Label-free detection of proteins from self-assembled protein-silver nanoparticle structures using surface-enhanced Raman scattering.

Proteins are one of the most versatile groups of molecules with vital functional roles in living systems. Their enormous diversity and structural flexibility make the detection of these molecules a challenging task. A simple and sensitive label-free protein detection method based on assembly of proteins and colloidal silver nanoparticles (AgNPs) on surfaces and surface-enhanced Raman scattering (SERS) is reported. The SERS spectra from the assembled AgNP/protein films show excellent reproducibility and high quality regardless of the proteins' charge status and size. A detection limit down to 0.5 μg/mL for three acidic proteins; BSA, catalase and pepsin, and three basic proteins; cytochrome c, avidin and lysozyme, is easily achieved. The minimum improvement in detection limit is more than 1 order of magnitude compared to the previously reported detection limits using the technique and the approach has the potential for label-free protein detection and identification.