Label-free nanoscale mapping of intracellular organelle chemistry

Abstract

The ability to image cell chemistry at the nanoscale is key for understanding cell biology, but many optical microscopies are restricted by the ~(200–250)nm diffraction limit. Electron microscopy and super-resolution fluorescence techniques beat this limit, but rely on staining and specialised labelling to generate image contrast. It is challenging, therefore, to obtain information about the functional chemistry of intracellular components. Here we demonstrate a technique for intracellular label-free chemical mapping with nanoscale (~30 nm) resolution. We use a probe-based optical microscope illuminated with a mid-infrared laser whose wavelengths excite vibrational modes of functional groups occurring within biological molecules. As a demonstration, we chemically map intracellular structures in human multiple myeloma cells and compare the morphologies with electron micrographs of the same cell line. We also demonstrate label-free mapping at wavelengths chosen to target the chemical signatures of proteins and nucleic acids, in a way that can be used to identify biochemical markers in the study of disease and pharmacology.

Infrared nanoimaging of neuronal ultrastructure and nanoparticle interaction with cells

“…Taken together, these findings argue that s-SNOM imaging using the amide I absorption band will allow us to locally map the protein/nucleobase distribution across the cellular organelles. 27,29 They also suggest that imaging at the 1738 cm −1 absorption feature should generate images that are most closely correlated with TEM imaging. This is partly because it is imaging the same OsO 4 stain that generates the TEM contrast, but it is also because at this wavelength, we are measuring the distribution of the resin, and this has a strong negative correlation with the local density of the biomaterial.…”

“…The main active vibrational modes excited in these samples are summarised in Table 1. The FTIR spectrometer averages over a large sample area with a high resin content dominates the absorption spectrum at these wavelengths, but this does not stop us from using s-SNOM in this wavelength range 29 for small-area nanoscale chemical mapping. These data agreed with previously reported FTIR spectra of non-embedded hippocampal neurons (900-1800 cm −1 ).…”

“…In contrast to TEM, s-SNOM has the advantage of being able to provide cell ultrastructure morphology whilst at the same time inferring chemical species. Such ultrastructural features include cell regions and organelles with enriched species, such as proteins [25][26][27][28][29][30] and nucleobases 29 .…”