Selective Detection of RGD-Integrin Binding in Cancer Cells Using Tip Enhanced Raman Scattering Microscopy

Ligand-receptor interactions play important roles in many biological processes. Cyclic arginine glycine aspartic acid (RGD) containing peptides are known to mimic the binding domain of extracellular matrix protein fibronectin and selectively bind to a subset of integrin receptors. Here we report the tip enhanced Raman scattering (TERS) detection of RGD-functionalized nanoparticles bound to integrins produces a Raman scattering signal specific to the bound protein. These results demonstrate that this method can detect and differentiate between two different integrins (alpha 5 beta 1 and alpha v beta 3) bound to RGD-conjugated gold nanoparticles both on surfaces and in a cancer cell membrane. In situ measurements of RGD nanoparticles bound to purified alpha 5 beta 1 and alpha v beta 3 receptors attached to a glass surface provide reference spectra for a multivariate regression model. The TERS spectra observed from nanoparticles bound to cell membranes are analyzed using this regression model and the identity of the receptor can be determined. The ability to distinguish between receptors in the cell membrane provides a new tool to chemically characterize ligand-receptor recognition at molecular level and provide chemical perspective on the molecular recognition of membrane receptors.