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Silver screen: Thin silver nanoparticle layers embedded within a 1 μm thick semiconducting WO3 film on conducting glass substrates enhance optical absorption over a broad wavelength region. The combination of light scattering and nearby electromagnetic‐field effects causes a large increase of photocurrents associated with water splitting generated at the WO3 photoanodes under simulated solar light irradiation.

Mixed thiol self-assembled monolayers (SAMs) presenting methyl and azobenzene head groups were prepared by chemical substitution from the original single-component n-decanethiol or [4-(phenylazo)phenoxy]hexane-1-thiol SAMs on polycrystalline gold substrates. Static contact-angle measurements were carried out to confirm a change in the hydrophobicity of the functionalized surfaces following the exchange reaction. The mixed SAMs presented contact-angle values between those of the more hydrophobic n-decanethiol and the more hydrophilic [4-(phenylazo)phenoxy]hexane-1-thiol single-component SAMs. By means of tip-enhanced Raman spectroscopy (TERS) mapping experiments, it was possible to highlight that molecular replacement takes place easily and first at grain boundaries: for two different mixed SAM compositions, TERS point-by-point maps with <50 nm step sizes showed different spectral signatures in correspondence to the grain boundaries. An example of the substitution extending beyond grain boundaries and affecting flat areas of the gold surface is also shown.

Rohit Chikkaraddy opened the discussion of the Introductory Lecture: Regarding quantifying the chemical enhancement, you showed a systematic change in the SERS enhancement for halide substituted molecules due to charge transfer from the metal. Is the extra enhancement due to an inherent increase in the Raman cross-section of the molecule? How do you go about referencing, as the charge transfer changes the vibrational frequency? Richard Van Duyne answered: The extra enhancement is not due to an increase in the Raman cross section, as that is ratioed out in the calculation of the enhancement factor. The charge transfer (CT) process does not transfer a complete electron, it is a fractional degree of CT. Thus the change in vibrational frequency is small. DFT calculations that provide eigenvectors allow one to reference the vibrational modes of the free molecule with those of the adsorbed molecule. Sylwester Gawinkowski asked: You have shown that the enhancement factor curve is redshifted relative to the plasmon resonance band and has a maximum at about 800 nm. This means that the SERS signal should be strongest for excitations in the near infrared spectral region. Why do most SERS reports, particularly related to single molecule SERS, have the excitation in the green or red spectral range and not in the near infrared? Richard Van Duyne replied: The SERS excitation spectrum for isolated nanoparticles (e.g. the NSL nanotriangles that I showed in Fig. 1 of the introductory lecture 1 ) is redshifted with respect to the localized surface plasmon resonance (LSPR) by half the Stokes frequency of the vibrational mode. As the nanoparticle size is decreased the LSPR shifts to the blue so it is only for a specific size that one gets an LSPR maximum at 800 nm. Essentially all single molecule SERS experiments are done with dye molecules and the laser excitation wavelength is chosen to get maximum resonance Raman (RR) as well as SERS enhancement. For Rhodamine 6G (R6G) the laser excitation wavelength of 532 nm is close to the absorption maximum of R6G. SMSERS should be possible in the NIR for a wide range of dye molecules with absorption maxima in that spectra region. 1 A.-I. Henry, T. W. Ueltschi, M. O. McAnally and R. P. Van Duyne, Faraday Discuss., 2017, DOI: 10.1039/c7fd00181a. Marc Porter asked: Why is the oxidized form of nitrobenzene (I may not have the name of the reactant correct; my notes are a bit fuzzy, which I blame on jet lag) more sensitive to the local environment than its reduced from. Does the supporting electrolyte play a role here? Richard Van Duyne replied: The redox system you are referring to is the dye Nile Blue. The oxidized form is positively charged and the adsorption has electrostatic character. Hence it is more sensitive to the electrostatics of the local environment than the neutral reduced form. Sumeet Mahajan commented: In your work on surface-enhanced FSRS with a high rep rate laser why does the signal to noise not increase when there are 10× more pulses with the 1 MHz setup compared to the 100 kHz...

Three dipeptides containing dehydroresidues (ΔAla, Δ((Z))Phe, and Δ((E))Phe) were examined by IR, Raman, and surface-enhanced Raman techniques for the first time. The effect of the size and isomer type of the β-substituent in the dehydroresidue on the conformational structure of the peptide was evaluated by using the analysis of IR and Raman bands. Additionally, SERS spectroscopy provided insight into the adsorption mechanism of these species on the metal surface. SERS spectra were recorded at alkaline pH on the silver sol using visible light excitation. The dehydroresidues studied here strongly influenced the SERS profile of the peptides. The most pronounced SERS signal for all dipeptides was assigned to the symmetric stretching vibration of the carboxylate ions. This indicates that the dehydropeptides studied here primarily adsorb via the deprotonated carboxylic group. Additionally, the enhanced SERS bands in the range 1550-1650 cm(-1) show differences in contribution of the dehydroresidue to the adsorption mechanism of the studied peptides.

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We report the first use of 3-amino-5-mercapto-1,2,4-triazole (AMT) to construct a surface-enhanced Raman scattering (SERS) based pH nano- and microsensor, utilizing silver nanoparticles. We optimize the procedure of homogenous attachment of colloidal silver to micrometer-sized silica beads via an aminosilane linker. Such micro-carriers are potential optically trappable SERS microprobes. It is demonstrated that the SERS spectrum of AMT is strongly dependent on the pH of the surroundings, as the transformation between two different adsorption modes, upright (A form) and lying flat (B form) orientation, is provoked by pH variation. The possibility of tuning the nanosensor working range by changing the concentration of AMT in the surrounding solution is demonstrated. A strong correlation between the pH response of the nanosensor and the AMT concentration in solution is found to be controlled by the interactions between the surface and solution molecules. In the absence of the AMT monomer, the performance of both the nano- and microsensor is shifted substantially to the strongly acidic pH range, from 1.5 to 2.5 and from 1.0 to 2.0, respectively, which is quite unique even for SERS-based sensors.

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