A photonic crystal fiber-based fluorescence sensor for simultaneous and sensitive detection of lactic acid enantiomers

A photonic crystal fiber (PCF)-based fluorescence sensor is developed for rapid and sensitive detection of lactic acid (LA) enantiomers in serum samples. The sensor is fabricated by chemical binding dual enzymes on the inner surface of the PCF with numerous pore structures and a large specific surface area, which is suitable to be utilized as an enzymatic reaction carrier. To achieve simultaneous detection of L-LA and D-LA, the PCF with an aldehyde-activated surface is cut into two separate pieces, one of which is coated with L-LDH/GPT enzymes and the other with D-LDH/GPT enzymes. By being connected and carefully aligned to each other by a suitable sleeve tube connector, the responses of both L-LA and D-LA sensors are determined by laser-induced flourescence (LIF) detection. With the aid of enzyme-linked catalytic reactions, the proposed PCF sensor can greatly improve the sensitivity and analysis speed for the detection of LA enantiomers. The PCF sensor exhibits a low limit of detection of 9.5 mu M and 0.8 mu M, and a wide linear range of 25-2000 mu M and 2-400 mu M for L-LA and D-LA, respectively. The sensor has been successfully applied to accurate determination of LA enantiomers in human serum with satisfactory reproducibility and stability. It is indicated that the present PCF sensors would be used as an attractive analytical platform for quantitative detection of trace-amount LA enantiomers in real biological samples, and thus would play a role in disease diagnosis and clinical monitoring in point-of-care testing.