Surface‐EnhancedRaman Scattering of Biological Materials

Abstract

Surface‐enhanced Raman spectroscopy (SERS) is a very powerful vibrational method that can be applied to a variety of biological samples provided that drawbacks, such as poor reproducibility of the signal and biocompatibility of the substrates, can be satisfactorily overcome. SERS is characterized by very low limits of detection, mainly due to the electromagnetic enhancement of the Raman signals, capable of achieving the single‐molecule level. Moreover, the spectra of small molecules represent authentic molecular fingerprints with very narrow linewidths that, along with the additional enhancement and inter‐/intramolecular selectivity gained through resonant laser excitation (surface‐enhanced resonance Raman spectroscopy, SERRS), make this technique particularly suited for multiplexing applications in complex biological samples. In this article, we introduce first the physical principles of SER(R)RS and describe the different types of substrates, as well as the basic modern instrumentation. We then provide an overview of recent biological applications, including biophysical mechanistic and structural studies on isolated biomolecules, their direct and indirect detection, chemical imaging of biological samples, and biomedical applications. Finally, we briefly discuss our outlook for the future research in this field.

Resonance Raman spectroscopy of Fe–S proteins and their redox properties

“…In the case when the electronic transition of the molecule matches the laser wavelength (RR) and the energy of surface plasmons of the metal (surface enhanced Raman, SER), these two effects combine to give origin to surface enhanced RR spectroscopy (SERR). In comparison with RR, the sensitivity of SERR increases by another couple of orders of magnitude for the immobilized molecules [2, 59]. …”

“…The electrochemical response is often enhanced in the presence of polycations, such as neomycin or polymyxin, when the proteins are negatively charged. Other methods rely on the adsorption of the protein onto Au or Ag metal working electrode surface, either bare or modified employing, e.g., SAMs (self-assembled monolayers), which facilitate protein adsorption via specific interactions and ensure biocompatibility [59]. While electrochemical methods may require small amounts of proteins, they do not allow the assignment of the detected signals to specific clusters in a protein, which is only achieved by EPR spectroscopy.…”

Surface Influence on the Metalation of Porphyrins at the Solid–Liquid Interface

“…SERR measurements were conducted using nanostructured Ag instead of Au(111) substrates in order to attain simultaneous resonance with the electronic transitions of the porphyrin and with the surface plasmons of the metal substrate, thus obtaining maximal signal enhancement. 43 Using Ag instead of Au for the SERR measurements should not influence PPIX bonding to the NH 2 C 16 SAM because: (i) long alkylthiol chains are employed in the SAM detaching a possible influence from the substrate and (ii) amine terminated alkylthiol SAMs are known to form compact monolayers similar to those formed over Au substrates. 44 The observed bands correspond to the PPIX molecules as the underlying SAM has no significant contribution under the experimental conditions employed.…”

Modulation of Functional Features in Electron Transferring Metalloproteins

“…It has been demonstrated, both theoretically and experimentally, that the interfacial electric fields in these model systems are of the same magnitude as in biological membranes. 12,[20][21][22] Furthermore, if the surfaces of the Au or Ag electrodes are nanostructured previous to the SAM-coating process, these modified surfaces behave as suitable platforms for surface-enhanced (resonance) Raman (SER/SERR) detection of the adsorbed Cyt-c. 13,23 Thus, thermodynamic and kinetic ET parameters can be obtained from spectral deconvolution of stationary or time-resolved potential-dependent SERR measurements, respectively. This methodology has the advantage over conventional electrochemical techniques of providing real time structural information of the immobilized protein under reactive conditions.…”