Abstract
Plasmonic hotspots generate a blinking Surface Enhanced Raman Spectroscopy (SERS) effect that can be processed using Stochastic Optical Reconstruction Microscopy (STORM) algorithms for super-resolved imaging. Furthermore, by imaging through a diffraction grating, STORM algorithms can be modified to extract a full SERS spectrum, thereby capturing spectral as well as spatial content simultaneously. Here we demonstrate SERS and STORM combined in this way for super-resolved chemical imaging using an ultra-thin silver substrate. Images of gram-positive and gram-negative bacteria taken with this technique show excellent agreement with scanning electron microscope images, high spatial resolution at <50 nm, and spectral SERS content that can be correlated to different regions. This may be used to identify unique chemical signatures of various cells. Finally, because we image through as-deposited, ultra-thin silver films, this technique requires no nanofabrication beyond a single deposition and looks at the cell samples from below. This allows direct imaging of the cell/substrate interface of thick specimens or imaging samples in turbid or opaque liquids since the optical path doesn’t pass through the sample. These results show promise that super-resolution chemical imaging may be used to differentiate chemical signatures from cells and could be applied to other biological structures of interest.
Highlights
Optical microscopy has historically been diffraction limited as defined by Abbe’s limit, with resolution based upon the numerical aperture of the imaging system and the wavelength of the light
We show that by exploiting a blinking SERS effect processed using Stochastic Optical Reconstruction Microscopy (STORM) algorithms[36] and imaging through an optical diffraction grating, we are able to capture SERS spectral content and super-resolution spatial content at the same time
We have previously shown that SERS-STORM provides high-fidelity images of biological structures, such as collagen protein fibers[53], and the light can be band-pass filtered to provide some rudimentary chemical information from the emitted SERS light[54]
Summary
Optical microscopy has historically been diffraction limited as defined by Abbe’s limit, with resolution based upon the numerical aperture of the imaging system and the wavelength of the light. Providing a solution for super-resolution chemical imaging of cells or other samples of interest on extended plasmonic imaging substrates has not yet been fully investigated.
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