The Evolving Role of Proteins in Wearable Sweat Biosensors

Advances in Non-Electrochemical Sensing of Human Sweat Biomarkers: From Sweat Sampling to Signal Reading

Sweat, commonly referred to as the ultrafiltrate of blood plasma, is an essential physiological fluid in the human body. It contains a wide range of metabolites, electrolytes, and other biologically significant markers that are closely linked to human health. Compared to other bodily fluids, such as blood, sweat offers distinct advantages in terms of ease of collection and non-invasive detection. In recent years, considerable attention has been focused on wearable sweat sensors due to their potential for continuous monitoring of biomarkers. Electrochemical methods have been extensively used for in situ sweat biomarker analysis, as thoroughly reviewed by various researchers. This comprehensive review aims to provide an overview of recent advances in non-electrochemical methods for analyzing sweat, including colorimetric methods, fluorescence techniques, surface-enhanced Raman spectroscopy, and more. The review covers multiple aspects of non-electrochemical sweat analysis, encompassing sweat sampling methodologies, detection techniques, signal processing, and diverse applications. Furthermore, it highlights the current bottlenecks and challenges faced by non-electrochemical sensors, such as limitations and interference issues. Finally, the review concludes by offering insights into the prospects for non-electrochemical sensing technologies. By providing a valuable reference and inspiring researchers engaged in the field of sweat sensor development, this paper aspires to foster the creation of innovative and practical advancements in this domain.

Innovative Metabolic Rate Sensing Approach for Probing Human Thermal Comfort

The human metabolic rate has attracted increasing interest as it is the most critical parameter in thermal comfort evaluation, a challenging field, while it is always determined imprecisely. The main issue hampering metabolic rate portable measurement is a lack of reliable methods. Current measuring solutions are unsatisfactory because nonportable bulky size systems and disturbance masks are required. This paper proposes a novel metabolic rate measurement model, which we believe is the first of its kind, to accurately identify and predict human metabolism values via wearable technology. Based on a newly developed theory, the designed wearable metabolic rate sensor was fabricated to measure key parameters: heart rate, heat loss, and skin resistance. Together with the body muscle rate, the new final linear metabolic rate model showed easy prediction capability. Eight volunteers were invited for the experiment under three conditions under four activity intensity states. First, the results significantly verify that a linear relationship exists between the metabolic rate tested by the Quark CPET instrument and our proposed model, with a high coefficient of determination (R2 ≈ 0.90). The correlation model is worth mentioning because it coincides with our hypothesis, with at least 95% overall accuracy and less than 2% uncertainty under each condition. Second, the most remarkable finding is that our model is exceedingly suitable (R2 ≈ 0.90) for the same person, regardless of the experimental temperature. Finally, validation is conducted in a wider metabolic range, further strengthening confidence in our metabolic rate estimation approach. In summary, based on an innovative methodology, our novel metabolic rate sensor is wearable, comfortable, real-time achievable, and miniaturized compared with the existing equipment. This paper sheds new light on human metabolic rate measurement and prediction. Furthermore, our approach and designed sensor can be applied to evaluate indoor thermal comfort precisely, thus leading to reduced energy consumption.

Enhancing On-Skin Analysis: A Microfluidic Device and Smartphone Imaging Module for Real-Time Quantitative Detection of Multianalytes in Sweat

Wearable sweat sensors present exciting opportunities for advancing personal health monitoring and noninvasive biomarker measurements. However, existing sensors often fall short in accurate detection of low analyte volumes and concentrations and lack multimodal sensing capabilities. Herein, we present a highly portable four-channel microfluidic device capable of conducting simultaneous sweat sampling and fluorometric sensing of potential biomarkers, such as l-Tyr, l-Trp, Crt, and NH4+, specifically designed for kidney disease monitoring. Our microfluidic device seamlessly integrates with smartphones, facilitating easy data retrieval and analysis. The core of the sensing array is a novel fluorometric solid-state mechanism utilizing carbon polymer dots derived from dopamine, catechol, and o-phenylenediamine monomers embedded in gelatin hydrogels. The sensors exhibit exceptional performance, offering linear ranges of 5-275, 6-170, 4-220, and 5-170 μM, with impressively low detection limits of 1.5, 1.2, 1.3, and 1.4 μM for l-Tyr, l-Trp, Crt, and NH4+, respectively. Through meticulous optimization of operational variables, comprising the temperature, sample volume, and assay time, we achieved the best performance of the device. Furthermore, the sensors exhibited remarkable selectivity, effectively distinguishing between biologically similar species and other potential biological compounds found in sweat. Our evaluation also extended to monitoring kidney diseases in patients and healthy individuals, showcasing the device's utility in world scenarios. Promising results showcase the potential of low-cost, multidiagnostic microfluidic sensor arrays, especially with synthetic skin integration, for enhanced disease detection and healthcare outcomes.

A wireless patch for the monitoring of C-reactive protein in sweat

The quantification of protein biomarkers in blood at picomolar-level sensitivity requires labour-intensive incubation and washing steps. Sensing proteins in sweat, which would allow for point-of-care monitoring, is hindered by the typically large interpersonal and intrapersonal variations in its composition. Here we report the design and performance of a wearable and wireless patch for the real-time electrochemical detection of the inflammatory biomarker C-reactive (CRP) protein in sweat. The device integrates iontophoretic sweat extraction, microfluidic channels for sweat sampling and for reagent routing and replacement, and a graphene-based sensor array for quantifying CRP (via an electrode functionalized with anti-CRP capture antibodies-conjugated gold nanoparticles), ionic strength, pH and temperature for the real-time calibration of the CRP sensor. In patients with chronic obstructive pulmonary disease, with active or past infections or who had heart failure, the elevated concentrations of CRP measured via the patch correlated well with the protein's levels in serum. Wearable biosensors for the real-time sensitive analysis of inflammatory proteins in sweat may facilitate the management of chronic diseases.

Endowing textiles with self-repairing ability through the fabrication of composites with a bacterial biofilm

To address the increasing environmental footprint of the fast-growing textile industry, self-repairing textile composites have been developed to allow torn or damaged textiles to restore their morphological, mechanical, and functional features. A sustainable way to create these textile composites is to introduce a coating material that is biologically derived, biodegradable, and can be produced through scalable processes. Here, we fabricated self-repairing textile composites by integrating the biofilms of Escherichia coli (E. coli) bacteria into conventional knitted textiles. The major structural protein component in E. coli biofilm is a matrix of curli fibers, which has demonstrated extraordinary abilities to self-assemble into mechanically strong macroscopic structures and self-heal upon contact with water. We demonstrated the integration of biofilm through three simple, fast, and scalable methods: adsorption, doctor blading, and vacuum filtration. We confirmed that the composites were breathable and mechanically strong after the integration, with improved Young's moduli or elongation at break depending on the fabrication method used. Through patching and welding, we showed that after rehydration, the composites made with all three methods effectively healed centimeter-scale defects. Upon observing that the biofilm strongly attached to the textiles by covering the extruding textile fibers from the self-repair failures, we proposed that the strength of the self-repairs relied on both the biofilm's cohesion and the biofilm-textile adhesion. Considering that curli fibers are genetically-tunable, the fabrication of self-repairing curli-expressing biofilm-textile composites opens new venues for industrially manufacturing affordable, durable, and sustainable functional textiles.

Wearable potentiometric biosensor for analysis of urea in sweat

Herein, we introduce wearable potentiometric biosensors on screen-printed carbon electrodes (SPCEs) for on-body and on-site monitoring of urea in sweat. The biosensor architecture was judiciously designed to detect urea at different pHs and incorporate a pH sensor, thus containing polyaniline ink, urease bioink and a polyvinylchloride membrane. Urea detection could be performed in the wide range from 5 to 200 mM at pH 7.0, encompassing urea levels in human sweat. The biosensor response was fast (incubation time 5 min), with no interference from other substances in sweat. Reliable urea detection could be done in undiluted human sweat with a skin-worn flexible device using the pH correction strategy afforded by the pH sensor. The performance of the epidermal biosensor was not affected by severe bending strains. The feasibility of mass production was demonstrated by fabricating epidermal flexible biosensors using slot-die coating with a roll-to-roll technique.

A Mini-Review on Reflectins, from Biochemical Properties to Bio-Inspired Applications

Some cephalopods (squids, octopuses, and cuttlefishes) produce dynamic structural colors, for camouflage or communication. The key to this remarkable capability is one group of specialized cells called iridocytes, which contain aligned membrane-enclosed platelets of high-reflective reflectins and work as intracellular Bragg reflectors. These reflectins have unusual amino acid compositions and sequential properties, which endows them with functional characteristics: an extremely high reflective index among natural proteins and the ability to answer various environmental stimuli. Based on their unique material composition and responsive self-organization properties, the material community has developed an impressive array of reflectin- or iridocyte-inspired optical systems with distinct tunable reflectance according to a series of internal and external factors. More recently, scientists have made creative attempts to engineer mammalian cells to explore the function potentials of reflectin proteins as well as their working mechanism in the cellular environment. Progress in wide scientific areas (biophysics, genomics, gene editing, etc.) brings in new opportunities to better understand reflectins and new approaches to fully utilize them. The work introduced the composition features, biochemical properties, the latest developments, future considerations of reflectins, and their inspiration applications to give newcomers a comprehensive understanding and mutually exchanged knowledge from different communities (e.g., biology and material).

Transducer Technologies for Biosensors and Their Wearable Applications

The development of new biosensor technologies and their active use as wearable devices have offered mobility and flexibility to conventional western medicine and personal fitness tracking. In the development of biosensors, transducers stand out as the main elements converting the signals sourced from a biological event into a detectable output. Combined with the suitable bio-receptors and the miniaturization of readout electronics, the functionality and design of the transducers play a key role in the construction of wearable devices for personal health control. Ever-growing research and industrial interest in new transducer technologies for point-of-care (POC) and wearable bio-detection have gained tremendous acceleration by the pandemic-induced digital health transformation. In this article, we provide a comprehensive review of transducers for biosensors and their wearable applications that empower users for the active tracking of biomarkers and personal health parameters.