Fragmentation of proteins in the corona of gold nanoparticles as observed in live cell surface-enhanced Raman scattering.

Surface-enhanced Raman scattering (SERS) can provide information on the structure, composition, and interaction of molecules in the proximity of gold nanoparticles, thereby enabling studies of adsorbed biomolecules in vivo. Here, the processing of the protein corona and the corresponding protein-nanoparticle interactions in live J774 cells incubated with gold nanoparticles was characterized by SERS. Samples of isolated cytoplasm, devoid of active processing, of the same cell line were used as references. The occurrence of the most important SERS signals was compared in both types of samples. The comparison of signal abundances, supported by multivariate assessment, suggests a decreased nanoparticle-peptide backbone interaction and an increased contribution of denatured proteins in endolysosomal compartments, indicating an interaction of protein fragments with the gold nanoparticles in the endolysosome of the living cells. To study the protein fragmentation in a model and to confirm the assignment of specific spectral signatures in the live cell spectra, SERS data were collected from a solution of bovine serum albumin (BSA) digested by trypsin as an enzymatic model and from solutions of intact BSA and trypsin. The spectra from the enzymatic model confirm the strong interaction of protein fragments with the gold nanoparticles in the endolysosomal compartments. By proteomic analysis, using combined sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry of the extracted hard corona, we directly identified protein fragments, some originating from the culture medium. The results illustrate the use of appropriate models for the validation of SERS spectra and have potential implications for further developments of SERS as an in vivo analytical and biomedical tool.