Application of EBL fabricated nanostructured substrates for surface enhanced Raman spectroscopy detection of protein A in aqueous solution

Surface enhanced Raman spectroscopy (SERS) allows detection of unique signatures of molecular vibrations, which identify molecules adsorbed on nanostructured substrates. However, for SERS detection techniques to be reproducible, highly regular metallic nanostructures must be fabricated. In this work, the authors have optimized high resolution electron beam lithography (EBL) to fabricate gold nanostructures on fused silica substrates for efficient SERS biodetection. 30 keV EBL exposures employing an appropriate anticharging scheme followed by development have been used to fabricate arrays of nanopits in PMMA on a fused silica substrate, with subsequent evaporation of Au and lift-off to obtain arrays of Au dots. The EBL process has been tuned to obtain arrays of dots with a 50 nm pitch and different interdot gaps. The SERS substrates have been biofunctionalized by self-assembled monolayers (of 11-mercaptoundecanoic acid) and a biological analyte protein A immobilized on the substrates. In order to detect the protein in its natural environment, the biofunctionalized samples were maintained in deionized water. SERS spectra of protein A were subsequently acquired allowing detection of many vibrational modes of protein A in aqueous solution.