Label-free optical biosensor based on localized surface plasmon resonance of immobilized gold nanorods.

We describe the fabrication and characterization of a localized surface plasmon resonance (LSPR) biosensor that utilizes gold nanorods immobilized as the optical transducer which requires the intensity change at a single wavelength to be monitored as a function of receptor-analyte binding at the nanorod surface. In contrary to free gold nanorods suspended in an aqueous solution with high sensitivity to the longitudinal plasmon wavelength to the surrounding environment, the intensity of the longitudinal plasmon band based on immobilized gold nanorods is more sensitive to changes in the surrounding dielectric properties than the change in the longitudinal plasmon wavelength. Quantitative calculation gives a linear equation between the concentration (X) of the test sample and intensity of LPB (Y) as Y=0.0881+12.9502X and 0.1 pM anti-goat can be detected using this IgG probe in this study. This sensor chip made of immobilized gold nanorods is very stable. The immobilized gold nanorods preserved under 4 degrees C for 1 year yield almost the same extinction spectrum as the original nanorods. This study reveals a reliable and sensitive method to measure the intensity of longitudinal plasmon bands based on the highly stable LSPR substrate. Moreover, the performance is comparable to dynamic SPR measurements in immunoassays and can monitor the receptor-analyte reactions in real time.