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A major limitation preventing the use of surface-enhanced Raman scattering (SERS) in routine analyses is the signal variability due to the heterogeneity of metallic nanoparticles used as SERS substrates. This study aimed to robustly optimise a synthesis process of silver nanoparticles to improve the measured SERS signal repeatability and the protocol synthesis repeatability. The process is inspired by a chemical reduction method associated with microwave irradiation to guarantee better controlled and uniform heating. The innovative Quality by Design strategy was implemented to optimise the different parameters of the process. A preliminary investigation design was firstly carried out to evaluate the influence of four parameters selected by means of an Ishikawa diagram. The critical quality attributes were to maximise the intensity of the SERS response and minimise its variance. The reaction time, temperature and stirring speed are critical process parameters. These were optimised using an I-optimal design. A robust operating zone covering the optimal reaction conditions (3.36 min–130 °C–600 rpm) associated with a probability of success was modelled. Validation of this point confirmed the prediction with intra- and inter-batch variabilities of less than 15%. In conclusion, this study successfully optimised silver nanoparticles by a rapid, low cost and simple technique enhancing the quantitative perspectives of SERS. [ABSTRACT FROM AUTHOR]

The urgent demand for addressing dye contaminants in water necessitates the development of microrobots that exhibit remote navigation, rapid removal, and molecular identification capabilities. The progress of microrobot development is currently hindered by the scarcity of multifunctional materials. In this study, a plasmonic MXene hydrogel (PM‐Gel) is synthesized by combining bimetallic nanocubes and Ti3C2Tx MXene through the rapid gelation of degradable alginate. The hydrogel can efficiently adsorb over 60% of dye contaminants within 2 min, ultimately achieving a removal rate of >90%. Meanwhile, the hydrogel exhibits excellent sensitivity in surface enhanced Raman scattering (SERS) detection, with a limit of detection (LOD) as low as 3.76 am. The properties of the plasmonic hydrogel can be further adjusted for various applications. As a proof‐of‐concept experiment, thermosensitive polymers and superparamagnetic particles are successfully integrated into this hydrogel to construct a versatile, light‐responsive microrobot for dye contaminants. With magnetic and optical actuation, the robot can remotely sample, identify, and remove pollutants in maze‐like channels. Moreover, light‐driven hydrophilic‐hydrophobic switch of the microrobots through photothermal effect can further enhance the adsorption capacity and reduced the dye residue by up to 58%. These findings indicate of a broad application potential in complex real‐world environments. [ABSTRACT FROM AUTHOR]

Abstract The urgent demand for addressing dye contaminants in water necessitates the development of microrobots that exhibit remote navigation, rapid removal, and molecular identification capabilities. The progress of microrobot development is currently hindered by the scarcity of multifunctional materials. In this study, a plasmonic MXene hydrogel (PM‐Gel) is synthesized by combining bimetallic nanocubes and Ti3C2Tx MXene through the rapid gelation of degradable alginate. The hydrogel can efficiently adsorb over 60% of dye contaminants within 2 min, ultimately achieving a removal rate of >90%. Meanwhile, the hydrogel exhibits excellent sensitivity in surface enhanced Raman scattering (SERS) detection, with a limit of detection (LOD) as low as 3.76 am. The properties of the plasmonic hydrogel can be further adjusted for various applications. As a proof‐of‐concept experiment, thermosensitive polymers and superparamagnetic particles are successfully integrated into this hydrogel to construct a versatile, light‐responsive microrobot for dye contaminants. With magnetic and optical actuation, the robot can remotely sample, identify, and remove pollutants in maze‐like channels. Moreover, light‐driven hydrophilic‐hydrophobic switch of the microrobots through photothermal effect can further enhance the adsorption capacity and reduced the dye residue by up to 58%. These findings indicate of a broad application potential in complex real‐world environments.

Objective: This study provided a new research direction for the detection of ofloxacin content. Methods: Using biomass reduction method to formulate a reduced graphene oxide-gold composite nanomaterials (rGO-AuNPs) , which had high surface enhanced Raman scattering (SERS) activity. The successful synthesis of rGO-AuNPs was demonstrated by ultraviolet visible spectroscopy, transmission electron microscopy and scanning electron microscopy, respectively. The Raman enhancement factor (EF) of rGO-AuNPs was measured and calculated. Based on the SERS hot spot effect and the specific binding ability of nucleic acid aptamer, ofloxacin content detection system was established, the detection conditions were optimized, the standard curve was established, and apply it to OFL detection in pond water sample. Results: rGO-AuNPs composite nanomaterials was successfully synthesized by using Lilium casa blanca petals biomass as reductants. Gold nanoparticles were observed on reduced graphene oxide sheets and the EF was 3.88×107. Additionally, SERS intensity had a good linear relationship with ofloxacin mass concentration in the range of 1 to 500 ng/mL, and the limit of detection was 0.3 ng/mL. The recovery was 96.28% to 102.84%, and the relative standard deviation was less than 10%. Conclusion: The synthesized rGO-AuNPs had high SERS activity and a positive application prospects in ofloxacin detection.

A major limitation preventing the use of surface-enhanced Raman scattering (SERS) in routine analyses is the signal variability due to the heterogeneity of metallic nanoparticles used as SERS substrates. This study aimed to robustly optimise a synthesis process of silver nanoparticles to improve the measured SERS signal repeatability and the protocol synthesis repeatability. The process is inspired by a chemical reduction method associated with microwave irradiation to guarantee better controlled and uniform heating. The innovative Quality by Design strategy was implemented to optimise the different parameters of the process. A preliminary investigation design was firstly carried out to evaluate the influence of four parameters selected by means of an Ishikawa diagram. The critical quality attributes were to maximise the intensity of the SERS response and minimise its variance. The reaction time, temperature and stirring speed are critical process parameters. These were optimised using an I-optimal design. A robust operating zone covering the optimal reaction conditions (3.36 min–130 °C–600 rpm) associated with a probability of success was modelled. Validation of this point confirmed the prediction with intra- and inter-batch variabilities of less than 15%. In conclusion, this study successfully optimised silver nanoparticles by a rapid, low cost and simple technique enhancing the quantitative perspectives of SERS.

Significant amplification of surface enhanced Raman scattering (SERS) signals can be achieved mainly by the electric field enhancement in metal core-shell nanostructures, and the enhanced magnetic field is rarely studied. In this study, we prepared multi-gap Au/AgAu core-shell hybrid nanostructures by using gold nanocup as the core. The overgrowth processes to grow one, two, and three layers of AgAu hybrid nanoshells can produce Au/AgAu¹, Au/AgAu², and Au/AgAu³ heteronanostructures. The strong plasmon coupling between the core and shell leads to significant electromagnetic field enhancement. Under the synergistic effect of electromagnetic plasmon resonance and plasmon coupling, Au/AgAu core-shell hybrid nanostructures exhibit excellent SERS signals. We also investigate the effect of the interstitial position of the rhodamine B (RhB) molecule on Raman enhancement in Au/AgAu³ heteronanostructures. This study can provide new ideas for the synthesis of multi-gap Raman signal amplifiers based on magnetic plasmon coupling. [ABSTRACT FROM AUTHOR]

Single-atom nanozymes (SAzymes) are emerging as promising alternatives to mimic natural enzyme, which is due to high atomic utilization efficiency, well-defined geometric, and unique electronic structure. Herein, Fe single atoms supported on Ti3C2Tx (Fe-SA/Ti3C2Tx) with intrinsic peroxidase activity is developed, further constructing a sensitive Raman sensor array for sensing of five antioxidants. Fe-SA/Ti3C2Tx shows excellent peroxidase-like performance in catalyzing the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) with colorimetric reactions. X-ray adsorption fine structure (XAFS) reveals that the electron transport between the Ti3C2Tx and Fe atoms occurs along Fe-O-Ti ligands, meanwhile the density functional theory (DFT) calculations confirm the spontaneous dissociation of H2O2 and the formation of OH radicals. Furthermore, the peroxidase-like Fe-SA/Ti3C2Tx was used as surface enhanced Raman scattering (SERS) substrate of oxidized TMB (TMB+) and achieved satisfied signal amplification performance. Using the blocking effects of free radical reactions, one-off identification of 5 antioxidants, including ascorbic acid (AA), uric acid (UA), glutathione (GSH), melatonin (Mel), and tea polyphenols (TPP), could be realized with this high identifiable catalytic property. This principle could realize 100% distinguish accuracy combined with linear discriminant analysis (LDA) and heat map data analysis. A wide detection concentration ranges from 10−8 to 10−3 M for five antioxidants was also achieved. [ABSTRACT FROM AUTHOR]

Surface-Enhanced Raman Scattering (SERS) can obtain the spectroscopic response of specific analytes. In controlled conditions, it is a powerful quantitative technique. However, often the sample and its SERS spectrum are complex. Pharmaceutical compounds in human biofluids with strong interfering signals from proteins and other biomolecules are a typical example. Among the techniques for drug dosage, SERS was reported to detect low drug concentrations, with analytical capability comparable to that of the assessed High-Performance Liquid Chromatography. Here, for the first time, we report the use of SERS for Therapeutic Drug Monitoring of the Anti-Epileptic Drug Perampanel (PER) in human saliva. We used inert substrates decorated with gold NPs deposited via Pulsed Laser Deposition as SERS sensors. We show that it is possible to detect PER in saliva via SERS after an optimized treatment of the saliva sample. Using a phase separation process, it is possible to extract all the diluted PER in saliva from the saliva phase to a chloroform phase. This allows us to detect PER in the saliva at initial concentrations of the order of 10−7 M, thus approaching those of clinical interest. [ABSTRACT FROM AUTHOR]

Cholinesterase (ChE) is a kind of important enzyme in a range of significant areas such as toxicology, pharmacology, and neurobiology. ChE, which can be irreversibly inhibited with organophosphorus agents (OPs), plays an important role in cholinergic syndrome. Recently, many efforts have been devoted to developing ChE sensor. Spectroscopic methods, including fluorescence, colorimetric and UV-vis, chemiluminescence (CL), and surface enhanced Raman scattering (SERS) are the most widely used techniques for the ChE activity detection. In these developed spectroscopic techniques, biosensors using nanomaterials or probe or chromogenic agent are highly promising because of the enhanced sensitivity, fast response time, wide detection range and system miniaturization. This paper reviews the development, application, and research trend of spectroscopic methods of ChE activity and its inhibitors in the last decade. Furthermore, the prospects for ChE detection are also discussed. [ABSTRACT FROM AUTHOR]

Rapid and precise detection of harmful substances in food products is essential for ensuring public health and safety. This study introduces a novel surface-enhanced Raman spectroscopy (SERS) substrate, composed of a molybdenum disulfide‑silver nanocomposite, applied to flexible, water-resistant filter paper for detecting melamine and bisphenol A (BPA) in milk. Optimized molybdenum disulfide (NMS) nanoflowers (NFs) were synthesized through hydrothermal methods and high-temperature annealing, then modified with silver (Ag) nanoparticles to form the NMS-Ag nanocomposite (NMSA 6). This substrate greatly enhances the Raman signal, achieving an enhancement factor of approximately 1.49 × 107 and a detection limit as low as 10−11 M for simultaneous multi-component analysis. Finite-difference time-domain (FDTD) simulations confirm the enhancement mechanism. The NMSA 6 substrate demonstrates remarkably low detection limits for BPA and melamine, facilitating the analysis of various hazardous substances. These findings highlight the substrate's potential for highly sensitive, label-free detection, presenting a viable tool for food safety monitoring. [Display omitted] • A flexible hydrophobic fiber filter paper modified with NMS NFs composite Ag NPs hybrid was prepared. • NMSA 6 has a high EF value of 1.496 × 107, and NMSA 6 was used as highly sensitive SERS substrates. • The detection limits of NMSA 6 -modified filter paper for BPA and melamine in milk are as low as 10−10 M and 10−8 M respectively. • There are three reasons for the excellent SERS activity of NMSA 6 substrate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Integrating SERS with convolutional neural networks results in 99.99 % classification accuracy for six bacterial biomarkers. • High-accuracy concentration predictions for bacterial biomarkers are achieved through CNN regression. • This approach overcomes challenges posed by spectral variability across different concentration ranges. • The study highlights the transformative potential of advanced machine learning algorithms to enhance biomedical diagnostics. The SERS spectra of six bacterial biomarkers, 2,3-DHBA, 2,5-DHBA, Pyocyanin, lipoteichoic acid (LTA), Enterobactin, and β-carotene, of various concentrations, were obtained from silver nanorod array substrates, and the spectral peaks and the corresponding vibrational modes were identified to classify different spectra. The spectral variations in three different concentration regions due to various reasons have imposed a challenge to use classic calibration curve methods to quantify the concentration of biomarkers. Depending on baseline removal strategy, i.e., local or global baseline removal, the calibration curve differed significantly. With the aid of convolutional neural network (CNN), a two-step process was established to classify and quantify biomarker solutions based on SERS spectra: using a specific CNN model, a remarkable differentiation and classification accuracy of 99.99 % for all six biomarkers regardless of the concentration can be achieved. After classification, six regression CNN models were established to predict the concentration of biomarkers, with coefficient of determination R 2 > 0.97 and mean absolute error (MAE) < 0.27. The feature of important calculations indicates the high classification and quantification accuracies were due to the intrinsic spectral features in SERS spectra. This study showcases the synergistic potential of SERS and advanced machine learning algorithms and holds significant promise for bacterial infection diagnostics. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel sea urchin-like chip with Au NPs as the shell, Ag NPs as the core and PSi as the substrate was synthesized by electrochemical etching and in situ reduction. • Three models, CNN, AlexNet, and RF, were selected to model and analyze the serum spectra of SLE patients and healthy controls, and the model classification accuracy reached 92 %. • A fast, accurate, and non-invasive screening method for SLE was established by combining SERS technology and deep learning algorithms. Systemic lupus erythematosus (SLE) is an autoimmune disease with multiple symptoms, and its rapid screening is the research focus of surface-enhanced Raman scattering (SERS) technology. In this study, gold@silver-porous silicon (Au@Ag-PSi) composite substrates were synthesized by electrochemical etching and in-situ reduction methods, which showed excellent sensitivity and accuracy in the detection of rhodamine 6G (R6G) and serum from SLE patients. SERS technology was combined with deep learning algorithms to model serum features using selected CNN, AlexNet, and RF models. 92 % accuracy was achieved in classifying SLE patients by CNN models, and the reliability of these models in accurately identifying sera was verified by ROC curve analysis. This study highlights the great potential of Au@Ag-PSi substrate in SERS detection and introduces a novel deep learning approach for SERS for accurate screening of SLE. The proposed method and composite substrate provide significant value for rapid, accurate, and noninvasive SLE screening and provide insights into SERS-based diagnostic techniques. [ABSTRACT FROM AUTHOR]

Glutathione (GSH) is a non-protein tripeptide thiol that plays a prominent role in oxidative stress defense. GSH concentration is particularly critical in the neonatal period, especially for premature newborns that face increased susceptibility to oxidative stress. Monitoring GSH levels provides valuable insights into newborn health, helping to tailor care to their specific needs. The aim of this study was the development of a sensor specifically targeted for its use in neonatology, enabling GSH determination in only 2 μL of whole blood. The newly developed sensing system simplifies sample processing, addressing a critical need in clinical applications. Unlike current methods that demand fast pre-processing of relatively large sample volumes, expensive equipment, and skilled personnel, the developed approach streamlines the analytical process. By using 2 μL of whole blood, a single syringe filter for sample treatment, a deuterated internal standard (IS) for signal normalization, and Surface Enhanced Raman Scattering (SERS) spectroscopy with a silver colloid substrate for GSH detection, the set-up's characteristics are compatible with point-of-care applications. The analytical procedure was validated and applied to diverse populations including healthy adults (N = 63) and newborns (N = 35), yielding GSH concentration values ranging from 0.6 to 1.8 and 0.8–2.1 mM, respectively. This new optical sensor offers a quick and cost-effective solution to support the assessment of GSH levels in newborns that can greatly benefit not only neonatal care, but also the study of adult populations for health monitoring. [Display omitted] • Novel analytical method for fast and reproducible glutathione (GSH) monitoring. • Surface Enhanced Raman Scattering (SERS) for POC testing of GSH levels in blood. • Fast and cost-effective alternative employing low volume blood micro-samples (2 μL). • GSH concentrations ranging from 0.6 to 1.8 (adults) and 0.8–2.1 mM (newborns). • Optical sensor supports the assessment of GSH levels in patient samples. [ABSTRACT FROM AUTHOR]

Rapid and inexpensive detection of heavy metal pollution is highly required these days in order to combat pollution. Noble metal nanoparticles coated by organic molecules having surface plasmon resonance have recently played key role in conceptualizing and fabricating sensing devices for the detection of heavy metals. The present study uses the utility of vanillic acid coated silver nanoparticles (V-AgNPs) synthesized by chemical reduction for the colorimetric and surface-enhanced Raman scattering detection of heavy metal ions in aqueous solution. The synthesized V-AgNPs are of approximately 5–15 nm in size. The addition of synthesized V-AgNPs colloidal solution to control and metal ion laced water samples turns the solution color grayish black except for Cr(III) ions. The addition of V-AgNPs colloidal solution to the water samples containing Cr(III) ions turns the solution transparent. Furthermore, the addition of V-AgNPs to water samples containing Cr(III) ions and Mo(VI) creates unique Raman spectral signatures with high intensities that were used for the identification of these metal ions in aqueous solution. The addition of V-AgNPs to metal ions causes aggregation of the nanoparticles which results in change in color and Raman scattering signals. The obtained color patterns and Raman spectral signatures show the potential of V-AgNPs for low cost, timeless, affordable, convenient, sensitive, selective, and rapid detection of heavy metal ions in aqueous media. [ABSTRACT FROM AUTHOR]

Surface Enhanced Raman Scattering (SERS) has been extensively utilized in therapeutic drug monitoring (TDM) due to its rapid detection speed, high sensitivity and straightforward sample pretreatment. In this study, Au/AgNPs were obtained through the reduction of AgNO 3 on the surface of AuNPs. Subsequently, Au/AgNPs were embedded into the tetrahedral lattice of ZIF-8 MOFs, resulting in the formation of Au/Ag@ZIF-8 nanocomposites. The Au/Ag@ZIF-8 nanocomposites exhibit a robust electromagnetic enhancement of Au/Ag bimetallic nanoparticles and a considerable adsorption capacity of ZIF-8 MOFs. This enables the pre-enrichment of target molecules in the vicinity of the electromagnetic field of the Au/AgNPs, thereby enhancing the sensitivity of SERS detection. The SERS substrate also exhibits high stability and reproducibility, as well as molecular sieving effects, due to the fact that Au/AgNPs are embedded into the tetrahedral lattice of ZIF-8. A TDM method for tacrolimus (FK506) in human serum was developed by using Au/Ag@ZIF-8 nanocomposites as solid phase extraction (SPE) adsorbent and SERS substrates. The results showed that under the optimized conditions, tacrolimus exhibited satisfactory linearity within the concentration range of 10−5-10−11 mol L−1, with a correlation coefficient (R2) of 0.9944, and the limit of detection (LOD) was as low as 6.4 pg mL−1. The recoveries were observed to range between 92 % and 105 %, with an RSD of below 8 %. The method is highly sensitive, exhibiting a sensitivity that is 3-6 orders of magnitude higher than that of existing analytical techniques. It has the potential to be applied in a clinical setting to biological samples. [Display omitted] • Synthesis of Au/Ag@ZIF-8 by embedding Au/Ag in the ZIF-8 tetrahedral lattice. • The detection limit of Au/Ag@ZIF-8 SERS substrate was as low as 6.4 pg mL−1. • Au/Ag@ZIF-8 SERS substrates showed high stability and molecular sieving effects. • Quantification of trace FK506 in human serum by an ultrasensitive TDM method. [ABSTRACT FROM AUTHOR]

The detection of the highly toxic per- and polyfluoroalkyl substances, PFAS, constitutes a challenging task in terms of developing a generic method that could be rapid and applicable simultaneously to both long and short-chain PFAS at ppt concentration level. In the present study, the method introduced by the USA Environmental Protection Agency, EPA, to detect surfactants, using methylene blue, MB, which is identified an ideal candidate for PFAS-MB ion pairing, is extended at the lowest concentration range by a simple additional step that involves the dissociation of the ion pairs in water. In this work, Surface Enhanced Raman Scattering, SERS, is applied via Ag nanocolloidal suspensions to probe MB and indirectly either/or both short-chain (perfluorobutyric acid, PFBA) and long-chain (perfluoloctanoic acid, PFOA) PFAS downt to 5 ppt. This method, which can be further optimized to sub-ppt level via a custom-made SERS-PFAS dedicated Raman system, offers the possibility to be applied to either specific PFAS (both short and long-chain) in a targeted analysis or to total PFAS in a non-targeted analysis at very low detection limits, following any type of MB detection method in aqueous solutions and obviously with any type of SERS substrate. [Display omitted] • Generic PFAS detection method applicable to both short and long chain PFAS. • SERS method achieved LOD down to 5 ppt of PFAS. • Ion pairing between PFAS-MB triggered the process. • Dissociation of the ion pairs resulted the better LODs. [ABSTRACT FROM AUTHOR]

Surface-Enhanced Raman Scattering (SERS) can obtain the spectroscopic response of specific analytes. In controlled conditions, it is a powerful quantitative technique. However, often the sample and its SERS spectrum are complex. Pharmaceutical compounds in human biofluids with strong interfering signals from proteins and other biomolecules are a typical example. Among the techniques for drug dosage, SERS was reported to detect low drug concentrations, with analytical capability comparable to that of the assessed High-Performance Liquid Chromatography. Here, for the first time, we report the use of SERS for Therapeutic Drug Monitoring of the Anti-Epileptic Drug Perampanel (PER) in human saliva. We used inert substrates decorated with gold NPs deposited via Pulsed Laser Deposition as SERS sensors. We show that it is possible to detect PER in saliva via SERS after an optimized treatment of the saliva sample. Using a phase separation process, it is possible to extract all the diluted PER in saliva from the saliva phase to a chloroform phase. This allows us to detect PER in the saliva at initial concentrations of the order of 10−7 M, thus approaching those of clinical interest.

[Display omitted] • The metal-dielectric-metal (MDM) 3D micro-pole-arrays structure based on SU-8 colloid lithography was fabricated. • The SU-8 micro-pole-arrays structure provides rich hot spots and stability for the SERS substrstes. • The MDM structure substrates could enhance the SERS performance further. • The SU-8 micro-pole-arrays-based MDM SERS substrates exhibit outstanding SERS activity. Dielectric layer-mediated surface-enhanced Raman scattering (SERS) substrates are currently explored for ultrasensitive detection and expected to provide uniform SERS response by the virtue of three-dimensional micro-nanostructures, dielectric layer, and plasmonic metal nanostructures. For this purpose, the present work reports on the development of the metal-dielectric-metal (MDM) three-dimensional (3D) micro-pole-arrays structure based on SU-8 colloid lithography. By utilizing the large-scale periodic arrangement characteristics of SU-8 colloidal lithography, along with the hot spot effect created by the nano-gap between MDM, we successfully prepared an array of SERS substrates that exhibit both periodicity and multi-dimensional plasmonic coupling effect. Compared to a single metal nanoparticle substrate, the SERS activity of the substrate is significantly enhanced, and the substrate has trace detection ability (LOD of detection of 10−12 mol/L for R6G). The enhancement factor (EF) is 5.72 × 107. Periodicity ensures that the prepared substrate has good reproducibility (RSD < 8 %) and stability. Furthermore, the substrate modified with HS-β-CD demonstrated potential for rapid trace SERS detection of polychlorinated biphenyls (PCB-77) (LOD of 10−8 mol/L for PCB-77). The results indicate that the proposed substrate has the potential for application in the preparation of SERS sensors with high sensitivity and uniformity. [ABSTRACT FROM AUTHOR]

Surface enhanced Raman spectroscopy (SERS) has attracted interest in the fields of hazardous substance detection and food safety. However, its limited sensitivity and SERS signal consistency inhibit the widespread use of SERS technology. Herein, a novel approach for the fabrication of a graphene/Au NP/rectangular pyramid PMMA hybrid SERS substrate (Gr/Au/RP PMMA) with high uniformity and sensitivity is presented. The Gr/Au/RP PMMA substrate is machined by indentation firstly, then following wet etching of the copper substrate. The Raman enhancement of Gr/Au/RP PMMA is studied in terms of both electromagnetic enhancement and chemical enhancement. The field strength enhancement of the obtained Gr/Au/RP PMMA substrate is more than 4.9 times greater than that of the Gr/Au/flat PMMA substrate, established using a COMSOL simulation. By actively modulating the machining parameters on a Cu-Gr surface, the number of Gr layers, as well as the Gr/Au/RP PMMA topography, can be controlled, which can effectively influence the performance of the SERS substrate. Moreover, compared with other SERS substrates, including Gr/Au/RP PMMA, Gr/Au/flat PMMA, Au/Gr/RP Cu, Gr/RP PMMA, and Au/RP PMMA, the Raman intensities of R6G were strongest on the Gr/Au/RP PMMA. In addition, the minimum detectable concentrations of paraquat (PQ) and 2,4-d used in situ detection were 10−8 M and 10−6 M, respectively, after being covered with the Gr/Au/RP PMMA flexible substrate. To test its practical applicability with actual fruit surfaces, the Gr/Au/RP PMMA flexible substrate was used for the in situ SERS detection of PQ on apples. Clear Raman peaks of 10−7 M PQ were detected on the apple surface. • A novel method combining identation with wet etching is proposed to fabricate the flexible SERS substrates. • The enhancement mechanism of the Gr/AuNPs/RP PMMA flexible substrate is revealed by EM and CM, respectively. • By modulating the machining parameters on a Cu-graphene surface, the number of graphene layers can be controlled. • The Gr/AuNPs/RP PMMA flexible substrate was covered for the in-situ SERS detection of paraquat@apple. [ABSTRACT FROM AUTHOR]

We propose and develop a simple and cost‐effective method to fabricate surface enhanced Raman scattering (SERS) substrates for the trace detection of antibiotics. A nanostructured silicon (Si) surface is prepared by the pulsed laser ablation (PLA) of a Si wafer in distilled water. Silver nanoparticles (AgNPs) synthesized via PLA in distilled water are deposited on the ablated Si surface to form a SERS substrate (AgNP/aSi). Malachite green (MG) is used as a probe analyte to examine the SERS activity of the AgNP/aSi substrate. The AgNP/aSi substrate can yield an SERS spectrum of MG with high resolution at a minimum concentration of 0.01 ppm. Using the AgNP/aSi substrate, we investigate its capacity for detecting tetracycline (TC) residue in shrimp. The Raman peak intensities at 1320 cm−1 for TC concentrations from 10 to 0.1 ppm show a linear relationship with the corresponding logarithmic concentrations. Our simple and efficient method can be used for the trace detection of MG, TC, and other antibiotics in various applications via SERS. [ABSTRACT FROM AUTHOR]

This review presents a comprehensive synopsis of the recent developments and achievements in the research of nanosensors composed of plasmonic nanoparticles (NPs) and silicon nanostructures (NSs) for effective trace-level molecular detection. This review focuses intensively on the methodologies for the preparation and enforcement of a variety of SiNSs including (a) metal nanoparticles decorated silicon nanowires (NWs), (b) metal nanodendrites (NDs) on Si substrate, (c) plasmonic NPs decorated nanocrystalline porous silicon (pSi), and (d) silicon composed hybrid nanostructures with favorable parameters of importance in sensing. Furthermore, their potency in wide molecular sensing applications, especially chemical, biological, and explosive molecules based on surface enhanced Raman scattering (SERS) phenomenon is discussed in detail. Various demonstrations and categorizations are provided on the topic of Si-based NSs for a clear understanding to diverse readers. A roadmap is also provided at the end for achieving superior sensing materials or devices in the future. [ABSTRACT FROM AUTHOR]

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Surface enhanced Raman scattering (SERS) is not restricted to the well-known one-photon excited spontaneous Raman process that gives information on molecular composition, structure, and interaction through vibrational probing with high sensitivity. The enhancement mainly originates in high local fields, specifically those provided by localized surface plasmon resonances of metal nanostructures. High local fields can particularly support nonlinear Raman scattering, as it depends on the fields to higher powers. By revealing plasmon-molecule interactions, nonlinear Raman processes provide a very sensitive access to the properties of metal nanomaterials and their interfaces with molecules and other materials. This Perspective discusses plasmon-enhanced spontaneous and coherent nonlinear Raman scattering with the aim of identifying advantages that lead to an advanced vibrational characterization of such systems. The discussion will highlight the aspects of vibrational information that can be gained based on specific advantages of different incoherent and coherent Raman scattering and their surface enhancement. While the incoherent process of surface enhanced hyper Raman scattering (SEHRS) gives highly selective and spectral information complementary to SERS, the incoherent process of surface enhanced pumped anti-Stokes Raman scattering (SEPARS) can help to infer effective nonresonant SERS cross sections and allows to see "hot" vibrational transitions. Surface enhanced coherent anti-Stokes Raman scattering (SECARS) and surface enhanced stimulated Raman scattering (SESRS) combine the advantages of high local fields and coherence, which gives rise to high detection sensitivity and offers possibilities to explore molecule-plasmon interactions for a comprehensive characterization of composite and hybrid structures in materials research, catalysis, and nanobiophotonics.

Surface enhanced Raman scattering (SERS) has emerged as a reliable and ultra-sensitive sensing technique used in analytical diagnostics, forensics, and biomedical applications. Although SERS may be sensitive enough to detect single molecules, such extreme performance is achieved with sophisticated and complex nanostructure designs that are hard to implement on an industrial scale. This work presents an understanding of the plasmonic and wetting phenomena taking place on Ag nanoparticles (supported on Si) produced by laser annealing and dewetting of sputtered ultra-thin layers enabling the fast (

The remarkable optical properties of surface-enhanced Raman scattering (SERS) has prompted the design and fabrication of SERS nanoparticles as biosensing and imaging labels. Among a variety of biosensing assay platforms within the growing point of care technology (POCT) field, lateral flow assay (LFA) has gained significant attention because of their simplicity, low cost, and user-friendly assay protocols. Herein, we show the development and performance benchmarking of SERS-based LFA for rapid and quantitative sensing of two important biomarkers: hCG and cTnT. The results suggest the feasibility of this platform for POCT applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Evidence of the influence of measurement conditions on the SERS signature of adenine. • Disruption of silver colloid stability to amplify Raman signal enhancement. • Use of Independent Component Analysis for a more rational processing of spectra. • Improving SERS response understanding. The SERS response of adenine is one of the most studied, due to its outstanding exaltation. However, the spectra obtained strongly differ according to the experimental conditions and still remain not well understood. To be able to search for the presence of this molecule in complex environments, it is essential to better understand the SERS response of adenine alone. After a brief presentation of the literature on the subject, we present results suggesting that the experimental spectra would result from the overlap of different spectroscopic signatures, that may probably be due to different non-covalent interactions or different electromagnetic fields experienced by adenine molecules. An independent component analysis is reported. Our results underline the difficulty to precisely analyze the experimental data, the need to continue this research and to constitute data banks that would allow comparing the spectra obtained in different laboratories according to the experimental conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Au nanoparticles on ZnO thin films were prepared by sputtering combined with thermal annealing. • In situ UV excitation significantly enhanced the SERS signal, up to 5.5 times. • PIER is attributed to the generation and separation of electrons and holes pairs. Surface-enhanced Raman scattering (SERS) is a powerful technique for detecting pollutants. Recent studies have shown that the sensitivity of SERS can be further improved by using appropriate light excitation before or during Raman measurements, a phenomenon known as photo-induced enhanced Raman scattering (PIERS). In this study, we developed a highly sensitive SERS substrate by fabricating a ZnO/Au thin film using radio frequency magnetron sputtering and post-annealing processes. The resulting substrate exhibited high crystallinity and high sensitivity for pollutant detection. The study found that in situ UV excitation significantly enhanced the Raman signal, up to 5.5 times more efficiently than the traditional SERS technique. The excitation process was reversible, leading to a quick recovery of the Raman intensity to its initial level when the UV excitation was turned off. This relaxation process is attributed to the recombination of electrons and holes. The investigation shows that ZnO/Au thin films was able to detect fungicide thiram with a limit of detection of 10−8 M. PIER also helps to lower the detection threshold down to 10−9 M. [ABSTRACT FROM AUTHOR]

Practical gas sensing application requires sensors to quantify target analytes with high sensitivity and reproducibility. However, conventional surface enhanced Raman scattering (SERS) sensor lacks reproducibility and quantification arising from variations of "hot spot" distribution and measurement conditions. Here, a ratio-dependent SERS sensor was developed for quantitative label-free gas sensing. Au@Ag-Au nanoparticles (NPs) were filtered onto anodic aluminum oxide (AAO) forming Au@Ag-Au@AAO SERS substrate. 4-MBA was encapsulated in the gap of Au@Ag-Au and served as the internal standard (IS) to calibrate SERS signal fluctuation for improved quantification ability. Combined with headspace sampling method, SO 2 residue in traditional Chinese medicine (TCM) can be extracted and captured on the immediate vicinity of Au@Ag-Au surface. The intensity ratio I 613 cm −1 /I 1078 cm −1 showed excellent linearity within the range of 0.5 mg/kg-500 mg/kg, demonstrating superior quantification performance for SO 2 detection. Signals for concentration as low as 0.05 mg/kg of SO 2 could be effectively collected, much lower than the strictest limit 10 mg/kg in Chinese Pharmacopoeia. Combined with a handheld Raman spectrometer, handy and quantitative TCM quality evaluation in aspect of SO 2 residue was realized. This ratiometric SERS sensor functioned well in rapid on-site SO 2 quantification, exhibiting excellent sensitivity and simple operability. [Display omitted] • Quantitative SO 2 detection in TCM without complex pretreatment. • Linear detection limit of 0.5 mg/kg far below the strictest limit in TCM. • Quantitative SO 2 detection with high sensitivity, reproducibility and selectivity. • Potential extension to POCT applications in food safety and environmental protection. [ABSTRACT FROM AUTHOR]

Extravasation, as one of the key steps in cancer metastasis, refers to the process where tumor cells escape the bloodstream by crossing the vascular endothelium and invade the targeted tissue, which accounts for the low five-year survival rate of cancer patients. Understanding the mechanism of cancer metastasis and inhibiting extravasation are crucial to improve patient prognosis. Here, a 3D organotypic microfluidic chip combined with SERS-based protein imprinted nanomaterials (SPINs) was proposed to study the extravasation process in vitro. The chip consists of a collagen gel channel and a vascular channel where human vein endothelial cells (HUVECs) and breast cancer cells are injected sequentially to induce extravasation. By comparing two subtypes of breast cancer cells (MCF-7 and MDA-MB-231), we successfully observed the difference in extravasation capabilities between two kinds of cells through fluorescence imaging. Meanwhile, thanks to the high specificity of molecular imprinting technology and the high sensitivity of surface enhanced Raman scattering (SERS), SPINs were utilized to analyze the concentration of several cancer secretions (interleukin-6 and interleukin-8) in complex biological fluid in real-time. Further, our model showed that downregulation of secretions by therapeutic drugs can inhibit the extravasation of breast cancers. This microfluidic model may pave the way for the fundamental research of the cancer metastasis and evaluating the therapeutic efficacy of potential drugs. [Display omitted] • A 3D organotypic microfluidic chip for in-situ visualization of cancer extravasation process. • SERS-based protein imprinted nanomaterials for multiple protein detection. • Real-time detection of cytokines in complex biological fluids. • Potential platform for anti-cancer drug screening. [ABSTRACT FROM AUTHOR]

In our recent studies we highlighted the role of adsorbed ions (adions) in turning on the surface-enhanced Raman scattering (SERS) effect in a specific mode for anionic and cationic analytes. In this work, we emphasize the role of Ag+, Ca2+, Pb2+ and Al3+ adions in the specific adsorption of anionic analytes such as the citrate capping agent and three organic acids. Our results suggest an adion-specific adsorption mechanism: the adsorption of anionic analytes is facilitated by positively charged adions such as Ag+, Ca2+, Pb2+ or Al3+, which provide adsorption sites specific for the anionic analytes. The turn-on of the SERS effect is explained in the context of the chemical mechanism of SERS. The adions form SERS-active sites on the silver surface enabling a charge transfer between the adsorbate and the silver surface. High-intensity SERS spectra of uric acid, salicylic acid and fumaric acid could be recorded at a concentration of 50 µM only after activation of the colloidal silver nanoparticles by Ca2+, Pb2+ or Al3+ (50 µM). The chemisorption of the three anionic species to the silver surface occurs competitively and is enhanced with the anions of higher affinities to the silver surface as indicated by the SERS spectra of corresponding mixed solutions.

Understanding the adsorption and interaction between porous materials and protein is of great importance in biomedical and interface sciences. Among the studied porous materials, TiO2 and its hybrid materials, featuring distinct, well-defined pore sizes, structural stability and excellent biocompatibility, are widely used. In this review, the use of four powerful, synergetic and complementary techniques to study protein-TiO2-based porous materials interactions at different scales is summarized, including high-performance liquid chromatography (HPLC), atomic force microscopy (AFM), surface-enhanced Raman scattering (SERS), and Molecular Dynamics (MD) simulations. We expect that this review could be helpful in optimizing the commonly used techniques to characterize the interfacial behavior of protein on porous TiO2 materials in different applications.

We derive analytical expressions for the surface‐ and orientation‐averaged surface enhanced Raman scattering factor (SERS EF) for small plasmonic spheroids. These expressions are derived taking into account the Stokes shift and are shown to result in very different EFs to those in the |E|4‐approximation for experimentally relevant parameters. The optical properties of spheroids are treated in terms of the common and improved electrostatic approximations (EA and IEA). The latter is newly introduced here and includes radiative damping, depolarization effects, and interactions with higher order multipoles, thus giving perfect agreement with exact T‐matrix calculations of far‐field cross sections and near‐field SERS EFs over a much wider range of sizes. These accurate analytical expressions will be particularly relevant to SERS experiments in colloidal solutions where surface averaging (because of random molecular adsorption) and particle orientation averaging must both be taken into account. Comparison with recent experimental data and simulations for cigar‐like particles show that the spheroid model tends to overestimate the SERS EF because of the higher curvature at the tips. Possible ways to generalize the analytic solution to other axially symmetrical particles are discussed. [ABSTRACT FROM AUTHOR]

Jayakumar Perumal,1 US Dinishm,1 Anne K Bendt,2 Agne Kazakeviciute,1,3 Chit Yaw Fu,1 Irvine Lian Hao Ong,4 Malini Olivo1 1Laboratory of Bio-optical Imaging, Singapore Bioimaging Consortium, Agency for Science, Technology, and Research (A*STAR), Singapore; 2Singapore Lipidomics Incubator, Life Sciences Institute, National University of Singapore, Singapore; 3Department of Statistical Science, University College London, London, UK; 4Matralix Pte Ltd, Singapore Background: Tuberculosis (TB) is the ninth leading cause of death worldwide and the leading cause from a single infectious agent, based on the WHO Global Tuberculosis Report in 2017. TB causes massive health care burdens in many parts of the world, specifically in the resource constrained developing world. Most deaths from TB could be prevented with cost effective early diagnosis and appropriate treatment.Purpose: Conventional TB detection methods are either too slow as it takes a few weeks for diagnosis or they lack the specificity and accuracy. Thus the objective of this study was to develop a fast and efficient detection for TB using surface enhanced Raman scattering (SERS) technique.Methods: SERS spectra for different forms of mycolic acids (MAs) that are both synthetic origin and actual extracts from the mycobacteria species were obtained by label-free direct detection mode. Similarly, we collected SERS spectra for γ-irradiated whole bacteria (WB). Measurements were done using silver (Ag) coated silicon nanopillar (Ag SNP) as SERS substrate.Results: We report the SERS based detection of MA, which is a biomarker for mycobacteria species including Mycobacterium tuberculosis. For the first time, we also establish the SERS spectral characterization of the three major forms of MA – αMA, methoxy-MA, and keto-MA, in bacterial extracts and also in γ-irradiated WB. We validated our findings by mass spectrometry. SERS detection of these three forms of MA could be useful in differentiating pathogenic and nonpathogenic Mycobacterium spp.Conclusions: We have demonstrated the direct detection of three major forms of MA – αMA, methoxy-MA, and keto-MA, in two different types of MA extracts from MTB bacteria, namely delipidated MA and undelipidated MA and finally in γ-irradiated WB. In the near future, this study could pave the way for a fast and efficient detection method for TB, which is of high clinical significance. Keywords: Mycobacterium tuberculosis, MTB, nontuberculosis mycobacteria, NTM, mycolic acid, MA, SERS, silver-coated silicon nanopillars, Ag SNPs, liquid chromatography mass spectrometry, LC-MS

Xiantong Yu,1 XiaoXiao He,1 Taiqun Yang,1 Litao Zhao,1 Qichen Chen,1 Sanjun Zhang,1,2 Jinquan Chen,1 Jianhua Xu1,2 1State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, China; 2Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi, China Background: Dopamine (DA) is an important neurotransmitter in the hypothalamus and pituitary gland, which can produce a direct influence on mammals’ emotions in midbrain. Additionally, the level of DA is highly related with some important neurologic diseases such as schizophrenia, Parkinson, and Huntington’s diseases, etc. In light of the important roles that DA plays in the disease modulation, it is of considerable significance to develop a sensitive and reproducible approach for monitoring DA. Purpose: The objective of this study was to develop an efficient approach to quantitatively monitor the level of DA using Ag nanoparticle (NP) dimers and enhanced Raman spectroscopy. Methods: Ag NP dimers were synthesized for the sensitive detection of DA via surface-enhanced Raman scattering (SERS). Citrate was used as both the capping agent of NPs and sensing agent to DA, which is self-assembled on the surface of Ag NP dimers by reacting with the surface carboxyl group to form a stable amide bond. To improve accuracy and precision, the multiplicative effects model for surface-enhanced Raman spectroscopy was utilized to analyze the SERS assays. Results: A low limits of detection (LOD) of 20 pM and a wide linear response range from 30 pM to 300 nM were obtained for DA quantitative detection. The SERS enhancement factor was theoretically valued at approximately 107 by discrete dipole approximation. DA was self-assembled on the citrate capped surface of Ag NPs dimers through the amide bond. The adsorption energy was estimated to be 256 KJ/mol using the Langmuir isotherm model. The density functional theory was used to simulate the spectral characteristics of SERS during the adsorption of DA on the surface of the Ag dimers. Furthermore, to improve the accuracy and precision of quantitative analysis of SERS assays with a multiplicative effects model for surface-enhanced Raman spectroscopy. Conclusion: A LOD of 20 pM DA-level was obtained, and the linear response ranged from 30 pM to 300 nM for quantitative DA detection. The absolute relative percentage error was 4.22% between the real and predicted DA concentrations. This detection scheme is expected to have good applications in the prevention and diagnosis of certain diseases caused by disorders in the DA level.Keywords: surface-enhanced Raman scattering, SERS, multiplicative effects model for surface-enhanced Raman spectroscopy, MEMSERS, dopamine detection, Ag NP dimers

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For maintaining water quality, planning remediation strategies and ecosystem restoration, the detection of metal ions in aquatic water bodies is very important. Colorimetry as well as plasmon-enhanced spectroscopy using plasmonic particles tailored and decorated by organic molecules provides promising simple, portable, robust and economically viable sensing systems for metal ions in field or in point of care settings. For this purpose, silver nanoparticles functionalized with pectin (P-AgNPs) have been synthesized by a microwave assisted method for the detection of metal ions [Cr(III), Cr(VI), Se(IV), Mn(II), Fe(II), As(V), and Hg(I)] in aqueous solution using colorimetry and SERS. The addition of P-AgNPs imparts a black and brown color to the water samples containing Fe(II) and Mn(II) ions while a reddish brown color is observed in water samples containing Cr(III) and As(V) ions. The Raman measurements of different concentrations of Cr(III), Cr(VI), Se(IV), Mn(II), As(V), and Hg(I) ions mixed with synthesized colloidal P-AgNPs solution have also been recorded. The addition of metal ions to the P-AgNPs solution induces alteration in the spectral features of the peaks of P-AgNPs. In addition, they also lead to formation of new characteristic bands. Significant enhancement in the intensity has been observed for these bands in the form of SERS signals. These peculiar characteristic peaks may be used for the detection of the metal ions in aqueous solution. This study demonstrates applicability of P-AgNPs as a colorimetric and plasmon enhancing spectroscopic agent for the simple, prompt, easily accessible and portable tool for the detection of metal ion pollution in aqueous medium. [ABSTRACT FROM AUTHOR]

Silicon nitride thin films are useful as etch-stop masks in micro- and nanofabrication. As structural elements, they are prevalent in applications as diverse as single-molecule sensing, transmission electron microscopy, ultrafast spectroscopy, superfluidity studies, and high flux liquid filtering. A hand-held "flameless" Tesla-coil lighter was used to create vias through 200 nm silicon nitride (SiNx) films coating silicon wafers. The processing allowed spatially directed KOH etching of the underlying Si. Patterning could be achieved with a hard mask or rastering of the spatially confined discharge, offeringwith low barriers to rapid useparticular capabilities that might otherwise be out of reach to researchers without access to conventional, instrumentation-intensive micro- and nanofabrication workflows. General patterning capabilities were demonstrated, followed by the formation of a trench suitable for microfluidic applications. Finally, a discharge-treated thin film surface was sputter coated with gold to create a surface enhanced Raman spectroscopy (SERS) substrate that was then used to detect a test analyte at ppm concentration. [ABSTRACT FROM AUTHOR]

Plexcitons are polaritonic modes that result from coherently coupled plasmons and excitons. Far‐ and near‐field properties of Ag/semiconductor core–shell nanoparticles on silica‐coated silver substrate were theoretically studied, using finite‐difference time‐domain method. Our calculations suggested that titanium dioxide (TiO2) would be a better coating material, useful for the design of high‐sensitive surface enhanced Raman scattering (SERS) substrate. The calculated Raman enhancement factor could be turned to as high as 4.0 × 1010 under the 633‐nm laser excitation. Surface plasmon‐coupled emission of SERS reveals an optimal collection angle of 5°, which shows a huge back scattering of the studied system. Our theoretical results could be used as a reference for the experimental design of semiconductor‐based SERS substrate with high efficiency. [ABSTRACT FROM AUTHOR]

In this study, we developed a simple, inexpensive and easily fabricable paper-based SERS substrate with high sensitivity and reproducibility. The filter paper has natural pleats and small pores that allow the metal nanoparticles to be deposited and arranged on the paper to form large area SERS 'active sites'. Silver nanoparticles can be embedded and grown on cellulose nanocrystals framework through the in situ reduction to form cellulose nanocrystal–silver (CNC–Ag) composites, which are coated on the filter paper to form composite paper-based substrates. The CNC–Ag composites further filled the pores on the surface of the filter paper and improved the adhesive rate of metal nanoparticles, thus the reproducibility of the SERS sensor has been improved. At the same time, because it has the agglomerating effect on samples, the hydrophobic dodecyl mercaptan covered on paper-based substrates can improve detection limit of analyte. Furthermore, we demonstrate that paper-based SERS substrates can efficiently detect two substances, including phenylethanolamine A and metronidazole. The limits of detection for phenylethanolamine A and metronidazole were found to as low as 5 × 10−9 M and 2 × 10−7 M, respectively. The paper-based SERS substrates offer great potential for label-free and on-site detection of trace substances. [ABSTRACT FROM AUTHOR]

Simple and highly sensitive SERS substrates were produced using Au nanoparticles (AuNPs) prepared by laser ablation in water and available Digital Video Discs (DVDs). We used the simple "drop-cast" method to deposit AuNPs on the grating pattern surface of a DVD in place of the other methods such as electrochemical deposition, electrophoretic deposition and sputtering method which require some more equipment. AuNPs were proposed to be synthesized in water by laser ablation to form a nearly circular AuNP stain of small size on a DVD surface. The protecting polycarbonate layer of a DVD was removed from the DVD surface. The bare metallic DVD surface was rinsed carefully with ethanol and distilled water. The width of tracks on a DVD surface is around 300 nm and distance between them is around 450 nm. We prepared AuNPs by pulsed laser ablation of a gold piece in distilled water. The colloidal gold nanoparticles were deposited on DVD templates. We studied to produce an effective layer of AuNPs on DVD template for SERS substrates (AuNPs/DVD). The average SERS enhancement factor of the AuNPs/DVD SERS substrates is about 106. The SERS substrates can detect SERS spectra of Malachite Green and Amoxicillin at low concentrations of around 0.1–1 ppm. [ABSTRACT FROM AUTHOR]

• From 25 to 250 °C, the interaction between [EMIm]Cl and silver substrate occurs through N-atoms. • The enhancement mechanism of silver substrate toward [EMIm]Cl resulted from the combination of EM and CM. • From 25 to 200 °C, [HO 2 CEtMIm]Cl interacted with the silver substrate through carboxyl group. • CM is the main enhancement mechanism for [HO 2 CEtMIm]Cl adsorbed on silver substrate. Ionic liquids (ILs) are unique solvents with a broad liquid temperature range. However, little has so far been done to investigate the ionic structures of ILs as a function of temperature. This can be performed by surface-enhanced Raman scattering (SERS) technique to effectively investigate the ionic structure and interface reaction of ILs at different temperature. Herein, in-situ SERS spectra of 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl) and 1-carboxyethyl-3-methylimidazolium chloride ([HO 2 CEtMIm]Cl) ILs adsorbed on silver substrates at variable temperatures were recorded to study the adsorption behaviors and enhancement mechanisms. The results suggested interaction between [EMIm]Cl and silver substrate through N-atoms with the imidazole ring standing on the substrate. The enhancement mechanism of silver substrates toward [EMIm]Cl originated from the combination of electromagnetic enhancement (EM) and chemical enhancement (CM). At temperatures of 25–200 °C, no significant changes in the adsorption behavior and ionic structure of [EMIm]Cl on the silver substrate surface were observed. However, a further temperature rise resulted in changes in SERS spectral intensity of [EMIm]Cl owing to the aggregation of silver particles, as well as the increment in the amount of adsorbed molecules. Besides, [HO 2 CEtMIm]Cl interacted with the silver substrate through the carboxyl group, resulting in a molecular configuration that greatly influenced the adsorption behavior of [HO 2 CEtMIm]Cl. Compared to [EMIm]Cl, the imidazole ring of [HO 2 CEtMIm]Cl was located farther away from the substrate surface, leading to weaker SERS enhancement. Finally, the temperature variation did not affect the adsorption behavior and ionic structure of [HO 2 CEtMIm]Cl on the substrate surface. Overall, these results look promising for future studies of ionic structure and interface reaction of various ILs for advanced synthesis processes. [ABSTRACT FROM AUTHOR]

Recent global warming has resulted in shifting of weather patterns and led to intensification of natural disasters and upsurges in pests and diseases. As a result, global food systems are under pressure and need adjustments to meet the change—often by pesticides. Unfortunately, such agrochemicals are harmful for humans and the environment, and consequently need to be monitored. Traditional detection methods currently used are time consuming in terms of sample preparation, are high cost, and devices are typically not portable. Recently, Surface Enhanced Raman Scattering (SERS) has emerged as an attractive candidate for rapid, high sensitivity and high selectivity detection of contaminants relevant to the food industry and environmental monitoring. In this review, the principles of SERS as well as recent SERS substrate fabrication methods are first discussed. Following this, their development and applications for agrifood safety is reviewed, with focus on detection of dye molecules, melamine in food products, and the detection of different classes of pesticides such as organophosphate and neonicotinoids.

Molecular imprinting and surface enhanced Raman scattering (SERS) were used to prepare a core-shell Ag@molecularly imprinting polymer (MIP) for the determination of p-nitroaniline. The obtained Ag@MIP exhibits a detection limit of 10−12 M, which demonstrates higher sensitivity toward p-nitroaniline than conventional approaches. In addition, the Ag@MIP shows good recyclability, and simultaneously offers better stability and high SERS activity for recognizing target molecules. To characterize the high SERS activity of the SERS-MIP hybrid material, a possible mechanism for the SERS substrate is proposed involving enhancement by the MIP. This study is expected to provide an alternative approach for the determination of p-nitroaniline in aqueous environments. [ABSTRACT FROM AUTHOR]

During the past several years, numerous efforts have been accomplished on designing efficient surface‐enhanced Raman scattering (SERS) substrates with high sensitivity, good reproducibility, and recyclable nature. However, it still remains a significant challenge to realize all these qualities in a single substrate. We have fabricated ripple‐like nanostructures (NSs) on Iron (Fe) substrate using femtosecond (fs) laser irradiation of Fe target in distilled water. These ripple‐like structures had periodicities in the range of ~90–190 nm, which was confirmed from the analysis of field emission scanning electron microscope (FESEM) data. We subsequently deposited a thin layer of gold on these ripple‐like Fe NSs using thermal evaporation. Later, these coated NSs were effectively utilized as SERS substrates for methylene blue (MB) detection and were found to be sensitive evident from the data obtained at a very low concentration of 500pM. Furthermore, we observed that the SERS signal variations on the substrate were <11.2% indicating the reproducible nature of these substrates. Additionally, we demonstrate that these substrates can be reused (we establish this for three times consecutively) by detecting malachite green (MG) and an explosive molecule (picric acid, PA) followed by the mixture compound (Rhodamine 6G+MB) through employment of simple cleaning procedures. The detected molecular concentrations in terms of masses were found to be 3.2 pg, 36.5 pg, and 23 ng for MB (for a concentration of 500pM), MG (for a concentration of 5nM), and PA (for a concentration of 5μM), respectively. Furthermore, these Fe NSs exhibited superior batch‐to‐batch reproducibility with a relative standard deviation (RSD) value of ~l4%. The proposed method of fabricating ripple structures as SERS platforms are highly feasible, reliable, and have great potential for on‐site detection of several analyte molecules with an easily transportable Raman spectrometer. [ABSTRACT FROM AUTHOR]

Composite of silver nanoparticles with reduced graphene oxide flakes is proposed for surface enhanced vibrational spectroscopy, particularly for detection of adenine and thymine as constituents of deoxyribonucleic acid. Composite was formed by original method implying simultaneous reduction of silver ions and graphene oxide by discharge plasma at the gas–liquid interface. Combination of nanosized silver with reduced graphene oxide provided greater enhancement of Raman light scattering and infrared light absorption in comparison with separately used components. Addition of the composite to water solutions of adenine and thymine allowed detection of these analytes at micromolar concentrations. Composite of nano-silver with reduced graphene oxide can be prospective for surface enhanced spectroscopy as an alternative to the expensive lithographically prepared noble metal substrates. [ABSTRACT FROM AUTHOR]

Abstract Ag triangular nanoplates have been widely used as the SERS substrate due to their anisotropic morphology and sharp corners. In this work, SERS activity of Ag triangular nanoplates on glass and paper substrates was investigated with different concentration and size. A tiny triangular nuclei based synthesis method was employed to produce Ag triangular nanoplates with different size. And the extinction coefficients of Ag triangular nanoplates with different size were quantified by inductively coupled plasma mass spectrometry (ICP-MS) and transmission electron microscopy (TEM). With definite concentration, Ag triangular nanoplates with small size showed stronger SERS intensity on glass substrate at high concentrations, while large Ag triangular nanoplates exhibited better SERS effect on paper substrate at low concentrations. The possible reasons for distinct SERS activity of Ag triangular nanoplates on glass and paper were discussed with scanning electron microscope (SEM) characterization. These results exhibited important implications for fabricating Raman substrates using Ag triangular nanoplates and could be applied to the SERS sensing with flexile substrate. Highlights • The extinction coefficients of Ag triangular nanoplates (Ag TPs) with different size were quantified. • Ag TPs showed distinct SERS activity on glass and paper substrates. • Ag TPs with small size showed better enhancement than that of big ones on glass substrates. • Ag TPs with big size exhibited stronger SERS intensity than that of small ones on paper substrates. [ABSTRACT FROM AUTHOR]

Hybrid colloids consisting of silica coated plasmonic core‐shell metal nanoparticles have driven progress in plethora of applications and are under intense investigation in diverse fields of research. In this regard, we have designed a multifunctional nanocomposite consisting of 1,4‐benzenedithiol (BDT) tagged gold nanorattles (Au‐NRT) as core embedded within a solid silica shell with an additional mesoporous silica shell coating forming an "IRIS" like morphology, referred to as Nano‐IRIS. The nanorattle structure with a solid gold octahedron core and porous cubic gold shell serves as an excellent SERS probe due to the presence of intrinsic electromagnetic (EM) hot‐spots. The intelligent design of incorporating a solid SiO2 layer in the core‐shell Nano‐IRIS structure helped in incorporating two different imaging functionalities, namely SERS and fluorescence‐based bioimaging into a single nanoplatform, thereby imparting a multimodal imaging attribute to Nano‐IRIS. The solid SiO2 layer not only helped in keeping the Raman reporter intact in the pores of AuNRT but also maintained the distance between the gold surface and the fluorescent drug Doxorubicin (DOX) encapsulated inside the mSiO2 layer to achieve fluorescence imaging without quenching. Additionally, Nano‐IRIS also emerged as a drug delivery system demonstrating highly efficient concentration dependent chemotherapy via ROS production and oxidative DNA damage. [ABSTRACT FROM AUTHOR]