Phosphorylation-Dependent SERS Readout for Activity Assay of Protein Kinase A in Cell Extracts

Positively Charged Silver and Gold Nanoparticles with Controllable Size Distribution for SERS Detection of Negatively Charged Molecules

Surface-enhanced Raman spectroscopy (SERS) has been demonstrated as an ultrasensitive tool for various molecules. However, for the negatively charged molecules, the widely used SERS substrate [negatively charged Ag and Au nanoparticles (Ag or Au NPs (-)] showed either low sensitivity or poor stability. The best solution is to synthesize positively charged silver or gold nanoparticles [Ag or Au NPs (+)] with high stability and excellent SERS performance, which are currently unavailable. To this end, we revitalized the strategy of "charge reversal and seed growth". By selection of ascorbic acid as the reductant and surfactant, the surface charge of Ag or Au NP (-) seeds is adjusted to a balanced state, where the surface charge is negative enough to satisfy the stabilization of the NPs (-) but does not hinder the subsequent charge reversal. By optimization of the chain length and electric charge of polyamine molecules, the highly stable and size-controllable uniform Ag NPs (+) and Au NPs (+) were seed-growth synthesized with high reproducibility. More importantly, the SERS performance of both Ag NPs (+) and Au NPs (+) achieved the trace detection of negatively charged molecules at the level of 1 μg/L, demonstrating an improved SERS sensitivity of up to 3 orders of magnitude compared to the previously reported sensitivity. Promisingly, the introduction of polyamine-capped Ag NPs (+) and Au NPs (+) as SERS substrates with high stability (1 year shelf life) will significantly broaden the application of SERS.

Plasmonic surface-enhanced Raman scattering nano-substrates for detection of anionic environmental contaminants: Current progress and future perspectives

Surface-enhanced Raman scattering spectroscopy (SERS) is a powerful technique of vibrational spectroscopy based on the inelastic scattering of incident photons by molecular species. It has unique properties such as ultra-sensitivity, selectivity, non-destructivity, speed, and fingerprinting properties for analytical and sensing applications. This enables SERS to be widely used in real-world sample analysis and basic plasmonic mechanistic studies. However, the desirable properties of SERS are compromised by the high cost and low reproducibility of the signals. The development of multifunctional, stable and reusable nano-engineered SERS substrates is a viable solution to circumvent these drawbacks. Recently, plasmonic SERS active nano-substrates with various morphologies have attracted the attention of researchers due to promising properties such as the formation of dense hot spots, additional stability, tunable and controlled morphology, and surface functionalization. This comprehensive review focused on the current advances in the field of SERS active nanosubstrates suitable for the detection and quantification of anionic environmental pollutants. The common fabrication methods, including the techniques for morphological adjustments and surface modification, substrate categories, and the design of nanotechnologically fabricated plasmonic SERS substrates for anion detection are systematically presented. Here, the need for the design, synthesis, and functionalization of SERS nano-substrates for anions of great environmental importance is explained in detail. In addition, the broad categories of SERS nano-substrates, namely colloid-based SERS substrates and solid-support SERS substrates are discussed. Moreover, a brief discussion of SERS detection of certain anionic pollutants in the environment is presented. Finally, the prospects in the fabrication and commercialization of pilot-scale handheld SERS sensors and the construction of smart nanosubstrates integrated with novel amplifying materials for the detection of anions of environmental and health concern are proposed.

Positively-charged plasmonic nanostructures for SERS sensing applications

Surface-enhanced Raman (SERS) spectroscopy has been establishing itself as an ultrasensitive analytical technique with a cross-disciplinary range of applications, which scientific growth is triggered by the continuous improvement in the design of advanced plasmonic materials with enhanced multifunctional abilities and tailorable surface chemistry. In this regard, conventional synthetic procedures yield negatively-charged plasmonic materials which can hamper the adhesion of negatively-charged species. To tackle this issue, metallic surfaces have been modified via diverse procedures with a broad array of surface ligands to impart positive charges. Cationic amines have been preferred because of their ability to retain a positive zeta potential even at alkaline pH as well as due to their wide accessibility in terms of structural features and cost. In this review, we will describe and discuss the different approaches for generating positively-charged plasmonic platforms and their applications in SERS sensing.

Integration of ligands equipped with quaternary amines on plasmonic surfaces generates positively-charged nanomaterials suitable for electrostatically binding negatively-charged species paving the way for their application in SERS sensing.

Applications of surface-enhanced Raman spectroscopy in detection fields

Surface-enhanced Raman spectroscopy (SERS) is a Raman spectroscopy technique that has been widely used in food safety, environmental monitoring, medical diagnosis and treatment and drug monitoring because of its high selectivity, sensitivity, rapidness, simplicity and specificity in identifying molecular structures. This review introduces the detection mechanism of SERS and summarizes the most recent progress concerning the use of SERS for the detection and characterization of molecules, providing references for the later research of SERS in detection fields.