ABSTRACT
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.
Subject(s)
Biosensing Techniques/instrumentation , Fiber Optic Technology , Glycerides/analysis , Metal Nanoparticles/chemistry , Silver/chemistry , Surface Plasmon Resonance , Reproducibility of ResultsABSTRACT
We report an analysis of the transmission characteristics of long period gratings written in a linearly tapered optical fiber. Such gratings are best analyzed by a coupled mode theory that includes several cladding modes simultaneously. However, the numerical solution needs to be modified to take into account the changing propagation constants along the length of the fiber. The transmission spectra show certain distinctive features that depend on the grating period and choice of the phase-matched coupled cladding modes. For low-order modes, the resonances broaden and tend to vanish as the taper of the angle increases. For higher-order modes, the resonances remain well defined but shift toward higher or lower wavelengths and broaden. The transmission spectrum is also highly sensitive to a change in the ambient atmosphere.
