A taper-in-taper fiber optic biosensor based on Mach-Zehnder interferometer for human sweat pH detection

Human sweat is mainly composed of water and small amounts of electrolytes (e.g. sodium, chloride, potassium, calcium), metabolites, amino acid and proteins. Variation of the pH value in sweat is closely associated with the health status of person that can indicate disease and metabolic activity. This study demonstrates a newly developed wearable sensor based on taper-in-taper structure for sweat pH detection with high sensitivity. To fabricate this biosensor, the pH sensitive PVA-PAA hydrogel layer (polyvinyl alcohol-polyacrylic acid) and pH sensitive indicator MO (Methyl Orange) are combined to be a coating layer of optical fiber with a three-dimensional network porous structure. The proposed optical biosensor in taper-in-taper structure for human sweat pH monitoring is demonstrated to have high sensitivity, wide dynamic range and short time response, which also present excellent long-term stability and durability that can be potentially applied in high-performance smart wearable device for health management.