Sweat-based sensors

Morris, D., Coyle, S., Wu, Y., Lau, K.T., Wallace, G., Diamond, D., 2009. Bio-sensing textile based patch with integrated optical detection system for sweat monitoring. Sensors and Actuators B Chemical 139 (1), 231—236. 

Human sweat contains abundant information about a person s health status and thus is an excellent biofluid for noninvasive chemosensing. For example, sodium, lactate, ammonium, and calcium levels in sweat are indicators of electrolyte imbalance, and cystic fibrosis, physical stress, osteoporosis, and bone mineral loss, respectively. Sweat has also been used for monitoring a person s intoxication level and signs of drug abuse. Noninvasive electrochemical sensors for monitoring sweat can mainly be divided in to two types fabric/flexible plastic-based sensors and the epidermal-based sensors. 

We work on amelioration in this explorative work, including better electrodes, electronics, sensor context to overcome deficiencies due to impedance converter, electrodes, hand operation context such as pressure and sweat. More sophisticated instrumentation or (CMOS) circuit integration should be considered. The scalable adaptive multi-sensor interface and PC-based soft-computing subsystem can be harmonized towards System-on-Chip for high-performance and low-power solution in the future. 

Solid-state sensors for chloride, iodide, and fluoride are based on the solubility product of silver chloride or silver iodide particles in silicone rubber and a doped lanthanum fluoride single crystal, respectively. The fluoride-selective electrode was applied for the analysis of urine and bone tissue of people exposed to industrial sources as well as for control of therapeutic fluoride application for osteoporosis, whereas the chloride-selective sensor was applied to the analysis of sweat for the diagnosis of cystic fibrosis. In solid-state contact electrodes the solvent polymeric membrane is directly contacted to the solid field transducing element, although the reference electrode is separated from the ion-selective sensing pad. 

Within the framework of the EU-funded project BIOTEX, a multiple setup was chosen to analyse human sweat. Three types of sensors were employed — a pH, a sodium and a conductivity sensor — measuring, respectively, the pH, sodium concentration and electrical resistance of the sweat. But, in order to receive a good sample of the sweat to be analysed when wearing, a fluid-handling system based on Lycra was developed (Morris et al., 2009). 

Figure 6.4 Microfluidics in wearable biosensors, (a) The photolithography method to produce microfluidic channels by nsing negative photoresist SU-8. (b) Fused silica embedded microfluidic channels fabricated by spatiotemporally focusing the femtosecond laser beam (He, F, Xu, H., Cheng, Y, Ni, J., Xiong, H., Xu, Z., Sugioka, K., Midorikawa, K., 2010. Fabrication of microfluidic channels with a circular cross section using spatiotemporally focused femtosecond laser pulses. Opt. Lett 35,1106-1108). (c) A powerless epidermal pH sensor based on microfluidics (Benito-Lopez, F., Coyle, S., Byrne, R., O toole, C., Barry, C., Diamond, D., 2010. Simple Barcode System Based on lorwgels for Real lime pH-Sweat Monitoring, pp. 291-296).

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