Highly porous gold supraparticles as surface-enhanced Raman spectroscopy (SERS) substrates for sensitive detection of environmental contaminants

Constructing graphene oxide/Au nanoparticle cellulose membranes for SERS detection of mixed pesticide residues in edible chrysanthemum

Edible chrysanthemum is widely cultivated and used as an important ingredient of medicine, tea and multifunctional food. During the planting of chrysanthemum, pesticides are extensively used for preventing plant diseases and insect pests. To ensure the food safety of edible chrysanthemum, rapid detection methods are urgently needed for on-site inspection. In this study, a graphene oxide/Au nanoparticle (GO/Au NP) cellulose substrate was prepared through layer-by-layer assembly of GO and Au NPs on a mixed cellulose ester membrane. Surface-enhanced Raman spectroscopy (SERS) detection of four types of organophosphorus and organosulfur pesticides was achieved by filtering the extracting solution through the substrate and analysing SERS spectra. Qualitative and semi-quantitative detection of fenthion, phoxim, isocarbophos and thiram was accomplished with the detection limits of 38.01, 8.13, 48.97 and 8.74 ng mL-1, respectively. A spiking experiment further demonstrated the feasibility of this method for rapid and on-site detection of mixed pesticides in chrysanthemum. This study provides a new approach for rapid detection of multiple hazardous substances in flowering and herbal plants.

Simple and Inexpensive Fabrication of High Surface-Area Paper-Based Gold Electrodes for Electrochemical and Surface-Enhanced Raman Scattering Sensing

Paper has emerged as an excellent alternative to create environmentally benign disposable electrochemical sensing devices. The critical step to fabricating electrochemical sensors is making paper conductive. In this work, paper-based electrodes with a high electroactive surface area (ESA) were fabricated using a simple electroless deposition technique. The polymerization time of a polydopamine adhesion layer and the gold salt concentration during the electroless deposition step were optimized to obtain uniformly conductive paper-based electrodes. The optimization of these fabrication parameters was key to obtaining the highest ESA possible. Roughening factors (Rf) of 7.2 and 2.3 were obtained when cyclic voltammetry was done in sulfuric acid and potassium ferricyanide, respectively, demonstrating a surface prone to fast electron transfer. As a proof of concept, mercury detection was done through anodic stripping, achieving a limit of quantification (LOQ) of 0.9 ppb. By changing the metal deposition conditions, the roughness of the metalized papers could also be tuned for their use as surface-enhanced Raman scattering (SERS) sensors. Metallized papers with the highest SERS signal for thiophenol detection yielded a LOQ of 10 ppb. We anticipate that this method of fabricating nanostructured paper-based electrodes can accelerate the development of simple, cost-effective, and highly sensitive electrochemical and SERS sensing platforms.

Determination of sulfide in complex biofilm matrices using silver-coated, 4-mercaptobenzonitrile-modified gold nanoparticles, encapsulated in ZIF-8 as surface-enhanced Raman scattering nanoprobe

A surface-enhanced Raman scattering nanoprobe has been developed for sulfide detection and applied to  complex bacterial biofilms. The nanoprobe, Au@4-MBN@Ag@ZIF-8, comprised a gold core modified with 4-mercaptobenzonitrile (4-MBN) as signaling source, a layer of silver shell as the sulfide sensitization material, and a zeolitic imidazolate framework-8 (ZIF-8) as surface barrier. ZIF-8, with its high surface area and mesoporous structure, was applied to preconcentrate sulfide around the nanoprobe with its excellent adsorption capacity. Besides, the external wrapping of ZIF-8 can not only prevent the interference of biomolecules, such as proteins, with the Au@4-MBN@Ag assay but also enhance the detection specificity through the sulfide cleavage function towards ZIF-8. These properties are critical for the application of this nanoprobe to complex environmental scenarios. In the presence of sulfide, it was first enriched through adsorption by the outer ZIF-8 layer, then destroyed the barrier layer, and subsequently reacted with the Ag shell, leading to changes in the Raman signal. Through this rational design, the Au@4-MBN@Ag@ZIF-8 nanoprobe exhibited excellent detection sensitivity, with a sulfide detection limit in the nanomolar range and strong linearity in the concentration range  50 nM to 500 μM. Furthermore, the proposed Au@4-MBN@Ag@ZIF-8 nanoprobe was effectively utilized for sulfide detection in intricate biofilm matrices, demonstrating its robust selectivity and reproducibility.

Advances in Surface-Enhanced Raman Scattering Sensors of Pollutants in Water Treatment

Water scarcity is a world issue, and a solution to address it is the use of treated wastewater. Indeed, in these wastewaters, pollutants such as pharmaceuticals, pesticides, herbicides, and heavy ions can be present at high concentrations. Thus, several analytical techniques were initiated throughout recent years for the detection and quantification of pollutants in different types of water. Among them, the surface-enhanced Raman scattering (SERS) technique was examined due to its high sensitivity and its ability to provide details on the molecular structure. Herein, we summarize the most recent advances (2021-2023) on SERS sensors of pollutants in water treatment. In this context, we present the results obtained with the SERS sensors in terms of detection limits serving as assessment of SERS performances of these sensors for the detection of various pollutants.