Quantitative SERS detection of low-concentration aromatic polychlorinated biphenyl-77 and 2,4,6-trinitrotoluene

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.

Sandwich-like CuNPs@AgNPs@PSB SERS substrates for sensitive detection of R6G and Forchlorfenuron

The development of a highly sensitive, synthetically simple and economical SERS substrate is technically very important. A fast, economical, sensitive and reproducible CuNPs@AgNPs@ Porous silicon Bragg reflector (PSB) SERS substrate was prepared by electrochemical etching and in situ reduction method. The developed CuNPs@AgNPs@PSB has a large specific surface area and abundant "hot spot" region, which makes the SERS performance excellent. Meanwhile, the successful synthesis of CuNPs@AgNPs can not only modulate the plasmon resonance properties of nanoparticles, but also effectively prolong the time stability of Cu nanoparticles. The basic performance of the substrate was evaluated using rhodamine 6G (R6G). (Detection limit reached 10-15 M, R2 = 0.9882, RSD = 5.3 %) The detection limit of Forchlorfenuron was 10 μg/L. The standard curve with a regression coefficient of 0.979 was established in the low concentration range of 10 μg/L -100 μg/L. This indicates that the prepared substrates can accomplish the detection of pesticide residues in the low concentration range. The prepared high-performance and high-sensitivity SERS substrate have a very promising application in detection technology.

SERS determination and multivariate classification of antibiotics in chicken meat using gold nanoparticle-decorated electrospun PVA nanofibers

The fabrication of SERS substrate by gold nanoparticle-decorated polyvinyl alcohol electrospun nanofibers which has been used to detect trace sensing of two widely used poultry antibiotics doxycycline hydrochloride and enrofloxacin is demonstrated. The performance of the backscattered Raman signals from the proposed SERS substrate has been initially evaluated with two standard Raman active compounds namely malachite green and rhodamine-6G. The limit of detection of the proposed substrate is estimated to be 7.32 nM. Following this, the usability of the proposed SERS substrate has been demonstrated through the detection of the aforementioned antibiotics in chicken meat samples. The presence of antibiotics in chicken meat sample has been validated with the standard analytical tool of liquid chromatography-mass spectrometry and the results were compared with the proposed sensing technique. Further, principal component analysis has been performed to classify the antibiotics that are present in the field-collected meat samples.

Ultra-rapid and highly efficient enrichment of organic pollutants via magnetic mesoporous nanosponge for ultrasensitive nanosensors

Currently, owing to the single-molecule-level sensitivity and highly informative spectroscopic characteristics, surface-enhanced Raman scattering (SERS) is regarded as the most direct and effective detection technique. However, SERS still faces several challenges in its practical applications, such as the complex matrix interferences, and low sensitivity to the molecules of intrinsic small cross-sections or weak affinity to the surface of metals. Here, we show an enrichment-typed sensing strategy with both excellent selectivity and ultrahigh detection sensitivity based on a powerful porous composite material, called mesoporous nanosponge. The nanosponge consists of porous β-cyclodextrin polymers immobilized with magnetic NPs, demonstrating remarkable capability of effective and fast removal of organic micropollutants, e.g., ~90% removal efficiency within ~1 min, and an enrichment factor up to ~10³. By means of this current enrichment strategy, the limit of detection for typical organic pollutants can be significantly improved by 2~3 orders of magnitude. Consequently, the current enrichment strategy is proved to be applicable in a variety of fields for portable and fast detection, such as Raman and fluorescent sensing.

The untapped potential of magnetic nanoparticles for forensic investigations: A comprehensive review

With a growing interest in precise and sensitive diagnosis for criminal investigations, nanoparticles (NPs) have intrigued scientific minds working in the field of forensic science due to their exceptional properties. Magnetic nanoparticles (MNPs) have emerged as a powerful tool for improving forensic analysis due to their super magnetic behavior combined with smaller dimensions. MNP-based applications can benefit criminologists to solve criminal mysteries with greater precision and pace. This review highlights the different types of MNP-based applications and their developmental and implicational aspects of forensic science. It also renders insight into the future prospects of a splendid blend of nanotechnology and forensic science, leading to a better scientific analysis.

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.

Nitrogen-doped carbon quantum dots conjugated isoreticular metal-organic framework-3 particles based luminescent probe for selective sensing of trinitrotoluene explosive

Amine group-containing isoreticular metal-organic framework (IRMOF-3) particles are utilized for the first time as a trinitrotoluene (TNT) sensing material. IRMOF-3 particles are synthesized using zinc nitrate as a metal precursor and 2-amino-1,4-benzenedicarboxylic acid as a linker. The nitrogen-doped carbon quantum dots (NCQDs) are synthesized from citric acid and ethylenediamine as carbon and nitrogen precursor, respectively. The NCQDs are conjugated with IRMOF-3 particles as IRMOF-3/NCQDs. The TEM micrograph revealed the average size of IRMOF-3 particles to be 363.66 nm. The photoluminescence emission intensity of IRMOF-3 particles at λ_em 430 nm is highly increased in the presence of NCQDs (λ_ex 330 nm). Both the as-synthesized IRMOF-3 and IRMOF-3/NCQD particles are explored for TNT detection to compare the effect of NCQDs on the IRMOF-3 particle surface. Lower limit of detection (7.5 × 10^-8 M) and higher Stern-Volmer constant (4.46 × 10⁶ M^-1) are achieved by IRMOF-3/NCQD particles. The association constant also increased from 5.3 × 10⁴ to 2.78 × 10⁶ M^-1 after the conjugation of IRMOF-3 particles with NCQDs. Moreover, enhanced selectivity for TNT over trinitrophenol is achieved using the IRMOF-3/NCQD particles. Graphical Abstract.

Synthesis and SERS application of gold and iron oxide functionalized bacterial cellulose nanocrystals (Au@Fe3O4@BCNCs)

Bacterial cellulose nanocrystals (BCNCs) are biocompatible cellulose nanomaterials that can host guest nanoparticles to form hybrid nanocomposites with a wide range of applications. Herein, we report the synthesis of a hybrid nanocomposite that consists of plasmonic gold nanoparticles (AuNPs) and superparamagnetic iron oxide (Fe3O4) nanoparticles supported on BCNCs. As a proof of concept, the hybrid nanocomposites were employed to isolate and detect malachite green isothiocyanate (MGITC) via magnetic separation and surface-enhanced Raman scattering (SERS). Different initial gold precursor (Au3+) concentrations altered the size and morphology of the AuNPs formed on the nanocomposites. The use of 5 and 10 mM Au3+ led to a heterogenous mix of spherical and nanoplate AuNPs with increased SERS enhancements, as compared to the more uniform AuNPs formed using 1 mM Au3+. Rapid and sensitive detection of MGITC at concentrations as low as 10-10 M was achieved. The SERS intensity of the normalized Raman peak at 1175 cm-1 exhibited a log-linear relationship for MGITC concentrations between 2 × 10-10 and 2 × 10-5 M for Au@Fe3O4@BCNCs. These results suggest the potential of these hybrid nanocomposites for application in a broad range of analyte detection strategies.

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.

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.

Preparation of the plasmonic Ag/AgBr/ZnO film substrate for reusable SERS detection: Implication to the Z-scheme photocatalytic mechanism

In this work, a novel Ag/AgBr/ZnO SERS substrate was prepared by calcinating spin-coated zinc acetate on glass slides in the presence of ethanolamine (EA), followed by the process of impregnating-precipitation-photoreduction treatment. The SERS performances of Ag/AgBr/ZnO substrates were evaluated using aqueous crystal violet (CV) and Rhodamine 6G (R6G) as target analytes. The effects of initial immersion precursor concentration and irradiation time on the SERS performance were systematically studied. The as-prepared SERS substrate exhibited good chemical detection sensitivity, reproducibility and reusability. The optimal Ag/AgBr/ZnO (10 mM-30 min) substrates were capable of detecting 10^-12 M CV and 10^-11 M R6G aqueous solutions. The quantitative detection by the SERS substrate was investigated by constructing a linear corresponding calibration plot. The Ag/AgBr/ZnO SERS substrate was regenerated by a simple visible light driven photocatalytic process. A plausible Z-scheme visible light photocatalytic mechanism seems to account for the Ag-ZnO-AgBr system. This SERS substrate can be separated from the reaction easily, and the results indicated that the film was reusable for eight times without significantly losing the SERS efficiency, each time accompanied by a simple photo-driven regeneration. This study reveals that the Ag/AgBr/ZnO film on glass is practically applicable as an ultra-highly sensitive SERS substrate that can be readily regenerated.

Gold Nanoparticles with Different Particle Sizes for the Quantitative Determination of Chlorpyrifos Residues in Soil by SERS

Chlorpyrifos (CPF) is widely used in the prevention and control of crop pests and diseases in agriculture. However, the irrational utilization of pesticides not only causes environmental pollution but also threatens human health. Compared with the conventional techniques for the determination of pesticides in soil, surface-enhanced Raman spectroscopy (SERS) has shown great potential in ultrasensitive and chemical analysis. Therefore, this paper reported a simple method for synthesizing gold nanoparticles (AuNPs) with different sizes used as a SERS substrate for the determination of CPF residues in soil for the first time. The results showed that there was a good linear correlation between the SERS characteristic peak intensity of CPF and particle size of the AuNPs with an R2 of 0.9973. Moreover, the prepared AuNPs performed great ultrasensitivity, reproducibility and chemical stability, and the limit of detection (LOD) of the CPF was found to be as low as 10 μg/L. Furthermore, the concentrations ranging from 0.01 to 10 mg/L were easily observed by SERS with the prepared AuNPs and the SERS intensity showed a good linear relationship with an R2 of 0.985. The determination coefficient (Rp2) reached 0.977 for CPF prediction using the partial least squares regression (PLSR) model and the LOD of CPF residues in soil was found to be as low as 0.025 mg/kg. The relative standard deviation (RSD) was less than 3.69% and the recovery ranged from 97.5 to 103.3%. In summary, this simple method for AuNPs fabrication with ultrasensitivity and reproducibility confirms that the SERS is highly promising for the determination of soil pesticide residues.

Applications of magnetic nanoparticles in surface-enhanced Raman scattering (SERS) detection of environmental pollutants

Environmental pollution, a major problem worldwide, poses considerable threat to human health and ecological environment. Efficient and reliable detection technologies, which focus on the appearance of emerging environmental and trace pollutants, are urgently needed. Surface-enhanced Raman scattering (SERS) has become an attractive analytical tool for sensing trace targets in environmental field because of its inherent molecular fingerprint specificity and high sensitivity. In this review, we focused on the recent developments in the integration of magnetic nanoparticles (MNPs) with SERS for facilitating sensitive detection of environmental pollutants. An overview and classification of different types of MNPs for SERS detection were initially provided, enabling us to categorize the huge amount of literature that was available in the interdisciplinary research field of MNPs based SERS technology. Then, the basic working principles and applications of MNPs in SERS detection were presented. Subsequently, the detection technologies integrating MNPs with SERS that eventually were used for the detection of various environmental pollutions were reviewed. Finally, the advantages of MNP-basedSERS detection technology for environmental pollutants were concluded, and the current challenges and future outlook of this technology in practical applications were highlighted. The application of the MNPs-basedSERS techniques for environmental analysis will be significantly advanced with the great progresses of the nanotechnologies, optics, and materials.

Graphene Oxide Nanoprisms for Sensitive Detection of Environmentally Important Aromatic Compounds with SERS

Recent advances in graphene-based sensors have shown that heavily oxidized (GO) and reduced graphene oxide (rGO) are attractive materials for environmental sensing due to their unique chemical and physical properties. We describe here the fabrication of nanostructured GO assemblies with Ag nanoprisms for improved detection with surface enhanced Raman scattering (SERS). Specifically, 100-μm-sized, periodic-nanoprism-array domains were fabricated on top of the GO layers by GO-assisted lithography (GOAL). The atomically thin GO underlayers are shown to attract cyclic aromatic molecules to the surface, likely via π-π stacking interactions. The close proximity of the analyte to GO and nanoprism (NP) tips effectively suppresses fluorescent background and affords a plausible tertiary enhancement of photon emissions via an electron charge transfer (CT) process. The adsorption of analyte to rGO-NP leads to the appearance and/or shift of several Raman bands, which provided a means to gain molecular insights into the graphene-enhanced scattering process. The analytical merits were characterized with model compound Rhodamine 6G, where the detection limit could reach subnanomolar concentrations. The nanoprism GO substrates also prove effective for SERS multiplex measurement of several legacy aromatic pollutants. Three tetrachlorobiphenyl isomers could be identified from a mixture using their autonomous nonoverlapping molecular fingerprints, and the substrate offers remarkable trace detection of 2,2',3,3'-tetrachlorobiphenyl (PCB-77).

A flexible transparent Ag-NC@PE film as a cut-and-paste SERS substrate for rapid in situ detection of organic pollutants

This report presents a simple and inexpensive fabrication approach to a flexible transparent composite film as a "cut-and-paste" surface-enhanced Raman scattering (SERS) substrate for in situ detection of organic pollutants. First, a self-assembled monolayer of Ag-nanocubes (Ag-NCs) is obtained at the air/water interface. Then, the Ag-NC monolayer is retrieved onto a flexible transparent polyethylene (PE) film to achieve an Ag-NC@PE composite film as a flexible SERS substrate. As the Ag-NCs in the monolayer are closely and uniformly packed on the PE film, the Ag-NC@PE composite film shows high SERS-activity with good signal homogeneity and reproducibility. Furthermore, the flexible transparent Ag-NC@PE composite film is "cut into" small pieces and directly "pasted" onto contaminated fruits for in situ SERS detection, as a result 10 nM thiram, 1 μM 4-polychlorinated biphenyl and 10 nM methyl parathion contaminants on oranges are detected, respectively. Therefore the Ag-NC@PE composite film is an inexpensive and effective SERS substrate for rapid in situ detection of organic pollutants in aqueous solutions, on fruits and other solid objects.

Highly Photoluminescent Molybdenum Oxide Quantum Dots: One-Pot Synthesis and Application in 2,4,6-Trinitrotoluene Determination

As a well-studied transition-metal semiconductor material, MoOx has a wider band gap than molybdenum disulfide (MoS2), and its property varies dramatically for the existence of several different allotropes and suboxide phases of molybdenum oxides (MoOx, x < 3). In this manuscript, a one-pot method possessing the advantages of one pot, easily prepared, rapid, and environmentally friendly, has been developed for facile synthesis of highly photoluminescent MoOx quantum dots (MoOx QDs), in which commercial molybdenum disulfide (MoS2) powder and hydrogen peroxide (H2O2) are employed as the precursor and oxidant, respectively. The obtained MoOx QDs can be further utilized as an efficient photoluminescent probe, and a new turn-off sensor is developed for 2,4,6-trinitrotoluene (TNT) determination based on the fact that the photoluminescence of MoOx QDs can be quenched by the Meisenheimer complexes formed in the strong alkali solution through the inner filter effect (IFE). Under the optimal conditions, the decreased photoluminescence of MoOx QDs shows a good linear relationship to the concentration of TNT ranging from 0.5 to 240.0 μM, and the limit of detection was 0.12 μM (3σ/k). With the present turn-off sensor, TNT in river water samples can be rapidly and selectively detected without tedious sample pretreatment processes.

Size effect of gold on Ag-coated Au nanoparticle-embedded silica nanospheres

Ag-coated Au nanoparticle (NP)-embedded silica nanospheres (SiO₂@Au@Ag NSs) were prepared using three different Au NPs of 2.5, 7 and 15 nm diameter to investigate their optical properties.

Explosive and chemical threat detection by surface-enhanced Raman scattering: a review

Acts of terror and warfare threats are challenging tasks for defense agencies around the world and of growing importance to security conscious policy makers and the general public. Explosives and chemical warfare agents are two of the major concerns in this context, as illustrated by the recent Boston Marathon bombing and nerve gas attacks on civilians in the Middle East. To prevent such tragic disasters, security personnel must be able to find, identify and deactivate the threats at multiple locations and levels. This involves major technical and practical challenges, such as detection of ultra-low quantities of hazardous compounds at remote locations for anti-terror purposes and monitoring of environmental sanitation of dumped or left behind toxic substances and explosives. Surface-enhanced Raman scattering (SERS) is one of todays most interesting and rapidly developing methods for label-free ultrasensitive vibrational "fingerprinting" of a variety of molecular compounds. Performance highlights include attomolar detection of TNT and DNT explosives, a sensitivity that few, if any, other technique can compete with. Moreover, instrumentation needed for SERS analysis are becoming progressively better, smaller and cheaper, and can today be acquired for a retail price close to 10,000 US$. This contribution aims to give a comprehensive overview of SERS as a technique for detection of explosives and chemical threats. We discuss the prospects of SERS becoming a major tool for convenient in-situ threat identification and we summarize existing SERS detection methods and substrates with particular focus on ultra-sensitive real-time detection. General concepts, detection capabilities and perspectives are discussed in order to guide potential users of the technique for homeland security and anti-warfare purposes.

Selective synthesis of different ZnO/Ag nanocomposites as surface enhanced Raman scattering substrates and highly efficient photocatalytic catalysts

Different ZnO–Ag nanocomposites with controlling SERS and photocatalytic performance were obtained only by adjusting solvents.

Squaramide-based lab-on-a-molecule for the detection of silver ion and nitroaromatic explosives

A squaramide based lab-on-a-molecule showed selective absorption enhancement and emission quenching towards Ag⁺ and nitroaromatic explosives, respectively in aqueous solution.

Superparamagnetic plasmonic nanoshells for improved imaging, separation and seeding of co-cultured cells

Multifunctional superparamagnetic nanoshells were applied for improved 2D and 3D two-photon luminescence imaging, separation and seeding of co-cultured cells.

Synthesis of surface-imprinted Ag nanoplates for detecting organic pollutants in water environments based on surface enhanced Raman scattering

Ag-molecularly imprinted polymer (MIP) hybrid composites (Ag@MIPs) were prepared for the ultra-sensitive detection of organic pollutants in water based on surface enhanced Raman scattering (SERS).

Improving the SERS detection sensitivity of aromatic molecules by a PDMS-coated Au nanoparticle monolayer film

In this paper, we reported a facile strategy to fabricate a PDMS film-coated Au nanoparticle monolayer film (Au MLF) composite substrate for improving SERS detection of aromatic molecules in water and in the atmosphere.