Surface enhanced Raman scattering substrate for the detection of explosives: Construction strategy and dimensional effect

High-uniformity, low-cost, ultra-dense arrays of Au-capped plastic nanopillars fabricated via nanoimprint lithography as reliable SERS substrates

Nanoimprint lithography (NIL) is gradually becoming a powerful tool for the fabrication of periodic nanostructures. This method can offer a more cost-effective solution for large-scale manufacturing compared to methods that only rely on deep ultraviolet (DUV) immersion, since the product of DUV immersion can be utilized as a Si mold to fabricate a reusable plastic stamp mold. In this work, arrays of plastic nanopillars coated with nanostructured gold film exhibiting ultra density prepared through NIL and Au sputtering are successfully developed. The obtained plastic nanopillar substrate is templated from Si nanopillar substrate with a pitch of 90 nm. As a result, the plastic nanopillar features a similar pitch size. Besides, benzenedithiol (BDT) was used as the standard analyte to evaluate the uniformity of the substrates as well as the SERS enhancement effect. Eventually, it is demonstrated that the substrate constituted of Au-capped plastic nanopillar shows a low coefficient of variation (CV) at 5.46 % along with a strong SERS enhancement effect. These performances match with the Si based SERS substrate manufactured via DUV immersion reported in our previous work.

Surface-enhanced Raman spectroscopy in pharmaceutical analysis: from component determination to mechanism research

Surface-enhanced Raman spectroscopy (SERS) technology, possessing extraordinary sensitivity and an outstanding ability to furnish molecular-level information, has emerged as a revolutionary technique within the domain of analytical chemistry. This review comprehensively and in-depthly investigates the application of SERS in the field of pharmaceutical analysis, encompassing detailed analyses in diverse aspects such as ingredient identification, quality control, mechanism of action, and efficacy evaluation. Firstly, we introduce the key aspects of SERS technology, including its working principle, substrate preparation methods, and crucial factors in the experimental design process. Subsequently, the specific application of SERS in drug ingredient analysis is elaborated in detail, emphasizing its capability to rapidly identify active ingredients in complex mixtures, particularly the significant advantages it exhibits when tracking low-concentration bioactive molecules. At the quality control level, the application of SERS can precisely identify illegal adulteration in regular drugs, effectively guaranteeing the quality and consistency of drugs. Additionally, SERS also demonstrates great potential in analyzing the mechanism of action of natural drugs. It can clearly disclose the interaction between drugs and organisms at the molecular level and evaluate the effect of drugs. Although SERS technology has manifested extremely significant application prospects in the field of drug research, its widespread implementation still encounters some challenges, including the standardization of substrates, the reproducibility of signals, and the complexity of data processing. The future development direction will concentrate on the innovative design of substrates, the automation of the analysis process, and the organic integration with other bioanalytical technologies to enhance its accuracy and practicability in pharmaceutical analysis. Through continuous technological innovation and interdisciplinary cooperation, SERS technology is anticipated to play a more crucial role in the research and development of drugs, further promoting the continuous growth and innovation of the drug industry. This article aims to provide researchers in related fields with a comprehensive perspective on the current application status and future development trend of SERS technology, and also offer scientific basis and technical support for drug quality control and new drug development.

Fast and eco-friendly synthesis of carbon dots from pinecone for highly effective detection of 2,4,6-trinitrophenol in environmental samples

2,4,6-Trinitrophenol (TNP) has high explosive risks and biological toxicity, and there has been considerable concern over the determination of TNP. In the present work, fluorescent carbon dots (CDs) stemmed from a green carbon source of pinecone by the facile hydrothermal approach. A novel environment- friendly fluorescent probe was developed to efficiently detect TNP by using the obtained CDs with remarkable fluorescence stability. The fluorescent CDs exhibited obvious excitation dependence with the highest peaks for excitation and emission occurring at 321 and 411 nm, respectively. The fluorescence intensity is significantly reduced by TNP owing to the inner filter effect with the CDs. The probe exhibited good linearity with TNP concentrations in the range of 0.025-20 μg mL-1, and the limit of detection was as low as 8.5 ng mL-1. Additionally, the probe proved successful in sensing TNP quantitatively in actual environmental samples with satisfied recoveries of 95.6-99.6%. The developed fluorescent probe offered an environment-friendly, efficient, rapid, and reliable platform for detecting trace TNP in the environmental field.Highlights Novel carbon dots were synthesised from green precursors of pineal powder.The highly effective quenching process was put down to the inner filter effect.The as-constructed fluorescent probe was successfully utilised for sensing 2,4,6-trinitrophenol in environmental samples.The proposed method was simple, rapid, efficient, economical, and eco-friendly.

Machine Learning-Assisted SERS Reveals the Biochemical Signature of Enhanced Protein Secretion from Surface-Modified Magnetic Nanoparticles

This study introduces a novel investigation of the interaction between Komagataella phaffii cells and iron oxide-based magnetic nanoparticles (Fe3O4 MNPs) via protein secretion and machine learning (ML)-assisted surface-enhanced Raman scattering (SERS). For the first time, we produced Fe3O4, Fe3O4@PEG, Fe3O4@PEI10kDa, and Fe3O4@PEI25kDa MNPs by a one-pot coprecipitation reaction. The addition of polymers to the reaction conditions significantly affected the shape, surface charge, size, and size distribution of the MNPs. The surface modification of MNPs is effectively accomplished using polyethylenimine (PEI), and the ζ-potential values of the MNPs exceed +25 mV under the NH4OH control. The homogeneity of MNPs synthesized with NH4OH is more pronounced according to transmission electron microscopy (TEM) pictures. All MNPs exhibited excellent immobilization efficiency (>92%) when we used 250 ppm Fe-containing MNP solutions. Smaller MNPs uniformly encapsulated the surface of K. phaffii cells, whereas larger MNPs exhibited irregular accumulation. K. phaffii cells exhibited excellent viability in all MNP solutions at up to 1000 ppm of Fe concentrations. Finally, the highest recombinant azurin protein secretion rate was obtained in Fe3O4@PEI10kDa MNP-immobilized cells (about 1.3 times). The ML-assisted SERS analysis revealed that MNP interactions with K. phaffii cells were mediated by proteins such as mannoproteins and membrane transporter proteins as well as N-acetylglucosamine (i.e., chitin). These findings revealed the effect of the size and surface properties of MNPs on the immobilization of K. phaffii cells and the enormous potential of magnetic immobilization for protein secretion.

Plasmonic nanoparticle sensors: current progress, challenges, and future prospects

Plasmonic nanoparticles (NPs) have played a significant role in the evolution of modern nanoscience and nanotechnology in terms of colloidal synthesis, general understanding of nanocrystal growth mechanisms, and their impact in a wide range of applications. They exhibit strong visible colors due to localized surface plasmon resonance (LSPR) that depends on their size, shape, composition, and the surrounding dielectric environment. Under resonant excitation, the LSPR of plasmonic NPs leads to a strong field enhancement near their surfaces and thus enhances various light-matter interactions. These unique optical properties of plasmonic NPs have been used to design chemical and biological sensors. Over the last few decades, colloidal plasmonic NPs have been greatly exploited in sensing applications through LSPR shifts (colorimetry), surface-enhanced Raman scattering, surface-enhanced fluorescence, and chiroptical activity. Although colloidal plasmonic NPs have emerged at the forefront of nanobiosensors, there are still several important challenges to be addressed for the realization of plasmonic NP-based sensor kits for routine use in daily life. In this comprehensive review, researchers of different disciplines (colloidal and analytical chemistry, biology, physics, and medicine) have joined together to summarize the past, present, and future of plasmonic NP-based sensors in terms of different sensing platforms, understanding of the sensing mechanisms, different chemical and biological analytes, and the expected future technologies. This review is expected to guide the researchers currently working in this field and inspire future generations of scientists to join this compelling research field and its branches.

Detecting antimony(III) on-site using novel gel-based techniques: Colorimetric diffusive equilibrium in thin films for two-dimensional imaging and surface-enhanced Raman scattering for sensitive quantification

Antimony (Sb) pollution has raised increasing public concerns and its rapid on-site screening is central for the risk assessment. Herein, we proposed two gel-based methods based on colorimetric diffusive equilibrium in thin films (DET) and surface-enhanced Raman scattering (SERS), for two-dimensional imaging and sensitive detection of Sb(III) by revisiting the phenylfluorone (PhF) complexation reaction. PhF was well dispersed in the polyvinyl alcohol (PVA) hydrogel and reacted with Sb(III) in the DET gel to form a strong PhF-Sb(III) complex. The distribution of Sb(III) was easily visualized at a submillimeter resolution using computer imaging densitometry, with a detection limit (LOD) of ∼100 nmol L-1. Field application in the Sb mine area reveals limited dissolved Sb(III) penetrating the redox barrier below the sediment-water interface by 20 mm in rivers and tailing pond sediments. To improve the detection sensitivity and apply the principle to trace Sb quantification, a SERS platform was established by anchoring PhF on the hydrogel-stabilized Ag nanoparticles via C-O-Ag bonding to specifically detect Raman-inactive Sb(III). Benefiting from the high SERS activity of PhF and enrichment ability of hydrogel, Sb(III) was quantified with a LOD of 1.2-10.7 nmol L-1 depending on the sample volume. The coexisting ions at a 100-fold higher concentration than Sb(III) resulted in only 3.3-10.4 % variation in SERS intensity, indicating a negligible interference on the SERS platform. The platform exhibited a RSD of 6.6-13.1 % and acceptable recoveries for various environmental matrices, highlighting its promise in on-site application.

Hazardous Materials from Threats to Safety: Molecularly Imprinted Polymers as Versatile Safeguarding Platforms

Hazards associated with highly dangerous pollutants/contaminants in water, air, and land resources, as well as food, are serious threats to public health and the environment. Thus, it is imperative to detect or decontaminate, as risk-control strategies, the possible harmful substances sensitively and efficiently. In this context, due to their capacity to be specifically designed for various types of hazardous compounds, the synthesis and use of molecularly imprinted polymers (MIPs) have become widespread. By molecular imprinting, affinity sites with complementary shape, size, and functionality can be created for any template molecule. MIPs' unique functions in response to external factors have attracted researchers to develop a broad range of MIP-based sensors with increased sensitivity, specificity, and selectivity of the recognition element toward target hazardous compounds. Therefore, this paper comprehensively reviews the very recent progress of MIPs and smart polymer applications for sensing or decontamination of hazardous compounds (e.g., drugs, explosives, and biological or chemical agents) in various fields from 2020 to 2024, providing researchers with a rapid tool for investigating the latest research status.

Nanosculptured tungsten oxide: High-efficiency SERS sensor for explosives tracing

The accurate and rapid identification of explosives and their toxic by-products is an important aspect of safety protocols, forensic investigations and pollution studies. Herein, surface-enhanced Raman scattering (SERS) is used to detect different explosive molecules using an improved substrate design by controllable oxidation of the tungsten surface and deposition of Au layers. The resulting furrow-like morphology formed at the intersection of the tungsten Wulff facets increases nanoroughness and improves the SERS response by over 300 % compared to the untreated surface. The substrate showed excellent reproducibility with a relative standard deviation of less than 15 % and a signal recovery of over 95 % after ultrafast Ar/O2 plasma cleanings. The detection limit for the "dried on a surface" measurement case was better than 10-8 M using the moving scanning regime and an acquisition time of 10 s, while for the "water droplets on a surface" scenario the LoD is 10-7, which is up to 2 orders of magnitude better than the UV-Vis spectroscopy method. The substrates were successfully used to classify the molecular fingerprints of HMX, Tetryl, TNB and TNT, demonstrating the efficiency of a sensor for label-free SERS screening in the practice of monitoring traces of explosives in the water medium.

Selective SERS Detection of TATB Explosives Based on Hydroxy-Terminal Nanodiamond-Multilayer Graphene Substrate

Selective surface-enhanced Raman scattering (SERS) detection of target explosives with good reproducibility is very important for monitoring soldiers' health and ecological environment. Here, the specific charge transfer pathway was constructed between a stable nanodiamond-multilayer graphene (MGD) film substrate and the target explosives. Two-step wet chemical oxidation methods of H2O2 (30%) and HNO3 (65%) solutions were used to regulate the terminal structure of MGD films. The experimental results showed that the hydroxyl (-OH) functional groups are successfully modified on the surface of MGD thin films, and the MGD-OH substrates having good selectivity for 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) explosive in mixed solutions of the TATB, 2,2-dinitroethene-1,1-diamine, 2,4,6-trinitrotoluene, and 1,3,5-trinitroperhydro-1,3,5-triazine explosives compared with MGD substrates were demonstrated. Finally, first-principles density functional theory simulations revealed that the SERS enhancement of the MGD-OH substrate is mainly attributed to the transferred electrons between the -NO2 groups of TATB and the -OH groups of the MGD-OH substrate.

Cellulose Nanofiber Films with Gold Nanoparticles Electrostatically Adsorbed for Facile Surface-Enhanced Raman Scattering Detection

Cellulose nanofiber (CNF) holds great promise in applications such as surface-enhanced Raman scattering (SERS), catalysis, esthesia, and detection. This study aimed to build novel CNF-based SERS substrates through a facile synthetic method. Citrate-reduced gold nanoparticles (AuNPs) were adsorbed on the cationized CNF surface due to electrostatic interactions, and uniform AuNPs@(2,3-epoxypropyl trimethylammonium chloride)EPTMAC@CNF flexible SERS substrates were prepared by a simple vacuum-assisted filtration method. The probe molecule methylene blue was chosen to assess the performance of the CNF-based SERS substrate with a sensitivity up to 10-9 M, superior signal reproducibility (relative standard deviation (RSD) = 4.67%), and storage stability (more than 30 days). Tensile strength tests indicated that the CNF-based films had good mechanical properties. In addition, CNF-based substrates can easily capture and visually identify microplastics in water. These results demonstrate the potential application of the flexible, self-assembled AuNPs@EPTMAC@CNF flexible SERS substrate for prompt and sensitive detection of trace substances.

Sensitive and high laser damage threshold substrates for surface-enhanced Raman scattering based on gold and silver nanoparticles

Surface-enhanced Raman scattering (SERS) is a sensitive and fast technique for sensing applications such as chemical trace analysis. However, a successful, high-throughput practical implementation necessitates the availability of simple-to-use and economical SERS substrates. In this work, we present a robust, reproducible, flexible and yet cost-effective SERS substrate suited for the sensitive detection of analytes at near-infrared (NIR) excitation wavelengths. The fabrication is based on a simple dropcast deposition of silver or gold nanomaterials on an aluminium foil support, making the design suitable for mass production. The fabricated SERS substrates can withstand very high average Raman laser power of up to 400 mW in the NIR wavelength range while maintaining a linear signal response of the analyte. This enables a combined high signal enhancement potential provided by (i) the field enhancement via the localized surface plasmon resonance introduced by the noble metal nanomaterials and (ii) additional enhancement proportional to an increase of the applicable Raman laser power without causing the thermal decomposition of the analyte. The application of the SERS substrates for the trace detection of melamine and rhodamine 6G is demonstrated, which shows limits of detection smaller than 0.1 ppm and analytical enhancement factors on the order of 104 as compared to bare aluminium foil.

Design of a versatile and selective electrochemical sensor based on dummy molecularly imprinted PEDOT/laser-induced graphene for nitroaromatic explosives detection

Considering the formidable explosive power and human carcinogenicity of nitroaromatic explosives, the implementation of an accurate and sensitive detection technology is imperative for ensuring public safety and monitoring post-blast environmental contamination. In the present work, a versatile and selective electrochemical sensor based on dummy molecularly imprinted poly (3,4-ethylenedioxythiophene)/laser-induced graphene (MIPEDOT/LIG) was successfully developed and the specific detection of multiple nitroaromatic explosives was realized in the single sensor. The accessible and nontoxic trimesic acid (TMA) and superior 3, 4-ethylenedioxythiophene (EDOT) were selected as the dummy-template and the functional monomer, respectively. The interaction between the functional monomer and the template, and the morphology, electrochemical properties and detection performance of the sensor were comprehensively investigated by ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, cyclic voltammetry, and differential pulse voltammetry. Benefiting from the alliance of TMA and EDOT, the MIPEDOT/LIG sensor manifested outstanding selectivity and sensitivity for 2,4,6-trinitrotolueen (TNT), 2,4,6-trinitrophenol (TNP), 2,4-dinitrotoluene (DNT), 1,3,5-trinitrobenzene (TNB), 2,4-dinitrophenol (DNP), and 1,3-dinitrobenzene (DNB) (representative nitroaromatic explosives) with limits of determination of 1.95 ppb, 3.06 ppb, 2.49 ppb, 1.67 ppb, 1.94 ppb, and 4.56 ppb, respectively. The sensor also exhibited extraordinary reliability and convenience for environmental sample detection. Therefore, a perfect combination of versatility and selectivity in the MIPEDOT/LIG sensor was achieved. The findings of this work provide a new direction for the development of multi-target electrochemical sensors using a versatile dummy template for explosives detection.

Fabrication of Ag-CaCO3 Nanocomposites for SERS Detection of Forchlorfenuron

In this study, Ag-CaCO3 nanocomposites were synthesized using silver nitrate as the precursor solution based on calcium carbonate nanoparticles (CaCO3 NPs). The synthesis involved the reaction of calcium lignosulphonate and sodium bicarbonate. The properties of Ag-CaCO3 nanocomposites were studied by various technologies, including an ultraviolet-visible spectrophotometer, a transmission electron microscope, and a Raman spectrometer. The results showed that Ag-CaCO3 nanocomposites exhibited a maximum UV absorption peak at 430 nm, the surface-enhanced Raman spectroscopy (SERS) activity of Ag-CaCO3 nanocomposites was evaluated using mercaptobenzoic acid (MBA) as the marker molecule, resulting in an enhancement factor of 6.5 × 104. Additionally, Ag-CaCO3 nanocomposites were utilized for the detection of forchlorfenuron. The results demonstrated a linear relationship in the concentration range of 0.01 mg/mL to 2 mg/mL, described by the equation y = 290.02x + 1598.8. The correlation coefficient was calculated to be 0.9772, and the limit of detection (LOD) was determined to be 0.001 mg/mL. These findings highlight the relatively high SERS activity of Ag-CaCO3 nanocomposites, making them suitable for analyzing pesticide residues and detecting toxic and harmful molecules, thereby contributing to environmental protection.

Self-assembled PVP-gold nanostar films as plasmonic substrates for surface-enhanced spectroscopies: influence of the polymeric coating on the enhancement efficiency

Colloidal nanoparticles exhibiting anisotropic morphologies are preferred in the structural design of spectroscopically active substrates due to the remarkable optical properties of this type of nano-object. In the particular case of star-like nanoparticles, their sharp tips can act as antennae for capturing and amplifying the incident light, as well as for enhancing the light emitted by nearby fluorophores or the scattering efficiency of Raman active molecules. In the current work, we aimed to implement such star-shaped nanoparticles in the fabrication of nanoparticle films and explore their use as solid plasmonic substrates for surface-enhanced optical spectroscopies. High-density, compact and robust self-assembled gold nanostar films were prepared by directly depositing them from aqueous colloidal suspension on polystyrene plates through convective self-assembly. We investigated the role of the polymeric coating, herein polyvinylpyrrolidone (PVP), in the particle assembly process, the resulting morphology and consequently, the plasmonic response of the obtained films. The efficacy of the plasmonic films as dual-mode surface-enhanced fluorescence (SEF) and surface-enhanced Raman scattering (SERS) substrates was evidenced by testing Nile Blue A (NB) and Rhodamine 800 (Rh800) molecular chromophores under visible (633 nm) versus NIR (785 nm) laser excitation. Steady-state and time-resolved fluorescence investigations highlight the fluorescence intensity and fluorescence lifetime modification effects. The experimental results were corroborated with theoretical modelling by finite-difference time-domain (FDTD) simulations. Furthermore, to prove the extended applicability of the proposed substrates in the detection of biologically relevant molecules, we tested their SERS efficiency for sensing metanephrine, a metabolite currently used for the biochemical diagnosis of neuroendocrine tumors, at concentration levels similar to other catecholamine metabolites.

Chemical reduction as a facile colorimetric approach for selective TNT detection by spectrophotometry and photothermal lens spectroscopy

In this study, the simple determination of TNT is achieved through the vivid stable red color products generated after chemically reduction by NaBH₄ as a common and accessible reducing/colorimetric reagent. Some other nitroaromatics were impressed under reduction reaction and led to the colorful products. The color of these reduced nitroaromatics were unstable and approximately vanished after some few minutes which ameliorated the selectivity in TNT determination. Utilizing the time-dependent selectivity, the method was applied specifically for discriminating of TNT from other nitroaromatic compounds (NACs). UV-vis spectrophotometry and photothermal lens spectrometry were employed as detection techniques. The former was simpler and more available in various laboratories while the latter provides higher sensitivity. It was revealed that the photothermal lens responses were linear from 2.0 to 55.0 nM with a limit of detection (LOD) of about 0.8 nM. The LOD of the photothermal lens measurement were found to be 241 times lower than that of the UV-vis spectrophotometry in TNT quantification. The evolved method was successfully carried out for TNT vapor determination after trapping into the colorimetric reagent. The recoveries and relative standard deviations (RSD, n = 3) calculated for 3 gas samples were ≥91% and ≤7%, respectively.

SERS performance of GaN/Ag substrates fabricated by Ag coating of GaN platforms

The results of comparative studies on the fabrication and characterization of GaN/Ag substrates using pulsed laser deposition (PLD) and magnetron sputtering (MS) and their evaluation as potential substrates for surface-enhanced Raman spectroscopy (SERS) are reported. Ag layers of comparable thicknesses were deposited using PLD and MS on nanostructured GaN platforms. All fabricated SERS substrates were examined regarding their optical properties using UV-vis spectroscopy and regarding their morphology using scanning electron microscopy. SERS properties of the fabricated GaN/Ag substrates were evaluated by measuring SERS spectra of 4-mercaptobenzoic acid molecules adsorbed on them. For all PLD-made GaN/Ag substrates, the estimated enhancement factors were higher than for MS-made substrates with a comparable thickness of the Ag layer. In the best case, the PLD-made GaN/Ag substrate exhibited an approximately 4.4 times higher enhancement factor than the best MS-made substrate.

TiO2 compact layer induced charge transfer enhancement in a three-dimensional TiO2-Ag array SERS substrate for quantitative and multiplex analysis

A highly sensitive and uniform surface-enhanced Raman scattering (SERS) substrate is the guarantee for reliable quantitative analysis. Herein, a three-dimensional TiO₂-Ag SERS substrate was prepared by growing a TiO₂ nanorods (NRs) array on a TiO₂ compact layer (c-TiO₂), followed by modification with Ag nanoparticles (AgNPs). The synergy between the c-TiO₂, semiconductor TiO₂ NRs and the plasmonic AgNPs collaboratively endowed it with high sensitivity, in which c-TiO₂ effectively blocked the recombination of electrons and holes, and the charge transfer enhancement contributed 10-fold improvement over that without the c-TiO₂ substrate. Besides the high sensitivity, the TiO₂-Ag hybrid array SERS substrate also showed quantitative and multi-component detecting capability. The limit of detection (LOD) for crystal violet (CV) was determined to be 10^-9 M even with a portable Raman instrument. The TiO₂-Ag composite structure was extended to detect organic pesticides (thiram, triazophos and fonofos), and the LODs for thiram, triazophos and fonofos were measured to be 10^-7 M, 10^-7 M and 10^-6 M, respectively. In addition, the realistic simulation detecting pesticide residues for a real sample of dendrobium was demonstrated. The sensitive, quantitative and multiplex analysis of the TiO₂-Ag hybrid array substrate indicated its great potential in the rapid detection of pesticide residues in real samples.

Nanogap-Rich Surface-Enhanced Raman Spectroscopy-Active Substrate Based on Double-Step Deposition and Annealing of the Au Film over the Back Side of Polished Si

Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive and rapid detection technique that is used for detection of various analytes in trace quantities. We present a sensitive, large-area, and nanogap-rich SERS-active substrate by altering a thin gold (Au) film on the unpolished side of a single-side polished silicon wafer by repeated thermal deposition and annealing in an argon environment. The repeated thermal deposition and annealing process was compared on both sides of a one-side-polished silicon wafer; however, the rear side (etched/unpolished side) demonstrated a more enhanced Raman signal owing to the larger effective area. The proposed substrate can be fabricated easily, having a high density of hotspots distributed uniformly all over the substrate. This ensures easy, rapid, and sensitive detection of analytes with a high degree of reproducibility, repeatability, and acceptable uniformity. The optimized substrate shows a high degree of stability with time when exposed to the ambient environment for a longer duration of 148 days. The reported substrate can detect up to 10-11 M concentrations of 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT), with limits of detection (LODs) of 1.22 and 1.26 ng/L, respectively. This work not only presents the efficient and sensitive SERS-active substrate but also shows the advantages of using the rear side of a one-side-polished silicon substrate as a SERS-active chip.

Core-shell Au@ZIF-67-based pollutant monitoring of thiram and carbendazim pesticides

A sensitive and stable substrate plays a vital role in the Raman spectroscopic techniques as an analytical method for detecting pesticides effectively from the environment. Enhancing signals from nanoparticles are weak and inconsistent in repeatability since analytes tend to degrade quickly under laser exposure. Herein, a novel substrate of Au@ZIF-67 is prepared on octahedral AuNPs by trapping pesticide molecules with small three-dimensional volumes by the flexibility of ZIF-67 for rapid detection with high sensitivity and stability. The two types of thiram and carbendazim pesticides, which are environmental pollutants that affect biodiversity, were successfully absorbed in Au@ZIF-67 nanostructures by adsorption-desorption equilibrium for analytical purposes in Raman spectroscopy. Spectra calculations of the thiram and carbendazim molecules on 8 atoms of Au using DFT were compared with the experimental data. The SERS enhancement factors for thiram and carbendazim were estimated to be 1.91 × 10⁸ and 3.12 × 10⁸, respectively, with the LOD values of trace amounts of ∼10^-10 mol L^-1. The novel substrate of Au@ZIF-67 is a propitious platform for detecting thiram and carbendazim in trace amounts, providing a helpful strategy for detecting residues with high performance in the environment at the laboratory and practical scales.

Application of Cotton Swab-Ag Composite as Flexible Surface-Enhanced Raman Scattering Substrate for DMMP Detection

It is both important and required to quickly and accurately detect chemical warfare agents, such as the highly toxic nerve agent sarin. Surface-enhanced Raman scattering (SERS) has received considerable attention due to its rapid results, high sensitivity, non-destructive data acquisition, and unique spectroscopic fingerprint. In this work, we successfully prepared SERS cotton swabs (CSs) for the detection of the sarin simulant agent dimethyl methyl phosphonate (DMMP) by anchoring N1-(3-trimethoxysilylpropyl) diethylenetriamine (ATS)/silver nanoparticle (AgNP) nanocomposites on CSs using ATS as the stabilizer and coupling agent. Simultaneously, the binding mode and reaction mechanics between the AgNP, ATS, and CS were confirmed by XPS. The modified CSs exhibited good uniformity, stability, and adsorption capability for SERS measurements, enabling the adsorption and detection of DMMP residue from an irregular surface via a simple swabbing process, with a detection limit of 1 g/L. The relative standard deviations (RSDs) of RSD₇₁₀ = 5.6% had high reproducibility. In this research, the fabrication method could easily be extended to other cellulose compounds, such as natural fibers and paper. Furthermore, the versatile SERS CSs can be used for the on-site detection of DMMP, particularly in civil and defense applications, to guarantee food security and the health of the population.

Investigation of the adsorption of pymetrozine on the Au@AgNPs surface and its application in the rapid detection of pymetrozine residues in apple

Pymetrozine is widely used in agriculture to control pests, and its residue may pose a threat to humans. In this study, the adsorption behavior of pymetrozine on Au@AgNPs surfaces in different solutions was investigated by calculation of ACD/Labs, density functional theory, UV-vis spectra, zeta potential and surface-enhanced Raman scattering. Then, a SERS method for detection of pymetrozine residues in apples was established based on the adsorption study. The results showed that pymetrozine was adsorbed on Au@AgNPs surface in different forms in various solutions and high SERS sensitivity of pymetrozine was obtained by the synergistic effect of pymetrozine, Au@AgNPs and NaOH. A simple SERS method has been established to detect pymetrozine in apples with a LOD of 0.038 mg/kg, linear range of 0.05-1.00 mg/kg, recovery of 71.93-117.49 % and RSD low than 11.70 %. This study provides a reference for rapid detection of pymetrozine in agricultural products.

Smartphone-Assisted Sensing of Trinitrotoluene by Optical Array

Here we report the design and fabrication of an array-based sensor, containing functionalized Carbon Dots, Bodipy's and Naphthalimide probes, that shows high fluorescence emissions and sensitivity in the presence of low amounts of TNT explosive. In particular, we have fabricated the first sensor device based on an optical array for the detection of TNT in real samples by using a smartphone as detector. The possibility to use a common smartphone as detector leads to a prototype that can be also used in a real-life field application. The key benefit lies in the possibility of even a nonspecialist operator in the field to simply collect and send data (photos) to the trained artificial intelligence server for rapid diagnosis but also directly to the bomb disposal unit for expert evaluation. This new array sensor contains seven different fluorescent probes that are able to interact via noncovalent interactions with TNT. The interaction of each probe with TNT has been tested in solution by fluorescence titrations. The solid device has been tested in terms of selectivity and linearity toward TNT concentration. Tests performed with other explosives and other nitrogen-based analytes demonstrate the high selectivity for TNT molecules, thus supporting the reliability of this sensor. In addition, TNT can be detected in the range of 98 ng∼985 μg, with a clear different response of each probe to the different amounts of TNT.

Green photoreduction synthesis of dispersible gold nanoparticles and their direct in situ assembling in multidimensional substrates for SERS detection

Gold nanoparticles (AuNPs) and their composites have been applied in surface-enhanced Raman scattering (SERS) detection methods, owing to their stable and excellent surface plasmon resonance. Unfortunately, methods for synthesizing AuNPs often require harsh conditions and complicated external steps. Additionally, removing residual surfactants or unreacted reductants is critical for improving the sensitivity of SERS detection, especially when employing AuNPs-assembled multidimensional substrates. In this study, we propose a simple and green method for AuNPs synthesis via photoreduction, which does not require external surfactant additives or stabilizers. All the processes were completed within 20 min. Along this way, only methanol was employed as the electron acceptor. Based on this photoreduction synthesis strategy, AuNPs can be directly and circularly assembled in situ in multidimensional substrates for SERS detection. The removal of residual methanol was easy because of its low boiling point. This strategy was employed for the preparation of three different dimensional SERS substrates: filter paper@AuNPs, g-C3N4@AuNPs, and MIL-101(Cr)@AuNPs. The limit of detection of filter paper@AuNPs for thiabendazole SERS detection was 1.0 × 10-7 mol/L, while the limits of detection of g-C3N4@AuNPs and MIL-101(Cr)@AuNPs for malachite green SERS detection were both 5.0 × 10-11 mol/L. This strategy presents potential in AuNP doping materials and SERS detection.

Centrifugation-induced assembly of dense hotspots based SERS substrate for enhanced Raman scattering and quenched fluorescence

Hanging (aggregation stuck to the centrifugal tube) in the centrifugation process is always regarded as an unwanted condition. In this work, we develop a centrifugation-induced assembly of dense hotspots surface-enhanced Raman scattering (SERS) substrates from the hanging phenomenon. We discovered interesting sintering-resistant behavior (maintain the sharp nanotip features) of star-like Au nanoparticles after centrifugation-induced assembly, which is in stark contrast with the sintering phenomenon of sphere-like nanoparticles. We also found that one side of centrifugal-induced Au assemblies is two-dimensional (2D, root mean square (rms) roughness down to ∼10 nm), while the other is three-dimensional (3D, rms roughness more than 100 nm). The close-packed feature of the Au assemblies makes them candidates as dense hotspots based SERS substrates. Through systematic investigation of SERS performance of centrifugation-induced assemblies with different morphology (star-like and sphere-like, 2D and 3D), it was found that the 3D side of star-like Au nanoparticles assembly exhibits the highest SERS enhancement together with quenched fluorescence. The star-like SERS substrate also displays high detection uniformity (with 10^-7M Rhodamine 6G) and a low detection limit (down to 10^-12M Rhodamine 6G).

Flexible 2D nanocellulose-based SERS substrate for pesticide residue detection

Nanocellulose holds considerable promise as an effective surface-enhanced Raman scattering (SERS) substrate for sensitive detection of trace targets. Flexible and high-sensitivity two-dimensional (2D) SERS substrates based on nanocrystalline cellulose (CNC) film were successfully developed via self assembly of two plasma nanoparticles: gold nanoflowers (AuNFs) and silver-coated gold nanocubes (Au@AgNCs). The loading process allows the precise control of nanoparticle distribution density and uniformity on CNC film, which are closely related to the plasma coupling effect between particles. The obtained CNC/Au@AgNC flexible two-dimensional substrate could sensitively detect pesticide residues on apple surface, and the detection limits (LOD) of dimethoate and acetamiprid were 4.1 and 10.7 μg/L, respectively. In addition, Raman signal intensity showed a good linear relationship with pesticide concentration in the range of 10-100 μg/L, which provided great potential for high sensitivity and field detection of dangerous targets.

Ultrasensitive and facile detection of multiple trace antibiotics with magnetic nanoparticles and core-shell nanostar SERS nanotags

Ultrasensitive, multiplex, rapid, and accurate quantitative determination of trace antibiotics remains a challenging issue, which is of importance to public health and safety. Herein, we presented a multiplex strategy based on magnetic nanoparticles and surface-enhanced Raman scattering (SERS) nanotags for simultaneous detection of chloramphenicol (CAP) and tetracycline (TTC). In practice, SERS nanotags based on Raman reporter probes (RRPs) encoded gold-silver core-shell nanostars were used as detection labels for identifying different types of antibiotics, and the magnetic nanoparticles could be separated simply by magnetic force, which significantly improves the detection efficiency, reduces the analysis cost, and simplifies the operation. Our results demonstrate that the as-proposed assay possesses the capacities of high sensitivity and multiplexing with the limits of detection (LODs) for CAP and TTC of 159.49 and 294.12 fg mL^-1, respectively, as well as good stability and reproducibility, and high selectivity and reliability. We believe that this strategy holds a great promising perspective for the detection of trace amounts of antibiotics in microsystems, which is crucial to our life. Additionally, the assay can also be used to detect other illegal additives by altering the appropriate antibodies or aptamers.

A pyrazinium-based fluorescent chemosensor for the selective detection of 2,4,6-trinitrophenol in an aqueous medium

A fluorescent pyrazinium-based chemosensor has been synthesized, characterized, and employed for the selective detection of 2,4,6-trinitrophenol in an aqueous medium.

A highly sensitive surface-enhanced Raman scattering substrate prepared on a hydrophobic surface using controlled evaporation

In the present work, we report the fabrication of a surface-enhanced Raman spectroscopy (SERS) substrate on a simple and easily fabricable hydrophobic surface. The substrates are prepared by slow and fast evaporation of a droplet of silver nanoparticle suspension in water. The corresponding identifiers for two substrates are “s_evp” and “f_evp” respectively. It is found that the dried spot size is small on s_evp compared to that on f_evp. This also minimizes the coffee stain effect and enriches the spot in a better way on s_evp compared to f_evp. Consequently, using SERS experimentation on our lab-built setup, concentration as low as 2.5*10⁻¹² M of rhodamine 6G molecules was detected on s_evp compared to 2.5 × 10⁻¹⁰ M on f_evp. The proposed s_evp SERS substrate is much easier to fabricate and easy to use compared to super-hydrophobic SERS substrates.

In the present work, we report the fabrication of a surface-enhanced Raman spectroscopy (SERS) substrate on a simple and easily fabricable hydrophobic surface.

Surface Enhanced Raman Spectroscopy: Applications in Agriculture and Food Safety

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.

Facial Fabrication of Large-Scale SERS-Active Substrate Based on Self-Assembled Monolayer of Silver Nanoparticles on CTAB-Modified Silicon for Analytical Applications

Surface-enhanced Raman spectroscopy (SERS) has been proven to be a promising analytical technique with sensitivity at the single-molecule level. However, one of the key problems preventing its real-world application lies in the great challenges that are encountered in the preparation of large-scale, reproducible, and highly sensitive SERS-active substrates. In this work, a new strategy is developed to fabricate an Ag collide SERS substrate by using cetyltrimethylammonium bromide (CTAB) as a connection agent. The developed SERS substrate can be developed on a large scale and is highly efficient, and it has high-density “hot spots” that enhance the yield enormously. We employed 4-methylbenzenethiol(4-MBT) as the SERS probe due to the strong Ag–S linkage. The SERS enhancement factor (EF) was calculated to be ~2.6 × 10⁶. The efficacy of the proposed substrate is demonstrated for the detection of malachite green (MG) as an example. The limit of detection (LOD) for the MG assay is brought down to 1.0 × 10⁻¹¹ M, and the relative standard deviation (RSD) for the intensity of the main Raman vibration modes (1620, 1038 cm⁻¹) is less than 20%.

A stable and plug-and-play aluminium/titanium dioxide/metal-organic framework/silver composite sheet for sensitive Raman detection and photocatalytic removal of 4-aminothiophenol

The sensitive detection and rapid removal of 4-aminothiophenol (4-ATP, a poisonous pesticide) demand special design to potential substrates. Herein, a metal-organic framework (ZIF-8) and Ag nanoparticles were fabricated one by one on the TiO₂ coated Al sheet, and thus the Al-TiO₂-ZIF-8-Ag sheet with sandwich structure was successfully synthesized. The cost-effective Al-TiO₂-ZIF-8-Ag sheet (3.7 wt% Ag) possessed a low detection concentration of 1 × 10^-9 M towards 4-ATP, and surface-enhanced Raman scattering (SERS) analytical enhanced factor (AEF) of the Al-TiO₂-ZIF-8-Ag was 2.6 × 10⁶, which was higher than other similar substrates. Furthermore, 4-ATP can be selectively and repeatedly detected on the Al-TiO₂-ZIF-8-Ag even through it was in real samples. It indicated that the Al-TiO₂-ZIF-8-Ag was a very active and stable SERS materials for the monitoring of 4-ATP. Importantly, the substrate exhibited faster and more efficient photocatalytic activity for 4-ATP degradation. The SERS and photocatalytic mechanisms of 4-ATP on the Al-TiO₂-ZIF-8-Ag substrate were proposed. The cost-effective Al-TiO₂-ZIF-8-Ag sheet with double function is plug-and-play, and could be used in the detection and treatment of pollutants in wastewater.

Bayesian Particle Instance Segmentation for Electron Microscopy Image Quantification

Automating the analysis portion of materials characterization by electron microscopy (EM) has the potential to accelerate the process of scientific discovery. To this end, we present a Bayesian deep-learning model for semantic segmentation and localization of particle instances in EM images. These segmentations can subsequently be used to compute quantitative measures such as particle-size distributions, radial- distribution functions, average sizes, and aspect ratios of the particles in an image. Moreover, by making use of the epistemic uncertainty of our model, we obtain uncertainty estimates of its outputs and use these to filter out false-positive predictions and hence produce more accurate quantitative measures. We incorporate our method into the ImageDataExtractor package, as ImageDataExtractor 2.0, which affords a full pipeline to automatically extract particle information for large-scale data-driven materials discovery. Finally, we present and make publicly available the Electron Microscopy Particle Segmentation (EMPS) data set. This is the first human-labeled particle instance segmentation data set, consisting of 465 EM images and their corresponding semantic instance segmentation maps.

Rapid Detection Method for Pathogenic Candida Captured by Magnetic Nanoparticles and Identified Using SERS via AgNPs. Int J Nanomedicine 2021;16:941-950. [PMID: 33603361 PMCID: PMC7884937 DOI: 10.2147/ijn.s285339]

Purpose

Candidemia infection is common in the clinic and has a high mortality rate. Candida albicans, Candida tropicalis, and Candida krusei are very important and common pathogenic species. Candida is difficult to isolate from clinical samples and culture, and immunological detection cannot distinguish these related strains. Furthermore, Candida has a complex cell wall, which causes difficulties in the extraction of DNA for nucleic acid detection. The purpose of this study was to establish a protocol for the direct identification of Candida from serum.

Materials and Methods

We synthesized Fe₃O₄@PEI (where PEI stands for polyethylenimine) magnetic nanoparticles to capture Candida and prepared positively charged silver nanoparticles (AgNPs⁺) as the substrate for surface-enhanced Raman scattering (SERS). Candida was directly identified from serum by SERS detection.

Results

Orthogonal partial least squares discriminant analysis (OPLS-DA) was used as the multivariate analysis tool. Principal component analysis confirmed that this method can clearly distinguish common Candida. After 10-fold cross-validation, the accuracy of training data in this model was 100% and the accuracy of test data was 99.8%, indicating that the model has good classification ability.

Conclusion

The detection could be completed within 40 minutes using Fe₃O₄@PEI and AgNPs⁺ prepared in advance. This is the first time that Fe₃O₄@PEI was used in the detection of Candida by SERS. We report the first rapid method to identify fungi directly from serum without breaking the cell wall to extract DNA from the fungi.

Nanostructured Raman substrates for the sensitive detection of submicrometer-sized plastic pollutants in water

We prepared novel Raman substrates for the sensitive detection of submicron-sized plastic spheres in water. Anisotropic nanostar dimer-embedded nanopore substrates were prepared for the efficient identification of submicron-sized plastic spheres by providing internal hot spots of electromagnetic field enhancements at the tips of nanoparticles. Silver-coated gold nanostars (AuNSs@Ag) were inserted into anodized aluminum oxide (AAO) nanopores for enhanced microplastic (MP) detection. We found that surface-enhanced Raman scattering (SERS) substrates of AuNSs@Ag@AAO yielded stronger signals at the same weight percentages for polystyrene MP particles with diameters as small as 0.4 μm, whereas such behaviors could not be observed for larger MPs (diameters of 0.8 μm, 2.3 μm, and 4.8 μm). The detection limit of the submicrometer-sized 0.4 μm in our Raman measurements were estimated to be 0.005% (∼0.05 mg/g =50 ppm) along with a fast detection time of only a few min without any sample pretreatments. Our nano-sized dimensional matching substrates may provide a useful tool for the application of SERS substrates for submicrometer MP pollutants in water.

Nanomaterial-based multiplex optical sensors

The drive for a simultaneous analysis of multiple targets with excellent accuracy and efficiency, which is often required in both basic biomedical research and clinical applications, demands the development of multiplexed bioassays with desired throughput. With the development of nanotechnologies, innovative multiplex optical bioassays have been achieved. Nanomaterials exhibit unique physical and chemical properties such as easily tunable size, large surface-to-volume ratio, excellent catalysis and the desired signal transduction mechanism, which makes them excellent candidates for the fabrication of novel optical nanoprobes. This mini review summarizes nanomaterial-based optical multiplex sensors from the last 5 years. Specific optical techniques covered in this review are fluorescence, surface-enhanced Raman scattering (SERS), localized surface plasmon resonance (LSPR), chemiluminescence (CL), and the multimodality with fundamentals and examples.