Enzymatic Plasmonic Optical Fiber Biosensor for Uric Acid Detection

Uric acid plays important roles in the body, acting as an antioxidant, contributing to the elimination of metabolic waste, and helping to combat some infections. Alterations in uric acid concentration can be important indicators of disease and their real-time and point-of-care monitoring is of extreme importance, for instance in primary care facilities. Optical fibre biosensors are a promising option, allowing real-time detection, quantification, and monitoring of uric acid concentrations in blood plasma or urine. In this work, enzymatic plasmonic sensors were developed for the detection of uric acid using multimode optical fibres composed of a 400 µm silica core and a polymer cladding. To prepare the sensors, the coating and cladding were removed from a section at the fibre tip, and nano film of gold was deposited on their surface, obtaining gold-coated sensors at the fibre tips (Au-tips). Initially, the sensor was characterized to bulk refractive index, exhibiting a sensitivity of 1420.7 ± 59.8 nm/RIU. The Au-tip was biofunctionalized with the enzyme uricase and detection tests were carried out. Uric acid detection tests revealed a response consistent with the Michaelis-Menten function, which was employed to assess the enzymatic kinetics of uricase immobilized on the Au-tips.