Sweating is a subtle way of regulating body temperature. In addition, like any other body fluid such as urine, blood or saliva, sweat too can disclose a lot about the physiological/pathological state of an individual. So far difficulties with sample collection had impeded progress in this direction. For example it is not as simple as you supplying a sample of urine or the technician's syringe drawing out a few millilitres of blood from your fingertip. One can't sweat copiously, as and when required; or even if one is forced to do so, after a session of vigorous exercise, sample collection and storage pose problems. Though not routinely analysed, as part of sports medicine or drug abuse detection sweat analysis is indeed done in the usual multistep process just as for blood or urine.
A multi-disciplinary team of scientists (Dept of Electrical Engg& Computer Science, Sensor & Actuator Centre, School of Integrative Biology, all part of the University of California, Berkeley; Stanford School of Medicine; Materials Science Division, Lawrence Berkeley Laboratory) asked the obvious question- What if we could overcome the barriers and design a simple, wearable sweat analysis device? A wristband or a headband would be both stylish and practical. Or an armband for those who don't like display.
They realised that the advantages of such a device would be multiple- first and foremost it will be noninvasive and can give a 24/7 account of the physiological status of the wearer. If data can be read out directly without having to reroute through a processing lab then it would be even better. The team had several challenges : understanding the complex chemistry of the sweat, identifying the biomarkers; selecting the appropriate sensors with controls, miniaturisation, mounting the arrays on a flexible band, so on and so forth. Their success story is reported in a recent issue of Nature(1). They have developed the wearable FISA, (Fexible Integrated Sensing Array) which could in real time monitor several biomarkers. Their device carries sensors for electrolytes( sodium and potassium ions), and metabolites (for glucose and lactate) and for body temperature. A combination of technologies are used for sensors. For example glucose and lactate sensors are based on the basic biochemistry of glucose oxidase and lactate oxidase reactions, ion selective electrodes for monitoring sodium and potassium and a resistance grid of chromium-gold micro wires for recording skin temperature.
The sensor array with appropriate reference systems designed as an FPCB, (flexible printed circuited board) is mounted on a polyester (polyethylene terephthalate) band. The elegance of the device rests in its simplicity and versatility. Signals from each of the sensors are put through an ADC( analog to digital converter) and fed to a micro controller. The built-in transciever enables data sharing.
The team subjected the device to extensive testing. Not only for its biochemical fidelity but also for its robustness. After all, the device must withstand the rough and tough lifestyle of the wearer.
The team subjected the device to extensive testing. Not only for its biochemical fidelity but also for its robustness. After all, the device must withstand the rough and tough lifestyle of the wearer.
References
1. Fully integrated wearable sensor arrays for multiplexed in situ perspiration analysis : Gao et al Nature 28 January 2016. ( Vol.529, page 509-514)
