Nonlinear plasmonics: SERS hot spot isolation and enhanced laser cell transfection

Surface-enhanced Raman scattering (SERS) is one of the most sensitive molecular spectroscopy techniques currently available. Using SERS, it is possible to obtain vibrational spectra from chemical quantities as small as a single molecule. However, it is challenging to have molecules of interest adsorb specifically to a substrate’s “hot spots,” or regions of largest electromagnetic enhancement. I will describe a nonlinear optical technique that masks SERS substrates such that only hot spots are available as molecular adsorption sites. Using this approach, we have demonstrated a 27-fold improvement in the SERS signal from 4 femtomoles of a test molecule. I will also describe the use of plasmonic substrates to enhance the interaction of ultrafast laser pulses with biological materials. In order to achieve high efficiency cell transfection, tightly focused femtosecond laser pulses have recently been employed to create sub-micron sized transient pores in cell membranes. Diffusion of external DNA through these pores can result in transfection of single cells. This process efficiently transfects cells, but suffers from extremely low throughput. I will describe our preliminary results in this area, achieved using large-area plasmonic substrates to eliminate the requirement of high numerical aperture focusing – an advance potentially enabling high efficiency cell transfection on clinically relevant scales.