Fluorescence imaging is typically used to study biomolecules with high sensitivity and resolution, but many biological molecules are fluorescent themselves, limiting the potential of this technique. Surface enhanced Raman spectroscopy (SERS) is capable of high sensitivity but is not inhibited by the problems of autofluorescence. Folate receptors (FRs) are known to be overexpressed in many cancer cells.
Scientists in China have made graphene oxide–silver nanoparticle composites functionalised with folic acid (which can bind to the FRs). These were introduced into cancer cells and the localisation was then visualised using SERS mapping (the graphene oxide signal is very strong and can be used as an identifier of the composite). Only the FR-positive cells show a signal on the SERS map. The method is very fast with an integration time of 0.06s per pixel.