Raman spectroscopy of individual monocytes reveals that single-beam optical trapping ofmononuclear cells occurs by their nucleus

Abstract

We show that laser tweezers Raman spectroscopy of eukaryotic cells with a significantlylarger diameter than the tight focus of a single-beam laser trap leads to optical trapping ofthe cell by its optically densest part, i.e. typically the cell’s nucleus. Raman spectraof individual optically trapped monocytes are compared with location-specificRaman spectra of monocytes adhered to a substrate. When the cell’s nucleus isstained with a fluorescent live cell stain, the Raman spectrum of the DNA-specificstain is observed only in the nucleus of individual monocytes. Optically trappedmonocytes display the same behavior. We also show that the Raman spectra ofindividual monocytes exhibit the characteristic Raman signature of cells thathave not yet fully differentiated and that individual primary monocytes can bedistinguished from transformed monocytes based on their Raman spectra. This workprovides further evidence that laser tweezers Raman spectroscopy of individualcells provides meaningful biochemical information in an entirely non-destructivefashion that permits discerning differences between cell types and cellular activity.