Rapid and fingerprinted monitoring of pesticide methyl parathion on the surface of fruits/leaves as well as in surface water enabled by gold nanorods based casting-and-sensing SERS platform

Fabrication of versatile Fe3O4/GO/Au composite nanomaterial as SERS-active substrate for detection of pesticide residue

Highly active Fe3O4/GO/Au composite nanomaterial was fabricated as a substrate of surface-enhanced Raman spectroscopy (SERS) and applied for pesticide residue detection. The three-layer multifunctional Fe3O4/GO/Au nanoparticles (NPs) were designed by facile method, with high hotspots, and were characterized by various techniques, including ultraviolet spectrophotometry (UV), X-ray diffraction (XRD), infrared absorption spectrometer (IR), and transmission electron microscopy (TEM). The performance of Fe3O4/GO/Au was evaluated by Raman spectroscopy with R6G as a probe molecule to verify its enhancement effect. It exhibited a strong Raman signal with 10-6 M of R6G. Furthermore, the presence of Fe3O4/GO/Au nanohybrid enabled the SERS-based method to detect mancozeb and showed an excellent linear relationship in the range of 0.25-25 ppm, with a low limit of detection (0.077 ppm), satisfactory EF, stability, and repeatability. In addition, the mechanism of SERS enhancement with electromagnetic mechanism (EM) and chemical mechanism (CM) was discussed in detail. Therefore, the proposed SERS approach holds promise as an auxiliary technique for screening contaminated agricultural products, environmental sample, and food in the future.

Synergistic enhancement mediated sensitive SERS-based immunoassay of PSA using versatile PDMS@AgNPs@ZIF-67 biomimetic substrates

Among various biomimetic polymer materials, polydimethylsiloxane (PDMS) stands out as an ideal matrix for surface-enhanced Raman scattering (SERS) due to its unique intrinsic Raman signal and tenacity. In order to realize the precise detection of prostate-specific antigen (PSA), we proposed a sandwich-type SERS-active immunostructure composed of PDMS@silver nanoparticles (Ag NPs)@ZIF-67 biomimetic film as the immunosubstrate and gold nanorods (Au NRs) as immunoprobes. Due to the synergistic effect of electromagnetic enhancement facilitated by biomimetic surfaces and chemical enhancement achieved by ZIF-67, this structure enabled an ultrasensitive and selective detection of PSA across a broad range from 10-3 to 10-9 mg/mL. The achieved limit of detection was as low as 3.0 × 10-10 mg/mL. Particularly, the intrinsic Raman signal of PDMS matrix at 2905 cm-1 was employed as a potential internal standard (IS) in the detection, achieving a high coefficient of determination (R2) value of 0.996. This multifunctional SERS substrate-mediated immunoassay holds vast potential for early diagnosis of prostate cancer, offering promising prospects for clinical applications.

Recent developments and applications of surface enhanced Raman scattering spectroscopy in safety detection of fruits and vegetables

This article reviewed the latest research progress of Surface-enhanced Raman Spectroscopy (SERS) in the security detection of fruits and vegetables in recent years, especially in three aspects: pesticide residues, microbial toxin contamination and harmful microorganism infection. The binding mechanism and application potential of SERS detection materials (including universal type and special type) and carrier materials (namely rigid and flexible materials) were discussed. Finally, the application prospect of SERS in fruit and vegetable safety detection was explored, and the problems to be solved and development trends were put forward. The poor stability and reproducibility of SERS substrates make it difficult for practical applications. It is necessary to continuously optimize SERS substrates and develop small and portable Raman spectroscopy analyzers. In the future, SERS technology is expected to play an important role in human health, food safety and economy.

Silver decahedral nanoparticles with uniform and adjustable sizes for surface-enhanced Raman scattering-based thiram residue detection

Surface-enhanced Raman scattering (SERS) has been widely used as a sensitive molecular spectroscopy technology in food safety detection. Precise morphology control of plasmonic nanoparticles for high sensitivity and high uniformity SERS substrates remains challenging. Herein, silver decahedral nanoparticles (AgDeNPs) with uniform and adjustable sizes were synthesized by a photochemical seed-mediated method and utilized as SERS substrates for pesticide residue detection. The SERS sensitivity was demonstrated by using 4-mercaptobenzoic acid (4-MBA) as a typical model molecule, and the limit of detection (LOD) reached 1.0 × 10-13 M. The pesticide residue detection of thiram in aqueous solution and on fruit peels was successfully realized; the LODs were 1.0 × 10-11 M and 0.96 ng cm-2, respectively, and SERS repeatability was also proved. Overall, size-tunable AgDeNPs show attractive SERS performances and are expected to hold potential application in sensitive food and environmental safety detection.

Convenient self-assembled PDADMAC/PSS/Au@Ag NRs filter paper for swift SERS evaluate of non-systemic pesticides on fruit and vegetable surfaces

The goal of food safety supervision is to directly identify the pesticide residues on the surface of fruits and vegetables. This study proposed to develop a facile, non-destructive, and sensitive method based on surface-enhanced Raman scattering (SERS) to detect non-systemic pesticides on the surface of fruits and vegetables. The composite material was prepared by loading CTAB guided Au@Ag NRs with positive charge onto filter paper which was modified with PDADMAC(+) and PSS(-) using electrostatic adsorption. Au@Ag NRs with bimetallic synergies were effectively adsorbed in the fiber grid to generate 3D SERS hotspots within a few microns of depth. The results showed that the 3D composite flexible substrate had a high SERS activity, great repeatability, and sensitivity when the method was utilized to detect 4-MBA, methyl-parathion, thiram and chlorpyrifos. Three kinds of non-systemic pesticides on the peel could be detected directly and quickly owing to the arbitrary bending of the substrate, demonstrating the efficiency of the SERS "paste-reading" method. The acquired findings demonstrated that PDADMAC/PSS/Au@Ag NRs composite filter paper had the potential to provide rapid feedback for in-situ analysis of pesticide residues on the surface of fruit and vegetable.

Sn/MoC@NC hollow nanospheres as Schottky catalyst for highly sensitive electrochemical detection of methyl parathion

Developing electrode materials with excellent electrocatalytic properties for detecting pesticide residues plays a vital role in the safety of agricultural products and environmental applications. Herein, we designed a new electrochemical sensor on the basis of N-doped carbon hollow nanospheres modified with Sn/MoC Schottky junction (Sn/MoC@NC) for methyl parathion (MP) detection. The Sn/MoC@NC was prepared by self-assembled polymerization-anchoring strategy and high-temperature carbonization design. Sn/MoC Schottky junction and hollow nanosphere structure endow Sn/MoC@NC with a larger surface area, more active sites, and faster electron transfer, which is beneficial to enhancing its electrocatalytic performance. The structural characterizations and physicochemical properties of Sn/MoC@NC were explored through various microscopy, spectroscopic and electrochemical techniques. The experimental results confirmed that the calibration curve for current and MP concentration (0.05-10 μg/mL) was available under optimized conditions, and the sensitivity and detection limit were respectively determined to be 9.02 μA μM¹ cm² and 8.9 ng/mL. Furthermore, the constructed sensor displayed excellent selectivity, repeatability, and stability, which qualified it for use in detecting MP in grapes and tap water with satisfactory recovery. This work may provide some interesting prospects for constructing high-performance electrocatalysts for MP detection.

Alternative methods of monitoring emerging contaminants in water: a review

Anthropogenic activities have steadily increased the release of emerging contaminants (ECs) in aquatic bodies, and these ECs may have adverse effects on humans even at their trace (μg L^-1) levels. Their occurrence in wastewater systems is more common, and the current wastewater treatment facilities are inefficient in eliminating many of such persistent ECs. "Gold standard" techniques such as chromatography, mass spectrometry, and other high-resolution mass spectrometers are used for the quantification of ECs of various kinds, but they all have significant limitations. This paper reviews the alternative methods for EC detection, which include voltammetry, potentiometry, amperometry, electrochemical impedance spectroscopy (EIS) based electrochemical methods, colorimetry, surface-enhanced Raman spectroscopy (SERS), fluorescence probes, and fluorescence spectroscopy-based optical techniques. These alternative techniques have several advantages over conventional techniques, including low sample volume, excludes solid phase extraction procedure, high sensitivity, selectivity, portability, reproducibility, rapidity, low cost, and the ability to monitor ECs in real time. This review summarises each of the alternative methods for detecting ECs in water samples and their respective limits of detection (LODs). The sensitivity of each technique varied depending on the type of EC measured, type of electrochemical probe and electrode, substrates, type of nanoparticle (NP), the physicochemical parameters of water samples tested, and more. Nevertheless, this paper also focuses on some of the current challenges encountered by these alternative methods in monitoring ECs.

Au Nanorods on Carbon-Based Nanomaterials as Nanohybrid Substrates for High-Efficiency Dynamic Surface-Enhanced Raman Scattering

Gold nanorods (AuNRs) with different aspect ratios were prepared by the seed-mediated growth method and combined with three carbon-based nanomaterials of multiple dimensions (i.e., zero-dimensional (0D) carbon black (CB), one-dimensional (1D) carbon nanotubes (CNTs), and two-dimensional (2D) graphene oxide (GO)). The AuNR/carbon-based nanomaterial hybrids were utilized in dynamic surface-enhanced Raman scattering (D-SERS). First, cetyltrimethylammonium bromide (CTAB) was used to stabilize and coat the AuNRs, enabling them to be dispersed in water and conferring a positive charge to the surface. AuNR/carbon-based nanomaterial hybrids were then formed via electrostatic attraction with the negatively charged carbon-based nanomaterials. Subsequently, the AuNR/carbon-based nanomaterial hybrids were utilized as large-area and highly sensitive Raman spectroscopy substrates. The AuNR/GO hybrids afforded the best signal enhancement because the thickness of GO was less than 5 nm, which enabled the AuNRs adsorbed on GO to produce a good three-dimensional hotspot effect. The enhancement factor (EF) of the AuNR/GO hybrids for the dye molecule Rhodamine 6G (R6G) reached 1 × 10⁷, where the limit of detection (LOD) was 10^-8 M. The hybrids were further applied in D-SERS (detecting samples transitioning from the wet state to the dry state). During solvent evaporation, the system spontaneously formed many hotspots, which greatly enhanced the SERS signal. The final experimental results demonstrated that the AuNR/GO hybrids afforded the best D-SERS signal enhancement. The EF value for R6G reached 1.1 × 10⁸ after 27 min, with a limit of detection of 10^-9 M at 27 min. Therefore, the AuNR/GO nanohybrids have extremely high sensitivity as molecular sensing elements for SERS and are also very suitable for the rapid detection of single molecules in water quality and environmental management.

Hydrophobic plasmonic silver membrane as SERS-active catcher for rapid and ultrasensitive Cu(II) detection

The rapid and selective identification of heavy metal ions is crucial for environmental water safety. In this study, a novel surface-enhanced Raman scattering (SERS)-active catcher was designed for Cu(II) detection using a hydrophobic hydroxyoxime-mediated plasmonic silver membrane (HOX@Ag-PVDF). Uniformly dispersed Ag nanoparticles (ca. 80 nm) and hydroxyoxime molecules were synchronously decorated on the skeleton of the polyvinylidene fluoride membrane via an in situ interfacial assembly strategy. HOX@Ag-PVDF shows excellent SERS activity (EF = 2.5 × 10⁷), high reproducibility (~8% RSD), and long-term stability (50 days) for detecting 4-nitrothiophenol (4-NTP). Moreover, HOX@Ag-PVDF can serve as a new platform for rapid and dry-free SERS detection of Cu(II) owing to its strong affinity and surface hydrophobicity. Cu(II) ions can be rapidly captured in 5 s and selectively recognized by SERS signals without interference from other metal ions. HOX@Ag-PVDF exhibits linear SERS response signals at low concentrations ranging from 10^-6 to 10^-10 mol/L Cu(II) (R² = 0.9893) with a low detection limit (LOD) of 52.0 pmol/L. This hydrophobic plasmonic membrane, with its simple sampling and rapid SERS response characteristics, provides ultrasensitive recognition and heavy metal detection for practical applications.

Surfactant stabilized gold nanomaterials for environmental sensing applications - A review

Surfactant stabilized Gold (Au) nanomaterials (NMs) have been documented extensively in recent years for numerous sensing applications in the academic literature. Despite the crucial role these surfactants play in the sensing applications, the comprehensive reviews that highlights the fundamentals associated with these assemblies and impact of these surfactants on the properties and sensing mechanisms are still quite scare. This review is an attempt in organizing the vast literature associated with this domain by providing critical insights into the fundamentals, preparation methodologies and sensing mechanisms of these surfactant stabilized Au NMs. For the simplification, the surfactants are divided into the typical and advanced surfactants and the Au NMs are classified into Au nanoparticles (NPs) and Au nanoclusters (NCs) depending upon the complexity in structure and size of the NMs respectively. The preparative methodologies are also elaborated for enhancing the understanding of the readers regarding such assemblies. The case studies regarding surfactant stabilized Au NMs were further divided into colorimetric sensors, surface plasmonic resonance (SPR) based sensors, luminescence-based sensors, and electrochemical/electrical sensors depending upon the property utilized by the sensor for the sensing of an analyte. Future perspectives are also discussed in detail for the researchers looking for further progress in that particular research domain.

Fabrication of paper-based SERS substrate using a simple vacuum filtration system for pesticides detection

Herein, we describe a simple and cost-effective fabrication of a paper-based SERS substrate by coating poly(diallyldimethylammonium chloride) (PDADMAC) and gold nanostars (AuNSs) on the filter paper using a vacuum filtration system. The paper-based SERS substrates were fabricated and ready to be used within an hour without any complicated equipment or processes. The cationic polymer, PDADAMAC, was pretreated on the filter paper to improve the absorbability of negatively charged AuNSs through electrostatic interaction. The PDADMAC/AuNS paper significantly intensified the SERS signal of 4-mercaptobenzoic acid (4-MBA) compared to that of pure AuNS-coated paper due to the high density of AuNSs absorbed on the SERS substrate. The PDADMAC/AuNS paper substrate provided a SERS enhancement factor (EF) of 1.08 × 10⁷ with a low detection limit of 1 nM 4-MBA. The substrate shows excellent spot-to-spot reproducibility with a relative standard deviation (RSD) of 5.03%, and substrate-to-substrate reproducibility with an RSD of 3.20% for the Raman shift at 1080 cm^-1. The paper substrate was then applied for the rapid detection of pesticides with a low detection limit of 0.51 μM (0.13 ppm) for paraquat, and 0.38 μM (0.09 ppm) for thiram, using a handheld Raman spectrometer. The development of this simple and cost-effective paper-based SERS substrate, and its applications for on-site monitoring of pesticides, could be beneficial for food security and environmental safety.

Emergence of Responsive Surface-Enhanced Raman Scattering Probes for Imaging Tumor-Associated Metabolites

As a core hallmark of cancer, metabolic reprogramming alters the metabolic networks of cancer cells to meet their insatiable appetite for energy and nutrient. Tumor-associated metabolites, the products of metabolic reprogramming, are valuable in evaluating tumor occurrence and progress timely and accurately because their concentration variations usually happen earlier than the aberrances demonstrated in tissue structure and function. As an optical spectroscopic technique, surface-enhanced Raman scattering (SERS) offers advantages in imaging tumor-associated metabolites, including ultrahigh sensitivity, high specificity, multiplexing capacity, and uncompromised signal intensity. This review first highlights recent advances in the development of stimuli-responsive SERS probes. Then the mechanisms leading to the responsive SERS signal triggered by tumor metabolites are summarized. Furthermore, biomedical applications of these responsive SERS probes, such as the image-guided tumor surgery and liquid biopsy examination for tumor molecular typing, are summarized. Finally, the challenges and prospects of the responsive SERS probes for clinical translation are also discussed.

A cyclodextrin-decorated plasmonic gold nanosatellite substrate for selective detection of bipyridylium pesticides

A cyclodextrin-decorated gold nanosatellite (AuNSL) substrate was developed as a surface-enhanced Raman scattering sensor for the selective sensing of bipyridylium pesticides such as paraquat (PQ), diquat (DQ), and difenzoquat (DIF). The AuNSL structure was fabricated via vacuum deposition of gold nanoparticles (AuNPs) on a gold nanopillar substrate, and a large density of hot-spots was formed for Raman signal enhancement. Thiolated β-cyclodextrin (SH-CD) was surface-modified on the AuNSL as a chemical receptor. The detection limit of PQ, DQ, and DIF on the SH-CD-coated AuNSL (CD-AuNSL) was 0.05 ppm for each, and showed linear correlation in a concentration range of 10 ppm-0.05 ppm. Then, selective bipyridylium pesticide detection was performed by comparing the Raman intensity of each pesticide with and without the washing step. After the washing step, 90% of the PQ, DQ, and DIF Raman signals were maintained on the CD-AuNSL substrate with a uniform selectivity in a mapping area of 200 μm × 200 μm. Furthermore, selective pesticide detection was performed using a ground-apple solution without pretreatment. Raman signals were clearly observed after the washing step and they showed a limit of detection down to a concentration of 0.05 ppm for each pesticide. Principal component analysis (PCA) of the binary and ternary mixtures of PQ, DQ, and DIF showed that each component could be easily identified via the typical Raman fingerprint analysis. The developed CD-AuNSL is expected to be applied for various chemical sensors, especially for pyridine-containing toxic substances in the environment and metabolite biomarkers in biofluids.

Silver-nanoparticle-grafted silicon nanocones for reproducible Raman detection of trace contaminants in complex liquid environments

Super-hydrophobic delivery (SHD) is an efficient approach to enrich trace analytes into hot spot regions for ultrasensitive surface-enhanced Raman scattering (SERS) detection. In this article, we propose an efficient and simple method to prepare a highly-uniform SHD-SERS platform of high performance in trace detection, named as "silver-nanoparticle-grafted silicon nanocones" (termed AgNPs/SiNC) platform. It is fabricated via droplet-confined electroless deposition on the super-hydrophobic SiNC array. The AgNPs/SiNC platform allows trace analytes enriched into hot spots formed by AgNPs, leading to an excellent reproducibility and sensitivity. The relative standard deviation (RSD) for detecting R6G (10^-7 M) is down to 4.70% and the lowest detection concentration for R6G is 10^-14 M. Moreover, various contaminants in complex liquid environments, such as, crystal violet (10^-9 M) in lake water, melamine (10^-7 M) in liquid milk and methyl parathion (10^-7 M) in tap water, can be detected using the SERS platform. This result demonstrates the great potential of the AgNPs/SiNC platform in the fields of food safety and environmental monitoring.

Towards a point-of-care SERS sensor for biomedical and agri-food analysis applications: a review of recent advancements

The growing demand for reliable and robust methodology in bio-chemical sensing calls for the continuous advancement of sensor technologies. Over the last two decades, surface-enhanced Raman spectroscopy (SERS) has emerged as one of the most promising analytical techniques for sensitive and trace analysis or detection in biomedical and agri-food applications. SERS overcomes the inherent sensitivity limitation associated with Raman spectroscopy, which provides vibrational "fingerprint" spectra of molecules that makes it unique and versatile among other spectroscopy techniques. This paper comprehensively reviews the recent advancements of SERS for biomedical, food and agricultural applications over the last 6 years, and we envision that, in the near future, some of these platforms have the potential to be translated as a point-of-care and rapid sensor for real-life end-user applications. The merits and limitations of various SERS sensor designs are analysed and discussed based on critical features such as sensitivity, specificity, usability, repeatability and reproducibility. We conclude by highlighting the opportunities and challenges in the field while stressing the technological gaps to be addressed in realizing commercially viable point-of-care SERS sensors for practical biomedical and agri-food technological applications.

Controlling silver morphology on a cramped optical fiber facet via a PVP-assisted silver mirror reaction for SERS fiber probe fabrication

Controlling the morphology of silver nanoparticles on a cramped and curved optical fiber facet is urgently needed to obtain SERS optical fiber probes with high performance.

The fabrication of paper separation channel based SERS substrate and its recyclable separation and detection of pesticides

In this article, a modified paper separation channel SERS substrate was fabricated by a pen writing method for the simultaneous separation and detection of thiuram and dimethoate. The hydrophilic channel was fabricated with both sides of hydrophobic barrier by the Alkylketene dimer (AKD) modified paper substrate, of which the flow dynamic was well conformed to the Lucas-Washburn model and could be used to separate pesticides effectively. As modified by Ag nanoparticles (AgNPs) and ZnO nanoparticles (ZnONPs), the hydrophilic channel exhibited high recyclable SERS detection activity and stability. The separation and detection performance with different target proportion, channel width and sample volume were studied in detail, which have significant influence on the diffusion process. Additionally, the Raman detects intensity on the substrate also showed linear relationship from 100 to 1000 μg/L. The calculated limit of detects (LODs) under optimal experimental conditions were 54.57 and 19.16 μg/L for dimethoate and thiuram, respectively. Due to the loading of ZnONPs, the substrate could be used repeatably with good stability. The convenient preparation, effective separation and repeatability make this paper based separation channel SERS substrate have great potential application on the fast separation and simultaneous detection of various pesticides in complex field.

A novel SERS selective detection sensor for trace trinitrotoluene based on meisenheimer complex of monoethanolamine molecule

Trinitrotoluene (TNT) is a primary component in chemical explosives, making them a common focus in public safety detection. However, it is very difficult to achieve selective and sensitive detection of the TNT molecule in practical application. In the present study, a simple surface enhanced Raman scattering (SERS) sensing based on monoethanolamine (MEA) - modified gold nanoparticles (Au NPs) was expanded for high selectivity and sensitive detecting of TNT in an envelope, luggage, lake water, and clothing through a quickly sampling and detection process. The monoethanolamine molecule based on Meisenheimer complex lights up ultra-high Raman scattering of a nonresonant molecule on the superficial coat of gold nanoparticles. Using this detection sensor, a molecular bridge can be established to selectively detect trinitrotoluene with a detection limit of 21.47 pM. We were able to rapidly identification trinitrotoluene molecule with a powerful selective over the familiar interfering substances nitrophenol, picric acid, 2,4-dinitrophenol, and 2,4-dinitrotoluene. The outcome in this work supply an efficient solution to the test of trinitrotoluene and to establishing a SERS sensor analytical strategy. The studies have demonstrated that the MEA-Au NPs based SERS sensing can be potentially used in field detection the trace amount of chemical explosives for public security.

Flexible paper-based SERS substrate strategy for rapid detection of methyl parathion on the surface of fruit

Herein, we reported a simple, flexible and sensitive surface-enhanced Raman scattering (SERS) substrate to detect methyl parathion residues in real life. The substrate was fabricated by filter paper and gold nanoparticles (Au NPs) with excellent reproducibility and stability. First, Au NPs were synthesized by the seed mediated growth method and assembled to the filter paper through immersion. The Raman probe molecule 4-MBA was used to evaluate performance of the substrate for an optimized signal using a portable Raman spectrometer coupled with 785 nm laser. Then, the paper-based substrate was applied to detect methyl parathion standard solution whose detection limit was down to 0.011 μg/cm², and the linear range was between 0.018 μg/cm² and 0.354 μg/cm². Afterwards, actual sample (apple) spiked with methyl parathion was taken to verify the practicality of the substrate by a simple way of "press-peel off". The recovery rate was ranged from 94.09% to 98.72%, indicating that this method is reliable in actual sample detection without complicated pretreatment steps. This work demonstrates that the flexible paper-based substrate combined with portable Raman instruments can be potentially applied to on-site detection of hazardous substances in the field of food safety.

Real-time monitoring of multicomponent reactive dye adsorption on cotton fabrics by Raman spectroscopy

Accurate real-time determination of each dye in combination dyeing is critical to the control of dyeing process, which plays an important role in upgrading the dyeing techniques of textile. In this work, Raman spectroscopy was applied to dyeing baths containing multiple dye species of varying structures to quantitatively monitor the dyeing process of each individual dye. Quantitative models were successfully established by partial least squares (PLS) for all combinations of the nine commonly used reactive dyes studied. The correlation coefficients were greater than 0.99, the root mean squared errors of calibration (RMSEC) were less than 0.2650 and the root mean squared errors of prediction (RMSEP) were less than 0.1340, even for the three-component mixture of Reactive Red 239 (RR239), Reactive Yellow 176 (RY176) and Reactive Blue 194 (RB194), which are similar in structures. The model was shown to be valid in the presence of added electrolytes (sodium sulfates). Real-time adsorption monitoring based on the model revealed that the dyes interacted with one another and competed for active sites. The adsorption kinetics obtained by Raman analysis shed light on dye compatibility and could be used to guide the design of dyeing recipe and dyeing process for optimum color reproduction. In addition, in situ monitoring by Raman spectroscopy maybe integrated with real-time on line control of dyeing parameters for fully automated production of dyed fabrics.

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

Surface-enhanced Raman spectroscopy (SERS) technology has been reported to be able to quickly and non-destructively identify target analytes. SERS substrate with high sensitivity and selectivity gave SERS technology a broad application prospect. This contribution aims to provide a detailed and systematic review of the current state of research on SERS-based explosive sensors, with particular attention to current research advances. This review mainly focuses on the strategies for improving SERS performance and the SERS substrates with different dimensions including zero-dimensional (0D) nanocolloids, one-dimensional (1D) nanowires and nanorods, two-dimensional (2D) arrays, and three-dimensional (3D) networks. The effects of elemental composition, the shape and size of metal nanoparticles, hot-spot structure and surface modification on the performance of explosive detection are also reviewed. In addition, the future development tendency and application of SERS-based explosive sensors are prospected.

Recent Progress in Optical Sensors for Biomedical Diagnostics

In recent years, several types of optical sensors have been probed for their aptitude in healthcare biosensing, making their applications in biomedical diagnostics a rapidly evolving subject. Optical sensors show versatility amongst different receptor types and even permit the integration of different detection mechanisms. Such conjugated sensing platforms facilitate the exploitation of their neoteric synergistic characteristics for sensor fabrication. This paper covers nearly 250 research articles since 2016 representing the emerging interest in rapid, reproducible and ultrasensitive assays in clinical analysis. Therefore, we present an elaborate review of biomedical diagnostics with the help of optical sensors working on varied principles such as surface plasmon resonance, localised surface plasmon resonance, evanescent wave fluorescence, bioluminescence and several others. These sensors are capable of investigating toxins, proteins, pathogens, disease biomarkers and whole cells in varied sensing media ranging from water to buffer to more complex environments such as serum, blood or urine. Hence, the recent trends discussed in this review hold enormous potential for the widespread use of optical sensors in early-stage disease prediction and point-of-care testing devices.

Sensors Applied for the Detection of Pesticides and Heavy Metals in Freshwaters

Water is essential for every life living on the planet. However, we are facing a more serious situation such as water pollution since the industrial revolution. Fortunately, many efforts have been done to alleviate/restore water quality in freshwaters. Numerous sensors have been developed to monitor the dynamic change of water quality for ecological, early warning, and protection reasons. In the present review, we briefly introduced the pollution status of two major pollutants, i.e., pesticides and heavy metals, in freshwaters worldwide. Then, we collected data on the sensors applied to detect the two categories of pollutants in freshwaters. Special focuses were given on the sensitivity of sensors indicated by the limit of detection (LOD), sensor types, and applied waterbodies. Our results showed that most of the sensors can be applied for stream and river water. The average LOD was72.53±12.69 ng/ml (n=180) for all pesticides, which is significantly higher than that for heavy metals (65.36±47.51 ng/ml,n=117). However, the LODs of a considerable part of pesticides and heavy metal sensors were higher than the criterion maximum concentration for aquatic life or the maximum contaminant limit concentration for drinking water. For pesticide sensors, the average LODs did not differ among insecticides (63.83±17.42 ng/ml,n=87), herbicides (98.06±23.39 ng/ml,n=71), and fungicides (24.60±14.41 ng/ml,n=22). The LODs that differed among sensor types with biosensors had the highest sensitivity, while electrochemical optical and biooptical sensors showed the lowest sensitivity. The sensitivity of heavy metal sensors varied among heavy metals and sensor types. Most of the sensors were targeted on lead, cadmium, mercury, and copper using electrochemical methods. These results imply that future development of pesticides and heavy metal sensors should (1) enhance the sensitivity to meet the requirements for the protection of aquatic ecosystems and human health and (2) cover more diverse pesticides and heavy metals especially those toxic pollutants that are widely used and frequently been detected in freshwaters (e.g., glyphosate, fungicides, zinc, chromium, and arsenic).

Plasmon-coupled 3D porous hotspot architecture for super-sensitive quantitative SERS sensing of toxic substances on real sample surfaces

This paper reports a facile, fast, and cost-effective method for the synthesis of three-dimensional (3D) porous AgNPs/Cu composites as SERS substrates for the super-sensitive and quantitative detection of food organic contaminations. Due to the 3D porous hotspot architecture and the strong plasmonic coupling between Ag and Cu, the porous AgNPs/Cu substrate achieves ultrasensitive detection of multiple analytes as low as 10^-11 M (crystal violet, CV), 10^-9 M (malachite green, MG), 10^-11 M (acephate), and 10^-9 M (thiram) even with a portable Raman device. Moreover, this 3D solid substrate has good signal uniformity (RSD < 11%) and superior stability (<14% signal loss), allowing for practical SERS detections. Importantly, by simply wiping the real sample surface using the substrate, it successfully detects CV and MG residues on crayfish, and the limit of detection (LOD) of CV and MG is determined to be 1.14 × 10^-9 M and 0.94 × 10^-7 M, respectively. Further, the substrate can also be applied to detect acephate on eggplant with a LOD of 1.41 × 10^-9 M and thiram on an apple surface with a LOD of 1.04 × 10^-7 M. Note that all these SERS detections on real samples have a broad dynamic concentration range and a good linear dependence. As a "proof of concept", multi-component detection on a real sample has also been demonstrated. This 3D solid substrate possesses excellent detection sensitivity, diversity, and accuracy, which allows rapid and reliable determination of toxic substances in foods.