A surface plasmon resonance based fiber optic sensor for the detection of triacylglycerides (TG) has been fabricated by immobilizing lipase enzyme (Lip11) on Zinc Oxide (ZnO) nanorods grown over a silver (Ag) film. The sensor probe exhibits high sensitivity for 0–500 mg/dl triacylglyceride concentration, which covers both the physiological range and high levels (which indicate coronary heart disease and hyperlipoprotenimia). After coating a silver layer of 40 nm on the fiber surface by the thermal evaporation, the ZnO nanorods are grown over the silver layer by first preparing nanoparticles (NPs) of ZnO using the Pacholski method. The silver coated fiber is then dipped into the ZnO nanoparticles solution and the ZnO NPs work as a seed layer for the growth of ZnO nanorods on the fiber surface. Here, ZnO nanorods play a double role in the sensing operation. They act as a matrix with high isoelectric point (9.5) which makes it possible to directly immobilize lipase enzyme which has low isoelectric point (4.9) by electrostatic adsorption without any requirement of functionalization. Second the ZnO nanorods layer enhances the sensitivity of the sensor as it works as a high index layer over the metal layer. As the concentration of TG change in the vicinity of the sensor, the refractive index and thickness of bio-recognition enzyme layer change and as a consequence the resonance wavelength in the absorbance spectra changes. The sensor has a fast response, high selectivity and sensitivity, low cost, label free detection and ease of fabrication.
A label-free technique for the detection of triacylglycerides by a localized surface plasmon resonance (LSPR)–based biosensor is demonstrated. An LSPR-based fiber-optic sensor probe is fabricated by immobilizing lipase enzyme on silver nanoparticles (Ag-NPs) coated on an unclad segment of a plastic clad optical fiber. The size and shape of nanoparticles were characterized by high-resolution transmission electron microscopy and UV–visible spectroscopy. The peak absorbance wavelength changes with concentration of triacylglycerides surrounding the sensor probe, and sensitivity is estimated from shift in the peak absorbance wavelength as a function of concentration. The fabricated sensor was characterized for the concentration of triacylglyceride solution in the range 0 to 7 mM. The sensor shows the best sensitivity at a temperature of 37°C and pH 7.4 of the triacylglycerides emulsion with a response time of 40 s. A sensitivity of 28.5 nm/mM of triacylglyceride solution is obtained with a limit of detection of 0.016 mM in the entire range of triacylglycerides. This compact biosensor shows good selectivity, stability, and reproducibility in the entire physiological range of triacylglycerides and is well-suited to real-time online monitoring and remote sensing.
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