Super-Resolution Chemical Imaging with Plasmonic Substrates

We demonstrate super-resolution chemical imaging with plasmonic nanoholes via surface-enhanced Raman spectroscopy (SERS). Due to large field enhancements, blinking behavior of SERS hot spots was observed and processed using a stochastic optical reconstruction microscopy (STORM) algorithm. This enabled localization to within 10 nm and high-resolution imaging. However, illumination of the sample with a static laser beam produced only SERS hot spots in fixed locations, leaving noticeable gaps in the final images. By randomly altering the phase profile of the incident beam with a simple optical diffuser, the hot spots were shifted across the plasmonic surface to illuminate different areas of the sample, thereby rendering a final image without the gaps. A tunable band-pass filter was used to preserve spectral information, allowing chemical contrast imaging. Images were then compared to those obtained with a scanning electron microscope. Finally, we show that super-resolution SERS images can also be obtained with our dynamic illumination technique on even the most basic plasmonic substrate: as-deposited rough silver films. These results show significant potential for the use of simple plasmonic substrates with straightforward illumination and collection schemes for super-resolution chemical imaging.