Detection of transdermal biomarkers using gradient-based colorimetric array sensor

Eye-Readable and Wearable Colorimetric Sensor Arrays for In Situ Monitoring of Volatile Organic Compounds

Wearable sensors utilize changes in color as a response to physiological stimuli, making them easily recognizable by the naked eye. These colorimetric wearable sensors offer benefits such as easy readability, rapid responsiveness, cost-effectiveness, and straightforward manufacturing techniques. However, their applications in detecting volatile organic compounds (VOCs) in situ have been limited due to the low concentration of complex VOCs and complicated external interferences. Aiming to address these challenges, we introduced readable and wearable colorimetric sensing arrays with a microchannel structure and highly gas-sensitive materials for in situ detection of complex VOCs. The highly gas-sensitive materials were designed by loading gas-sensitive dyes into the porous metal-organic frameworks and further depositing the composites on the electrospun nanofiber membrane. The colorimetric sensor arrays were fabricated using various gas-sensitive composites, including eight dye/MOF composites that respond to various VOCs and two Pd2+/dye/MOF composites that respond to ethylene. This enables the specific recognition of multiple characteristic VOCs. A microfluidic channel made of polydimethylsiloxane (PDMS) was integrated with different colorimetric elements to create a wearable sensor array. It was attached to the surface of fruits to collect and monitor VOCs using the DenseNet classification method. As a proof of concept, we demonstrated the feasibility of the wearable sensing system in monitoring the ripening process of fruits by continuously measuring the VOC emissions from the skin of the fruit.

Predicting Chronological Age via the Skin Volatile Profile

Skin volatile emissions offer a noninvasive insight into metabolic activity within the body as well as the skin microbiome and specific volatile compounds have been shown to correlate with age, albeit only in a few small studies. Building on this, here skin volatiles were collected and analyzed in a healthy participant study (n = 60) using a robust headspace-solid phase microextraction (HS-SPME) gas chromatography-mass spectrometry (GC-MS) workflow. Following processing, 18 identified compounds were deemed suitable for this study. These were classified according to gender influences and their correlations with age were investigated. Finally, 6 volatiles (of both endogenous and exogenous origin) were identified as significantly changing in abundance with participant age (p < 0.1). The potential origins of these dysregulations are discussed. Multiple linear regression (MLR) analysis was employed to model age based on these significant volatiles as independent variables, along with gender. Our analysis shows that skin volatiles show a strong predictive ability for age (explained variance of 68%), stronger than other biochemical measures collected in this study (skin surface pH, water content) which are understood to vary with chronological age. Overall, this work provides new insights into the impact of aging on the skin volatile profiles which comprises both endogenously and exogenously derived volatile compounds. It goes toward demonstrating the biological significance of skin volatiles and will help pave the way for more rigorous consideration of the healthy "baseline" skin volatile profile in volatilomics-based health diagnostics development going forward.

MXene-based wireless facemask enabled wearable breath acetone detection for lipid metabolic monitoring

Breath acetone (BrAC) detection presents a promising scheme for noninvasive monitoring of metabolic health due to its close correlation to diets and exercise-regulated lipolysis. Herein, we report a Ti₃C₂T_x MXene-based wireless facemask for on-body BrAC detection and real-time tracking of lipid metabolism, where Ti₃C₂T_x MXene serves as a versatile nanoplatform for not only acetone detection but also breath interference filtration. The incorporation of in situ grown TiO₂ and short peptides with Ti₃C₂T_x MXene further improves the acetone sensitivity and selectivity, while TiO₂-MXene interfaces facilitate light-assisted response calibration. To further realize wearable breath monitoring, a miniaturized flexible detection tag has been integrated with a commercially available facemask, which enables facile BrAC detection and wireless data transmission. Through the hierarchically designed filtration-detection-calibration-transmission system, we realize BrAC detection down to 0.31 ppm (part per million) in breath. On-body breath tests validate the facemask in dynamically monitoring of lipid metabolism, which could guide dieter, athletes, and fitness enthusiasts to arrange diets and exercise activities. The proposed wearable platform opens up new possibility toward the practice of breath analysis as well as daily lipid metabolic management.

The development of wearable technologies and their potential for measuring nutrient intake: Towards precision nutrition

Appropriate food intake and nutritional status are crucial for the maintenance of health and disease prevention. Conventional dietary assessment is mainly based on comparisons of nutrient intakes with reference intakes, failing to meet the needs of personalised nutritional guidance based on individual nutritional status. Given their capability of providing insights into health information non-invasively in real time, wearable technologies offer great opportunities for nutrition monitoring. Nutrient metabolic profiles can be monitored immediately and continuously which could potentially offer the possibility for the tracking and guiding of nutrient intake. Here, we review and highlight the recent advances in wearable sensors from the perspective of sensing technologies for nutrient detection in biofluids. The integration of biosensors with wearable devices serves as an ideal platform for the analysis of biofluids including sweat, saliva and tears. The wearable sensing systems applied to the analysis of typical nutrients and important metabolites are demonstrated in terms of carbohydrates, proteins, lipids, vitamins, minerals and others. Taking advantage of their high flexibility and lightweight, wearable sensors have been widely developed for the in situ quantitative detection of metabolic biomarkers. The technical principles, detection methods and applications are summarised. The challenges and future perspectives for wearable nutrition monitoring devices are discussed including the need to better determine relationships among nutrient metabolic profile, nutrient intake and food intake. With the development of materials, sensing techniques and manufacturing processes, wearable technologies are paving the way towards personalised precision nutrition, although there is still a long way to go before they can be utilised for practical clinical applications. Joint research efforts between nutrition scientists, doctors, engineers and sensor researchers are essential to further accelerate the realisation of reliable and practical wearable nutrition monitoring platforms.

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.