Over the last few years, the unique localized surface plasmon resonance (LSPR) properties of plasmonic nanostructures have been used to design label-free biosensors. In this research, we demonstrate that it is the difference in edge length of gold nanoprisms that significantly influences their bulk refractive index sensitivity and local sensing efficiency. Nanoprisms with edge lengths in the range of 28-51 nm were synthesized by the chemicalreduction method and sensing platforms were fabricated by chemisorptions of these nanoprisms onto silanized glass substrates. The plasmonic nanosensors prepared from 28 nm edge length nanoprisms exhibited the largest sensitivity to change in bulk refractive index with a value of 647 nm/RIU. The refractive index sensitivity decreased with increasing edge length, with nanoprisms of 51 nm edge lengths displaying a sensitivity of 384 nm/RIU. In contrast, we found that the biosensing efficiency of sensing platforms modified with biotin increased with increasing edge length, and the sensing platforms fabricated from 51 nm edge length nanoprisms displaying the highest local sensing efficiency. The lowest concentration of streptavidin that could be measured reliably was 1.0 pM and the limit of detection for the sensing platforms fabricated from 51 nm edge length nanoprisms was 0.5 pM, which is much lower than found with gold bipyramids, nanostars, and nanorods.

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 (l 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 l max upon streptavidin (SA) binding. The lowest SA concentration was measured to be 50 pM, much lower than gold nanospheres, nanorods, bipyramids, and nanostars.