Advances in surface-enhanced Raman spectroscopy (SERS) substrates for lipid and protein characterization: sensing and beyond

Surface-enhanced Raman spectroscopy (SERS) has become an essential ultrasensitive analytical tool for biomolecular analysis of small molecules, macromolecular proteins, and even cells. SERS enables label-free, direct detection of molecules through their intrinsic Raman fingerprint. In particular, protein and lipid bilayers are dynamic three-dimensional structures that necessitate label-free methods of characterization. Beyond direct detection and quantitation, the structural information contained in SERS spectra also enables deeper biophysical characterization of biomolecules near metallic surfaces. Therefore, SERS offers enormous potential for such systems, although making measurements in a nonperturbative manner that captures the full range of interactions and activity remains a challenge. Many of these challenges have been overcome through advances in SERS substrate development, which have expanded the applications and targets of SERS for direct biomolecular quantitation and biophysical characterization. In this review, we will first discuss different categories of SERS substrates including solution-phase, solid-supported, tip-enhanced Raman spectroscopy (TERS), and single-molecule substrates for biomolecular analysis. We then discuss detection of protein and biological lipid membranes. Lastly, biophysical insights into proteins, lipids and live cells gained through SERS measurements of these systems are reviewed.

Surface-enhanced resonance Raman scattering of hemoproteins and those in complicated biological systems

The SERRS spectra of heme are influenced by structural changes, orientation, and selective adsorption on the Ag surface.

Comment on "Sensitive marker bands for the detection of spin states of heme in surface-enhanced resonance Raman scattering spectra of metmyoglobin" by Y. Kitahama, M. Egashira, T. Suzuki, I. Tanabe and Y. Ozaki

We contrast recently reported surface-enhanced resonance Raman spectra (SERRS) of myoglobin on silver nanoparticles with established knowledge about this complex. We conclude that the detected bands are not related to the spin states of the protein cofactor, being rather originated by a heme coordination change induced by the metal surface.

Reply to the comment on "Sensitive marker bands for the detection of spin states of heme in surface-enhanced resonance Raman scattering spectra of metmyoglobin"

In our SERRS spectra of metmyoglobin by excitation at 514 nm, the peak at 1510 cm(-1), which is assigned to the 6-coordinated heme in the low spin state, was observed by the addition of imidazole and NaN3. Thus, the SERRS likely originates not from the non-native 5-coordinated heme, which is in the high spin state.