Substrate development in surface-enhanced Raman spectroscopy (SERS) continues to attract research interest. In order to determine performance metrics, researchers in foundational SERS studies use a variety of experimental means to characterize the nature of substrates. However, often this process would appear to be performed indiscriminately without consideration for the physical scale of the enhancement phenomena. Herein, we differentiate between SERS substrates whose primary enhancing structures are on the hundreds of nanometer scale (analytical SERS nanosubstrates) and those whose main mechanism derives from nanometric-sized gaps (hot-spot dominated SERS substrates), assessing the utility of various characterization methods for each substrate class. In this context, characterization approaches in white-light spectroscopy, electron beam methods, and scanning probe spectroscopies are reviewed. Tip-enhanced Raman spectroscopy, wavelength-scanned SERS studies, and the impact of surface hydrophobicity are also discussed. Conclusions are thus drawn on the applicability of each characterization technique regarding amenability for SERS experiments that have features at different length scales. For instance, while white light spectroscopy can provide an indication of the plasmon resonances associated with 10 s–100 s nm-scale structures, it may not reveal information about finer surface texturing on the true nm-scale, critical for SERS’ sensitivity, and in need of investigation via scanning probe techniques.

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.

A comprehensive guide to selecting the optimum laser wavelength in Raman spectroscopy experiments.

This study is directed towards developing a fast, non-destructive, and easy-to-use handheld multimode spectroscopic system for fish quality assessment. We apply data fusion of visible near infra-red (VIS-NIR) and short wave infra-red (SWIR) reflectance and fluorescence (FL) spectroscopy data features to classify fish from fresh to spoiled condition. Farmed Atlantic and wild coho and chinook salmon and sablefish fillets were measured. Three hundred measurement points on each of four fillets were taken every two days over 14 days for a total of 8400 measurements for each spectral mode. Multiple machine learning techniques including principal component analysis, self-organized maps, linear and quadratic discriminant analyses, k-nearest neighbors, random forest, support vector machine, and linear regression, as well as ensemble and majority voting methods, were used to explore spectroscopy data measured on fillets and to train classification models to predict freshness. Our results show that multi-mode spectroscopy achieves 95% accuracy, improving the accuracies of the FL, VIS-NIR and SWIR single-mode spectroscopies by 26, 10 and 9%, respectively. We conclude that multi-mode spectroscopy and data fusion analysis has the potential to accurately assess freshness and predict shelf life for fish fillets and recommend this study be expanded to a larger number of species in the future.

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

The study of salivary manifestation of various health disorders via Raman spectroscopy, as a noninvasive molecular sensing technique to analyze molecular signatures in the saliva projections of health, is an emerging field of investigation of combined spectroscopy-biofluidics for early-diagnostics and monitoring, enabling structural and chemical biomarkers to be monitored overtime to predict prognosis for translation to real-world sensing applications. Here, we review the potential uses in healthcare, illicit drug detection, forensics and dental/orthodontic uses, and expound the specific challenges related to the detection of certain classes of biomolecules or smaller compounds. We highlight the potential of extracellular vesicles, a salivary constituent and its potential as an emerging vehicle for medical applications. Furthermore, portable devices for Raman-saliva based detection are discussed with a specific attention on the associated microfluidic advances for miniaturization and integration of such technologies and multimodal systems are examined. Given the low concentrations of target analytes and thus, the high analytical sensitivity required, surface-enhanced Raman spectroscopy (SERS) methods are noted across the different application areas and for development of portable devices.