A SERS Responsive DGT Sensing Device for On-Site Determination of Organic Contaminants Underwater

Innovative quantum dots-based SERS for ultrasensitive reporting of contaminants in food: Fundamental concepts and practical implementations

Food contamination poses serious health risks, compelling the discovery of new methods to guarantee regulatory compliance and build consumer conviction. Surface Enhanced Raman Spectroscopy (SERS) has come into sight as a sophisticated approach for the ultrasensitive discovery of toxins in food and water, proposing non-destructive, quick, and precise analysis. Instantaneously, quantum dots (QDs) are astonishing nanomaterials, characterized by distinctive attributes such as quantum confinement and optical photostability. This article extends a decisive outline of SERS technology, pointing out its amalgamation with QDs and discussing numerous augmentation approaches i.e., chemical enhancement, electromagnetic enhancement, Van Hove singularities, the Brus equation, Förster resonance energy transfer, band gap energy, and quantum yield. The amalgamation of SERS with QDs commands an important promise in international food security and conservational sustainability. Nevertheless, QDs provide several compensations, they also aspect a few concerns, counting probable toxicity, stability problems, and predisposition to interference. To tackle these items, further research is required to synthesize safer, more stable QD materials and to refine protocols for practical real-world applications. While some reviews on SERS have been published recently, to our knowledge, the current review is the first one dedicated to QDs-assisted SERS in food safety.

Determination of diffusion coefficients through gels with non-negligible finite-volume effects in the compartments of the diffusion cell

Diffusion cells are used to measure diffusion coefficients (DM) in gels. These measurements are of interest to understand and predict the availability of nutritive or toxic chemical species in waters, soils and sediments. When the diffusive flux from the donor to the acceptor compartment is constant (steady-state regime), DM is determined from the slope of the linear plot of the acceptor concentration vs time. However, at long enough times, there is a non-negligible concentration depletion in the donor compartment concomitant to a concentration increase in the acceptor compartment. Accordingly, the accumulation plot bends downwards preventing a linear fitting. This is the case of metals whose solubility (especially depending on pH values) limits the concentration in the donor compartment and the time required to reach concentrations above the limit of quantification in the acceptor compartment implies a non-negligible decrease of the concentration in the donor compartment. In this work, a simple linear regression is shown to provide the diffusion coefficient values from experiments exhibiting finite-volume effects. This expression is validated against rigorous numerical simulation as well as reported values in the literature. Diffusion coefficients of Zn, Ni and Pb in agarose cross-linked polyacrylamide (APA) gels (used in Diffusive Gradients in Thin-Film devices, DGT) are determined under finite-volume effects. The resulting values agree with those obtained under the standard linear regime.

Long-term deployment of commonly used DGT devices for trace element measurement across laboratory and field settings

Diffusive Gradients in Thin-films (DGT) technique is a promising passive sampling technique, which was used for the determination of lots of inorganic and organic pollutants. Although many DGT devices have not been extensively tested and verified in field, DGT device such as LSNP-NP, LSNT-NP, LSNZ-NP, and LSNM-NP DGT were widely employed for the assessment of various trace elements. However, the deployment time of these DGTs were much shorter than the theoretical time in the preexisting literature. Therefore, the performance of DGT for long-term application in different water bodies is not known. This investigation utilized the four DGTs for the assessment of various trace elements across extended periods both in controlled laboratory settings and natural field environments. Synthetic soft, hard, and seawater compositions served as media for laboratory deployments. Most elements can be measured accurately in 4-7 days in soft and hard water. Deployment durations in seawater exhibited a notable reduction compared to those in freshwater matrices. LSNZ-NP DGT excelling in oxyanion determination, while LSNT-NP DGT showcased superior efficacy in phosphorus quantification. Field deployments in rivers and sea affirmed the robustness of LSNZ-NP DGT, evidencing prolonged deployment capabilities for various elements, such as Mo, Se, As, Sb, and P, spanning 7-28 days. Assessment of pollution levels across four sampling sites revealed heightened concentrations of most elements in marine waters relative to riverine environments, except for phosphorus. Notably, all assessed elements, except for phosphorus, conformed to Class I water quality standards. This study demonstrated the difference between the theoretical application time and actual application time for the first time. It raises new questions for the application of DGT in nature water bodies. The mechanization of the difference between the theoretical and actual application time should be studied in the future research. The measures to extend the application time should be studied too.

Development and application of diffusive gradients in thin-films for in-situ monitoring of 6PPD-Quinone in urban waters

The occurrence and risk of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q), derived from the oxidation of the tire antidegradant 6PPD, has raised significant concern since it was found to cause acute mortality in coho salmon when exposed to urban runoff. Given the short half-life period and low solubility of 6PPD-Q, reliable in situ measurement techniques are required to accurately understand its occurrence and behaviour in aquatic environments. Here, using the diffusive gradients in thin-films (DGT) method with HLB as a binding agent, we developed a new methodology to measure 6PPD-Q in urban waters. 6PPD-Q was rapidly and strongly adsorbed on the HLB-binding gel and was efficiently extracted using organic solvents. The HLB-DGT accumulated 6PPD-Q linearly for >7 d and its performance was not significantly affected by pH (6.5-8.5), ionic strength (0.0001-0.5 M) or dissolved organic matter (0-20 mg L-1). Field evaluation of the DGT method demonstrated its effectiveness in urban runoff, detecting 6PPD-Q levels of 15.8-39.5 ng L-1 in rivers. In snowmelt, DGT detected 6PPD-Q levels of 210 ng L-1 which is two times higher than the value obtained by grab sampling. 6PPD-Q levels were much higher in snowmelt than those in rivers. This indicates that snowfall constitutes an important transport pathway for 6PPD-Q and that DGT effectively captured the fraction continuously released from dust particles in the snow samples. 6PPD-Q posed a substantial risk to migratory fish in urban waters, and its release from tire wear particles requires further investigation. This study is the first to develop a DGT-based method for 6PPD-Q determination in urban waters, and the method can ensure an accurate measurement of the release of 6PPD-Q to the environment, particularly in rainfall or snowmelt, important pathways for its entry into the aquatic environment.

Fast On-Site Speciation and High Spatial Resolution Imaging of Labile Arsenic in Freshwater and Sediment Using the DGT-SERS Sensor

Diffusive gradients in thin films (DGT) technique is renowned for in situ passive sampling but not for rapid on-site analysis, whereas surface-enhanced Raman spectroscopy (SERS) excels in ultrasensitive on-site detection but is limited by substrate contamination from complex matrices. Here, a hierarchical nanostructure of silver (Ag) mirror-supported large Ag nanoparticles (∼120 nm) was grown in situ in polyacrylamide hydrogel with a restricted pore size (PAM/Ag mirror/AgNPs) to serve as both the DGT binding phase and the SERS substrate. The substrate exhibited a maximum electric field enhancement factor of 9.9 × 108 and a signal relative standard error of 4.8%. Using the DGT-SERS sensor, As(III) and As(V) in freshwater were simultaneously detected at limits of 0.9 and 0.8 μg L-1, respectively, applicable across a wide range of environmental conditions. The DGT-SERS effectively mitigated the interfacial reduction of As(V) caused by humic acid by excluding it from plasmonic hotspots through size exclusion of the diffusive layer. The Raman analysis of a DGT sample in the field requires only 2 s using a portable spectrometer without DGT device disassembly. More importantly, the DGT-SERS captured the first two-dimensional image of As(III) and As(V) in one DGT at the micron scale resolution, revealing their spatially supplementary distribution patterns at the sediment-water interface. This study paves the way for next-generation speciation imaging DGT and the application of SERS in complex environments.

Core-Satellite Nanoassemblies as SPR/SERS Dual-Mode Plasmonic Sensors for Sensitively Detecting Ractopamine in Complex Media

Highly sensitive and reliable detection of β-adrenergic agonists is especially necessary due to the illegal abuse of growth-promoting feed additives. Here, we develop a novel surface plasmon resonance/surface-enhanced Raman scattering (SPR/SERS) dual-mode plasmonic sensor based on core-satellite nanoassemblies for the highly sensitive and reliable detection of ractopamine (RAC). The addition of RAC results in the decomposition of core-satellite nanoassemblies and consequently changes the Rayleigh scattering color of dark-field microscopy (DFM) images and the Raman scattering intensity of SERS spectra. The excellent sensitivity, specificity, and uniformity of this strategy were confirmed by detecting RAC in various complex media in the farm-to-table chain, and the limit of detection (LOD) was 0.03 ng/mL in an aqueous solution. In particular, the convenient access to livestock sewage not only ensures animal welfare but also provides great convenience for the market regulation of β-agonists. The success of our on-site strategy only with a portable Raman device promises great application prospects for β-agonist detection.