An Intrinsic Optical Fiber Uric Acid Sensor Using a Molecularly Imprinted Chitosan Membrane-Coated Optical Fiber as a Transducer

An intrinsic optical fiber uric acid (UA) sensor has been developed using a molecularly imprinted chitosan (MIC) membrane-coated optical fiber as a transducer. The MIC was prepared by crosslinking chitosan with glutaraldehyde as a crosslinking reagent and UA as the template molecule. After an MIC membrane was coated on the surface of a bent optical fiber probe (BOFP), the template UA molecules were washed out of the membrane by using a diluted ammonia solution (0.10 M). This MIC membrane-coated BOFP was deployed into a sample solution for analyzing UA concentration. UA in the sample solution was selectively extracted/concentrated into the MIC membrane, while interference species in the sample solution were blocked from entering into the membrane. UA extracted into the MIC membrane was detected by passing a light beam through the BOFP and the intrinsic optical absorption signal at 315 nm by UA itself was detected as a sensing signal. There is no chemical reaction involved, and no chemical reagent is needed when using this sensor to analyze UA in a sample solution. Compared with a bare fiber BOFP, MIC membrane extraction of UA from a sample solution increased the sensor’s sensitivity by 1.0 × 104 times. The sensor achieved a detection limit of 0.049 µg/mL with a linear calibration concentration that ranged up to 5.0 µg/mL. The sensor demonstrates a good precision in analyzing UA in a urine sample with RSD% = 2.9%. This is a selective sensor; species potentially co-existing in regular urine samples with UA were tested, and were found not to cause interference. This sensor selectively responds to UA in its acid form, but is not sensitive to urate anions, which is different from most reported methods for analyzing UA. The sensor has been tested for analyzing UA in a urine sample and the obtained results demonstrate the feasibility of this sensor in real-world applications of analyzing UA in urine samples.