Protein:Colloid Conjugates for Surface Enhanced Raman Scattering:  Stability and Control of Protein Orientation

• Published in: The journal of physical chemistry. B Vol. 102; no. 47; pp. 9404 - 9413
• Main Authors: Keating, Christine D, Kovaleski, Kenneth M, Natan, Michael J
• Format: Journal Article
• Language: English
• Published: American Chemical Society 19.11.1998
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp982723z

Conjugates between cytochrome c (Cc) and colloidal Au particles have been prepared. These conjugates, purified by centrifugation/resuspension, provide a reproducible means of positioning a biomolecule analyte between two metal surfaces:  the metal nanoparticle to which the biomolecule is bound and an aggregated Ag sol used as a substrate for surface enhanced Raman scattering (SERS). SERS spectra for Ag:Cc:Au sandwiches made by addition of Cc:Au conjugates to aggregated Ag show that the protein retains its native conformation. Conjugation of Cc to colloidal metal nanoparticles prior to exposure to the SERS substrate can be used as a means of controlling protein orientation with respect to the substrate. In addition, Cc molecules bound to 12-nm diameter Au nanoparticles prior to adsorption to aggregated Ag are more stable to changes in the orientation of the heme with respect to the surface and to surface-induced heme spin state conversion than adsorbed, free Cc. These experiments show that protein:Au conjugates offer benefits as reagents for protein SERS.