Surface Enhanced Raman Spectroscopy Detection Research Articles

MoSe2 monolayer crystallinity improvement and phase engineering for ultrasensitive SERS detection

Alkali metal halides (AMHs) interaction with metal oxide precursors has been demonstrated to be an exciting and reliable method in the deposition of several atomically thin layered materials since the reaction rate is considerably enhanced. Using three different AMHs (KBr, NaCl, and KCl), we assisted the synthesis of MoSe2 monolayers (MLs) in the atmospheric pressure chemical vapor deposition (APCVD) process in demonstrating that it is possible to improve the crystallinity of the MoSe2 flakes and to induce the formation of 1T domains in the 2H MoSe2 lattice that can be used to perform ultrahigh sensitive surface-enhanced Raman spectroscopy (SERS) detection. We observed that even though NaCl promotes the growth of large-sized MoSe2 MLs, we found critical photoluminescence (PL) quenching originated from forming a Na-O layer underneath the MoSe2 crystals. On the other hand, resonant Raman measurements show a prominent peak around 255 cm−1 only in KBr-MoSe2 single crystals originated from a double-resonant Raman process involving the ZA acoustic phonon and the C exciton, indicating optoelectronic-grade crystalline quality, thus explicating the higher PL emission in comparison with the other two AMH-assisted samples. KCl-MoSe2 X-ray photoelectron spectroscopy (XPS) and Raman spectra display features matching the structural properties of 1T-MoSe2 polyphase, confirming the existence of 1T domains embedded in the 2H-MoSe2 lattice. Moreover, thermogravimetric analysis (TGA) measurements show that the KCl-MoO2 mixture induces different sublimation processes compared with pure MoO2, probably producing potassium-rich eutectic compounds that could stabilize the 1T-MoSe2 domains. Finally, we demonstrate that the 1T-2H MoSe2 monolayers synthesized at 750 °C showed a significant surface enhance Raman scattering activity towards the Rhodamine 6G and Methylene blue, with a detection limit comparable with plasmonic surfaces.

Crystallinity engineering of Au nanoparticles on graphene for in situ SERS monitoring of Fenton-like reaction

Fabrication of multifunctional nanoplatform to in situ monitor Fenton reaction is of vital importance to probe the underlying reaction process and design high-performance catalyst. Herein, a hybrid catalyst comprising of single-crystalline Au nanoparticles (SC Au NPs) on reduced graphene oxide (RGO) sheet was prepared, which not only exhibited an excellent 1O2 mediated Fenton-like catalytic activity in promoting rhodamine 6G (R6G) degradation by activating H2O2, but also displayed a sensitive surface-enhanced Raman spectroscopy (SERS) detection performance to R6G with a linear response range from 1.0 × 10−8 mol/L to 1.0 × 10−5 mol/L thus providing a powerful and versatile nanoplatform for in situ SERS monitoring Fenton-like catalytic reaction. The integration of catalytic and SERS activities into a single nanostructure are expected to provide great potentials for practical applications in environmental catalysis.

Highly Sensitive and Reliable microRNA Detection with a Recyclable Microfluidic Device and an Easily Assembled SERS Substrate.

Surface-enhanced Raman spectroscopy (SERS) detection in microfluidics is an interesting topic because of its high sensitivity, miniaturization, and ability to perform online detection. However, the difficulties in generating SERS-based microfluidic devices with uniform signal reproducibility and high sensitivity have hindered their widespread application. In addition, the recyclability of the SERS-based microfluidic devices can contribute to their broad commercialization, but the possible contamination in the detection area and cumbersome cleaning procedures remain a challenge. In this study, we describe a repeatable SERS-based microfluidic device comprising a disposable SERS substrate and a reusable microfluidic channel. The microfluidic channel was prepared via mechanical processing, and the SERS substrate was fabricated by nanoimprint lithography and electrodeposition. The SERS substrate and microfluidic channel can be attached easily because they were assembled using screws. The SERS substrate achieved an excellent SERS enhancement factor greater than 108 over a large sample area, signal uniformity, and substrate-to-substrate reproducibility. This guaranteed reliable and sensitive signals in every experiment. Furthermore, the disposable SERS substrate contributed exact detection of target molecules. Finally, their practical application was demonstrated with the repeated use of the microfluidic device by detecting a specific micro-RNA, (miR-34a) at a concentration as low as 5 fM.

Ultrasensitive surface-enhanced Raman spectroscopy detection of gaseous sulfur-mustard simulant based on thin oxide-coated gold nanocone arrays

Surface Enhanced Raman Spectroscopy (SERS) could be a powerful technique for detecting trace gaseous sulfur-mustard, but it is still challenging due to the difficulty in efficiently capturing sulfur-mustard molecules by normal SERS substrates. Here, a chemically trapping strategy is presented for such detection via coating an ultrathin metal-oxide sensing layer on a SERS substrate. In the strategy, a SERS substrate Au-wrapped Si nanocone array is designed and fabricated by Si wafer-based organic template-etching and appropriate Au deposition, and coated with an ultrathin CuO for chemically capturing sulfur-mustard molecules. The validity of such strategy has been demonstrated via taking the gaseous 2-chloroethyl ethyl sulfide (a simulant of sulfur-mustard, or 2-CEES for short) as the target molecules. The response of the CuO-coated SERS substrate to the gaseous 2-CEES is detectable within 10 min, and the lowest detectable concentration is 10 ppb or less. Further experiments have shown that there exists an optimal CuO coating thickness which is about 6 nm. The CuO coating-based capture of 2-CEES molecules is attributed to the surface hydroxyl-induced specific adsorption, which is subject to the pseudo-second-order kinetics and Freundlich-typed model. This study presents the practical SERS chips and new route for the trace detection of gaseous sulfur-mustard.

Rapid Surface-Enhanced Raman Spectroscopy Detection of Chlorothalonil in Standard Solution and Orange Peels with Pretreatment of Ultraviolet Irradiation.

At present, the detection of chlorothalonil is generally based on chromatography and immunoassay; both of which are time-consuming and costly. In this study, Surface-enhanced Raman Spectroscopy (SERS) has been successfully utilized in the detection of chlorothalonil coupled with photochemistry and meanwhile, gold nanoparticles were prepared to enhance the Raman signal. Two Raman peaks (2246cm- 1 and 2140cm- 1) of chlorothalonil were appeared after ultraviolet (UV) irradiation compared to the original solution. Chlorothalonil generated excited and weakened C≡N bonds in its structure by absorbing UV energy, thus leading to two kinds of corresponding peaks. These two kinds of peaks were both selected as analytical peaks in chlorothalonil detection. Different light sources and solvents were made different contributions to the final spectra. Chlorothalonil methanol solution under 302 nm wavelength irradiation was performed the best. The 2246cm- 1 sharp peak represented to the normal C≡N bond appeared at first, which overall trend was significantly increased followed by a gradual decrease. The 2140cm- 1 broad peak represented to the weakened C≡N bond appeared later, which overall trend was increased as the irradiation time passing by and then kept stable. Natural bond orbital (NBO) analysis indicates that the downshift of C≡N bond from 2246cm- 1 to 2140cm- 1 is due to the increase of electronic populations of π* orbital of C≡N bond transited from π orbital excited by UV irradiation. The positively charged C≡N bond had more chance to approach negatively charged gold nanoparticles. The detection limit of chlorothalonil was as low as 0.1 ppm in the standard solution. Orange peels spiked with chlorothalonil oil were also detected in this paper to confirm the practical operability of this method. The SERS method may be further developed as a rapid detection of pesticides that contains a triple bond by utilizing photochemistry.

Short Silk Nanoribbons Decorated by Au Nanoparticles as Substrates for Sensitive and Uniform Surface-Enhanced Raman Spectroscopy Detection

The optimal design of “hot spot” nanostructures governs the sensitivity and uniformity of surface-enhanced Raman scattering (SERS) substrates. Au–silk nanoribbon (SNR) aggregates have achieved excellent SERS sensitivity with SNR as hot spot reservoirs but are inferior to complicated laser ablation and electrochemical deposition systems. Here, nanostructures of SNR were designed to further enrich the hot spots of Au-SNR substrates via blending of Au nanoparticles (AuNPs) and SNR in aqueous solutions to achieve better sensitivity. The materials were on par with some of the best complex SERS systems previously reported. The length of the SNR templates was shortened from 2000 nm to 100–400 nm through ultrasonic treatment to minimize steric hindrance, facilitating the formation of hot spot structures. More than 4 times the amount of AuNPs adhered on these shortened SNRs, resulting in superior SERS sensitivity of 10–15–10–16 M, up to 100-fold higher than previous Au-SNR substrates. The reproducibility in detection was improved with a relative standard deviation (RSD) of 9.5%, superior to most solution-based systems. Similar to our previous Au-SNR substrates, the optimized Au-SNR assemblies exhibited excellent cytocompatibility, strengthening potential utility in biomedical applications. Ultrafast SERS imaging of cells could be completed within 8 s through these modified probe-laden Au-SNR assemblies. Considering the superior SERS performance and cytocompatibility, along with the simple, controllable, and green aqueous fabrication process, the present Au-SNR SERS substrates offer significant advantages in versatile applications.

Label-free surface-enhanced Raman spectroscopy detection for tyrosine-methionine-aspartate-aspartate (YMDD)-motif mutants of HBV DNA

Hepatitis B is a widespread and potentially life-threatening disease caused by the hepatitis B virus, tyrosine-methionine-aspartate-aspartate (YMDD) - motif mutant is a known HBV variant and responsible for the drug resistance during Long-term lamivudine treatment. In this work, spermine-coated silver nanoparticles were used as surface-enhanced Raman scattering enhancement matrices to detect mutations in single sites of the hepatitis B virus single-stranded DNA. The unique Raman finger-print spectrum of DNA based on spermine-coated silver nanoparticles was detected. And the signals from the phosphate backbone allowed to be an internal standard for standardize the surface-enhanced Raman spectrum of DNA oligonucleotides. The spectral changes were quantitatively related to the composition of adenine in the DNA strand, and the correlation performance reached 0.99. The relative standard deviation of surface-enhanced Raman spectroscopy signal corresponding to the tyrosine-isoleucine-aspartate-aspartate (YIDD), tyrosine-valine-aspartate-aspartate (YVDD), and YMDD was 5.43 %, 7.5 %, and 7.28 %, respectively. The proposed method provides a potential tool for YMDD-motif mutants detection and reference for therapeutic drug monitoring.

Recent progress of microfluidics in surface-enhanced Raman spectroscopic analysis.

Surface-enhanced Raman spectroscopy is a significant analytical tool capable of fingerprint identification of molecule in a rapid and ultrasensitive manner. However, it is still hard to meet the requirements of practical sample analysis. The introduction of microfluidics can effectively enhance the performance of surface-enhanced Raman spectroscopy in complex sample analysis including reproducibility, selectivity, sensitivity, and speed. This review summarizes the recent progress of microfluidics in surface-enhanced Raman spectroscopic analysis through four combination approaches. First, microfluidic synthetic techniques offer uniform nano-/microparticle fabrication approaches for reproductive surface-enhanced Raman spectroscopic analysis. Second, the integration of microchip and surface-enhanced Raman spectroscopic substrate provides advanced devices for sensitive and efficient detection. Third, microfluidic sample preparations enable rapid separation and preconcentration of analyte prior to surface-enhanced Raman spectroscopic detection. Fourth, highly integrated microfluidic devices can be employed to realize multistep surface-enhanced Raman spectroscopic analysis containing material fabrication, sample preparation, and detection processes. Furthermore, the challenges and outlooks of the application of microfluidics in surface-enhanced Raman spectroscopic analysis are discussed.

Surface-enhanced shifted excitation Raman difference spectroscopy for trace detection of fentanyl in beverages.

In recognition of the misuse risks of fentanyl, there is an urgent need to develop a useful and rapid analytical method to detect and monitor the opioid drug. The surface-enhanced shifted excitation Raman difference spectroscopy (SE-SERDS) method has been demonstrated to suppress background interference and enhance Raman signals. In this study, the SE-SERDS method was used for trace detection of fentanyl in beverages. To prepare the simulated illegal drug-beverages, fentanyls were dissolved into distilled water or Mizone as a series of test samples. Based on our previous work, the surface-enhanced Raman spectroscopy detection was performed on the beverages containing fentanyl by the prepared AgNPs and the SE-SERDS spectra of test samples were collected by the dual-wavelength rapid excitation Raman difference spectroscopy system. In addition, the quantitative relationship between fentanyl concentrations and the Raman peaks was constructed by the Langmuir equation. The experimental results show that the limits of quantitation for fentanyl in distilled water and Mizone were 10 ng/mL and 200 ng/mL, respectively; the correlation coefficients for the nonlinear regression were as high as 0.9802 and 0.9794, respectively; and the relative standard deviation was less than 15%. Hence, the SE-SERDS method will be a promising method for the trace analyses of food safety and forensics.

Ag Nanocubes Coupled with Heating-Enhanced DSN-Assisted Cycling Amplification for Surface-Enhanced Raman Spectroscopy Detection of MicroRNA-21

Surface-enhanced Raman scattering (SERS)-based biosensing has strong potential owing to its high sensitivity and good selectivity. In this study, a SERS biosensing platform for microRNA-21 detectio...

Tip-to-tip assembly of urchin-like Au nanostar at water-oil interface for surface-enhanced Raman spectroscopy detection

Au Nanostar (NS) monolayer as a surface enhanced Raman scattering (SERS) substrate has been synthesized by self-assembly at a water-oil interface. It is confirmed from the experiment and simulation results that the Au NS monolayer includes lots of “hot spots” at or between the tips of the Au NSs, enhancing the local electromagnetic fields and giving rise to strong SERS signals sequentially. The limit of detection is determined to be down to 4.2 × 10−12 M for rhodamine 6G. Furthermore, the Au NS monolayer can detect multiple molecules, including thiabendazole, methylene blue, 4-mercaptobenzoic acid, and p-amino thiophenol, indicating that the SERS substrate composed of Au NS monolayer has potential applications in analytical chemistry, food safety, and environmental safety.

Preparation of QSS@AuNPs and Solvent Inducing Enhancement Strategy for Raman Determination of Salivary Thiocyanate.

Making the substrates form highly dense, homogeneous, and stable hotspots regions is important for the sensitive detection of surface-enhanced Raman spectroscopy (SERS). A new strategy based on solvent-induced (SI) SERS substrate to form a stable interval of the hotspot for detection was explored and the enhancement factor (EF) of our SERS substrates could reach about 1.4 × 109. By preferential adsorption of alcohol solutions by Q-Sepharose microsphere (QSS) in mixed water and alcohol solutions, the size of QSS@AuNPs was dynamically adjusted and the spacing between gold nanoparticles (AuNPs) was adjusted to keep the substrate in the optimal hotspot mode for the sensitive detection of SERS in the liquid state. As a real application case, such a SI-SERS strategy was employed to determine SCN- in saliva and a limit of detection (LOD) of about 10-10 M could be achieved.

Strategies for SERS Detection of Organochlorine Pesticides.

Organochlorine pesticides (OCPs) embody highly lipophilic hazardous chemicals that are being phased out globally. Due to their persistent nature, they are still contaminating the environment, being classified as persistent organic pollutants (POPs). They bioaccumulate through bioconcentration and biomagnification, leading to elevated concentrations at higher trophic levels. Studies show that human long-term exposure to OCPs is correlated with a large panel of common chronic diseases. Due to toxicity concerns, most OCPs are listed as persistent organic pollutants (POPs). Conventionally, separation techniques such as gas chromatography are used to analyze OCPs (e.g., gas chromatography coupled with mass spectrometry (GC/MS)) or electron capture detection (GC/ECD). These are accurate, but expensive and time-consuming methods, which can only be performed in centralized lab environments after extensive pretreatment of the collected samples. Thus, researchers are continuously fueling the need to pursue new faster and less expensive alternatives for their detection and quantification that can be used in the field, possibly in miniaturized lab-on-a-chip systems. In this context, surface enhanced Raman spectroscopy (SERS) represents an exceptional analytical tool for the trace detection of pollutants, offering molecular fingerprint-type data and high sensitivity. For maximum signal amplification, two conditions are imposed: an efficient substrate and a high affinity toward the analyte. Unfortunately, due to the highly hydrophobic nature of these pollutants (OCPs,) they usually have a low affinity toward SERS substrates, increasing the challenge in their SERS detection. In order to overcome this limitation and take advantage of on-site Raman analysis of pollutants, researchers are devising ingenious strategies that are synthetically discussed in this review paper. Aiming to maximize the weak Raman signal of organochlorine pesticides, current practices of increasing the substrate’s performance, along with efforts in improving the selectivity by SERS substrate functionalization meant to adsorb the OCPs in close proximity (via covalent, electrostatic or hydrophobic bonds), are both discussed. Moreover, the prospects of multiplex analysis are also approached. Finally, other perspectives for capturing such hydrophobic molecules (MIPs—molecularly imprinted polymers, immunoassays) and SERS coupled techniques (microfluidics—SERS, electrochemistry—SERS) to overcome some of the restraints are presented.

A novel serum protein purification technique combined with surface-enhanced Raman spectroscopy for liver cancer detection

In this study, silver nanoparticles-based surface-enhanced Raman spectroscopy combined with a serum protein purification method was employed to screen liver tumors. The cellulose acetate membrane was used to separate proteins from human serum, and then the purified serum proteins were mixed with silver nanoparticles for surface-enhanced Raman spectroscopy detection. High-quality spectra were recorded from serum protein samples belonging to 45 healthy volunteers and 42 liver cancer patients, and the diagnostic sensitivity and specificity of liver cancer were 90.5% and 95.6%, respectively, indicating that this method has great application potential for the detection and screening of liver cancer.

Simultaneous extraction and surface enhanced Raman spectroscopy detection for the rapid and reliable identification of nicotine released from snus products.

Surface enhanced Raman spectroscopy (SERS) is a highly sensitive analytical detection technique that provides unique chemical and structural information on target molecules. Here, simultaneous extraction and SERS detection of nicotine for the rapid and reliable identification of nicotine released from snus products were performed based on a nano-Au assembly hierarchy structure in the capillary. Based on this strategy, the time evolution of the concentrations of nicotine released from the snus products was measured. Through comparison of the intensities of the spectral peaks of the symmetrical breathing of the pyridine moiety of nicotine molecules, with the prolongation of time, the concentration of nicotine released decreased significantly, which is helpful for establishing a method for the rapid evaluation of the processing and selection of excipients of snus products, and provides a new idea for further study of the production of snus pouches and related tobacco products. Moreover, based on data fitting, it can be calculated that the concentration of nicotine in the extraction presented an obvious quadratic relationship with time, and the release of most of the nicotine in the snus pouch, which is held through the gums and palate, was basically completed after ∼15 min. Such destruction-free simultaneous measurements of snus products are opening up new perspectives for further research about the impact of nicotinoids on smokers' health and cessation programs.

Quantitative detection of dithiocarbamate pesticides by surface-enhanced Raman spectroscopy combined with an exhaustive peak-seeking method.

Surface-enhanced Raman spectroscopy (SERS) based on nanosilver colloid substrates has great potential for rapid detection of pesticide residues because of its advantages of sensitivity, rapidity, simplicity, low cost, etc. However, its poor repeatability and narrow linear quantitative range limit its practical application. In this paper, a silver colloid SERS analysis method combined with an exhaustive peak-seeking method was introduced for quantitative determination of thiram and ziram. This method can establish a linear quantitative relationship in a wide range by use of an own characteristic peak of analysis as an internal standard (IS) which is found via judging the linear correlation between the intensity ratios of two SERS peaks of analytes and the concentrations. Combined with improving the preparation method of silver colloids, adding suitable activators and optimizing the detection process, a liquid detection system with good repeatability and a wide linear quantitation range was obtained. The relative standard deviation (RSD) of the strongest SERS peak is no more than 8.98%, which is better than the general case of the silver colloid SERS substrate. The ratio of I1384/I1148 has a good linear relationship with the concentration of thiram solution, and the 1148 cm-1 characteristic peak was utilized as the IS to establish the standard curve equation for the determination of thiram concentration. The equation is I1384/I1148 = -1.7930 × lg[cthiram (ppm)] + 6.0078 with a linear range of 10-2 to 102 ppm (4.16 × 10-8 to 4.16 × 10-4 mol L-1) and a limit of detection (LOD) of 10-2 ppm. The peak of IS for the determination of ziram concentration is at 938 cm-1, and the equation is I1384/I938 = 4.5531 × lg[cziram (ppm)] + 6.4792 with a linear range of 10-1 to 102 ppm (3.27 × 10-7 to 3.27 × 10-4 mol L-1) and a LOD of 10-4 ppm. Thiram or ziram in apple juice was successfully detected by using this liquid detection system. This analysis system effectively solves the problem of poor repeatability and a narrow linear quantification range in SERS analysis based on silver colloid substrates, and the linear quantification range meets the requirements of the national standard (GB-2763-2019).

An antibody-free liver cancer screening approach based on nanoplasmonics biosensing chips via spectrum-based deep learning

The clinical needs of rapidly screening liver cancer in large populations have asked for a facile and low-cost point-of-care testing (POCT) method. We present a nanoplasmonics biosensing chip (NBC) that would empower antibody-free detection with simplified analysis procedures for POCT. The cheaply fabricable NBC consists of multiple silver nanoparticle-decorated ZnO nanorods on cellulose filter paper and would enable one-drop blood tests through surface-enhanced Raman spectroscopy (SERS) detection. In this work, utilizing such an NBC and deep neural network (DNN) modeling, a direct serological detection platform was constructed for automatically identifying liver cancer within minutes. This chip could enhance Raman signals enough to be applied to POCT. A classification DNN model was established by spectrum-based deep learning with 1140 serum SERS spectra in equal proportions from hepatocellular carcinoma (HCC) patients and healthy individuals, achieving an identification accuracy of 91% on an external validation set of 100 spectra (50 HCC versus 50 healthy). The intelligent platform, based on the biosensing chip and DNN, has the potential for clinical applications and generalizable use in quickly screening or detecting other types of cancer.

Surface adsorption of hydroxyanthraquinones on CTAB-modified gold nanosurfaces

Gold nanosurfaces are widely applied to the surface-enhanced Raman spectroscopy (SERS) detection of the biological systems. The surface modification of gold nanoparticles (AuNPs) is often required when the analytes do not efficiently adsorb on the surface. In this paper, an aggregation of AuNPs with cetyltrimethylammonium bromide (CTAB) was introduced for the efficient surface adsorption and strong SERS enhancement for a number of hydroxyanthraquinones (HAQs). The SERS of HAQs including 1,2-dihydroxyanthraquinone (alizarin) were strongly enhanced with CTAB-modified AuNPs and deprotonation of alizarin was clearly observed upon the pH change. The CTAB-modified AuNPs are regarded as efficient SERS substrates for many biological molecules with weak surface adsorption.

High signal collection efficiency in a 3D SERS chip using a micro-reflector.

To improve the sensitivity of surface-enhanced Raman spectroscopy (SERS) detection, we propose a three-dimensional (3D) SERS chip based on an inverted pyramid micro-reflector (IPMR) that converges Raman scattering light signals to improve the signal collection efficiency. The influence of the geometric parameters of the inverted pyramid structure on the Raman signal collection efficiency was analyzed by simulation for the determination of the optimal design parameters. The inverted pyramid through-hole structure was prepared on the silicon wafer through an anisotropic wet etching process, followed by the sputtering of a gold film to form the IPMR. The 3D SERS chip was constructed by bonding the IPMR and the active substrate that assembled with silver nanoparticles. Using Rhodamine 6G molecules, the Raman intensity measured with the 3D SERS chip was threefold greater than that of the silicon-based SERS substrate under the same test conditions. These experimental results show that the 3D SERS chip can significantly improve the SERS signal intensity. Its 3D structure is convenient for integration with microfluidic devices and has great potential in biochemical detection applications.

Determination of nanomolar dissolved sulfides in water by coupling the classical methylene blue method with surface-enhanced Raman scattering detection

In this study, we proposed a novel method for the determination of nanomolar dissolved sulfides, including H2S, HS−, and S2− (defined as S(–II)) in water by coupling the classical methylene blue (MB) method with surface-enhanced Raman spectroscopy (SERS) detection. Overall, the following analytical procedures were employed: i) precipitation of S(–II) as zinc sulfide, ii) centrifugation to collect zinc sulfide, iii) derivatization of S(–II) to MB by the reaction with N, N-dimethyl-p-phenylenediamine in the presence of FeCl3 under acidic conditions, and iv) SERS detection. Parameters affecting the derivatization and SERS detection were optimized. Under the optimized conditions, a linear range of 12.3 nmol/L–200 nmol/L for S(–II) was obtained with a correlation coefficient (R2) of 0.99. Limits of detection and quantification of the developed method were estimated to be 3.7 nmol/L and 12.3 nmol/L, respectively. In addition, the proposed method demonstrated excellent tolerance to coexisting substances, such as NO2−, NO3−, SO32−, and other common ions. The proposed method demonstrates immense promise for the determination of nanomolar S(–II) in surface waters and wastewater.