Tip-Enhanced Raman Detects Interactions On Cell Surfaces

Tip-enhanced Raman spectroscopy (TERS) can be used to probe the interactions of receptors and ligands on cell membranes, reported Zachary D. Schultz of the University of Notre Dame. TERS gives Schultz and his coworkers a way to monitor molecules on cell surfaces without chemical modifications that could perturb the system. In TERS, a metal nanoparticle attached to an atomic force microscope tip is used to enhance Raman signals. The signal can be enhanced even more with ligand-conjugated metal nanoparticles. So Schultz used TERS to examine how antigen-labeled gold nanoparticles bind the antibody immunoglobulin G on cancer cell surfaces (Anal. Chem., DOI: 10.1021/ac301739k). The nanoparticle is incorporated into the membrane but remains on the surface; TERS distance sensitivity means that nanoparticles inside the cell can’t be detected. The large antibody swamps other contributions to the TERS spectrum, but previous experiments with biotin and streptavidin suggested that TERS spectra contain information about interactions between proteins and nearby molecules in the membrane.