| Surface enhanced Raman scattering (SERS) is of interest for biomedical analysis and imaging due to its sensitivity, specificity and multiplexing capabilities. The successful application of SERS for in vivo biosensing necessitates probes to be biocompatible and procedures to be minimally invasive, challenges that have respectively been met by the design of nanoprobes and instrumentation. This Review presents recent developments in these areas, describing case studies in which sensors have been implemented, as well as outlining shortcomings that have to be addressed before SERS sees clinical use.In 1928, C. V. Raman first reported the scattering phenomenon that now bears his name.1,2 Raman scattering has since become a powerful analytical technique, including for biomedical applications, 3 where label-free and objective tissue diagnostics 4-6 ex vivo and in vivo, as well as drug-cell interaction studies in vitro have been conducted. [7][8][9] The majority of incident photons experience elastic (Rayleigh) scattering, with only about 1 in 10 7 photons undergoing inelastic (Raman) scattering. 10 In 1974, Fleischmann and co-workers described a phenomenon that would later become known as surface enhanced Raman scattering (SERS) 11 . They observed a large enhancement in inelastic scattering from pyridine when the analyte was adsorbed onto a Ag electrode, an effect that had previously been mentioned by the team of A. J. McQuillan in 1973, 12 with Van Duyne later attributing the signal enhancement to the roughened metal surface via the physical phenomenon he coined SERS.13 Unlike conventional Raman spectroscopy, SERS analyses require samples to be labelled, a disadvantage offset by the large intensity enhancement that makes SERS an important analytical tool with high sensitivity and low detection limits.14,15 The exact mechanism of SERS is not fully understood but an electromagnetic enhancement factor plays the major role 16 , whereby free electrons in a metal nanoparticle (NP) encounter applied radiation whose electromagnetic field varies at a frequency matching the oscillation frequency of electrons in the NPs. Such plasmon resonance at the NP surface arises from an intense electric field, which intensifies Raman modes arising from molecules near or attached to the NP surface. The Raman signals can also be enhanced due to the formation of chargetransfer complexes between the roughened metal surface and molecules bound to it. We now leave our discussion of the SERS mechanism, but refer readers interested in these fundamental principles to some comprehensive articles on the subject. [17][18][19] Well-known selection rules allow for one to predict if a given vibrational mode is infrared-and/or Raman-active. Indeed, by considering the magnitude of the change in dipole moment or polarizability associated with a vibration, one can rationalize infrared or Raman data, respectively. Compared to Raman spectroscopy, SERS involves analyte molecules interacting with a roughened metal substrate, such that the symmetry ...

The ability to detect multiple disease-related targets from a single biological sample in a quick and reliable manner is of high importance in diagnosing and monitoring disease. The technique known as surface enhanced Raman scattering (SERS) has been developed for the simultaneous detection of multiple targets present in biological samples. Advances in the SERS method have allowed for the sensitive and specific detection of biologically relevant targets, such as DNA and proteins, which could be useful for the detection and control of disease. This review focuses on the strengths of SERS for the detection of target molecules from complex mixtures and the clinical relevance of recent work combining SERS with multiplexed detection of biological targets.

Tumor necrosis factor α is an inflammatory cytokine which has been linked with many infectious and inflammatory diseases. Detection and quantification of this key biomarker is commonly achieved by use of an enzyme-linked immunosorbent assay (ELISA). This fundamental technique uses the spectroscopic detection of a chromogen such as 3,3',5,5'-tetramethylbenzidine (TMB). Horseradish peroxidase (HRP), bound to the detection antibody, catalyzes the oxidation of TMB by hydrogen peroxide to generate colored products which may be measured spectrophotometrically. In this study we have used a conventional ELISA kit and shown that, by replacing the traditional colorimetric detection with resonance Raman spectroscopy, we can achieve 50 times lower detection limits and the potential for multiplexed analysis is increased. In this approach, the laser wavelength was tuned to be in resonance with an electronic transition of the oxidized TMB. The relative intensity of the enhanced Raman bands is proportional to the amount of TMB, thus providing a means of improved quantification. Furthermore, TMB is one of the most widely used chromogenic substrates for HRP-based detection and commercial ELISA test kits, indicating that this detection technique is applicable to a large number of target analytes.

Surface-enhanced Raman scattering (SERS) is a powerful and sensitive technique for the detection of fingerprint signals of molecules and for the investigation of a series of surface chemical reactions. Many studies introduced quantitative applications of SERS in various fields, and several SERS methods have been implemented for each specific application, ranging in performance characteristics, analytes used, instruments, and analytical matrices. In general, very few methods have been validated according to international guidelines. As a consequence, the application of SERS in highly regulated environments is still considered risky, and the perception of a poorly reproducible and insufficiently robust analytical technique has persistently retarded its routine implementation. Collaborative trials are a type of interlaboratory study (ILS) frequently performed to ascertain the quality of a single analytical method. The idea of an ILS of quantification with SERS arose within the framework of Working Group 1 (WG1) of the EU COST Action BM1401 Raman4Clinics in an effort to overcome the problematic perception of quantitative SERS methods. Here, we report the first interlaboratory SERS study ever conducted, involving 15 laboratories and 44 researchers. In this study, we tried to define a methodology to assess the reproducibility and trueness of a quantitative SERS method and to compare different methods. In our opinion, this is a first important step toward a “standardization” process of SERS protocols, not proposed by a single laboratory but by a larger community.

aArtificial enzymes have become an increasingly interesting area of research due to their many advantages over natural protein enzymes which are expensive, difficult to isolate and unable to stand harsh environments. An important area of this research involves using metal nanoparticles as artificial enzymes, known as nanozymes, which exhibit peroxidase-like activity enabling them to catalyse the oxidation of substrates such as 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2), giving a colorimetric response. Here we exploit the catalytic activity of silver nanoparticles (Ag NPs) in a surface based silver-linked immunosorbent assay (SLISA) to detect human C-reactive protein (CRP), an inflammatory marker. Ag NPs were conjugated to antibodies with specific recognition for the corresponding target antigenic molecule, CRP, and the Ag NPs were used to catalyse the oxidation of TMB by H2O2. The resulting coloured oxidation product was detected using SERRS. We demonstrate that Ag NPs can replace the enzymes used in a conventional ELISA and a detection limit of 1.09 ng/mL of CRP can be achieved. It indicates the promise for SLISAs for biomarker detection and opens the way for further assays of this nature to be created. This novel assay has the potential to be optimised to detect lower levels of CRP and can be further extended for the sensitive and specific detection of other relevant biomarkers.