Protein-specific Raman imaging of glycosylation on single cells with zone-controllable SERS effect

A zone-controllable SERS effect is presented for Raman imaging of protein-specific glycosylation on a cell surface using two types of newly designed nanoprobes. The signal probe, prepared using a Raman signal molecule and dibenzocyclooctyne-amine to functionalize a 10 nm Au nanoparticle, exhibits a negligible SERS effect and can recognize and link the azide-tagged glycan via a click reaction. The substrate probe, an aptamer modified 30 or 40 nm Au nanoparticles, can specifically recognize the target protein to create an efficient SERS zone on the target protein. By controlling the size of the substrate probe to match the expression zone of the protein-specific glycan, an efficient SERS signal can be generated. This method has been successfully used for in situ imaging of sialic acids on the target protein EpCAM on an MCF-7 cell surface and for the monitoring of the expression variation of protein-specific glycosylation during drug treatment. The concept of zone control can also be used to measure the distance between glycoproteins on a cell surface. This protocol shows promise in uncovering glycosylation-related biological processes.