The use of Raman spectroscopy combined with saliva is an exciting emerging spectroscopy-biofluid combination. In this review, we summarize current methods employed in such studies, in particular the collection, pretreatment, and storage of saliva, as well as measurement procedures and Raman parameters used. Given the need for sensitive detection, surface-enhanced Raman methods are also surveyed, alongside chemometric techniques. A meta-analysis of variables is compiled. We observe a wide range of approaches and conclude that standardization of methods and progress to more extensive validation Raman-saliva studies is necessary. Nevertheless, the studies show tremendous promise toward the improvement of speed, diagnostic accuracy, and portable device possibilities in applications such as healthcare, law enforcement, and forensics.

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...

No abstract

Ashish Tripathi opened a discussion of the paper by Volker Deckert: TERS imaging of the triangular shaped nanoparticle with a D3ATP monolayer is shown in Fig. 3 of your paper. 1 The chemical map of the 1438 cm À1 band of the D3ATP monolayer suggests that the signal intensities are higher at the edges than near the centre (Fig. 3, bottom le). Can you comment?

A simple derivatization methodology is shown to extend the application of surface-enhanced Raman spectroscopy (SERS) to the detection of trace concentration of contaminants in liquid form. Normally in SERS the target analyte species is already present in the molecular form in which it is to be detected and is extracted from solution to occupy sites of enhanced electromagnetic field on the substrate by means of chemisorption or drop-casting and subsequent evaporation of the solvent. However, these methods are very ineffective for the detection of low concentrations of contaminant in liquid form because the target (ionic) species (a) exhibits extremely low occupancy of enhancing surface sites in the bulk liquid environment and (b) coevaporates with the solvent. In this study, the target analyte species (acid) is detected via its solid derivative (salt) offering very significant enhancement of the SERS signal because of preferential deposition of the salt at the enhancing surface but without loss of chemical discrimination. The detection of nitric acid and sulfuric acid is demonstrated down to 100 ppb via reaction with ammonium hydroxide to produce the corresponding ammonium salt. This yields an improvement of ~4 orders of magnitude in the low-concentration detection limit compared with liquid phase detection.

No abstract

No abstract

Crystallization is fundamental to much drug manufacture. Consequently a great deal of attention is focused on trying to attain a reproducible, robust process with predictable outcomes.Crystallization may be interrogated by various means including laser light scattering, infra-red spectroscopy, calorimetery, x-ray diffraction, solid state NMR analysis and optical and electron microscopy. Although laser backscattering is applicable to real time, in-situ studies it detects chord length and hence it is most accurate when all particles are spherical. This is clearly is not so with drug crystals. Crystal analysis by microscopy is usually conducted on samples removed from the reactor. While this approach has value it may lead to post-sampling changes and is not capable of fully characterising the real time dynamics of particle morphology. In-situ epifluorescence microscopy of cells within a bioreactor has been reported. However, this required insertion of a quartz window into the reactor wall which limited the observation position to one fixed location, which would be less appropriate for batch crystallization reactors.