Graphene-embedded oblique V-shaped silver nanoarrays for hydrophobic pollutants pre-concentration and high-sensitivity SERS detection

Shining a light on environmental science: Recent advances in SERS technology for rapid detection of persistent toxic substances

Persistent toxic substances (PTS) represent a paramount environmental issue in the 21st century. Understanding the concentrations and forms of PTS in the environment is crucial for accurately assessing their environmental health impacts. This article presents a concise overview of the components of PTS, pertinent environmental regulations, and conventional detection methodologies. Additionally, we offer an in-depth review of the principles, development, and practical applications of surface-enhanced Raman scattering (SERS) in environmental monitoring, emphasizing the advancements in detecting trace amounts of PTS in complex environmental matrices. Recent progress in enhancing SERS sensitivity, improving selectivity, and practical implementations are detailed, showcasing innovative materials and methods. Integrating SERS with advanced algorithms are highlighted as pivotal areas for future research.

Prussian Blue Nanosphere/Fe-Metal Organic Frameworks/Ce Nanocomposite as a Colorimetric Sensing Platform for Direct Detection in Organophosphorus Pesticides in Fetal Bovine Serum

Acute pesticide poisoning has resulted in several symptoms that threaten life safety. Thus, developing a rapid detection method would facilitate the identification of toxicants as soon as possible. This study presented an affordable and straightforward detection platform based on a core-shell structure nanocomposite of Prussian blue/Fe-metal-organic frameworks/Ce nanocomposite material, which exhibited peroxidase-like activity and multiple capture sites [marked as phosphate buffer (PB)/Fe-MOF/Ce NPs]. Fe3+ and Fe2+ are located at the core of PB nanoparticles (PB NPs), metal-porphyrin as a metal-organic framework (MOF) shell, and Ce NPs grown on the shell. A practical, economical, accurate, and colorimetric strategy was synthesized to detect organophosphorus pesticides directly in fetal bovine serum. The solution-based PB/Fe-MOF/Ce NP colorimetric sensor demonstrated an ultrasensitive detection performance and excellent reproducibility. The absorbance variation of dichlorvos, methamidophos, and dimethoate follows the linear equation of y = 0.093x + 0.024, y = 0.083x + 0.017, and y = 0.114x + 0.117 under a low content, and the limit of detection (LOD) of the colorimetric sensor was determined using 3s/slope, which was as low as 5.6, 4.8, and 6.5 μg/L, respectively, with the recovery rates ranging from 83.4% to 98.6% and an RSD less than 6%. This study provides an excellent method for effectively detecting acute poisoning samples and offers profound insights for further improving the treatment efficiency of pesticide poisoning, and it has excellent prospects in clinical point-of-care testing.

Deep eutectic solvent induced silver-gel as a flexible SERS substrate for sensitive detection of antibiotics under low temperature conditions

Antibiotic residues pose a significant threat to global health. Traditional detection methods for antibiotics are cumbersome, time-consuming and often incapable of achieving non-destructive detection at low temperatures. This research introduces a groundbreaking innovation in antibiotic detection: a flexible Surface-Enhanced Raman Scattering substrate based on a silver composite deep eutectic solvent (DES) gel, specifically engineered for low-temperature antibiotic detection. To address the challenge of low SERS response for antibiotics, we utilize R6G (Rhodamine 6 G) to effectively label them. This unique SERS substrate exhibits exceptional mechanical robustness, stability, and frost-resistance. Remarkably, it enables the direct and sensitive detection of six types of labeled antibiotics across four categories in frozen chicken wings at -25 °C, with a limit of detection (LOD) below 1.3 × 10-9 mol/L. Additionally, the substrate demonstrates outstanding homogeneity (relative standard deviation (RSD< 6.4 %), reproducibility (RSD < 6.2 %), and long-term stability over 30 days, ensuring highly sensitive and quantitative antibiotic detection. Theoretical insights reveal that the labeled antibiotics exhibit higher binding energy with silver, further enhancing detection sensitivity. This novel, flexible substrate holds immense potential for quantifying antibiotics in frozen foods and heralds a new era of expanded detection capabilities for a broader spectrum of antibiotics at low temperatures.

Uniformly aligned Ag NPs/graphene paper for enhanced SERS detection of pesticide residue

The surface-enhanced Raman scattering (SERS) technique provides a quick and reliable method for detecting pesticide residues. In this study, flexible substrates, composed of orderly arranged silver nanospheres (Ag NPs) films on graphene paper, were fabricated through a simple, low-cost Ag NP self-assembly process at a liquid-liquid interface, followed by transfer of the films onto the graphene paper. The SERS performance of the fabricated substrates was evaluated using a portable Raman spectrometer, with rhodamine 6G (R6G) serving as the probe molecule. The results indicate that the bilayer Ag NP films-covered graphene paper exhibits optimal overall performance, characterized by high sensitivity and high uniformity. The limit of detection (LOD) for the R6G molecule is as low as 8.73 × 10-9 M, demonstrating the strong signal amplification capability of the SERS substrate. Moreover, the relative standard deviation (RSD) of the Raman intensity at 1508 cm-1 for different selected points on the substrate is 5.018 %, indicating high uniformity of the SERS substrate. Finally, the performance of the SERS substrate was further evaluated by detecting thiram in fresh orange juice, demonstrating the capability to detect concentrations as low as 10-6 M. This result highlights the significant potential of the developed SERS substrate for practical applications in food safety and quality control.

An Ag-nanoplate decorated cavity-nanorod array SERS substrate for trace detection of PCB-77

We report the fabrication of a substrate with cavity-nanorods and decorated with Ag-nanoplates (C-NR@Ag). The cavities on the substrate are formed by metal assistant chemical etching, and the Ag-nanoplates in the cavities by galvanic cell deposition enhance the SERS performance effectively. Analytes in solution are adsorbed on Ag-nanoplates and located in hot spots, which enhance the SERS performance effectively. The enhancement factor of the Ag-nanoplates decorated on nanorod cavities is calculated to be 3.6 × 106, which is about 3 fold higher than that on the nanorods. The C-NR@Ag substrate is able to detect polychlorinated biphenyls (PCBs) with the lower limit of detection at 1.0 × 10-12 M. Additionally, due to the semi-volatile nature of PCB-77, the lower limit of detection of the C-NR@Ag substrate for PCB-77 was 1.0 × 10-11 M by the non-contact collection method. These results present a novel approach towards enhancing SERS performance and facilitating the rapid detection of PCB-77.

Multi-channel surface-enhanced Raman spectroscopy (SERS) platform for pollutant detection in water fabricated on polydimethylsiloxane

A miniature multi-channel surface-enhanced Raman scattering (SERS) sensor based on polydimethylsiloxane (PDMS) is constructed to achieve rapid delivery of polluted water and specific identification of multiple components. Hg2+, organic pollutants, and sodium nitrite are successfully identified by the multi-channel SERS sensor using Cy5, cyclodextrin, and urea in the corresponding detection area. This multi-channel sensor exhibits excellent sensitivity and specificity, with detection limits of 3.2 × 10-10 M for Hg2+, 1.0 × 10-8 M for aniline, 6.9 × 10-9 M for diphenylamine, 9.1 × 10-8 M for PCB-77, and 7.5 × 10-9 M for pyrene, and 5.0 × 10-7 M for sodium nitrite. Compared with traditional analysis techniques, this method exhibited excellent recovery for the water pollutants ranging from 82.1 to 115.8%. The PDMS-based microchannel allows for simultaneous and rapid identification of multiple environmental pollutants, offering a portable detection method for emergency testing of environmental pollutants and routine determination of water pollutants.

A novel strategy for specific sensing and inactivation of Escherichia coli: Constructing a targeted sandwich-type biosensor with multiple SERS hotspots to enhance SERS detection sensitivity and near-infrared light-triggered photothermal sterilization performance

Human health is greatly threatened by bacterial infection, which raises the risk of serious illness and death in humans. For early screening and accurate treatment of bacterial infection, there is a strong desire to undertake ultrasensitive detection and effective killing of pathogenic bacteria. Herein, a novel surface-enhanced Raman scattering (SERS) biosensor based on sandwich structure consisting of capture probes/bacteria/SERS tags was established for specific identification, capture and photothermal killing of Escherichia coli (E. coli). Finite-difference time-domain (FDTD) technique was used to simulate the electromagnetic field distribution of capture probes, SERS tags and sandwich-type SERS substrate, and a possible SERS enhancement mechanism based on sandwich structure was presented and discussed. Sandwich-type SERS biosensor successfully achieved distinctive identification and magnetic beneficiation of E. coli. In addition, a single SERS substrate, including capture probes and SERS tags, could also achieve outstanding photothermal effects as a consequence of localized surface plasmon resonance (LSPR) effect. Intriguingly, sandwich-type SERS biosensor demonstrated a higher photothermal conversion efficiency (50.03 %) than the single substrate, which might be attributed to the formation of target bacterial clusters. The superior biocompatibility and the low toxicity of the sandwich-type biosensor were confirmed. Our approach offers a fresh method for constructing sandwich-type biosensor with multiple SERS hotspots based on extremely effective hybrid plasmonic nanoparticles, and has a wide range of potential applications in the recognition and treatment of bacteria.

Porous rod-shaped Fe2O3/Ag/BP: a novel substrate for highly sensitive SERS detection of persistent organic pollutants

A surface enhanced Raman scattering (SERS) substrate of porous rod-shaped ferric oxide (Fe2O3) combined with silver nanoparticles (Ag NPs) and black phosphorus (Fe2O3/Ag/BP) was fabricated to detect the persistent organic pollutants (POPs) at low concentration. The organic pollutant Rhodamine 6G (R6G) was used as the probe molecule to study the performances of Fe2O3/Ag/BP, and 4-chlorobiphenyl (PCB-3) was the target of detection. The limit of detection (LOD) of R6G based on this novel SERS substrate Fe2O3/Ag/BP was as low as 1.0 × 10-15M, which was five orders of magnitude lower than that of Fe2O3/Ag (10-10M). The enhancement factor (EF) of Fe2O3/Ag/BP was 6.44 × 108, which was 3.1 times higher than that of porous rod-shaped Fe2O3/Ag (2.08 × 108). The Raman signal of R6G based on Fe2O3/Ag/BP had a good homogeneity, and the relative standard deviation (RSD) of Raman signal intensities of R6G at 1643 cm-1was only 5.97%. Furthermore, the Fe2O3/Ag/BP substrate exhibited a recyclability through the photocatalytic degradation of R6G. The LOD of PCB-3 based on Fe2O3/Ag/BP was 10-9M. Besides, Fe2O3/Ag/BP had a high SERS activity even it was kept in a centrifuge tube without requiring complicated treatment. These results highlight the potential application of Fe2O3/Ag/BP for ultra-trace detection of POPs in the environment.

Unveiling practical considerations for reliable and standardized SERS measurements: lessons from a comprehensive review of oblique angle deposition-fabricated silver nanorod array substrates

Recently, there has been an exponential growth in the number of publications focusing on surface-enhanced Raman scattering (SERS), primarily driven by advancements in nanotechnology and the increasing demand for chemical and biological detection. While many of these publications have focused on the development of new substrates and detection-based applications, there is a noticeable lack of attention given to various practical issues related to SERS measurements and detection. This review aims to fill this gap by utilizing silver nanorod (AgNR) SERS substrates fabricated through the oblique angle deposition method as an illustrative example. The review highlights and addresses a range of practical issues associated with SERS measurements and detection. These include the optimization of SERS substrates in terms of morphology and structural design, considerations for measurement configurations such as polarization and the incident angle of the excitation laser, and exploration of enhancement mechanisms encompassing both intrinsic properties induced by the structure and materials, as well as extrinsic factors arising from wetting/dewetting phenomena and analyte size. The manufacturing and storage aspects of SERS substrates, including scalable fabrication techniques, contamination control, cleaning procedures, and appropriate storage methods, are also discussed. Furthermore, the review delves into device design considerations, such as well arrays, flow cells, and fiber probes, and explores various sample preparation methods such as drop-cast and immersion. Measurement issues, including the effect of excitation laser wavelength and power, as well as the influence of buffer, are thoroughly examined. Additionally, the review discusses spectral analysis techniques, encompassing baseline removal, chemometric analysis, and machine learning approaches. The wide range of AgNR-based applications of SERS, across various fields, is also explored. Throughout the comprehensive review, key lessons learned from collective findings are outlined and analyzed, particularly in the context of detailed SERS measurements and standardization. The review also provides insights into future challenges and perspectives in the field of SERS. It is our hope that this comprehensive review will serve as a valuable reference for researchers seeking to embark on in-depth studies and applications involving their own SERS substrates.

Ultrasensitive dual-enhanced sandwich strategy for simultaneous detection of Escherichia coli and Staphylococcus aureus based on optimized aptamers-functionalized magnetic capture probes and graphene oxide-Au nanostars SERS tags

In this work, a novel surface-enhanced Raman scattering (SERS) sandwich strategy biosensing platform has been established for simultaneously detecting Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Fe₃O₄@SiO₂-Au nanocomposites (NCs) with varying amounts of Au nanocrystals were prepared, and the effect of interparticle gaps on SERS activity was studied by finite-difference time-domain (FDTD) method. The optimal magnetic SERS-active substrates (FS-A5) were functionalized with the specific aptamers to act as capture probes. Meanwhile, graphene oxide-Au nanostars (GO-Au NSs) decorated with Raman reporters and aptamers were used as SERS tags. The loading density of Au NSs on GO was tuned to change the number of SERS active sites. In this proposal, E. coli and S. aureus were first captured by capture probes and then bound with SERS tags to form a sandwich-like structure, which caused enhanced electromagnetic field because of the dual enhancement strategy. Under optimal conditions, SERS platform could detect E. coli and S. aureus simultaneously, and the detection limit was as low as 10 cfu/mL. Our sandwich assay-based dual-enhanced SERS platform provides a new idea for simultaneously detecting multiple pathogens with high selectivity and sensitivity, and thus will have more hopeful prospects in the field of food safety.

Highly sensitive AuNSs@AgNR SERS substrates for rapid determination of aromatic amines

The leakage of aromatic amines will pose a great threat to human health and the ecological environment. Therefore, there is an urgent need to achieve rapid and high-sensitivity detection of such substances. In this study, a simple surface-enhanced Raman scattering (SERS) method based on gold nanostars-modified silver nanorods (AuNSs@AgNRs) was established for the detection of benzidine and 4-aminobiphenyl (4-ABP). The enhancement factors of the substrate towards rhodamine 6G (R6G) and crystal violet (CV) were 4.67 × 10⁸ and 1.11 × 10⁸, respectively. Combined with density functional theory (DFT), the AuNSs@AgNR substrate achieved the rapid detection of benzidine and 4-ABP and obtained low detection limits (LOD_benzidine = 7.09 × 10^-9 M; LOD_4-ABP = 1.20 × 10^-9 M). Furthermore, the AuNSs@AgNR substrate can realize the high-sensitivity detection of benzidine and 4-ABP in the spiked river water samples within 3 min, which means that the AuNSs@AgNR-based SERS method can be used as a portable platform to realize the on-site rapid detection of environmental pollutants.

Design an efficient photoelectrochemical aptasensor for PCB72 based on CdTe@CdS core@shell quantum dots-decorated TiO2 nanotubes

In this work, an efficient and novel photoelectrochemical (PEC) aptasensor for 2,3',5,5'-tetrachlorobiphenyl (PCB72) was constructed based on CdTe@CdS core@shell quantum dots (CdTe@CdS QDs)-decorated TiO₂ nanotubes (TiO₂ NTs). CdTe@CdS QDs were prepared by the combination of CdTe and CdS with a proper lattice mismatch. Due to their large band offsets, core@shell QDs can reduce undesirable carrier recombination, significantly improving their charge separation efficiency. Then the synthesized CdTe@CdS QDs were modified on TiO₂ NTs (CdTe@CdS QDs/TiO₂ NTs) through electrostatic adsorption method. The as-prepared composites exhibit a wide visible light absorption range, good PEC activity and high photoelectric conversion efficiency. Also, the PEC aptasensor prepared via the immobilization of anti-PCB72 aptamer on the composites exhibits outstanding analytical performance with high sensitivity and specificity for PCB72 under visible-light irradiation, achieving a detection limit as low as 0.03 ng/L. It was also applied to detect PCB72 in four different real environmental samples with satisfactory results.

Molecular–substrate interaction on dynamic SERS detection of butylated hydroxyanisole on a silver nano-tripod substrate

A SERS enhancement model with a surface adsorption effect is proposed by dynamical SERS analysis of butylated hydroxyanisole on a silver nano-tripod substrate.