Optical sensing for perspiration

Perspiration monitoring has uses in personal health, fitness and hygiene and is a measure of both physical and mental condition. We developed a sensor that can be worn during daily activity and is unobtrusive, hygienic, with sterilised sensing elements that were easily interchangeable. In this presentation we show the results of stress induced perspiration in a number of human volunteers. Polymer optical coatings to detect moisture were developed to clad polymer optical fibres (POF). These claddings were sensitized to moisture to affect the evanescent field and thus the light guided within the fibre, forming POF sensors to continuously monitor human perspiration in response to changes in environmental conditions, physical and mental activity, medical condition or psychological stress. The cladding for these experiments consisted of a HEMA polymer and the dye was a sodium fluorescein. The HEMA polymer was chosen for its hydrophilic properties and has a similar refractive index to the PMMA cladding it replaced. Sodium Fluorescein responds to humidity by fluorescing in the green at 516nm when exited by blue light at 490nm. For this project we wanted to differentiate between high levels of humidity and droplets of liquid sweat, to do this we chose not measure the fluorescent properties of the dye but instead exploited the difference in absorption of the dye in its dry state and in solution. The results show that the sensors can detect perspiration induced physically in a controlled hot room environment and when induced by mental stress at ambient temperature and humidity.