Surface-enhanced Raman scattering (SERS) characterization of trace organoarsenic antimicrobials using silver/polydimethylsiloxane nanocomposites

Design and fabrication of La-based perovskites incorporated with functionalized carbon nanofibers for the electrochemical detection of roxarsone in water and food samples

The pentavalent arsenic compound roxarsone (RSN) is used as a feed additive in poultry for rapid growth, eventually ending up in poultry litter. Poultry litter contains chicken manure, which plays a vital role as an affordable fertilizer by providing rich nutrients to agricultural land. Consequently, the extensive use of poultry droppings serves as a conduit for the spread of toxic forms of arsenic in the soil and surface water. RSN can be easily oxidized to release highly carcinogenic As(III) and As(IV) species. Thus, investigations were conducted for the sensitive detection of RSN electrochemically by developing a sensor material based on lanthanum manganese oxide (LMO) and functionalized carbon nanofibers (f-CNFs). The successfully synthesised LMO/f-CNF composite was confirmed by chemical, compositional, and morphological studies. The electrochemical activity of the prepared composite material was examined using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The obtained results confirmed that LMO/f-CNF showed enhanced electrocatalytic activity and improved current response with a good linear range (0.01-0.78 μM and 2.08-497 μM, respectively), exhibiting a low limit of detection (LOD) of 0.004 μM with a high sensitivity of 13.24 μA μM-1 cm-2 towards the detection of RSN. The noteworthy features of LMO/f-CNF composite with its superior electrochemical performance enabled reliable reproducibility, exceptional stability and reliable practical application in the analysis of tap water and food sample, affording a recovery range of 86.1-98.87%.

Facet-dependent adsorption of aromatic organoarsenicals on hematite: The mechanism and environmental impact

Aromatic organoarsenic feed additives have been extensively used in poultry and livestock farming; however, a risk of releasing toxic inorganic arsenic exists when they are exposed to the environment. An in-depth understanding of the adsorption -migration behavior of aromatic organoarsenicals on environmental media is limited. In this study, p-arsanilic acid (p-ASA) and roxarsone (ROX) were considered as examples to systematically study their adsorption behaviors on the surface of hematite, a representative iron oxide in soil. By comparing the adsorption abilities and adsorption kinetics of hematite exposed with different facets (hexagonal nanoplates, HNPs, mainly exposed with {001} facets and hexagonal nanocubes, HNCs, exposed with {012} facets), combined with in situ shell-isolated nanoparticle enhanced Raman spectroscopy characterization and density functional theory simulation, the facet-dependent adsorption performance was observed and the mechanism revealed. The results showed that p-ASA formed a bidentate binuclear complex on HNCs and HNPs, whereas ROX formed monodentate mononuclear and bidentate binuclear configurations on the {001} and {012} facets, respectively. These differences not only lead to facet-dependent adsorption capacities but also affect their stability, as verified by sequential extraction experiments, affecting the environmental behavior and fate of aromatic organoarsenicals. This study not only provides insights into the environmental behavior of aromatic organoarsenicals but also offers theoretical support for the development of functional adsorbents and remediation strategies.

Application of surface-enhanced Raman scattering to qualitative and quantitative analysis of arsenic species

Given the toxicity of arsenic, there is an urgent need for the development of efficient and reliable detection systems. Raman spectroscopy, a powerful tool for material characterization and analysis, can be used to explore the properties of a wide range of different materials. Surface-enhanced Raman spectroscopy (SERS) can detect low concentrations of chemicals. This review focuses on the progress of qualitative and quantitative studies of the adsorption processes of inorganic arsenic and organic arsenic in aqueous media using Raman spectroscopy in recent years and discusses the application of Raman spectroscopy theory simulations to arsenic adsorption processes. Sliver nanoparticles are generally used as the SERS substrate to detect arsenic. Inorganic arsenic is chemisorbed onto the silver surface by forming As-O-Ag bonds, and the Raman shift difference in the As-O stretching (∼60 cm-1) between As(V) and As(III) allows SERS to detect and distinguish between As(V) and As(III) in groundwater samples. For organic arsenicals, specific compounds can be identified based on spectral differences in the vibration modes of the chemical bonds. Under the same laser excitation, the intensity of the Raman spectra for different arsenic concentrations is linearly related to the concentration, thus allowing quantitative analysis of arsenic. Molecular modeling of adsorbed analytes via density functional theory calculation (DFT) can predict the Raman shifts of analytes in different laser wavelengths.

Electrochemical Behavior of Three-Dimensional Cobalt Manganate with Flowerlike Structures for Effective Roxarsone Sensing

Rational design and construction of the finest electrocatalytic materials are important for improving the performance of electrochemical sensors. Spinel bioxides based on cobalt manganate (CoMn₂O₄) are of particular importance for electrochemical sensors due to their excellent catalytic performance. In this study, three-dimensional CoMn₂O₄ with the petal-free, flowerlike structure is synthesized by facile hydrothermal and calcination methods for the electrochemical sensing of roxarsone (RXS). The effect of calcination temperature on the characteristics of CoMn₂O₄ was thoroughly studied by in-depth electron microscopic, spectroscopic, and analytical methods. Compared to previous reports, CoMn₂O₄-modified screen-printed carbon electrodes display superior performance for the RXS detection, including a wide linear range (0.01-0.84 μM; 0.84-1130 μM), a low limit of detection (0.002 μM), and a high sensitivity (33.13 μA μM^-1 cm^-2). The remarkable electrocatalytic performance can be attributed to its excellent physical properties, such as good conductivity, hybrid architectures, high specific surface area, and rapid electron transportation. More significantly, the proposed electrochemical sensor presents excellent selectivity, good stability, and high reproducibility. Besides, the detection of RXS in river water samples using the CoMn₂O₄-based electrochemical sensor shows satisfactory recovery values in the range of 98.00-99.80%. This work opens a new strategy to design an electrocatalyst with the hybrid architecture for high-performance electrochemical sensing.

Nano-Enabled sensors for detection of arsenic in water

The elevated cases of arsenic contamination reported across the globe have made its early detection and remediation an active area of research. Although, the World Health Organisation has set the maximum provisional value for arsenic in drinking water at 10 parts per billion, yet concentrations as high as 5000 parts per billion are still reported. In human beings, chronic arsenic exposure can culminate into lethal diseases such as cancer. Thus, there is a need for urgent emergence of efficient and reliable detection system. This paper offers an overview of the state-of-art knowledge on current arsenic detection mechanisms. The central agenda of this paper is to develop an understanding into the nano-enabled methods for arsenic detection with an emphasis on strategic fabrication of nanostructures and the modulation of nanomaterial chemistry in order to strengthen the knowledge into novel nano-enabled solutions for arsenic contamination. Towards the end prospects for arsenic detection in water are also prompted.

A rapid and convenient screening method for detection of restricted monensin, decoquinate, and lasalocid in animal feed by applying SERS and chemometrics

The surface-enhanced activities of size- and shape-controlled gold nanoparticles (AuNPs) with superior chemical stability were investigated to explore a possible development of a simple and non-destructive spectroscopic method to help the regulatory agency's analytical services for rapid detection and characterization of selected antimicrobials in animal feeds. Feed samples spiked at different concentration ranges of antimicrobials were evaluated using AuNPs as a surface-enhanced Raman spectroscopy (SERS) agent. The collected SERS spectra were mathematically preprocessed for further analysis. The classification models obtained 100% predictive accuracy with zero or little misclassification. The first two canonical variables (p = 0.001) could explain >95% of the variability in preprocessed spectral data. Most chemometric models for predicting MON, DEC, and LAS concentrations showed a high predictive accuracy (r² > 0.90), lower predictive error (<20 mg/kg), and satisfactory regression quality (slope close to 1.0). The statistical results showed no statistically significant difference between the reference and SERS predicted values (p > 0.05). The findings and implications from the study indicate that SERS would be a powerful and efficient technique possessing a great potential serving as an excellent monitoring and screening tool for antimicrobial contaminated samples in the on-site analysis.

Corncob-derived activated carbon for roxarsone removal from aqueous solution: isotherms, kinetics, and mechanism

In this study, the adsorption of roxarsone (ROX) onto corncob-derived activated carbon (AC) was optimized using response surface methodology (RSM). Following this, the AC was comprehensively characterized by FT-IR, SEM, and EDS analysis. The results showed that the highest ROX adsorption efficiency of 304.34 mg/g was obtained at the contact time of 262 min, initial pH of 2.5, adsorbent dosage of 0.4 g/L, and initial concentration of 240 mg/L. Besides, it was found that the adsorption equilibrium data was fitted well to the Langmuir and Sips isotherm models. The thermodynamic parameters (e.g., ΔG, ΔH, and ΔS) revealed the spontaneous and exothermic nature of ROX adsorption. As indicated by pseudo second-order kinetics model, the adsorption of ROX onto AC could be achieved through the hydrogen bond, π-π adsorbate-adsorbent interaction, and electrostatic interaction between AC surface functional group and molecular species variations of ROX at different pH values. Overall, it can be concluded that corncob-derived AC is an alternative option for removing ROX from aqueous solution.

Arsenic Speciation on Silver Nanofilms by Surface-Enhanced Raman Spectroscopy

Surface-enhanced Raman spectroscopy (SERS), as a nondestructive and fast detection technique, is a promising alternative approach for arsenic detection, particularly for in situ applications. SERS-based speciation analysis according to the fingerprint SERS signals of different arsenicals has the potential to provide a superior technique in species preservation over the conventional chromatographic separation methods, albeit with some difficulties due to the similarity in SERS patterns. In this study, we explored a novel SERS method for arsenic speciation by using the separation potential of the coffee ring effect on negatively charged silver nanofilms (AgNFs). Four arsenic species, including arsenite (As^III), arsenate (As^V), monomethylarsonic acid (MMA^V), and dimethylarsinic acid (DMA^V), were measured for fingerprint SERS signals in solution and on the films. Significant enhancement of SERS signals on the dried coffee ring stains by the AgNFs were observed except for As^III, and more importantly, arsenicals migrated varying distances during coffee ring development, promoting better speciation. Sodium dodecyl sulfate was then introduced into the droplet to reduce the droplet surface tension, facilitating the migration of solution into the peripheral region. Under the combined interactions of arsenicals with the AgNFs, solvent, and surfactant, enhanced separation between arsenicals was observed as a result of the formation of two concentric rings. Combining the SERS fingerprint signals and physical separation of arsenicals on the surface, arsenic speciation was achieved using the AgNFs substrate-based SERS technology, demonstrating the potential of the coffee ring effect for rapid separation and analysis of small molecules by SERS.

Unique Surface Enhanced Raman Scattering Substrate for the Study of Arsenic Speciation and Detection

In this study, a three-dimensional surface enhanced Raman scattering (SERS) substrate comprised of silver coated gold nanorods (Ag/AuNRs) decorated on electrospun polycaprolactone (PCL) fibers has been applied,  for the first time, to quantitative analytical measurements on various arsenic species: p-arsanilic acid ( pAsA), roxarsone (Rox), and arsenate (As^V), with a demonstrated sensitivity below 5 ppb. As^V detection in a solution of common salt ions has been demonstrated, showing the tolerance of the substrate to more complex environments. pAsA adsorption behavior on the substrate surface has been investigated in detail using these unique SERS substrates. Calculations based on density functional theory (DFT) support the spectral observation for pAsA. This substrate also has been shown to serve as a platform for in situ studies of arsenic desorption and reduction. This SERS substrate is potentially an excellent environmental sensor for both fundamental studies and practical applications.

Performance Characteristics of Bio-Inspired Metal Nanostructures as Surface-Enhanced Raman Scattered (SERS) Substrates

The fabrication of high-performance plasmonic nanomaterials for bio-sensing and trace chemical detection is a field of intense theoretical and experimental research. The use of metal-silicon nanopillar arrays as analytical sensors has been reported with reasonable results in recent years. The use of bio-inspired nanocomposite structures that follow the Fibonacci numerical architecture offers the opportunity to develop nanostructures with theoretically higher and more reproducible plasmonic fields over extended areas. The work presented here describes the nanofabrication process for a series of 40 µm × 40 µm bio-inspired arrays classified as asymmetric fractals (sunflower seeds and romanesco broccoli), bilaterally symmetric (acacia leaves and honeycombs), and radially symmetric (such as orchids and lily flowers) using electron beam lithography. In addition, analytical capabilities were evaluated using surface-enhanced Raman scattering (SERS). The substrate characterization and SERS performance of the developed substrates as the strategies to assess the design performance are presented and discussed.

On-line sensitive detection of aromatic vapor through PDMS/C3H7S-assisted SERS amplification

A PDMS/C₃H₇S-assisted SERS amplification method was developed for on-line detection of aromatic vapor. This approach provides a rapid, efficient route to significantly improve the capture and immobilization of vapor molecules on the plasmonic surface in the flowing system.

SERS detection of arsenic in water: A review

Arsenic (As) is one of the most toxic contaminants found in the environment. Development of novel detection methods for As species in water with the potential for field use has been an urgent need in recent years. In past decades, surface-enhanced Raman scattering (SERS) has gained a reputation as one of the most sensitive spectroscopic methods for chemical and biomolecular sensing. The SERS technique has emerged as an extremely promising solution for in-situ detection of arsenic species in the field, particularly when coupled with portable/handheld Raman spectrometers. In this article, the recent advances in SERS analysis of arsenic species in water media are reviewed, and the potential of this technique for fast screening and field testing of arsenic-contaminated environmental water samples is discussed. The problems that remain in the field are also discussed and an outlook for the future is featured at the end of the article.

Improving the SERS detection sensitivity of aromatic molecules by a PDMS-coated Au nanoparticle monolayer film

In this paper, we reported a facile strategy to fabricate a PDMS film-coated Au nanoparticle monolayer film (Au MLF) composite substrate for improving SERS detection of aromatic molecules in water and in the atmosphere.

Interactions between the antifungal drug myclobutanil and gold and silver nanoparticles in Penicillium digitatum investigated by surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) of an antifungal reagent, myclobutanil (MCB), was performed on Au and Ag nanoparticles (NPs) to estimate the drug-release behaviors in fungal cells. A density functional theory (DFT) calculation was introduced to predict a favorable binding site of MCB to either the Ag or Au atom. Myclobutanil was presumed to bind more strongly to Au than to Ag in their most stable, optimized geometries of the N4 atom in its 1,2,4-triazole unit binding to the metal atom. Strong intensities were observed in the Ag SERS spectra only at acidic pH values, whereas the most prominent peaks in the Au SERS spectra of MCB matched quite well with those of 1,2,4-triazole regardless of pH conditions. The Raman spectral intensities of the MCB-assembled Ag and Au NPs decreased after treatment with either potato dextrose agar (PDA) or glutathione (GSH). Darkfield microscopy and confocal SERS were performed to analyze the MCB-assembled metal NPs inside Penicillium digitatum fungal cells. The results suggested that MCB was released from the metal NPs in the intracellular GSH in the fungi because we observed only fungal cell peaks.

Design and characterization of hybrid morphology nanoarrays as plasmonic Raman probes for antimicrobial detection

Advances in nanofabrication have allowed the production of new and more reproducible substrates for the Raman detection of trace antimicrobials in water. The superior substrate uniformity combined with the ability to control surface morphology represents a significant step forward in the design of substrates with improved enhancement factors and trace-detection capabilities. The work presented herein successfully combines electron-beam lithography (EBL) and reactive ion-etching (RIE) protocols for the construction, testing, and validation of plasmonic hybrid morphology nanoarrays for the detection of arsenic antimicrobials in water. The fabricated substrates consist of 2500 μm(2) Ag-coated silicon dioxide (SiO2)/Si pillar nanoarrays of alternating hexagonal and elliptical features. Control of simple fabrication parameters such as inter-particle spacing (gap) and its orientation relative to the laser polarization vector (parallel or orthogonal) result in over a tenfold improvement in the apparent Raman response under optimized conditions. At a 633 nm excitation frequency, the best substrate performance was observed on parallel-oriented features with a 200 nm gap, with over one order of magnitude increase in the apparent surface-enhanced Raman scattering (SERS) signal relative to standard silver-polydimethylsiloxane (Ag-PDMS) nanocomposites. Monitoring of the characteristic As-C stretching band at 594 cm(-1) allowed the detection of arsenic antimicrobials in water well within the parts per million range. Calculated surface-enhancement factors (SEF) for this substrate, employing 532, 785, and 633 nm excitation wavelengths, was within five, six, and seven orders of magnitude, respectively. The effect of substrate morphology and nanofabrication process on the Raman enhancement factor is presented.