Magnetic assembled 3D SERS substrate for sensitive detection of pesticide residue in soil

Microfluidics-aided fabrication of 3D micro-nano hierarchical SERS substrate for rapid detection of dual hepatocellular carcinoma biomarkers

The simultaneous analysis of trace amounts of dual biomarkers is crucial in the early diagnosis, treatment, and prognosis of hepatocellular carcinoma (HCC). In this study, we prepared SERS-active hydrogel microparticles (SAHMs) with 3D hierarchical gold nanoparticles (AuNPs) micro-nanostructures by microdroplet technology and in situ synthesis, which demonstrated high reproducibility and sensitivity. Compared with traditional 2D SERS substrates, this newly prepared 3D SERS substrate provided a high density of nano-wrinkled structures and numerous AuNPs. Furthermore, a newly designed SERS-active substrate was proposed for the simultaneous microfluidic detection of AFP and AFU. The Raman signals of sandwich immunocomplexes on the surface of the SAHMs were measured for the trace analysis of these biomarkers. The proposed microfluidic platform achieved AFP and AFU detection in the range of 0.1-100 ng mL-1 and 0.01-100 ng mL-1, respectively, which represents a good response. Indeed, this platform is easy to fabricate, of low cost and has short detection time and comparable detection limits to other methods. As far as we know, this is the first study to achieve the simultaneous detection of AFP and AFU on a microfluidic platform. Therefore, we proposed a new simultaneous detection platform for dual HCC biomarkers that shows strong potential for the early diagnosis of HCC.

Preparation of 3D nano silver trees/sea urchin-like gold and SERS detection of uric acid

In this paper, 3D nano-silver trees/sea urchin-like gold Surface Enhanced Raman Spectroscopy (SERS) substrates were prepared by chemical reduction method, characterized by SEM, EDS, UV-Vis and XRD et.al, and the preparation process was optimized using Rhodamine B (RB) as the Raman signal molecule. The SERS characteristics of Uric Acid on this substrate were investigated and the results showed that the SERS substrate had a Raman enhancement factor of 1.9 × 107 for RB, and also had a significant Raman enhancement effect on Uric Acid. The SERS intensity (ISERS) at 1400 cm-1 showed a good linear relationship with the logarithm value of uric acid concentration (log C) between the range of 5 × 10-4 M to 1 × 10-7 M. The linear fitting equation was ISERS = 890 (log C) + 8066 (R2 = 0.983), and the LOD = 2.8 × 10-8 M. The spiked test was performed in human serum with recoveries ranging from 82.86% to 125.13% and RSD (n = 3) < 3.5%.

Rapid and Robust Analysis of Coumatetralyl in Environmental Water and Human Urine Using a Portable Raman Spectrometer

The widespread use and exposure of coumatetralyl (CMTT) has led to its accumulation in the environment and organisms, causing damage to ecosystems and adverse health effects in humans. Unfortunately, achieving fast detection of CMTT remains challenging. Herein, a rapid and robust surface-enhanced Raman spectroscopy (SERS) method was developed for rapid on-site detection of CMTT in environmental water and human urine. Clear trends were observed between the signal intensity and the logarithmic concentration of CMTT, ranging from 0.025 to 5.0 μg/mL with high reproducibility. The detection limits in water and human urine were as low as 1.53 and 13.71 ng/mL, respectively. The recoveries of CMTT for environmental water and urine samples were 90.2-98.2 and 82.0-87.5%, respectively, satisfactory for practical applications. The quantitative results of this approach were highly comparable to those obtained by high-performance liquid chromatography. Most importantly, it is cost-effective, operationally simple, and without a complicated sample preparation step. Detecting CMTT in water samples took only 5 min, and the detection of urine samples was completed within 8 min. This simple yet practical SERS approach offers a reliable application prospect for on-site CMTT detection in environmental water and point-of-care monitoring of poisoned patients.

Recent Advances in Nanoparticle-Based Optical Sensors for Detection of Pesticide Residues in Soil

The excessive and unreasonable use of pesticides has adversely affected the environment and human health. The soil, one of the most critical natural resources supporting human survival and development, accumulates large amounts of pesticide residues. Compared to traditional spectrophotometry analytical methods, nanoparticle-based sensors stand out for their simplicity of operation as well as their high sensitivity and low detection limits. In this review, we focus primarily on the functions that various nanoparticles have and how they can be used to detect various pesticide residues in soil. A detailed discussion was conducted on the properties of nanoparticles, including their color changeability, Raman enhancement, fluorescence enhancement and quenching, and catalysis. We have also systematically reviewed the methodology for detecting insecticides, herbicides, and fungicides in soil by using nanoparticles.

An anti-scratch flexible SERS substrate for pesticide residue detection on the surface of fruits and vegetables

We propose an anti-scratch flexible surface-enhanced Raman scattering substrate with arrayed nanocavity microstructures fabricated by colloidal lithography. The nanocavity microstructure of the substrate can well protect the inner gold nanoparticles during wipe sampling. The prepared flexible substrate was able to detect 4-aminothiophenol (4-ATP) with a concentration down to 1 fM. Furthermore, the substrate was used to detect 6-BA residues on the surface of apples and bean sprouts through wipe sampling, which shows great potential in the field of rapid on-site detection, especially in the detection of pesticide residues on the surface of fruits and vegetables.

Fabrication of highly sensitive and uniform Ag/PS/PDMS SERS substrate and its application forin-situdetection

In this study, we developed a flexible and transparent silver/polystyrene/polydimethylsiloxane (Ag/PS/PDMS) substrate with both high density of hot spots and satisfactory uniformity using a cost-effective approach. Via template-guided self-assembly, PS beads were arranged regularly in nanobowls of a square array on PDMS, whose surface structure was transferred from a commercial complementary metal oxide semiconductor chip. Roughness was introduced onto the PS bead surface by nitrogen plasma treatment, followed by sputtering of Ag which generated many hot spots. Differential roughness on the PS bead surface greatly influenced the morphology of the Ag/PS/PDMS substrate. A meat-ball like surface structure was formed with a plasma etching time of 5 min, whose growth mechanism was proposed based on the scanning electron microscope analysis. The high sensitivity and desirable uniformity of the meat-ball like Ag/PS/PDMS substrate were demonstrated by using crystal violet as a Raman reporter, exhibiting an enhancement factor of 2.7 × 10⁷and a relative standard deviation of 5.04%. Thiram of a lower concentration than the maximum residue limit on the cucumber surface could easily be detectedin situby the proposed substrate, demonstrating its great potential forin-situfood safety analysis.

Surface Enhanced Raman Spectroscopy: Applications in Agriculture and Food Safety

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

3D hotspot matrix of Au nanoparticles on Au island film with a spacer layer of dithiol molecules for highly sensitive surface-enhanced Raman spectroscopy

Engineering of efficient plasmonic hotspots has been receiving great attention to enhance the sensitivity of surface-enhanced Raman scattering (SERS). In the present study, we propose a highly sensitive SERS platform based on Au nanoparticles (AuNPs) on Au island film (AuIF) with a spacer layer of 1,4-benzenedimethanethiol (BDMT). The three-dimensional (3D) hotspot matrix has been rationally designed based on the idea of employing 3D hotspots with a vertical nanogap between AuIF and AuNPs after generating large area two-dimensional hotspots of AuIF. AuNPs@BDMT@AuIF are fabricated by functionalizing BDMT on AuIF and then immobilizing AuNPs. The SERS performance is investigated with Rhodamine 6G as a probe molecule and the determined enhancement factor is 1.3 × 10⁵. The AuNPs@BDMT@AuIF are then employed to detect thiram, which is used as a fungicide, with a detection limit of 13 nM. Our proposed platform thus shows significant potential for use in highly sensitive SERS sensors.

Rapid field trace detection of pesticide residue in food based on surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy is an alternative detection tool for monitoring food security. However, there is still a lack of a conclusion of SERS detection with respect to pesticides and real sample analysis, and the summary of intelligent algorithms in SERS is also a blank. In this review, a comprehensive report of pesticides detection using SERS technology is given. The SERS detection characteristics of different types of pesticides and the influence of substrate on inspection are discussed and compared by the typical ways of classification. The key points, including the progress in real sample analysis and Raman data processing methods with intelligent algorithm, are highlighted. Lastly, major challenges and future research trends of SERS analysis of pesticide residue are also addressed. SERS has been proven to be a powerful technique for rapid test of residue pesticides in complex food matrices, but there still is a tremendous development space for future research.

Investigation of photocatalysis reactions on the single-crystal and polycrystalline graphenes

Graphene has been extensive studied in the field of photocatalysis. Herein, single-crystal and polycrystalline graphenes are prepared by mechanical exfoliation and chemical vapor deposition (CVD), respectively. The photocatalytic properties of polycrystalline graphene are carefully assessed by using 4-nitrobenzenethiol (4-NBT), as a probe molecule, under incident 532 nm laser beam. Similarly, the photocatalytic properties of single-crystal graphene are also investigated with 4-aminothiophenol (PATP) under incident 633 nm laser radiation. In order to solve the problem of uneven distribution of probe molecules on graphene, the internal standard method is adopted by using 2-naphthalenethiol (2-NT), as the internal standard molecule. The experimental findings indicate that PATP can be catalyzed onto the surface of single-crystal graphene under the irradiation of 633 nm laser beam and its catalytic properties significantly increase with decreasing the number of graphene layers. In addition, when single-crystal graphene is used as the Surface-enhanced Raman scattering (SERS) enhancement substrate, the SERS enhancement was also increased with the decrease of the number of layers.

Strategies for SERS Detection of Organochlorine Pesticides

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.

Fabrication optimization and application of 3D hybrid SERS substrates

Three-dimensional (3D) plasmonic nanostructures with nanoparticles that can be tuned have got a lot of attention in surface-enhanced Raman scattering (SERS) due to the unique 3D plasmonic coupling. Here, two nanoparticles, gold nanosphere (AuNS) and gold nanooctahedra (AuNO), were used to construct 3D hybrid SERS substrates to investigate the effect of nanoparticle spatial position on the SERS performance of the 3D nanostructure and to obtain 3D substrates with high SERS activity. And more hybrid combination possibilities were tested to explore the variation trend of hot spots generated when the nanoparticles were near. First, two-dimensional (2D) planar substrates were prepared using the air–liquid interface-assisted self-assembly method, to examine the effect of nanoparticle size on SERS performance. Then, 3D hybrid SERS substrates were further prepared layer by layer to discuss the effect of different combination methods within three layers on SERS performance. The optimized 3D hybrid substrate with the sandwich structure of AuNS/AuNO/AuNS performed the strongest SERS enhancement effect, whose intensity was 4.1 and 1.9 times that of AuNS/AuNS/AuNS and AuNO/AuNO/AuNO, respectively, and had good reproducibility (relative standard deviation (RSD) of 1.08%). Furthermore, the thiram molecular result showed that the prepared AuNS/AuNO/AuNS had good linear relationship (R² of 0.991) and good molecule detection sensitivity (the minimum detection volume of thiram is 100 ppb), which demonstrated the great potential of the 3D hybrid SERS substrates in practical analysis.

The SERS effect of 3D hybrid substrate composed of AuNS and AuNO can be adjusted by changing the size and location of nanoparticles in the substrate, and SERS effect of the optimized substrate was better than that prepared by single nanoparticles.

Inkjet printed silver nanoparticles on hydrophobic papers for efficient detection of thiram

Silver nanoparticles coated paper (AgNPs-paper) substrates were prepared by inkjet printing Ag ink on four different wettability papers. Scanning electron microscope and contact angle analyzer were used to characterize their surface morphology and wettability. AgNPs-paper substrates were used to detect the surface-enhanced Raman scattering (SERS) spectra of thiram aqueous solution. Relationships between the surface wettability, surface morphology and SERS activities of the substrates were systematically studied. The silver nanoparticles deposited on the hydrophobic papers (photographic paper, graph paper, and weighing paper) were evenly and densely arranged. While in-homogeneous distribution was observed on the hydrophilic printing paper. It can be found that the AgNPs-photographic paper with the maximum contact angle exhibited the highest SERS enhancement. The detection limit for thiram adsorbed on the AgNPs-photographic paper was 10^-10 mol/L, which was lower than the others. Good linear responses (R² = 0.9918, 0.9897) between the SERS intensities and logarithmic concentrations were obtained from 10⁴ to 10^-10 mol/L. Moreover, the substrate had good uniformity and reproducibility with relative standard deviation values of 4.20% and 4.90% measured by eight points and ten substrates, respectively. The AgNPs-photographic paper exhibited high stability within eight months.

Silver microspheres aggregation-induced Raman enhanced scattering used for rapid detection of carbendazim in Chinese tea

Due to the excessive use of fungicides, pesticide residues have become a growing concern in recent years. Herein, we demonstrated an easy-prepared and low-cost surface enhanced Raman Scattering (SERS) chip composed of 3D silver microspheres (AgMSs) pattern for the quantitative testing of carbendazim in Chinese tea. Compared with the common monolayer SERS substrate, the 3D patterns formed by self-assembly AgMSs with fine nanostructure can offer much more aggregation-induced hotspots and generate strong 3D synergetic effects. Furthermore, when the thickness of the 3D pattern exceeded 6 μm, we replaced the conductive supporting coatings using the glass slides to reduce the cost without any impact on SERS properties. The prepared 3D chips achieved the determination of carbendazim within the linear range of 0.1-10 mg/L and the detection limit of 0.01 mg/L. It is simple and sensitive enough for the detection of most pesticide residues or other harmful organic molecules in our food or environment.