Electron Beam Lithography (EBL) engineered nanostructures for biosensing

Surface-Enhanced-Raman-Scattering (SERS) is potentially a very sensitive spectroscopic technique for the detection of biological agents (i.e., proteins, viruses or bacteria). However, since initial reports, its utility has not been realized. Its limited acceptance as a routine analysis technique for biological agents is largely due to the lack of reproducible SERS-active substrates. Most established SERS substrate fabrication schemes are based on self-assembly of the metallic (typically, Au, Ag, Pt, Pd or Cu) particles responsible for enhancement. Further, these protocols do not lend themselves to the stringent control over the enhancing feature shape, size, and placement on a nanometer scale. SERS can be made a more robust and attractive spectroscopic technique for biological agents by developing quantifiable, highly sensitive, and highly selective SERS-active substrates. Electron Beam Lithography (EBL), a semiconductor fabrication technique, can be utilized to address many of the obstacles which have limited the broad acceptance of SERS. Specifically, EBL can be employed to precisely control the shape, size and position (on a nanometer scale) of the SERS substrate enhancing features. Since Ashkin's seminal work in the early 1970s, the optical trapping phenomenon has been broadly accepted as a powerful tool to study micrometer-scale biological particles. Recently, research in our laboratory has demonstrated that it is possible to combine the Optical Trapping phenomenon and SERS to develop a high sensitivity spectroscopic technique for the detection of individual bacterial spores. Highly reproducible SERS-active substrates fabricated using EBL have been utilized with this novel spectroscopic technique to investigate the utility of SERS technique for the spectral discrimination of bacterial spores. The SERS substrate fabrication methodology, substrate reproducibility and SERS spectral reproducibility will be discussed.