Improved localized surface plasmon resonance biosensing sensitivity based on chemically-synthesized gold nanoprisms as plasmonic transducers

Abstract

Supporting substrate attached gold nanostructures display localized surface plasmon resonance (LSPR) properties at the visible and near-infrared (NIR) wavelengths. The LSPR wavelength is very responsive to the refractive index of the surrounding medium, allowing simple label-free biosensing when biomolecules are irreversibly adsorbed onto nanostructures. Herein, we show that chemically synthesized gold nanoprisms with 22 nm average edge lengths are very efficient plasmonic transducers for label-free biosensing. The LSPR properties of gold nanoprisms on silanized glass substrate were investigated and readily influenced by bulk refractive index changes and local changes very close to the sensing surface due to the analyte adsorption. The nanoprisms had a 583 nm/RIU (1.62 eV/RIU) refractive index sensitivity and a 4.9 figure of merit (FOM). In addition, the nanoprism surface was modified with straight chain alkanethiols. The LSPR wavelength (λ_max) of chemisorbed nanoprisms on glass was very sensitive to surface modification by straight chain alkanethiols and linearly red-shifted by 2.5 nm with every methylene unit of the alkanethiol chain. Importantly, the biotin functionalized nanoprisms displayed red-shifts in λ_max upon streptavidin (SA) binding. The lowest SA concentration was measured to be 50 pM, much lower than gold nanospheres, nanorods, bipyramids, and nanostars.