Plasmonic metal nanostructure array by glancing angle deposition for biosensing application

This paper investigates the application of gold nanostructure array fabricated on a layer of closely packed polystyrene (PS) nanospheres as a plasmonic chemical or biological sensor. The sensing chip was fabricated by first functionalizing a layer of closely packed PS nanospheres as a colloidal template, and then depositing the gold at an oblique angle, where the nanospheres shaded each other and formed a gold nanostructure on the top of the PS nanospheres. The surface profiles of the gold nanostructures on PS nanospheres were investigated by Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM). A chip fabricated at the deposition angle of 30° was found to have a high consistency for keeping the shape of the nanostructures on a large fabrication area. The sensorʹs bulk refractive index sensitivity was detected to be 255 nm per RIU. In the study of biotin–streptavidin binding, the limit of detection (LOD) for streptavidin was 10 nM, and the surface-confined thermodynamic binding constant is 3 × 109 M−1. The plasmonic signal is amplified by using biotinylated Au colloids as labels. To further demonstrate the sensing capability, biotin–antibiotin IgG binding with a lower affinity constant was tested. The obtained LSPR peak shift caused by IgG (molecular weight 150 kDa) was about 2 times larger than that by streptavidin (molecular weight 60 kDa). The correlation of peak shift to the molecular weight further confirms the sensing capability of the chip for quantitative detection of proteins.