Bio-chemical Raman imaging using targeted-SERS

Raman and SERS spectral imaging, which consists in reconstructing a Raman intensity profile over a 2D or 3D section of a given sample (in presence or not of a nanosubstrate), allow to visualise the variation of the chemical composition associated with the micro-structure of the sample. In particular, targeted-SERS imaging also enables the specific imaging of various macromolecules targeted by SERS probes in complex biological samples such as cancerous cells. To illustrate the versatility of Raman imaging, we describe two applications that were investigated recently in our laboratory. First, 3D Raman imaging was used to investigate a microcavity in a matrix of gypsum, revealing fossilised carbonaceous compounds dispersed in a filamentous shape, highly suggesting the presence of fossilised bacteria. Secondly, SERS probes were synthesised to specifically target the FRα receptor of folic acid which are often over-expressed at the surface of cancerous cells. Confocal Raman imaging was used to study the localization of the probes after incubation with KB cells (oral cancer) to confirm the specific targeting of FRα membrane receptors (Fig. 1). Moreover, our SERS probes allowed us to distinguish two different cancerous cell lines (namely KB and PC-3), based on the degree of expression of the FRα receptor of these two lines (high for KB and low for PC-3). In the future, these SERS probes may be used for distinguishing between cancerous and healthy cells since healthy cells have a lower degree of expression of FRα.