's physiological state.

The paper reviews the existing literature on wearable sweat sensors, particularly those utilizing electrochemical detection methods. It highlights the rapid advancements in areas like multiplexed biosensing, energy harvesting devices, and soft microfluidics, all contributing to the progress of wearable electrochemical sweat-sensing platforms.

The methodology involves a comprehensive review of existing research on wearable electrochemical sweat sensors. The paper is structured to provide a detailed overview of the field. It begins by discussing the advantages of using sweat for analysis, including its biomarker content and methods for stimulating and collecting sweat. Next, it delves into the components of wearable electrochemical sweat sensors, covering sensing elements, electronic components, and power supply technologies. This section provides a thorough exploration of materials, electrochemical detection methods, and the integration of microfluidics. The review further explores typical sensing platforms for different analytes, such as electrolytes, metabolites, drugs, and trace metals. Lastly, the paper concludes by outlining future challenges and prospective advancements in the development of wearable sweat sensors.

The paper highlights several key findings: * **Advantages of Sweat for Wearable Sensing:** Sweat offers significant advantages over other biofluids due to its accessibility, non-invasive nature, and rich content of biomarkers reflecting the body's physiological state. * **Biomarkers in Sweat:** Sweat contains a variety of biomarkers, including electrolytes (Na+, K+, Cl-, Ca2+, NH4+), metabolites (glucose, lactate, alcohol, uric acid), trace elements (Zn, Cu), and other analytes (cortisol, tyrosine, neuropeptides, cytokines). These biomarkers can provide valuable information about hydration, electrolyte balance, muscle fatigue, blood glucose levels, stress, and other health conditions. * **Sweat Stimulation and Collection Methods:** Sweat can be collected using passive methods (intense exercise) or active methods (iontophoresis). Iontophoresis uses electrical stimulation to induce sweat secretion even in sedentary scenarios. * **Microfluidic Devices:** Microfluidic devices play a crucial role in enhancing sweat collection and transport, minimizing sample leakage, evaporation, and contamination. They improve temporal resolution and accuracy in sweat analyte measurements. * **Electrochemical Detection Methods:** Electrochemical detection methods, including amperometry, potentiometry, and voltammetry, are widely used in wearable sweat sensors. The choice of method depends on the characteristics of the target analyte. * **Materials for Wearable Sweat Sensors:** The materials used for wearable sweat sensors must be flexible, stretchable, and biocompatible. Common materials include polymers (PET, PI, PDMS, PU, PMMA), fabrics, and paper. * **Electronic Components:** Electronic components are essential for signal processing, conditioning, and transmission. Wireless communication protocols like Bluetooth, NFC, and RFID are used to transfer data to a smartphone application for analysis and monitoring. * **Power Components:** The power supply is critical for continuous operation of wearable sweat sensors. Lithium-ion batteries, energy harvesting devices (solar cells, triboelectric nanogenerators, microbial biofuel cells), and supercapacitors are employed as power sources. * **Typical Wearable Electrochemical Sweat Sensors:** The paper highlights the development of wearable sweat sensors for monitoring electrolytes and metabolites, detecting heavy metals and drugs, and analyzing other analytes like hormones, proteins, and cytokines. These sensors have evolved from single analyte sensing to multiplexed detection, with ongoing advancements in integration and functionality.

The paper discusses the significance of wearable electrochemical sweat sensors for personalized health monitoring. The authors highlight the potential for these sensors to revolutionize healthcare by enabling continuous, non-invasive monitoring of various physiological parameters. They emphasize the importance of addressing current challenges, such as improving the reliability of sweat samples, developing efficient energy utilization devices, and enhancing detection methods for low-concentration analytes. The paper also underscores the need for more research on methods to stimulate and collect sweat in sedentary environments.

The review concludes by highlighting the significant progress made in the field of wearable electrochemical sweat sensors, showcasing their potential for personalized health monitoring and disease detection. It emphasizes the importance of addressing challenges related to sweat sample reliability, energy utilization, and detection of low-concentration analytes. The authors suggest that future research should focus on developing more integrated, multifunctional sweat sensing platforms, improving sweat stimulation and collection methods, and exploring alternative power sources.

While the review provides a comprehensive overview of wearable electrochemical sweat sensors, it acknowledges certain limitations. One limitation is the lack of standardized protocols for sweat stimulation and collection, which can lead to variability in sweat composition and affect the reliability of results. Additionally, the review acknowledges the challenges in detecting low-concentration analytes in sweat, requiring further advancements in sensor design and sensitivity. The review also points out the need for more research on power components, particularly in developing energy harvesting devices that can provide reliable and efficient power for continuous monitoring.