An Enzyme-Catalyzed Optical Fiber Optofluidic Laser Sensor for Cholesterol Detection Using Rhodamine B Hydrazide

A method for the determination of cholesterol using rhodamine derivatives as chromogenic substrates was proposed in this study. The oxidation of rhodamine B hydrazide (RBH) by hydrogen peroxide (H₂O₂) was catalyzed by a peroxide-mimicking enzyme to produce the fluorescent product. The reaction was further combined with the oxidase system to achieve indirect determination of cholesterol concentration, which can be catalyzed by cholesterol oxidase to produce H₂O₂ as an intermediate product. Optical fiber optofluidic lasers (FOFLs), as a sensitive biochemical detection platform, have the ability to distinguish small differences in the amount of fluorescence products generated by the reaction and were used to achieve sensitive cholesterol detection. Under optimized experimental conditions, the dynamic range of three orders of magnitude was obtained in the determination of H₂O₂ with a lower limit of detection (LOD) of 1.63 μM, and the assay time was as short as 3.5 min. On this basis, the designed cholesterol sensor obtained a linear range of 2.55-652.67 μM with a lower LOD of 2.55 μM and proved to have good selectivity. The possibility of cholesterol determination in human serum was initially tested. The sensor was also characterized by easy signal collection, wash-free procedure, controlled sample consumption, fast assay, low cost, and simple operation.