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SERS-based pesticide detection by using nanofinger sensors

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Abstract

Simple, sensitive, and rapid detection of trace levels of extensively used and highly toxic pesticides are in urgent demand for public health. Surface-enhanced Raman scattering (SERS)-based sensor was designed to achieve ultrasensitive and simple pesticide sensing. We developed a portable sensor system composed of high performance and reliable gold nanofinger sensor strips and a custom-built portable Raman spectrometer. Compared to the general procedure and previously reported studies that are limited to laboratory settings, our analytical method is simple, sensitive, rapid, and cost-effective. Based on the SERS results, the chemical interaction of two pesticides, chlorpyrifos (CPF) and thiabendazole (TBZ), with gold nanofingers was studied to determine a fingerprint for each pesticide. The portable SERS-sensor system was successfully demonstrated to detect CPF and TBZ pesticides within 15 min with a detection limit of 35 ppt in drinking water and 7 ppb on apple skin, respectively.

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... This latter points out a nice affinity of adsorption for the pesticide thiram on the Au portion of assembled Au/ZnO nano-urchins. Moreover, the experimental results are fitted by employing another model named Hill equation [55][56][57]: ...
... This value of 1.2 × 10 −7 M for k corroborates the large affinity of thiram regarding the metal surface. Nonetheless, the obtained n is less than 1, which indicates a decrease in the affinity of the thiram molecules moving towards the metal surface that already has thiram molecules grafted to its surface [55]. Finally, we calculate the analytical enhancement factor (AEF) of the plasmonic nano-urchins at LOD, with the following expression [58]: ...
Article
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In this paper, we are relating a significant improvement of the SERS effect achieved with assembled Au/ZnO nano-urchins. This improvement is realized thanks to an excellent capacity of adsorption (denoted K) for thiram molecules on these plasmonic nano-urchins, which is a key point to be taken into account for obtaining a SERS spectrum. Moreover, this outlook may be employed for different types of plasmonic substrates and for a wide number of molecules. We studied the capacity of the assembled Au/ZnO nano-urchins to be sensitive to the pesticide thiram, which adsorbs well on metals via the metal-sulfur bond. For the thiram detection, we found a limit concentration of 10 pM, a value of this capacity of adsorption (K) of 9.5 × 10^6 M−1 and a factor of analytical enhancement equal to 1.9 × 10^8.
... The detection of TBZ upto 7 ng per mL in liquid by fluorescence spectroscopy has been reported [1]. Similarly, the detection of CV and 4-ATP at concentration of $10 À15 M to 10 À16 M by the SERS methods has been reported [7,8], though it's based on poor quality surface enhanced Raman scattering (SERS) spectra [8][9][10]. Similarly, the detection of Rhodamine at a concentration of 7.5 Â 10 À17 M has been reported, but the method used is sophisticated [11]. ...
... There are challenges in the development of new, reliable and simple methods for the detection of pesticides and other chemicals below a concentration of 10 À17 M. During the last few years the work on SERS was focused on the design and fabrication of new types of SERS substrates using nanoparticles to achieve higher values of enhancement factors for the detection of chemicals at ultra low concentrations [8][9][10]. It has been observed that spherical gold (Au) nanoparticles with diameters in the range of 10-50 nm exhibit localized surface plasmon resonance (LSPR) peaks in the range of 520 nm to 560 nm. ...
Article
The surface properties of substrates made of 3 nm gold nanoparticles embedded on SiO2 nanospheres enabled fingerprint detection of thiabendazole (TBZ), crystal violet (CV) and 4-Aminothiophenol (4-ATP) at an ultralow concentration of ∼10⁻¹⁸ M by surface enhanced Raman spectroscopy (SERS). Gold nanoparticles of an average size of ∼3 nm were synthesized and simultaneously embedded on SiO2 nanospheres by the electron irradiation method. The substrates made from the 3 nm gold nanoparticles embedded on SiO2 nanospheres were successfully used for recording fingerprint SERS spectra of TBZ, CV and 4-ATP over a wide range of concentrations from 10⁻⁶ M to 10⁻¹⁸ M using 785 nm laser. The unique features of these substrates are roughness near the surface due to the inherent structural defects of 3 nm gold nanoparticles, nanogaps of ≤ 1 nm between the embedded nanoparticles and their high number. These produced an abundance of nanocavities which act as active centers of hot-spots and provided a high electric field at the reporter molecules and thus an enhancement factor required to record the SERS spectra at ultra low concentration of 10⁻¹⁸ M. The SERS spectra recorded by the substrates of 4 nm and 6 nm gold nanoparticles are discussed.
... SERS has attracted scientists interest because of its high sensitivity, rapid response, unique spectroscopic fingerprint, and nondestructive data acquisition, in cases enabling the detection of individual molecules [1,2]. Some of the chemical species that this technique can detect are toxic or radioactive cations/anions, ionic nutrients [3], pesticides [4], drugs and pharmaceuticals, or explosive materials [5]. ...
... This is why, in general, the enhancement is proportional to the fourthpower of the local electric field. In a first approximation, the electric field amplitude, E, due to the LSPR decays as a dipole field, E d -3 , so, to benefit from the SERS mechanism, the molecule must be in close proximity to the NP (d) [4,14]. For individual gold NPs, in the range R=20 to 50 nm, deposited on a mirror, the larger the NP size the higher the enhancement has been reported [15] while the optimum size for Ag NP colloids was found to be around R= 25 nm within the 10-35 nm studied range [16], which is close to the optimum radius provided by Mie analytical calculations (around 20 nm) for non-interacting spheres [17]. ...
Article
Full-text available
Size, shape and hot spots are crucial to optimize Raman amplification from metallic nanoparticle (NPs). The amplification from radius = 1.8 ± 0.4 nm ultra-small silver NPs was explored. Increasing NP density redshifts and widens their plasmon that, according to simulations for NPs arrays, is originated by the reduction of the interparticle distance, d, becoming remarkable for d ≤ R. Inter-particle interaction red-shifts (>130 nm) and widens (>90 nm) the standard plasmon of non-interacting spherical particles. Graphene partly delocalizes the carriers enhancing the NIR spectral weight. Raman amplification of graphene phonons is moderate and depends smoothly on d while that of Rhodamine 6G (R6G) varies almost exponentially due to their location at hot-spots that depend strongly on d. The experimental correlation between amplification and plasmon position is well reproduced by simulations. The amplification originated by the ultra-small NPs is compared to that of larger particles, granular silver films with 7 < R < 15 nm grains, with similar extinction values. The amplification is found to be larger for the 1.8 nm NPs due to the higher surface/volume ration that allows higher density of hot spots. It is demonstrated that Raman amplification can be efficiently increased by depositing low density layers of ultra-small NPs on top of granular films.
... Moreover, this EF value is higher than those obtained with gold dimer arrays on gold film (50 nm), where the dimer is composed of two disks (or rectangles or bowties) with a diameter of 140 nm, a gap of 20 nm and a height of 40 nm (EF = 3 × 10 5 -4 × 10 5 ) [24], and with 3D donut-like gold nanorings on a gold film (EF = 3.84 × 10 7 ) [54]. Furthermore, we have fitted the experimental results with another model called Hill equation, and defined it as follows [55,56]: ...
... This value of k = 3.3 × 10 −7 M confirms the high affinity of thiophenol molecules towards the gold surface. However, the value n = 0.46 is inferior to 1 indicating that thiophenol molecules already bound to the gold surface reduces the affinity of the incoming molecules to this surface [55]. ...
Article
Full-text available
Maximizing the surface-enhanced Raman scattering (SERS) is a significant effort focused on the substrate design. In this paper, we are reporting on an important enhancement in the SERS signal that has been reached with a hybrid asymmetric dimer array on gold film coupled to the efficient adsorption of thiophenol molecules on this array. Indeed, the key factor for the SERS effect is the adsorption efficiency of chemical molecules on the surface of plasmonic nanostructures, which is measured by the value of the adsorption constant usually named K. In addition, this approach can be applied to several SERS substrates allowing a prescriptive estimate of their relative performance as sensor and to probe the affinity of substrates for a target analyte. Moreover, this prescriptive estimate leads to higher predictability of SERS activity of molecules, which is also a key point for the development of sensors for a broad spectrum of analytes. We experimentally investigated the sensitivity of the Au/Si asymmetric dimer array on the gold film for SERS sensing of thiophenol molecules, which are well-known for their excellent adsorption on noble metals and serving as a proof-of-concept in our study. For this sensing, a detection limit of 10 pM was achieved as well as an adsorption constant K of 6 × 10^6 M−1. The enhancement factor of 5.2 × 10^10 was found at the detection limit of 10 pM for thiophenol molecules.
... Employing nanoimprint lithography, electrochemical or laser assisted methods could help manufacture reproducible patterns. Kim et al. used nanoimprint lithography to fabricate high-density and uniform arrays of gold nanofingers [65] that could trap pesticides between their tips after exposure to the analyte. Applying this novel technique on chlorpyrifos, an organophosphate pesticide with chlorine atoms, the interactions with the gold fingertips was put on the account of either the phosphate or chlorine groups. ...
Article
Full-text available
Organochlorine pesticides (OCPs) embody highly lipophilic hazardous chemicals that are being phased out globally. Due to their persistent nature, they are still contaminating the environment, being classified as persistent organic pollutants (POPs). They bioaccumulate through bioconcentration and biomagnification, leading to elevated concentrations at higher trophic levels. Studies show that human long-term exposure to OCPs is correlated with a large panel of common chronic diseases. Due to toxicity concerns, most OCPs are listed as persistent organic pollutants (POPs). Conventionally, separation techniques such as gas chromatography are used to analyze OCPs (e.g., gas chromatography coupled with mass spectrometry (GC/MS)) or electron capture detection (GC/ECD). These are accurate, but expensive and time-consuming methods, which can only be performed in centralized lab environments after extensive pretreatment of the collected samples. Thus, researchers are continuously fueling the need to pursue new faster and less expensive alternatives for their detection and quantification that can be used in the field, possibly in miniaturized lab-on-a-chip systems. In this context, surface enhanced Raman spectroscopy (SERS) represents an exceptional analytical tool for the trace detection of pollutants, offering molecular fingerprint-type data and high sensitivity. For maximum signal amplification, two conditions are imposed: an efficient substrate and a high affinity toward the analyte. Unfortunately, due to the highly hydrophobic nature of these pollutants (OCPs,) they usually have a low affinity toward SERS substrates, increasing the challenge in their SERS detection. In order to overcome this limitation and take advantage of on-site Raman analysis of pollutants, researchers are devising ingenious strategies that are synthetically discussed in this review paper. Aiming to maximize the weak Raman signal of organochlorine pesticides, current practices of increasing the substrate’s performance, along with efforts in improving the selectivity by SERS substrate functionalization meant to adsorb the OCPs in close proximity (via covalent, electrostatic or hydrophobic bonds), are both discussed. Moreover, the prospects of multiplex analysis are also approached. Finally, other perspectives for capturing such hydrophobic molecules (MIPs—molecularly imprinted polymers, immunoassays) and SERS coupled techniques (microfluidics—SERS, electrochemistry—SERS) to overcome some of the restraints are presented.
... However, pesticide residues could remain in plant tissues after they are applied to crops. Some pesticides are mutagenic, cytotoxic, or even carcinogenic (Kim, Barcelo, & Li, 2014). Pesticide residues in foods can cause harm to public health and the environment. ...
Article
The aim of this study was to develop surface-enhanced Raman spectroscopy (SERS) methods in combination with novel gold nanomaterial-based substrates for rapid measurement and quantification of pesticides extracted from lemon, carrot, and mango juice. Facile synthesis of a sensitive and robust SERS substrate was achieved by assembling gold nanorods (AuNRs) into vertically aligned arrays on silicon slides. The nanorod arrays were orderly aligned and can induce vigorous electromagnetic field for SERS measurement. The synthesized SERS substrate was utilized for detection and quantification of thiabendazole in juice samples using partial least squares analysis with R values of 0.99, 0.98, and 0.99 for lemon, carrot, and mango juice, respectively. The detection limits of thiabendazole were 149, 216, and 179 μg/L in lemon, carrot, and mango juice, respectively. These results demonstrate that SERS combined with AuNR substrates is a quick, convenient, and highly sensitive technique for detection of thiabendazole residues in fruits juice.
... Kim et al. [135] used as a SERS substrate an array of polymer nanopillars on top of which a layer of gold was deposited: The evaporation of the solvent in which the analyte was dissolved made the nanopillars collapse on each other, creating hot spots. The authors detected chlorpyrifos and thiabendazole in water, measuring LODs of 35 ppt and 1 ppb, respectively. ...
Article
Surface‐enhanced Raman scattering (SERS) has been emerging as a powerful tool for the detection of a variety of analytes due to its very high sensitivity and fingerprinting recognition capabilities. Technological progresses in the equipment for Raman analysis are contributing to its transition from a technically demanding research method to a more widely available analytical technique. In particular, the commercialization of portable or handheld instruments has opened up the possibility of performing in situ analysis. In this review, a selection of the SERS substrates that are expected to be more suitable for use in combination with portable instruments is presented: Substrates are compared, for example, in terms of performance, reproducibility, ease of fabrication, and surface area. Moreover, this paper provides a survey of the current diffusion of portable Raman instruments in the SERS detection of food contaminants: The investigation of several analytes is summarized (mainly toxins, virus, bacteria, pesticides, forbidden food dyes, and preservatives), reporting on the limits of detection and on the eventual coupling with concentration or separation techniques. A brief perspective on possible future developments of the SERS detection with portable instruments is also provided.
... Sharp tip and narrow metal nanogaps (or SERS hot spots) on the nanometer scale are efficient in detecting molecules from highly enhanced Raman signal. [105][106][107] HL is advantageous for fabricating sharp tip structures or narrow metallic gap structures with high reproducibility. [108][109][110][111] Figure 8a,b shows a hexagonal array of nanotip arrays obtained using SF 6 etching of two fcc nanostructure layers fabricated using prism HL. [108] The SERS signal obtained from the sharptipped array was higher than that obtained from the smoothtipped array because the incident electric field was focused on The k-space frequencies at the x, y coordinates under condition 1 < d/λ < 2 . ...
Article
In this paper, the authors review the optical principles underlying the fabrication of 3D periodic nanostructures prepared using holographic lithography (HL) as well as their applications toward chemical sensors and energy storage devices using 3D functional nanomaterials. HL is potentially useful for the simple and rapid fabrication of defect‐free large‐area periodic nanostructures with various structural geometries. The use of optical elements, such as well‐designed prisms and diffraction gratings, improves the reproducibility of the manufacturing process by simplifying complicated optical setups. 3D functional nanostructures, including semiconductor and metallic nanomaterials, are useful in highly sensitive photonic crystals and plasmonic sensors, and high‐performance 3D electrodes for use in energy production and storage devices. Holographic lithography is a powerful technique for fabricating uniform 3D nanostructures over large areas. By controlling the wavevector, polarization, and phase, a variety of 3D nanostructures may be generated using a single laser exposure. The high surface area, porosity, and periodicity of 3D nanostructures render them useful as energy storage electrodes and optical and mechanical sensors.
... SERS analysis involves spotting sample volume in microliter range onto a SERS substrate, allowing it to dry at room temperature and detect the probe analytes by Raman scattering. Detection of trace compounds (ppm-ppb) like explosives [16][17][18], drugs and pharmaceuticals [19][20][21], pesticides [22][23][24], antibiotics [25,26] and organic compounds [27] has been reported with various SERS substrates in previous literature. However, there are still some limitations for this technique. ...
Article
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.
... One of techniques of direct superplastic nanoimprinting of crystalline metals used a temperature mode well below the melting temperatures of the metals [70]. SERS-biosensors of this type have been already used to detect bacteria and toxins [71,72]. ...
Article
Full-text available
Viral infections are among the main causes of morbidity and mortality of humans; sensitive and specific diagnostic methods for the rapid identification of viral pathogens are required. Surface-enhanced Raman spectroscopy (SERS) is one of the most promising techniques for routine analysis due to its excellent sensitivity, simple and low-cost instrumentation and minimal required sample preparation. The outstanding sensitivity of SERS is achieved due to tiny nanostructures which must be assembled before or during the analysis. As for specificity, it may be provided using recognition elements. Antibodies, complimentary nucleic acids and aptamers are the most usable recognition elements for virus identification. Here, SERS-based biosensors for virus identification with oligonucleotides as recognition elements are reviewed, and the potential of these biosensors is discussed.
... Nanoimprint lithography (NIL) is a simple, reproducible, and scalable method to create plasmonic nanostructures over a large area so that it has been used for fabrication of SERS substrates [21][22][23][24][25]. The NIL enables the production of various periodic nanostructures on both rigid and flexible substrates. ...
Article
Full-text available
We report on a quasi-three-dimensional (3D) plasmonic nanowell array with high structural uniformity for molecular detection. The quasi-3D plasmonic nanowell array was composed of periodic hexagonal Au nanowells whose surface is densely covered with gold nanoparticles (Au NPs), separated by an ultrathin dielectric interlayer. The uniform array of the Au nanowells was fabricated by nanoimprint lithography and deposition of Au thin film. A self-assembled monolayer (SAM) of perfluorodecanethiol (PFDT) was coated on the Au surface, on which Au was further deposited. Interestingly, the PFDT-coated Au nanowells were fully covered with Au NPs with an ultra-high density of 375 μm−2 rather than a smooth film due to the anti-wetting property of the low-energy surface. The plasmonic nanogaps formed among the high-density Au NPs led to a strong near-field enhancement via coupled localized surface plasmon resonance and produced a uniform surface-enhanced Raman spectroscopy (SERS) response with a small relative standard deviation of 5.3%. Importantly, the highly uniform nanostructure, featured by the nanoimprint lithography and 3D growth of densely-packed Au NPs, minimizes the spatial variation of Raman intensity, potentially providing quantitative analysis. Moreover, analyte molecules were highly concentrated and selectively deposited in nanowells when a water droplet containing the analyte was evaporated on the plasmonic substrate. The analyte formed a relatively thick overcoat in the nanowells near the triple line due to the coffee-ring effects. Combining 3D plasmonic nanowell substrates with molecular enrichments, highly sensitive detection of lactic acid was demonstrated. Given its combination of high sensitivity and signal uniformity, the quasi-3D plasmonic nanowell substrate is expected to provide a superior molecular detection platform for biosensing applications.
... 4,5 SERS of various chemical pesticides have been investigated using both experimental and computational approaches alike. Many common synthetic pesticide families detected in the extract of consumable agricultural products have successfully been identified using SERS techniques such as organophosphate (acephate in urine, 6 chlorpyrifos in the extract of apple skin, 7,8 chlorpyrifos in rice, 9 and phosmet in the extract of apples and tomatoes 10,11 ), dithiocarbamate (thiram in apple, orange, grape, or tea leaf 12−17 ), carbamate (carbaryl in the apple juice 18 ), and benzimidazole (thiabendazole in the extract of apple skin 7 ), etc. Moreover, silver and gold nanomaterials turn out to be the preferred SERS substrates owing to their air stability, as compared to the copper surface which is more reactive. ...
Article
Surface enhanced Raman scattering (SERS) experiments and quantum chemical calculations (using density functional theory) on the interactions of chlorpyrifos (CPF), which is an intensively used pesticide, with roughed silver nanoparticle surface were thoroughly investigated to study the inherent molecular mechanism. Ligand–cluster interaction geometries show that the CPF molecule is mainly adsorbed on the silver surface via both S atom and pyridine ring involving a covalent Ag•••S coordination as well as van der Waals physisorption. Raman vibrational modes of CPF are centered at 474, 632, 678, 1277 and 1551 cm1 characterizing the P-O-C bending, P=S stretching, Cl-ring mode and pyridine ring stretching, respectively, which are all enhanced when CPF is adsorbed on a silver surface. The concentration-dependent effect of CPF on silver substrates has been reproduced for the first time by coordinating 2 and 3 CPF molecules on an Ag20 silver cluster model simulated by DFT computations. The intensities of the characteristic peaks of CPF as shown in the calculated SERS spectra are increased by 2 and 3 times with respect to those of the CPF–Ag20 complex which indicate positive influence of high analyst concentration on SERS signal. This observation can be explained by the electron donating effect of CPF upon adsorption. The latter donates electron from its lone pair on S and Cl atoms,  electron on S=P bond to silver atoms on surface, and then the positive charge of silver surface is displaced to the CPF moiety via Ag•••S and Ag•••Cl contacts. The information obtained from the adsorption of CPF on silver by SERS is helpful to understand the molecular mechanism of adsorption process involving chlorpyrifos ligand coordinated on silver nanoparticle surfaces. It also contributes to design field detection methods for rapid screening and monitoring of pesticides in environment or agricultural products by using portable detection systems such as paper-based or fiber-based SERS sensors.
... These functionalized nanomaterials were successfully employed for the environmental remediation in the form of detection and degradation of pesticides by FNMs. Even though use of pesticides helps in increasing the productivity and storage of crops in fulfilling the demand of huge population, they are great threat to environment and living system as it is toxic in nature and causes many types of diseases and pollution [25]. Hence, detection and degradation are necessary for the benefit of the society. ...
Chapter
Nanomaterials empower the advances of innovative solutions to environmental problems. Among the broad range of nanomaterials, functionalized nanomaterials emerged as promising catalyst for environmental issues. Functionalization of nanomaterials offers a great advantage on cost effectiveness and enhances the properties in many folds. Implementation of bare nanomaterials has a few challenges as well as limitations such as instability, agglomeration and reusability. Functionalization of the nanomaterials facilitates to overcome these problems. Addition of functional groups helps in tailoring the nanomaterial surface to enrich the specific sites on the surface level. This chapter discusses the engineering of functionalized nanomaterials and focuses on environmental applications. Different materials such as cellulose, chitosan, silica, metal oxides, and other polymers are added to nanomaterials and the introduction of functional groups on the surface which results composite materials of enhanced capability. Different process of functionalization namely direct functionalization, postsynthetic functionalization, grafting‐to, grafting‐from, and grafting‐through methods are illustrated. Nanomaterial and functional group interaction such as covalent and noncovalent bonding is described. This chapter highlights the limitations of different materials in various aspects of environmental applications. It provides a clear overview on selectivity of functionalized nanomaterials for the protection of environment using suitable real‐time techniques.
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Herein, we report a method to produce surface-enhanced Raman scattering (SERS) active and excellent non-enzymatic glucose and ascorbic acid (AA) sensing substrate by electroless deposition technique. Palladium (Pd) nanoparticles were deposited on different semiconductor (Si and Ge) and patterned (pyramidal Si) surfaces without any use of surfactant. Growth rate and the final morphology of the Pd nanostructures are observed to be dependent heavily on surface energy of the substrate and number of defects present on the substrate surface. Highest SERS enhancement is observed for Pd nanoparticles deposited on pyramidal Si substrate. Finite-difference time-domain (FDTD) simulation substantiate the experimental observation by showing that the sharp tip and the gap between the shafts are main contributing factor to the large enhancement of the incident electric field. Our result shows superior SERS enhancement compared to previously reported literature using pure Pd nanoparticles and also Pd nanoparticles deposited on different substrates. The substrates showed very good sensing properties for glucose and AA detection. The highest sensitivity (18.67 μA mM-1 cm-2) for AA is observed for Pd deposited on Ge substrate for 60 minutes in the linear range of 20 µΜ to 40 mM and for glucose the highest sensitivity (2.658 μA Mm-1 cm-2) is also observed for the same substrate in the linear range of 1 mM to 40 mM. Lowest detection limit for AA and glucose is 2.19 µΜ and 7.19 µΜ, respectively for the same substrate. Substrates we prepared are very useful for multifunctional applications like SERS and electrochemical non-enzymatic sensor.
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Plasmonics has drawn significant attention in the area of biosensors for decades due to the unique optical properties of plasmonic resonant nanostructures. While the sensitivity and specificity of molecular detection relies significantly on the resonance conditions, significant attention has been dedicated to the design, fabrication, and optimization of plasmonic substrates. The adequate choice of materials, structures, and functionality goes hand in hand with a fundamental understanding of plasmonics to enable the development of practical biosensors that can be deployed in real life situations. Here we provide a brief review of plasmonic biosensors detailing most recent developments and applications. Besides metals, novel plasmonic materials such as graphene are highlighted. Sensors based on Surface Plasmon Resonance (SPR), Localized Surface Plasmon Resonance (LSPR), and Surface Enhanced Raman Spectroscopy (SERS) are presented and classified based on their materials and structure. In addition, most recent applications to environment monitoring, health diagnosis, and food safety are presented. Potential problems related to the implementation in such applications are discussed and an outlook is presented.
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We present a calibration method for quantitative Surface Enhanced Raman Scattering (SERS) on a single-chip based on inkjet dispense (ID-SERS). We exploit the ability of inkjet to precisely pattern micro-droplets at high resolution to encode multiple standard curves on the surface of a single 1 mm2 SERS substrate. We demonstrate quantitative SERS measure-ments with a Relative Standard Error (RSE) below 3% for aqueous solutions of 1,2-bis(4-pyridyl)ethylene (BPE), the lowest reported to date. Most importantly, the RSE scales with patterning density and sensor size, showing the potential for even higher measurement accuracy. This calibration technique can be generalized to other plasmonic substrates and offers sever-al additional advantages including speed (sub-sec drop-and-dry), low sample volumes (< 1 nL) and automation. Finally, we investigate factors impacting the limit of detection of this approach and demonstrate a 30-fold enhancement of sensitivity via layered inkjet dispense. We believe that ID-SERS paves the way for the development of reproducible plasmonic sensing for real-world quantitative applications.
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The interaction of plasmonic nanoparticles with a dielectric platform gives rise to unique optical behaviors and this can be maneuvered to improve the plasmonic/SERS performances of a substrate. Herein, dielectric modified plasmonic-paper SERS substrate is developed by assembling Ag@SiO2 nanocubes on Fe-TiO2 nanosheets (NS) modified paper. The Fe-TiO2 NS being visible light responsive significantly alters the optical property of the paper and serves as a dielectric underlay for the Ag nanocubes. Hence, the incident light reflected back from the dielectric nanosheets couples with the scattered light from the Ag nanocubes leading to spatially enhanced electromagnetic field improving the SERS enhancement. The prepared dielectric modified plasmonic-paper has an average enhancement factor (EF) of 1.49 × 107 using R6G as a probe molecule. This value is superior to unmodified plasmonic-paper highlighting the coupling effect of the dielectric nanosheets. The substrate shows robust detection performance for thiabendazole and achieves a limit of detection (LOD) of 19 μg/L, which is 4-fold more sensitive than unmodified plasmonic paper. Direct swabbing test of thiabendazole sprayed apple fruit shows a discernible Raman signal down to 15 ppb indicating the utility of the substrate for point-of-need applications in food safety.
Chapter
The nanomaterials have a great impact and draw high attention in the food safety improvement. They are almost manmade. Due to its tiny size, shape, and orientation, in conjunction with distinctive physicochemical properties, it is often terribly totally different from its respective bulk materials and provides outstanding opportunities for the event of processes, products, and utilities within food safety that raise public cause of concern. Among them are metals and metal oxide nanoparticles, that is, Ag/Au/Cu/Fe/ CuO/Fe3O4/, etc., carbon-based nanomaterials including C60, carbon nanotubes, graphene, and quantum dots, as well as their composites. They are the most important nanomaterials applied for the determination of pollutants/toxicants/carcinogens/adulterants in food samples for the food safety. This chapter is aimed at describing the most recent utilities of such nanomaterials in food safety control and security, including their uses as sorbents and sensors, etc.
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The high sensitivity and long-term storage stability of a plasmonic substrate are vital for practical applications of the surface-enhanced Raman scattering (SERS) technique in real world analysis. In this study, a rationally designed ternary films-packaged silver-coated-gold nanoparticles ([email protected] NPs) plasmonic array was fabricated and applied as a stable and high-performance SERS chip for highly sensitive sensing of thiabendazole (TBZ) residues in fruit juices. The ternary films played different roles in the plasmonic chip: a newborn poly(methyl methacrylate) (PMMA) film serving as a template for fixing the self-assembly closely-packed monolayer [email protected] NPs array that provided intensive hotspot; a fluorescent quantitative polymerase chain reaction adhesive film (qPCR film) acting as a carrier to retrieve [email protected]/PMMA film that was used to improve the robustness of the plasmonic array; and a polyethylene terephthalate (PET) film covered over the [email protected]/PMMA/qPCR film performing as a barrier to improve the stability of the chip. The [email protected]/PMMA/qPCR-PET film chip showed high sensitivity with an enhancement factor of 3.14x106, long-term storage stability without changing SERS signals for more than 2 months at room temperatures, and low limit of detection for sensing TBZ in pear juice (21.8 ppb), orange juice (43.3 ppb) and grape juice (69.2 ppb). In addition, the procedure for fabricating the [email protected]/PMMA/qPCR-PET film chip was easy to handle, offering a new strategy to develop flexible and wearable sensors for on-site monitoring chemical contaminants with a portable Raman spectrometer in the future.
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Metallic nanogaps are a kind of fundamental building blocks for nanoelectronics and nanoplasmonics. However, its reliable fabrication remains challenging and thus developing additional approaches to fabricate ultrasmall metallic nanogaps is still required. In this work, we report a directed self-assembly approach to fabricate metallic nanogaps based on glass-transition-induced micro-reflow of polymer/metal hybrid structures. The process involves three main steps: electron-beam lithography process to obtain initial polymer structures, metal deposition onto the pre-patterned polymer nanostructures, and the solvent-assisted reflow process. It is interesting that the flowing orientation of polymer/metal hybrid nanostructures undergoing glass transition can be determined via several asymmetrical geometrical parameters including shapes and initial nanogaps. Mechanical simulations based on thermo-mechanical coupled finite element method are used to qualitatively understand the mechanism of the deterministic thermal reflow phenomenon. We demonstrate that this method is effective to fabricate sub-10-nm metallic nanogaps in gold nanostructures, which may have potential applications in plasmon-enhanced light-matter interactions, ultrafast nanotransistors, nanoelectronics and molecular electronics.
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By coupling headspace solid‐phase microextraction (HS‐SPME) with surface‐enhanced Raman scattering (SERS), a facile and rapid method was developed for the detection of organophosphorus insecticides (phorate and isocarbophos) and organic sulfur bactericide (ferbam) in the vapour phase. Two types of SPME fibres based on stainless steel wires coated with gold (Au) nanoparticles were prepared. The fibre (Fibre II) prepared by an etching approach showed better sensitivity than did the fibre (Fibre I) prepared using a layer‐by‐layer self‐assembly method. The Raman spectra of phorate, isocarbophos, and ferbam obtained from Fibre II showed stronger and clearer characteristic peaks compared with those from Fibre I, at 634, 1,043, and 1,380 cm⁻¹, respectively. It was found that the Raman intensity of phorate adsorbed on the Fibre II was nearly three times as high as that on Fibre I at 634 cm⁻¹, whereas the Raman intensity of isocarbophos was around 10 times at 1,043 cm⁻¹ and ferbam was approximately four times at 1,380 cm⁻¹. Using Fibre II, we were able to detect vapour‐phase phorate, isocarbophos, and ferbam at concentrations as low as 0.02, 0.02, and 0.05 ppm, respectively, as well as their mixture. This approach can be simply extended to detect a wide range of volatile organic compounds and shows potential as an easier and faster alternative to gas chromatography methods for studying volatile chemicals in some cases.
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nowadays, detection of pesticide residues is generally conducted in the laboratory using large-scale equipment such as liquid chromatography and mass spectrometry, etc. These detection methods usually require complicated pre-treatments and professional operators, which are time-consuming and expensive. Surface Enhanced Raman Scattering (SERS) technology makes trace detection of pesticide residues implementable, but currently the devices for SERS on the market are all large-scale and rapid detection of pesticide residues has not been achieved yet. In this paper, a novel SERS system integrated with a cellphone is designed for the detection of pesticide residues. In the current system, the SERS chip is inserted directly onto the, and measurement of pesticide residues can be conducted by one-click through the cellphone application. We achieved successfully detection of 12 kinds of pesticides with characteristic Raman spectra and the limit of detection was less than 10 ppm, which makes rapid and on-site detection of pesticide residues feasible in future point of care test (POCT) applications. IEEE
Article
Simultaneous detection of biomolecules with high sensitivity and selectivity is highly demanded for point-of-care diagnosis. Here, a simple solution-based surface-enhanced Raman spectroscopy (SERS) method is presented to facilitate rapid and direct ternary detections of ascorbic acid (AA), dopamine (DA) and uric acid (UA) in urine. The approach focuses on in situ surface modification of Au nanopillar electrode by Au electrodeposition in the presence of target molecules. Formation of new plasmonic nanostructures on the nanopillar array effectively perturbs the biomolecules adsorbed on the Au surface and confines the target molecules in solution into active regions of the generated hotspots, resulting in the significant amplifications of Raman signals within 60 s. The method enabled reliable label-free detections of AA, DA, and UA at relevant physiological ranges with detection limits of 1, 0.1 and 1 nM, respectively. To the best of our knowledge, this is the first demonstration of simultaneous detection and quantification of the biomolecules by SERS. The practical applicability of this novel method was ascertained by the analysis with non-pretreated human urine.
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Nitrogen dioxide (NO2) produced by hydrocarbon combustion has a significant adverse impact on human health and the environment. In the current work, we developed a high-performance (limit of detection: 0.1...
Article
The application of surface-enhanced Raman scattering (SERS) as analytical tool remains a challenge due signal intensity fluctuations, which depends on experimental parameters such as size, shape, and aggregation of the metallic nanoparticles responsible for enhancing the Raman signal. Colloidal nanoparticles can overtake this difficulty by optimizing some experimental conditions for each analyte. Here, we applied SERS as analytical technique to detect thiabendazole (TBZ) at low concentrations using Ag colloid. TBZ stock solutions were added into Ag colloids and SERS spectra were recorded in triplicate. Within the TBZ concentration from 1.6 × 10⁻⁷ to 8.0 × 10⁻⁸ mol/L a linear regimen for SERS intensity was achieved, leading to a TBZ limit of detection of 13.8 ppb. Besides, the main enhanced bands of the TBZ SERS spectrum suggest the TBZ adsorption mechanism on Ag surface takes place by the thiazole moiety. Theoretical calculations support the experimental data and indicate the interaction is stablished by S atom. Complementary to analytical application and adsorption mechanism, the dependence of SERS intensity on TBZ concentration follows a sigmoidal adsorption isotherm, which has a direct relation with the extinction spectra of Ag colloid containing TBZ at different concentrations, revealing intermolecular TBZ interactions and formation of Ag nanoparticle aggregates with distinct morphologies.
Article
Here we demonstrate a facile, two step formation of silver core - gold shell (Ag-Au) nanostructures using microelectrodes and assess their performance as surface-enhanced Raman scattering (SERS) substrates to detect and quantify toxicants. Ag nanostructures, serving as the scaffolds for the bimetallic structures, were grown first by using electrochemical deposition on the edges of microelectrodes functionalized with the alkanethiol, 11-mercaptoundecanoic acid. Subsequently, different concentrations of HAuCl4 were used to perform a galvanic reaction on the surfaces of the Ag nanostructures with aqueous droplets being placed on the microelectrodes for 10 minutes before the substrate was rinsed and dried. Lower HAuCl4 concentrations were found to better preserve the fractal morphology of the formed Ag-Au nanostructures, while higher concentrations resulted in Ag-Au fragments. The SERS enhancement factor for the Ag-Au nanostructures was estimated to have a max value of 6.51 x 10⁵. Combining a data reduction technique with a linear classifier, both identification and quantification were demonstrated with 100% success. The toxicants thiram, thiabendazole, malachite green and biphenyl-4-thiol were all detected and identified at 1 ppm. Lastly, as a proof of concept, the Ag-Au nanostructures were transferred to a PDMS film resulting in a flexible SERS substrate capable of direct detection of thiram on an apple peel without any additional sample pre-treatment.
Article
Food sensors have been developed for quality monitoring and contaminant detection to improve food management. Despite the alarming rates of food waste and food‐related illness, few food sensor technologies are utilized and translated into commercial products. This review aims to explore challenges and opportunities relating to sensor translation by first documenting recent advances in state‐of‐the‐art optical and electronic food sensors that target common analytes including temperature, humidity, pH, gases, pesticides, and pathogens. Promising sensors are designed with careful consideration of the chemistry of the contaminant or quality marker which they detect and the inherent challenges of analyte recognition in complex food samples. Recent advances focus on the incorporation of sensors into materials and devices for food packaging and processing. Challenges and opportunities for food sensor translation are then identified and discussed including the complexity of and natural variation in food products, different causes of food spoilage, the food–sensor interface, signal processing and governing legislation. For the successful translation of sensors into ubiquitous features on food products, these issues must be addressed through material and design advances.
Article
Thiabendazole (TBZ), has been extensively employed as a pesticide and/or a fungicide in agriculture, while its residues would threaten to public health and safety. Simple, rapid and sensitive probes for detection of TBZ in real food samples is significantly desirable. In present work, a highly selective and sensitive luminescent sensor for monitoring TBZ in oranges has been constructed based on a Tb³⁺-functionalized Zr-MOF (Tb³⁺@1). Tb³⁺@1 exhibited many attractive sensing properties toward TBZ, including broad linear range (0–80 μM), high selectivity, low LOD (0.271 μM) and rapid response time (less than1 min). Moreover, the probe was employed to determine TBZ in real orange samples, in which good recoveries from 98.41 to 104.48% were obtained. It only takes 35 min for the whole process of detection TBZ in real orange samples combined with QuEChERS method. Therefore, this work provided a reliable and rapid method for monitoring the TBZ in real orange samples.
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The search for novel platforms and metamaterials for the enhancement of optical and particularly Raman signals is still an objective since optical techniques offer affordable, noninvasive methods with high spatial resolution and penetration depth adequate to detect and image a large variety of systems, from 2D materials to molecules in complex media and tissues. Definitely, plasmonic materials produce the most efficient enhancement through the surface-enhanced Raman scattering (SERS) process, allowing single-molecule detection, and are the most studied ones. Here we focus on less explored aspects of SERS such as the role of the inter-nanoparticle (NP) distance and the ultra-small NP size limit (down to a few nm) and on novel approaches involving graphene and graphene-related materials. The issues on reproducibility and homogeneity for the quantification of the probe molecules will also be discussed. Other light enhancement mechanisms, in particular resonant and interference Raman scatterings, as well as the platforms that allow combining several of them, are presented in this review with a special focus on the possibilities that graphene offers for the design and fabrication of novel architectures. Recent fluorescence enhancement platforms and strategies, so important for bio-detection and imaging, are reviewed as well as the relevance of graphene oxide and graphene/carbon nanodots in the field.
Article
Surface-enhanced Raman scattering (SERS) with fast and intuitive property has been extensively utilized in the field of food safety. Here, we demonstrated a novel noble metal-polymer hybrid film as a SERS substrate for food fungicide analysis. Benefiting from its transparency and flexibility, poly(dimethylsiloxane) (PDMS) film was chosen as a versatile supporting matrix to grow gold nanobushes (Au NBs) through a seed-mediated process. The as-prepared AuNB-PDMS hybrid film performed satisfactorily in testing 4-nitrothiophenol (4NTP) and exhibited an enhancement factor (EF) of 2.56 × 106. Moreover, the high sensitivity and elastic properties make the hybrid film a promising substrate in practical detection. Hence, the in situ sensing of TBZ, carbaryl, and their mixture was finally realized using the developed hybrid film, which exhibited higher sensitivity than that obtained by the swabbing method. This high-performance SERS substrate based on the flexible and transparent AuNB-PDMS hybrid film has great potential applications in the fast in situ monitoring of biochemical molecules.
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It is a challenging and valuable work to synthesize surface enhanced Raman scattering (SERS) substrate with low cost and high performance by simple methods, and use it to detect pesticide residues in food. Here, Ferrero® chocolate-like Cu2[email protected] microspheres (FRC-Cu2[email protected]) were fabricated by a facile in-situ redox reaction. Cu2O directly acted as templates and reducing agents to induce the nucleation and growth of Ag nanoparticles on the microspheres surfaces. The prepared semiconductor-noble metal hybrids of Cu2[email protected] were utilized as SERS substrates to detect 4-mercaptobenzoic acid (4-MBA) and thiram molecules. The distinguished SERS effect was achieved when target molecules absorbed on the FRC-Cu2[email protected] composite. The substrate presented excellent sensitivity and reproducibility for the detection of 4-MBA and thiram with the limit of 10⁻¹⁰ and 10⁻⁹ M, respectively. Due to combining both advantages of electromagnetic enhancement of Ag metals and chemical enhancement of Cu2O semiconductors, the obtained FRC-Cu2[email protected] microspheres provided a SERS platform to conveniently detect molecules with thiol groups. When it was applied to detect thiram residues on apple peel and the detection limit was 1.2×10⁻⁷ M, low than maximal residue limit (MRL) of 7×10⁻⁶ M in fruit prescribed by the U.S. Environmental Protection Agency (EPA).
Article
Biosensors based on surface-enhanced Raman scattering (SERS) represent an efficient tool that can quickly detect even very low concentrations of the target molecule. Recent SERS-based biosensing has been moving toward a multiplex detection platform to analyze samples containing a variety of molecules, such as blood and urine. In this study, shape-coded suspension arrays have been developed for SERS-based multiplex biosensing. The suspension microarrays were fabricated using different shapes of poly(ethylene glycol) (PEG)-based hydrogel microparticles, which were prepared by a simple photopatterning process. The resultant hydrogel particles were coated with silver nanoparticles by a silver mirror reaction and then divided into two groups depending on the shape. As a proof of concept, square-shaped particles were coated with 4-mercaptophenylboronic acid by self-assembly to detect glucose, while circular particles were functionalized with anti-human serum albumin (HSA) to detect HSA. The assay was performed in the concentration range of 1 pg/mL to 1 µg/mL for both glucose and HSA without crosstalk. Target selectivity was also confirmed from Raman mapping, which shows that each group of particles reveals a different pattern. Moreover, we verified the potential of our method in multiplex immunoassays by quantifying two different antigens using SERS nanotags. The performance of the developed SERS-based multiplex immunoassay platform was demonstrated by the detection of a very low concentration of biomolecules with excellent selectivity.
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A three dimensional porous SERS powder material, Ag nanoparticles-engineered-silica aerogel, is developed. Utilizing in-situ chemical reduction strategy, Ag nanoparticles are densely assembled on porous aerogel structures, forming three dimensional “hot spots” distribution with intrinsic large specific surface area and high porosity. These features can effectively enrich the analytes on metal surface and provide huge near field enhancement. Highly sensitive and homogeneous SERS detections are achieved not only on conventional liquid analytes but also on gas, with the enhancement factor up to ~10⁸ and relative standard deviation as small as ~13%. Robust calibration curves are also obtained from the SERS data, which demonstrates the potential for quantification analysis. Moreover, the SERS powder show extraordinary SERS stability than conventional Ag nanostructures, which makes long term storage and convenient usage available. With all of these advantages, the porous SERS powder material can be further extended to on-site SERS “nose” applications, such as liquid and gas detections for chemical analysis, environmental monitoring and anti-terrorism, etc.
Article
The spectroscopic method based on surface-enhanced Raman spectroscopy (SERS) technique combined with chemometric methods was developed for simple, cost-effective, and efficient analysis of chlorpyrifos (CPF) and aldicarb (ALD) pesticide residues in animal feed. Animal feeds free from the pesticides were spiked at different concentrations of CPF (0-20 mg/kg) and aldicarb (0-100 µg/kg). Gold nanoparticles were mixed with sample extract for SERS measurement. A significant spectral difference induced by the presence and different level of CPF and ALD concentration in animal feed was observed between the pesticide spiking groups. Different chemometric models applied on training datasets showed excellent classification rates (100 percent) while the models on external validation dataset exhibited lower correct classification rates (50.0-76.7 percent) with no false-negative error. The selected chemometric models for CPF and ALD quantification also showed a high predictive ability and performance. The developed models displayed no statistical significant difference between model predicted and reference values in the external validation dataset (p < 0.01). The study results indicate that the SERS spectroscopic method could be an effective and efficient analytical tool for pesticide analysis in highly complex animal feed matrices for screening at a point of sampling to improve food and feed safety.
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This review summarizes the evolution that has been made for organophosphates (OPs) detection technique using conventional technique (lab-based) and compact technique (colorimetric and electrochemical). Right after introduction section, a first section covers the types, chemical structure and risks of OPs. Methods for detection using conventional and compact technique were discussed next. An additional section covers the limitation of conventional detection technique and advantages of compact detection technique are addressed. Several Tables are presented that give an overview on the OPs detection using conventional and compact detection technique. A concluding section addresses a brief idea on the detection method available nowadays.
Article
Hierarchical anisotropic superparticles derived from the controlled assembly of individual plasmonic nanoparticles have been recognized as promising building blocks for surface enhanced Raman spectroscopy (SERS) nanosensors. Thus, the protocols that precisely control the near-field coupling of individual plasmonic nanoparticles and the diffusion of highly diluted analytes to the plasmonic surface are of great interests. Herein, we have synthesized a series of aromatic amphiphilic block copolymers named as polyarylene ether nitrile (amPEN in short), containing a hydrophobic backbone of aromatic moieties with hydrophilic sulfonate/carboxyl and cyano groups in the side chain. Next, the surfactant stabilized water-in-oil (W/O) reverse emulsion is constructed to induce the confined self-assembly of amPEN, leading to the formation of functional micro-reactors for the in-situ synthesis and organization of silver nanoparticles, which finally contributes to the generation of sub-micrometer cube-like plasmonic superparticles (PSP). Furthermore, the SERS nanosensors are created by drop-casting of synthesized PSPs on silicon substrate followed by depositing an additional thin layer of silver. Finally, the optimized SERS nanosensors with a Raman enhancement factor of 10⁸ are able to detect chlorpyrifos pesticide down to 10⁻¹⁰ M, thanks to the presence of abundant Raman hot-spots on the synthesized PSP and the effective analyte enrichment derived from π-π interaction between pesticide molecules and aromatic backbone of amPEN.
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Pesticide and veterinary drug residues in food and environment pose a threat to human health, and a rapid, super-sensitive, accurate and cost-effective analysis technique is therefore highly required to overcome the disadvantages of conventional techniques based on mass spectrometry. Recently, the surface-enhanced Raman spectroscopy (SERS) technique emerges as a potential promising analytical tool for rapid, sensitive and selective detections of environmental pollutants, mostly owing to its possible simplified sample pretreatment, gigantic detectable signal amplification and quick target analyte identification via finger-printing SERS spectra. So theoretically the SERS detection technology has inherent advantages over other competitors especially in complex environmental matrices. The progress in nanostructure SERS substrates and portable Raman appliances will promote this novel detection technology to play an important role in future rapid on-site assay. This paper reviews the advances in nanostructure-based SERS substrates, sensors and relevant portable integrated systems for environmental analysis, highlights the potential applications in the detections of synthetic chemicals such as pesticide and veterinary drug residues, and also discusses the challenges of SERS detection technique for actual environmental monitoring in the future.
Article
Ever increasing demand for food and agricultural resources have led to escalation of pesticide poisoning and environmental hazards. An efficient system for pesticide detection is a constant endeavour and several technologies are working hand in hand to generate effective biosensors for various classes of pesticides. Innovative technologies are being developed for pesticides detection which overcome issues such as time and costs involved in sample preparation. Moreover, improvements in ease of operation and better sensitivity have been achieved using techniques such as fluorescence spectroscopy and electrochemical methods. Many tools such as aptamers, gold nanoparticles, quantum dots, molecularly imprinted polymers and, antibodies are used to develop hybrid biosensors where the sensitivity is increased several folds and limit of detection is as low as 0.1 pM. The time of detection is reduced to minutes along with simultaneous detection of multiple pesticides using the biosensors. We reviewed the latest biosensors developed which can be utilized for on-site sensing and optical biosensors are at the forefront of technology with advantages such as easy protocols, simple operation, high sensitivity, broad linearity range and cost-effectiveness. Colorimetric and fluorescence biosensors have rapid detection of pesticides with 90% recovery in food and serum samples. Chemiluminescence utilising biosensors have low detection time while photoluminescent sensors are highly sensitive and can be easily combined with smartphones for real-time detection. Many commercially available Surface Enhanced Raman Scattering (SERS) substrates are also present. For a cost-effective point-of-care biosensor, sample pre-treatment and expensive instrumentation are few hurdles that are conquered in electrochemical sensors. With amperometric, impedimetric and potentiometric techniques used in these biosensors, a low detection limit and time is observed in agriculture, water and food samples containing variety of pesticides. The review covers all the major techniques which can potentially be used for the development of point-of care biosensors such as, colorimetric, fluorescence, chemiluminescence, photoluminescence, surface enhanced Raman scattering and electrochemical in detailed and up-to-date analysis.
Article
In this study, a simultaneous detection platform utilizing SERS coupled chemometric models was developed to sensitively detect chlorpyrifos and carbendazim pesticides in rice in a single step for the first time. Initially, silver nanoflowers (AgNFs) were synthesized and used as the SERS substrate to acquire the spectra of pesticides. AgNFs have multiple chinks on their surface that can generate strong electromagnetic enhancement for SERS signal of chlorpyrifos and carbendazim. To obtain effective variables from the dataset, a novel wavelength selection method called interval combination population analysis (ICPA) was used. The ICPA-partially least square (ICPA-PLS) method showed a significant linear relationship over the concentration range of 0.01–1000 μg/mL for both pesticides when compared to other established chemometric methods. This model, yielded correlation coefficients in the calibration of 0.9802 and 0.9995, with an RPD of 3.74 and 7.8 for chlorpyrifos and carbendazim, respectively. A limit of detection of 0.01 μg/mL was determined using PCA analysis. Finally, the method was compared to HPLC, and the results revealed no significant differences (t < t0.05 (3), P>0.05) between two methods, implying that the proposed method could be used for food safety monitoring.
Article
The rapid, ultra-low detection, degradation and complete removal of pesticides demands the design of potential substrates. Herein, we discussed gold nanorods (Au NRs) as the potential substrate for the naked eye detection and degradation of two common and broad-spectrum pesticides; Chlorpyrifos (CPF) and Malathion (MLT) upto 0.15 ppt concentration within two minutes. Under certain environmental conditions, both the pesticides degraded and adsorbed on the surface of Au NRs. The degraded moiety of CPF and MLT on the surface of Au NRs forms side to side and end to end interaction, respectively leads to long range assembly. This shows no external agent is required, only CPF and MLT analytes are quite enough for the formation of assembly of Au NRs. Assembly of Au NRs is confirmed by TEM analysis and degradation is supported by FT-IR, Raman and GC-MS analysis. Au NRs was recovered and reused for four consecutive cycles. The fast and ultralow detection of pesticides demonstrates that Au NRs are potential substrate for the detection and degradation of pesticides.
Article
Accurate and rapid quantitative detection of pesticide and pollutant levels in the actual sample can aid in protecting food security, environmental security, and human health. A high Raman enhancement factor and good repeatability of the surface-enhanced Raman spectroscopy (SERS) substrates are favorable to quantitative analysis. Herein, a quantitative SERS sensor based on constructed self-assembled plasmonic Au@Ag heterogeneous nanocuboids (Au@Ag NCs) monolayer was developed. The sensor was used to quantitatively detect the trace pesticides extracted from pear surfaces and pollutants in fishpond water. Densely packed Au@Ag NCs fabricated into large-scale monolayer films were chemically functionalized using 4-methyl-thiobenzoic acid (4-MBA) at the organic/aqueous interface, in which plentiful nanogaps contribute to increase hotspots. Their sharp corners and edges make the sensor have high SERS performance through providing abundant “hot spots.” The obtained optically SERS-based sensor with uniform liquid-state interfacial nanoparticle arrays appeared to have nice SERS performance and uniformity using crystal violet (CV) as a probe molecule. In particular, the proposed SERS sensor was applied for quantitative detection of thiabendazole (TBZ) extracted from pear surfaces and malachite green (MG) in fishpond water down to levels of 0.0105 nM and 0.87 nM for SERS assay respectively. As a result, our proposed SERS quantitative detection strategy is quite preferred to on-site analysis and supervision of contaminant in food samples.
Chapter
Life on the planet earth has existed for billions of years, animal for hundreds of millions of years, and man for a few million years with a harmonious ecological development. The balanced situation was not affected significantly by man until this century. Man is the original and basic pollutant who has caused the disturbance in nature reason being the rate at which chemical and other industries are pumping material into water and the atmosphere. Natural process of recycling, mostly bacterial and photochemical does exist for dealing with the ingress of new materials into the waters and atmosphere, however is unable to catch up with the rate happening. The result is visible pollution, and a whole series of changes which come upon the loss of long-lasting balanced system. The development of electrochemical detectors for high performance liquid chromatography is also a major breakthrough in the determination of organics based on oxidation at solid electrodes. Voltammetric experiments allow determination of compounds in solution which have an oxidizable or reducible moiety; as a result numerous metals, nonmetals, anions, organics, organometallics, and heterocyclic compounds can be determined in a wide variety of sample matrices. Organic applications of voltammetry have been reviewed extensively. This chapter is dealing with the extensive use of electrochemical techniques in the field of determination of pesticides and development of sensors for pesticide detection in water samples.
Chapter
As the population of the world grows, the demand for food and other agricultural resources has led to escalation of pesticide poisoning and environmental hazards. Thus, an efficient system of pesticide detection is a constant endeavor, and a number of technologies are working hand in hand to generate effective biosensors for various classes of pesticides. Many commercial biosensors for detection of pesticides are available based on amperometric or fluorescence detection. Yet more innovative technologies are being developed which overcome issues by reducing time and costs involved in sample preparation. In addition to that, improvements in ease of operation with minimum expertise and better sensitivity have been achieved using various techniques such as optical, colorimetric, fluorescence, chemiluminescence, photoluminescence, SERS, and electrochemical. The essential characteristics of biosensors include limit of detection (LOD) and recovery.
Article
Chlorpyrifos (CP) is one of the most popular organophosphorus pesticides that is commonly used in agricultural and nonagricultural environments to combat pests. However, several concerns regarding contamination due to the unmitigated use of chlorpyrifos have come up over recent years. This has popularized research on various techniques for chlorpyrifos detection. Since conventional methods do not enable smooth detection, the recent trends of chlorpyrifos detection have shifted toward electrochemical and optical sensing techniques that offer higher sensitivity and selectivity. The objective of this review is to provide a brief overview of some of the important and innovative contributions in the field of electrochemical and optical sensing of chlorpyrifos with a primary focus on the comparative advantages and shortcomings of these techniques. This review paper will help to offer better perspectives for research in organophosphorus pesticide detection in the future.
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Well-resolved Raman spectra of gypsum, anglesite and baryte were detected using a portable Raman instrument (Ahura First Defender XL) in the laboratory and outdoor under atmospheric conditions. Spectra were obtained using a 785-nm excitation. The portable spectrometers display generally lower spectral resolution compared with the laboratory confocal instrument but permit the fast, unambiguous detection of minerals under field conditions. Portable Raman instruments can be advocated as excellent tools for field geological, environmental as well as exobiological applications. A miniaturized Raman instrument will be included in the Pasteur analytical package of the ESA ExoMars mission and interesting research applications can now be proposed for in situ field planetary studies. Additionally, portable Raman instruments represent an ideal tool for demonstrating possible applications of Raman spectroscopic techniques outdoor. In geosciences this approach represents a new field which could completely change classical field work. Copyright © 2009 John Wiley & Sons, Ltd.
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Melamine, a nitrogen-rich chemical, was implicated in the pet and human food recalls in 2007 and in the global food safety scares in 2008 involving milk and other milk-derived products. In this study, we investigated the feasibility of using surface-enhanced Raman spectroscopy (SERS) coupled with SERS-active gold substrates for rapid detection of trace amounts of melamine and its analogue (that is, cyanuric acid) in liquid milk. Raman signals of tested samples were significantly enhanced by SERS. The identification limit for SERS using gold substrate can reach 2ppm of melamine in liquid milk. Partial least squares (PLS) models were established for the quantification of melamine in liquid milk by SERS: R=0.90, RMSEP=1.48×10−5. Our results demonstrate that rapid detection of melamine in milk can be achieved by SERS; while detection of cyanuric acid in milk remains a challenging task due to rapid enol-keto tautomerism of cyanuric acid. The SERS method is faster and simpler than other traditional methods, and requires minimum sample preparation. These results demonstrate that SERS could be used to detect food contaminants such as melamine in foods and food ingredients quickly and accurately. KeywordsMelamine-Cyanuric acid-Milk-SERS-Gold substrates
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It is estimated that 20–50% of crops are saved from infestation through the use of pesticides. However, US inspectors find that more than 4% of fruits and vegetables imported exceed concentration levels considered safe for human consumption. This represents millions of tons of food brought to market annually that cannot be inspected using current hour-long laboratory methods. In an effort to provide inspectors with a simple, fast, field-usable analyzer and method, we have been developing a sampling device that includes surface-enhanced Raman spectroscopy (SERS) to detect, identify, and quantify pesticides below part-per-million (μg/mL) concentrations in approximately 10min using a portable Raman analyzer. The entire method, including solvent extraction, solid-phase extraction, and SERS-detection, was used to detect 50 parts-per-billion (ppb) Chlorpyrifos-methyl (CPM) artificially added to orange juice in 12min. The same method and analyzer can be readily adapted to other pesticides and foods. KeywordsChlorpyrifos-methyl-Pesticides-Food inspection-Raman-SERS
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Multiparticle assemblies of nanoscale structures are the fundamental building blocks for powerful plasmonic devices. Here we show the controlled formation of polygonal metal nanostructure assemblies, including digon, trigon, tetragon, pentagon, and hexagon arrays, which were formed on top of predefined flexible polymer pillars that undergo self-coalescence, analogous to finger closing, with the aid of microcapillary forces. This hybrid approach of combining top-down fabrication with self-assembly enables the formation of complex nanoplasmonic structures with sub-nanometer gaps between gold nanoparticles. On comparison of the polygon-shaped assemblies, the symmetry dependence of the nanoplasmonic structures was determined for application to surface enhanced Raman spectroscopy (SERS), with the pentagonal assembly having the largest Raman enhancement for the tested molecules. Electromagnetic simulations of the polygonal structures were performed to visualize the field enhancements of the hot spots so as to guide the rational design of optimal SERS structures.
Article
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Here we demonstrate a molecular trap structure that can be formed to capture analyte molecules in solution for detection and identification. The structure is based on gold-coated nanoscale polymer fingers made by nanoimprinting technique. The nanofingers are flexible and their tips can be brought together to trap molecules, while at the same time the gold-coated fingertips form a reliable Raman hot spot for molecule detection and identification based on surface enhanced Raman spectroscopy (SERS). The molecule self-limiting gap size control between fingertips ensures ultimate SERS enhancement for sensitive molecule detection. Furthermore, these type of structures, resulting from top-down meeting self-assembly, can be generalized for other applications, such as plasmonics, meta-materials, and other nanophotonic systems.
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Surface-enhanced Raman scattering (SERS) is a powerful spectroscopy technique that can provide non-destructive and ultra-sensitive characterization down to single molecular level, comparable to single-molecule fluorescence spectroscopy. However, generally substrates based on metals such as Ag, Au and Cu, either with roughened surfaces or in the form of nanoparticles, are required to realise a substantial SERS effect, and this has severely limited the breadth of practical applications of SERS. A number of approaches have extended the technique to non-traditional substrates, most notably tip-enhanced Raman spectroscopy (TERS) where the probed substance (molecule or material surface) can be on a generic substrate and where a nanoscale gold tip above the substrate acts as the Raman signal amplifier. The drawback is that the total Raman scattering signal from the tip area is rather weak, thus limiting TERS studies to molecules with large Raman cross-sections. Here, we report an approach, which we name shell-isolated nanoparticle-enhanced Raman spectroscopy, in which the Raman signal amplification is provided by gold nanoparticles with an ultrathin silica or alumina shell. A monolayer of such nanoparticles is spread as 'smart dust' over the surface that is to be probed. The ultrathin coating keeps the nanoparticles from agglomerating, separates them from direct contact with the probed material and allows the nanoparticles to conform to different contours of substrates. High-quality Raman spectra were obtained on various molecules adsorbed at Pt and Au single-crystal surfaces and from Si surfaces with hydrogen monolayers. These measurements and our studies on yeast cells and citrus fruits with pesticide residues illustrate that our method significantly expands the flexibility of SERS for useful applications in the materials and life sciences, as well as for the inspection of food safety, drugs, explosives and environment pollutants.
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We describe biocompatible and nontoxic nanoparticles for in vivo tumor targeting and detection based on pegylated gold nanoparticles and surface-enhanced Raman scattering (SERS). Colloidal gold has been safely used to treat rheumatoid arthritis for 50 years, and has recently been found to amplify the efficiency of Raman scattering by 14-15 orders of magnitude. Here we show that large optical enhancements can be achieved under in vivo conditions for tumor detection in live animals. An important finding is that small-molecule Raman reporters such as organic dyes were not displaced but were stabilized by thiol-modified polyethylene glycols. These pegylated SERS nanoparticles were considerably brighter than semiconductor quantum dots with light emission in the near-infrared window. When conjugated to tumor-targeting ligands such as single-chain variable fragment (ScFv) antibodies, the conjugated nanoparticles were able to target tumor biomarkers such as epidermal growth factor receptors on human cancer cells and in xenograft tumor models.
Article
Surface-enhanced Raman spectroscopy (SERS) is evaluated as a quantitative analytical tool for low concentrations of melamine and melamine derivatives in solution. Substantial variations in absolute and relative intensities of SERS bands were encountered using silver sols, which cannot be controlled. Alternatively, it was shown that SERS using a roughened silver electrode, while conditioning the applied potential, permits the acquisition of Raman spectra from electrode spots down to 1 μm in size, and the results of multiple measurements using a hard cathodic cleaning step in between each adsorption experiment gave a relative standard deviation of 15%. The high enhancement factor of the electrode micro-Raman scattering intensity creates a new trace analytical technique for obtaining high-resolution spectra of melamine from dilute aqueous solution (detection limit ∼ 10-7 mol L-1) in the opto-electrochemical cell. As an alternative for the hard cathodic cleaning step, we demonstrated that the cationic surfactant molecule cetylpyridinium chloride is able to remove preadsorbed melamine within a few seconds. The surfactant molecules can subsequently be removed from the surface by switching to a negative applied potential. This procedure results in a relative standard deviation of 10%. The effects of electrode potential on the observed SERS spectra are consistent with current ‘SERS surface selection rules'. The electrode potential and the surface concentration of the chloride counterions strongly affect the intensity of the out-of-plane modes in the adsorbed state. However, additional experiments using various excitation lines showed that an alternative theory, surface complex formation combined with charge transfer resonance Raman processes with Herzberg−Teller contributions, plays an important role.
Article
We developed a rapid and simple method which combines a surface swab capture method and surface-enhanced Raman spectroscopy for recovery and quantitative detection of thiabendazole on apple surfaces. The whole apple surface was swabbed and the swab was vortexed in methanol releasing the pesticide. Silver dendrites were then added to bind the pesticide and used for enhancing the Raman signals. The recovery of the surface swab method was calculated to be 59.4-76.6% for intentionally contaminated apples at different levels (0.1, 0.3, 3, and 5ppm, μg/g per weight). After considering the releasing factor (66.6%) from the swab, the final accuracy of the swab-SERS method was calculated to be between 89.2% and 115.4%. This swab-SERS method is simple, sensitive, rapid (∼10min), and quantitative enough for QA/QC in plant procedure. This can be extended to detect other pesticides on raw agricultural produce like pears, carrots, and melons etc.
Article
Simple and rapid detection of trace amounts of melamine in milk products has been achieved with a portable sensor system based on surface-enhanced Raman scattering (SERS). The sensor system comprised high-performance gold nanofinger SERS sensor chips and a custom-built prototype portable Raman spectrometer. Compared to the FDA procedure and previously reported studies that were limited to laboratory settings, our sampling and analytical methods are simple (with one sampling step), less time-consuming, and cost-effective. We found the limit of detection (LOD) of the melamine is 120 parts per trillion (ppt) in water and 100 parts per billion (ppb) in infant formula, which are well below the FDA's tolerance level of 1 ppm in infant formula.
Article
Molecular surface enhanced Raman scattering (SERS) in compact clusters of 30−70 nm Ag nanocrystals has shown single molecule Raman scattering cross sections that are orders of magnitude larger than free space single molecule luminescence cross sections. We analyze certain aspects of this phenomenon with new numerical electromagnetic calculations, and we also present new spectral depolarization data for single molecule rhodamine 6G scattering. We stress the central role of the Ag femtosecond radiative lifetime, and the spatial distribution of the excited Ag electrons, in the near field and far field optical properties. The fundamental nature of the Ag plasmon excited-electronic-state changes from a volume excitation to a surface junction excitation as two particles approach each other within 1 nm. Adsorbed molecules in the junction interact directly with the metallic excited-state wave function, showing electron-transfer-initiated photochemistry as well as enhanced Raman scattering. Depolarization studies show an uniaxial local electromagnetic symmetry at the junction site. Simultaneous intensity fluctuations in both the R6G molecular lines and the accompanying Ag electronic Raman continuum appear to reflect R6G adsorption−desorption kinetics. We outline the wavelength-dependent properties of a hybrid molecular-metallic wave function as the Raman resonant state.
Article
A new methodology for the rapid and efficient derivation of a class II energy surface of a molecule has been demonstrated. It is shown that, where there is no existing adequate force field and insufficient experimental data from which to derive one, the method can be used to obtain a reliable representation of the energy surface. The resulting force field has been used to achieve the objective of interpreting the vibrational spectrum of melamine.
Article
Melamine, a nitrogen-rich chemical, has recently caused enormous economic losses to the food industry due to the cases of milk products adulterated by melamine. This has led to an urgent need of rapid and reliable methods for detection of melamine in food. In this study, surface-enhanced Raman scattering (SERS) spectroscopy was used to detect melamine in liquid milk. The sample preparation with liquid milk is very easy; it has to be only diluted with double-distilled water followed by centrifugation. By using a silver colloid, at least a 105-fold enhancement of the Raman signal was achieved for the measurement of melamine. The limit of detection by this method was 0.01 µg ml−1 for melamine standard samples. Based on the intensity of the Raman vibrational bands normalised to that of the band at 928 cm−1 (CH2), an external standard method was employed for quantitative analysis. The linear regression square (R2) of the curve was 0.9998; the limit of quantitation using this approach was 0.5 µg ml−1 of melamine in liquid milk; the relative standard deviation was ≤10%; and recoveries were from 93 to 109%. The test results for SERS were very precise and as good as those obtained by liquid chromatography/tandem mass spectrometry. The method was simple, fast(only needs about 3 min), cost effective, and sensitive for the detection of melamine in liquid milk samples. Therefore, it is more suitable for the field detection of melamine in liquid milk. Copyright © 2010 John Wiley & Sons, Ltd.
Article
The electromagnetic theory of surface-enhanced Raman spectroscopy (SERS), despite its simplicity, can account for all major SERS observations, including: the need for a nanostructured material as the SERS-active system; the observation that some metals form good SERS-active systems while others do not; the observation that strongly interacting metal nanoparticles result in very much more effective SERS-active systems; the observed polarization sensitivity shown by nanoparticle aggregates; and the optical behavior of nanostructured metals in the absence of a molecular adsorbate. By extending the ideas inherent in the electromagnetic model one can also understand the seminal features reported for single-molecule SERS, including the puzzling observation that only a few silver ‘particles’ in an ensemble are ‘hot’ (they are appropriately structured nanoparticle clusters) and that for a hot particle, once one is able to observe SERS, adding more adsorbate does not significantly alter the intensity (once the electromagnetic hot spot is occupied, adding adsorbate to other sites on the nanoparticle cluster will not add greatly to the observed intensity). However, the electromagnetic model does not account for all that is learned through SERS. Molecular resonances, charge-transfer transitions and other processes such as ballistic electrons transiently probing the region where the molecule resides and then modulating electronic processes of the metal as a result certainly contribute to the rich information SERS reports; and by virtue of the fact that these contributions will vary from molecule to molecule, they will constitute the most interesting aspects reported by SERS. But, the overall reason why SERS produces such inordinate enhancements is largely an electromagnetic property of nanostructures. Copyright © 2005 John Wiley & Sons, Ltd.
Article
The inelastic neutron scattering spectrum of melamine has been measured and a normal coordinates analysis has been performed in order to interpret the vibrational dynamics. This study reveals the anisotropy in the external mode spectrum and its important role in the internal modes region. Thus, the Debye–Waller factor has taken a value for the out-of-plane vibrations four times greater than that for the in-plane vibrations. A molecular force field refinement has been carried out in independent symmetry coordinates (D3h) in order to confirm the vibrational assignments. The final force field is free of redundancies and therefore the corresponding force constants are unambiguous.
Article
Deterministic patterning or assembly of nanoparticles often requires complex processes that are not easily incorporated into system architectures of arbitrary design. We have developed a technique to fabricate deterministic nanoparticle assemblies using simple and inexpensive nanoimprinting equipment and procedures. First, a metal film is evaporated onto flexible polymer pillars made by nanoimprinting. The resulting metal caps on top of the pillars can be pulled into assemblies of arbitrary design by collapsing the pillars in a well-controlled manner. The nanoparticle assemblies are then transferred from the pillars onto a new substrate via nanoimprinting with the aid of either cold welding or chemical bonding. Using this technique, a variety of patterned nanoparticle assemblies of Au and Ag with a critical dimension less than 2 nm were fabricated and transferred to silicon-, glass-, and metal-coated substrates. Separating the nanostructure assembly from the final architecture removes significant design constraints from devices incorporating nanoparticle assemblies. The application of this process as a technique for generating surface-enhanced Raman spectroscopy substrates is presented.
Article
A novel fast ultra-sensitive approach was developed herein to identify melamine contaminant in eggs using portable compact surface-enhanced Raman Spectroscopy (SERS) on gold nanosubstrates. Trace amounts of melamine spiked in albumen and yolk were characterized and quantified by SERS with partial least squares (PLS) analysis, good models were acquired for melamine in albumen at concentration range of 2.5–100 mg/kg with the determination coefficient of actual concentration versus predicted concentration R2 = 0.94, the root mean standard error of cross validation RMSECV = 12.38, the limit of detection (LOD) 1.1 mg/kg, and in yolk 5.0–200 mg/kg with R2 = 0.98, RMSECV = 12.14, LOD = 2.1 mg/kg, respectively. The assay was rapid in less than 30 min, and the detection was sensitive. As a fast screening scheme, the method could be suitably applied to the domain of on-site egg products quality control and market surveillance thereof.
Article
By exploiting the extremely large effective cross sections ( 10-17-10-16 cm2/molecule) available from surface-enhanced Raman scattering (SERS), we achieved the first observation of single molecule Raman scattering. Measured spectra of a single crystal violet molecule in aqueous colloidal silver solution using one second collection time and about 2×105 W/cm2 nonresonant near-infrared excitation show a clear ``fingerprint'' of its Raman features between 700 and 1700 cm-1. Spectra observed in a time sequence for an average of 0.6 dye molecule in the probed volume exhibited the expected Poisson distribution for actually measuring 0, 1, 2, or 3 molecules.
Article
In 2007, it was determined that melamine, ammeline, ammelide, and cyanuric acid (abbreviated as MARC for melamine and related contaminants) had been added to wheat gluten and rice protein that were subsequently incorporated into pet food. The consumption of food tainted by MARC compounds was implicated in numerous instances of renal failure in cats and dogs. A method for the analysis of MARC compounds in kidney tissue using high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) has been developed. MARC analytes were extracted by homogenization of kidney tissue in 50/40/10 acetonitrile/water/diethylamine. The homogenate was centrifuged, and an aliquot of supernatant was diluted with acetonitrile, concentrated, and fortified with a stable isotope-labeled analogue of melamine. Analytes were detected using atmospheric pressure chemical ionization and multiple reaction monitoring. Quantitation of positive samples was performed using the internal standard method and five-point calibration curves ranging between 50 and 1000 ng/mL of each analyte. The method was validated by analysis of replicate kidney tissue samples fortified with the individual analytes and by analysis of kidney samples fortified with melamine cyanurate powder at two different concentrations. This method was successfully used for routine postmortem diagnosis of melamine toxicosis in animals. Melamine was also detected by this method in paraffin-embedded tissue from animals suspected to have died of melamine toxicosis.
Article
The binding of trans-1,2-bis(4-pyridyl)-ethylene (BPE) molecules on substrates arrayed with flexible gold nanofingers has been studied by surface-enhanced Raman spectroscopy (SERS) and angle-resolved X-ray photoelectron spectroscopy (AR-XPS). On the basis of the SERS and XPS results, BPE molecules are found to interact with the gold nanofingers through the lone pair electrons of pyridyl nitrogens, not through delocalized π electrons. Furthermore, after comparing the AR-XPS spectra of finger arrays preclosed before exposure to BPE with the spectra of arrays that closed after exposure to BPE, we observed in the latter case, at grazing takeoff angles, an increase in the component of the nitrogen photoelectron peak associated with pyridyl nitrogen atoms residing on bridging sites. These results demonstrate that a small percentage of BPE molecules was trapped between the neighboring gold finger tips during the finger closing process. However, because these trapped BPE molecules coincidently resided in the hot spots formed among the touching finger tips, the substantial increase in the observed SERS signal was dominated by the contribution from this small minority of BPE molecules.
Article
Despite extensive efforts to protect public health, disease outbreaks still occur when toxic chemicals and microbial threats evade detection. Peanut butter and produce tainted with Escherichia coli 0157:117, drinking water in Milwaukee, WI and Walkerton, ON (Canada) polluted by Cryptosporidium, surface waters contaminated by cyanotoxins, and mail laced with anthrax spores each represent an outbreak that may have been prevented with faster and more readily available pathogen or chemical detection methods. Although numerous techniques for contaminant detection in a variety of matrices exist, monitoring each analyte class generally requires specific instrumentation. Today, however, there is growing excitement about the potential use of surface-enhanced Raman spectroscopy (SERS) for simultaneous multiplex detection of infectious and noninfectious contaminants in a range of environmental milieu. As currently envisioned, SERS is a platform for simple, fast, inexpensive, reliable, and robust methods to screen single or multiple contaminant classes simultaneously (1-4). Thousands of SERS publications document significant progress in achieving such a vision; however, as outlined herein several surmountable obstacles must be overcome to achieve these goals.
Article
Silver nanorod (AgNR) array substrates are investigated to detect pure melamine dissolved in 50% methanol using surface-enhanced Raman spectroscopy (SERS). We find that sample preparation conditions have a great influence on melamine detection. When the samples are prepared under a nitrogen glove box, the SERS characteristic peak intensities of melamine at Deltanu = 497 cm(-1), 704 cm(-1), and 983 cm(-1) are studied as functions of melamine concentration and/or the mass of melamine. The peak intensities increase almost linearly when the melamine concentration increases from 0.1 mg/L to 10 mg/L and saturate when melamine concentration is greater than 50 mg/L. The bulk melamine limit of detection (LOD) is 0.1 mg/L, which is one order of magnitude less than the current standard. This study shows that AgNR based SERS detection can be used as a fast, highly sensitive, and quantitative detection method for melamine.
Article
A FTIR methodology has been developed for the simultaneous determination of Cypermethrin and Chlorpyrifos in pesticide commercially available formulations. The method involves the extraction of both active principles with CHCl(3) and direct measurement of the peak area values between 1747 and 1737cm(-1) corrected with a baseline defined at 2000cm(-1) for Cypermethrin and peak height values established at 1549cm(-1) corrected using a baseline situated at 1650cm(-1) for Chlorpyrifos. The limits of detection achieved were of the order of 0.7 and 0.4% (w/w), and the relative standard deviation 0.4 and 0.2% for Cypermethrin and Chlorpyrifos, respectively. The developed procedure provided statistically comparable results with those obtained by HPLC, for a series of commercial samples, which validated the FTIR method. The procedure developed reduces organic solvent consumption, per sample preparation, from 51ml CH(3)CN required for HPLC to 2.5ml CHCl(3), and reduces waste generation also increasing the sample measurement frequency, from 3 to 30 samples/h, as compared with the HPLC-UV reference method.
The Raman spectra of malathion, ethion, methyl parathion, parathion, EPN, 0,0-diethyl-0-(2,4-dichlorophenyl) phosphorothioate, dichlorvos, mevinphos, tributyl phosphorotrithioite, and 2,4-dichlorobenzyltributylphosphonium chloride have been recorded. These spectra are presented, along with tables giving values for the frequencies.
Article
(Graph Presented) Getting to the bottom of groundwater: The development of a reliable, portable, and simple-to-use device for detecting arsenic in groundwater is urgently needed in developing nations such as Bangladesh, where contaminated groundwater is at the root of a public health crisis. Toward this end, a highly sensitive platform utilizing surface-enhanced Raman spectroscopy (SERS, see picture) is used to quantitatively detect arsenate in water down to 1 ppb.
Casarett and Doull’s Toxicology: The Basic Science of Poisons
  • C D Klaassen
  • M Admur
  • J M Chalmers
  • P Griffiths
  • Chalmers J M
  • Hill A V