Abstract

A biosensor based on the localized surface plasmon resonance (LSPR) response of a single Au nanoparticle was fabricated for the highly sensitive detection and quantification of a specific cancer biomarker. The spectral position changes of single Au nanoparticles induced by the binding of adsorbates and target analytes were effectively utilized as sensing tools. The LSPR responses of single Au nanoparticles were obtained by tracking the wavelength shift of the corresponding resonant Rayleigh light scattering spectra via dark-field microspectroscopy. Using prostate specific antigen as a model, an LSPR lambda max shift of about 2.75 nm was recorded by a primary immunoresponse corresponding to 0.1 pg/mL of the target antigen. The sensitivity of the immunoassay can be substantially enhanced, however, by a sandwich strategy. A PSA polyclonal antibody was used as an amplifying agent in the strategy. As a result, the linear dynamic range of the sensing platform was determined to be within the concentration range of 10(-4) to 0.1 ng/mL and a detectable minimum concentration of 0.1 pg/mL was identified, with an LSPR lambda max shift of about 4.96 nm. The results indicate that the aforementioned approach can significantly contribute to the fabrication of ultrasensitive biosensors, allowing the quantitative analysis of cancer-associated proteins