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Since the discovery of SERS nearly thirty years ago, it has progressed from model-system studies of pyridine to state-of-the-art surface-science studies coupled with real-world applications. We have demonstrated a SERS-based glucose sensor as an example of the latter. A SERS-active surface functionalized with a mixed SAM was shown to partition and departition glucose efficiently. The two components of the SAM, DT and MH, provide the appropriate balance of hydrophobic and hydrophilic groups. The DT/MH-functionalized SERS surface partitioned and departitioned glucose in less than 1 min, which indicates that the sensor can be used in real-time, continuous sensing. Furthermore, quantitative glucose measurements, in the physiological concentration range, in a mixture of interfering analytes and in bovine plasma were also demonstrated. Finally, the DT/MH-functionalized SERS surface showed temporal stability for at least 10 days in bovine plasma, making it a potential candidate for implantable sensing. [ABSTRACT FROM AUTHOR]

In this Chapter, we adhere to a basic philosophy for obtaining quantitative SERRS. Effective quantitative SERRS is best obtained where the analyte is preselected either by choosing a suitable molecule such as mitoxantrone that has an intrinsic SERRS activity or by the use of labeling/derivatization chemistry. For the best results, the molecule should adhere strongly to the SERRS surface and have a chromophore close to the excitation frequency. Quantitation is easily obtained by averaging a number of events such as those that will occur if a suspension of colloid is used. The advantages in sensitivity and selectivity of SERRS detection make it very attractive for the next generation of bioanalytical equipment and for the solution to problems where extreme sensitivity is required. [ABSTRACT FROM AUTHOR]

Surface-enhanced vibrational spectroelectrochemistry constitutes a powerful approach for elucidating the reaction mechanisms and dynamics of immobilized redox proteins. In contrast to traditional electrochemical methods, the combination of SERR and SEIRA provides a direct and detailed molecular picture of all potential-dependent processes of the adsorbed species, including those that are non-Faradaic reactions. In this respect, these techniques may gain increasing importance in both fundamental and applied science. On the one hand, a profound knowledge of the molecular structure and dynamics of immobilized proteins and enzymes that can be obtained by these methods is a prerequisite for the rational design of bioelectronic devices of technological importance. On the other hand, surface-enhanced vibrational spectroscopies open new possibilities to study complex biomimetic systems, thereby providing novel insight into fundamental biological processes. In this contribution we have presented a simple way for studying the influence of electric-fields on the various parameters that control electron-and proton-transfer reactions of soluble and membrane-bound proteins like Cyt-c and CcO. We have shown that electric fields of a magnitude comparable to those at the interfaces of biomembranes, i.e., the natural reaction environment, may have a substantial influence on redox potentials, protein structure, redox-linked conformational changes and orientation/reorientation of electrostatic complexes. These studies do not directly prove a functional role of the electric-field effects in vivo, but they clearly indicate that such effects might be present and deserve further investigation. The application of surfaceenhanced vibrational spectroscopic methods in combination with more realistic model systems appears to be a promising strategy towards that goal. [ABSTRACT FROM AUTHOR]

We have investigated SM-SERRS spectra and intensity trajectories of individual EGFP molecules adsorbed on silver colloids. Spectral jumps, in a timescale of seconds, were observed in the SM-SERRS spectral trajectories. These jumps were attributed to a slow, reversible conversion between the protonated and deprotonated form of the chromophore in EGFP based on comparison with an ensemble Raman spectra of EGFP at different pH. The timescale of the conversion seems to match the timescale of the (long) off-periods observed in SM-fluorescence intensity trajectories. SM-SERRS intensity trajectories show, beside the slow fluctuations of the order of seconds, several faster timescales of fluctuations. We present a possible rational for those fluctuations based on literature data. We demonstrate that SM-SERRS data can be used to elucidate some of the complex photophysical processes occurring in GFPs. [ABSTRACT FROM AUTHOR]

Tip-enhanced Raman spectroscopy is a vibrational spectroscopy with hitherto unprecedented sensitivity and spatial resolution. Since the enhancement is mainly provided by the near-field excited at the apex of a suitable tip, TERS appears to be a widely applicable spectroscopy and microscopy tool, in contrast to its parents, surface-enhanced Raman spectroscopy (SERS) and scanning near-field optical microscopy (SNOM). TER scattering has been observed for a number of molecules adsorbed at various substrates, including single-crystalline metal surfaces, showing thereby a more than million-fold enhancement of the Raman scattering. It is important to note that the field-enhancement provides, beyond TERS, promising avenues for applications to other optical techniques, such as tip-enhanced CARS, two-photon fluorescence and infrared scattering-type near-field microscopy. Common to all these approaches is the high spatial resolution that is by far better than Abbe's diffraction limit of λ/2. The lateral resolution achieved today is in the range of 10 nm to 20 nm. Optical microscopy with such an excellent resolution has a very promising future. The keys for further advances in the application of enhanced near-fields to scientific and technological (analytical) tasks include the optimization of tips, excitation and collection optics as well as of imaging techniques. Last but not least, it is necessary to achieve a deeper theoretical understanding of the optical properties of the cavity formed between tip and substrate as well as of the influence of (light-absorbing) adsorbates on the optical resonances of this cavity. [ABSTRACT FROM AUTHOR]

In this Chapter, we have described several applications of the enhancement of resonance Raman scattering and molecular fluorescence toward the characterization of single molecules, monolayers, and thin solid films on metal-island films, colloidal metal nanoparticles, and nanocomposite films. While this review is by no means extensive, we believe it does serve to shed light on some of the more critical considerations of this work, and also to highlight some of the very powerful potential uses of resonant surface-enhanced spectroscopies. [ABSTRACT FROM AUTHOR]

In this Chapter, we employed the 3D-FDTD method to calculate and evaluate the local electromagnetic field by investigating the effect of the surface geometry, the size, shape, and aggregation forms of nanoparticles on the SERS activity of transition metal systems. Our calculation on the cauliflowerstructured nanoparticles shows that the em enhancement is sensitive not only to the polarization of the exciting light, the electronic property of metal and the surface morphology, but also to the symmetric nature of the SERS nanostructures. We demonstrated that the reason for the high enhancement in the nanocube system could be due to the large effective volume involved in the strong coupling between neighboring nanocubes. For the core-shell system, we show that the em enhancement decreases rapidly with increasing shell thickness and when the shell thickness exceeds 6 nm, the core no longer influences the SERS of the shell. The detection of a reasonably good UVSERS signal on Pt, Rh, Ru and Co surfaces rather than Ag and Au is mainly due to the intrinsically suitable optical properties of transition metals in the UV region. Overall, the extension of SERS substrate to the transition-metal systems and use of UV excitation have improved the generality of the SERS technique and could be helpful for comprehensive understanding of SERS. [ABSTRACT FROM AUTHOR]

Using generalized Mie theory, it is possible to estimate field-enhancement effects in strongly interacting nanoparticle systems, including dense aggregates of several nanoparticles. Apart from the inherent approximation of a spherical particle shape, the method is a complete solution to Maxwell's equations. Based on GMT, we have shown that Ag nanoparticle aggregates exhibit polarization-dependent "hot" gap sites that will dominate the SERS response. This result is in agreement with the majority of SERS experiments and in line with previous theory results from the 1980s. The "hot" gap sites can be expected to yield SERS enhancements factors of the order of 1010 or above. When combined with a proper description of the quantum optical response of the molecule, this factor quantitatively explains SERS from single resonant molecules. We have also discussed optical forces in SERS and shown that molecules could be attracted to sites with high surface enhancement while properly aligned particles could be pulled closer together, even for relatively modest irradiation levels. These effects could be of both fundamental and practical importance. [ABSTRACT FROM AUTHOR]

The present studies show that array structures can be used to produce local field enhancements that are considerably larger than is found for isolated particles or dimers. These enhancements are large enough, in fact, that singlemolecule SERS measurements may be possible. The largest enhancements were obtained using a structure of two one-dimensional arrays, one parallel to the wavevector direction and one perpendicular to it. The particle at the crossing point of the two arrays is replaced by a dimer of particles, so that the local field between the particles is enhanced both by short-range near-field behavior of the dimer and also by long-range photonic interactions associated with resonances in the two arrays. This structure produced a field enhancement of 3.9 × 105 for a dimer of spheres, which is twice what we have been able to generate for a dimer in a single chain. Computational limitations make it impossible for us to study a dimer of nonspherical particles for this array structure, but similar studies for an isolated dimer of truncated tetrahedrons produced an extra factor of over 102 in the enhancement over the equivalent sphere result, suggesting that ∥E∥2 values of over 107 are possible for the "+" structure with a truncated tetrahedron dimer at the center. Furthermore, the resonance structures in this case are broad enough that significant enhancements at both the incoming and outgoing wavelengths is possible. Thus we conclude that this structure holds promise for single-molecule SERS measurements. [ABSTRACT FROM AUTHOR]