Trace Detection Research Articles

Construction and Application of Au NRs/4-MBA/PAM Ratiometric Surface-Enhanced Raman Scattering Substrate for Fish Veterinary Drug Residue Detection

Surface-enhanced Raman scattering (SERS) is widely used for trace detection of substances, and the key to this technology lies in the preparation of the substrate material. In this study, a composite SERS material of Au NRs/4-MBA/PAM was constructed and characterized to better immobilize the reference molecule 4-mercaptobenzoic acid (4-MBA). Electron transmission microscopy results demonstrated that the PAM film helps Au NRs to pack closely, enhancing the stability of the material structure and reducing the interference of external environmental factors on the response of 4-MBA, thus improving the accuracy of quantitative determination. Comparative experimental results with the Au NRs/4-MBA substrate showed that the relative standard deviations (RSDs) of the detection results for MG on different batches of Au NRs/4-MBA/PAM were less than 8.0%, and the RSDs of different points on the same material were less than 10.0%, indicating that the Au NRs/4-MBA/PAM has higher uniformity, better reproducibility, and higher sensitivity in detecting malachite green (MG). Applying this material in the recovery determination of fish extract showed that the recovery rates of MG were between 75.60% and 83.24%. Therefore, the Au NRs/4-MBA/PAM substrate can accurately detect and quantify veterinary drug residue in complex matrices such as food tissue.

Structure-based design and screening of hydrogel copolymer/Fe3O4 composite microspheres for magnetic solid phase extraction of bisphenol A from aqueous samples

It is of great significance to monitor bisphenol A (BPA) in the environment because of its potential environmental and health risks. However, the detection of trace or ultratrace BPA in complicated environmental samples is challenging due to the relatively low affinity and poor selectivity of existing adsorbents used in sample pretreatment. Herein, we report a high-affinity, low environment-dependent and strong interference-resistant abiotic affinity ligand, a N-methacryloyl-l-lysine-NH2 (MLys)-based hydrogel copolymer (HP 17) screened from a small focused polymer library engineered by incorporating various combinations and ratios of candidate functional monomers. The selection of these monomers was guided by molecular mechanism between BPA and the ligand-binding pocket of its estrogen receptors. The BPA–HP17 binding is mainly a synergistic effect of π-cation and hydrophobic interactions. The screened HP 17 has high adsorption capacity (349.4 mg/g) for BPA under wide pH (3.0–10.0) and ionic strength (0–150 mM) range. To improve its practicability, a hydrogel copolymer/Fe3O4 composite microspheres (Fe3O4@HP 17) was synthesized and applied for magnetic solid phase extraction–high-performance liquid chromatography (MSPE–HPLC) analysis of BPA in tap water, lake water and industrial effluents. The method shows wide linear range (2.5⁓100 ng/mL), high sensitivity (detection limit of 0.22 ng/mL even without further concentration after desorption), high accuracies (92.6⁓103.0 %) and good precisions (0.57⁓4.53 %), indicating a great potential of this material and method in the detection of trace or ultratrace BPA in complex environmental water samples.

Visual monitoring of hydrazine in food and environmental samples by wearable probe

Hydrazine is a poisonous compound that has been widely applied in the agricultural and chemical industry, leading to serious environmental pollution. Thus, the detection of hydrazine remained extremely important for ensuring food safety and environmental protection. Considering the importance of hydrazine detection for human health, a novel colorimetric/fluorescent probe (TPB) for the detection of hydrazine in various samples has been developed. In the presence of hydrazine, TPB emits a blue emission band at 452nm with high sensitivity (limit of detection equal to 40nM), ultrafast detection (less than 10s), broad working pH range (6−10), and strong anti-interference capabilities. These excellent performances have been exploited to fabricate hydrogel-based sensing labels (test kits, cotton swabs, glass rods, and gloves), which allowed the detection of hydrazine traces in soil, earthworms, plant samples, and living cells. This work presents a novel sensing approach for future research, aiming to develop a novel fluorescent probe exploiting the ICT process for the detection of hydrazine.

Protein-bridged size-permeable DNAzyme@PEG hollow nanosphere reactor facilitates direct and rapid monitoring of trace circulating microRNAs in undiluted cancer patient serums

The direct monitoring of low levels of circulating microRNAs (miRNAs) in undiluted human serums is of significant clinical importance for the diagnosis of different diseases in the early stages; however, this is highly challenged by both the short lengths, low abundance and homogeneity nature of miRNAs and the complicated sample matrix of human serums. In this work, we show the synthesis of a new protein-bridged and size-permeable DNAzyme@PEG hollow nanosphere reactor (p-DPHNR) that enables direct and rapid detection of trace circulating microRNAs in undiluted serums from prostate carcinoma patients. The hydrophilic PEG shell of p-DPHNR efficiently reduces protein adsorption; its size-permeability only allows short miRNAs to enter the core cavity and protects the core DNA signal probes from digestion; and the confinement of the NIR signal amplification DNA probes in the nanosphere core accelerates the reaction kinetics and minimizes the serum background fluorescence. Such p-DPHNR exhibits a 1.8 pM detection limit with a short 20 min assay time for miRNA-141 and can realize clear discrimination of prostate carcinoma patients from healthy donors, thereby manifesting its robust clinical applications for the convenient and early diagnosis of various diseases

Post-Burn and Post-Blast Rapid Detection of Trace and Bulk Energetics by 3D-Printed Cone Spray Ionization Mass Spectrometry

Forensic analysis of post-blast and post-burn materials can be critical to a law enforcement or military investigation. 3D-printed cone spray ionization (3D-PCSI) coupled to a field portable mass spectrometer (MS) has been demonstrated as a rapid and low-cost alternative to traditional laboratory-based techniques (high resolution liquid or gas chromatography mass spectrometry) for the detection and analysis of energetic materials. 3D-PCSI-MS can sample trace or bulk energetics within or upon solid matrices with no sample preparation. Solid samples, in this case post-blast or post-burn energetics, are placed within the hollow cavity of the cone that has an approximately 100 µm spray-based emitter at the apex. An extraction/spray solvent is added, and a high voltage is subsequently applied. When coupled to a field portable MS, post-burn and post-blast analyses can be performed in the field. Double base propellant was burned on a variety of substrates and examined via 3D-PCSI-MS. An energetic material and stabilizers used in propellants were detected from the post-burn samples with no sample preparation. Trinitrotoluene (TNT, used in military and commercial explosives) and triacetone triperoxide (TATP, a homemade explosive) were examined post-blast on the US ton scale and the gram scale, respectively.

SERS-lateral flow immunoassay based on AuNR@Ag@SiO2-AuNP assembly for ultra-sensitive detection of deoxynivalenol in grain

In view of the serious harm and widespread pollution caused by deoxynivalenol (DON), it is crucial to quantify its presence in the food safety assessment process. Here, we designed a core-shell-satellite nano assembly structure as a probe, composed of an anisotropic AuNR@Ag core, an ultra-thin SiO2 layer and a high surface coverage AuNPs satellites, which showed outstanding SERS activity and high stability. Anti-DON antibodies were modified on the surface of the prepared core-shell-satellite nano-assembly structure as SERS immunoprobe for DON specific detection using SERS-based lateral flow immunoassay (LFIA) with the advantages of simplicity, rapidity, and high sensitivity. Under optimal conditions, the detection limit for detecting DON using the SERS-LFIA method was 0.053 fg/mL, and the linear detection ranged from 0.1 fg/mL to 1 μg/mL. The SERS-LFIA strips based on AuNR@Ag@SiO2-AuNP nanostructures demonstrated the great potential for quick quantitative DON detection, providing a reference for trace detection of highly toxin mycotoxins.

Trace detection of benzene, toluene and xylene (BTX) by chemiresistive metal oxide-based gas sensors: Recent advances in heterojunction materials design

Trace detection of benzene, toluene and xylene (BTX) by chemiresistive metal oxide-based gas sensors: Recent advances in heterojunction materials design

Fluorescence sensor based on Methionine-Modified silver nanoparticles located on Fe-BTC metal–organic framework (Meth-AgNPs@Fe-BTC) for trace detection of fenitrothion pesticide in aqueous samples

This research introduces a new “turn-on mode” fluorescence sensor for the detection of fenitrothion (FNT) pesticide in various samples. The sensor is constructed using a porous metal–organic framework (Fe-BTC) as a template to locate silver nanoparticles (AgNPs) and methionine amino acid (Meth). Methionine acts as a bridge, facilitating the interaction between FNT and AgNPs, which subsequently results in the release of AgNPs from the composite structure. The physicochemical properties of the synthesized Meth-AgNPs@Fe-BTC composite were analyzed by Fourier-transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDAX), Transmission electron microscopy (TEM), and elemental mapping (MAP) analysis. The sensing system is based on tracking the fluorescence of the synthetic composite in such a way that the intensity of the fluorescence of the composite increases in the presence of different concentrations of fenitrothion (FNT). The effective parameters on the sensor signal, including composite dosage, pH, sonication and reaction time were investigated and optimized. The calibration graph, under optimal conditions, exhibited linearity in the concentration range of 2–95 nM for FNT, with a limit of detection of 1.9 nM. The suggested sensor was successfully validated by analyzing FNT in several real water samples and fruit juices. This research presents a significant technical achievement in the development of a fluorescence sensor for the detection of FNT, offering a sensitive and reliable method for environmental monitoring and public health preservation.

Dual trace detection of hazardous substances by aptamer-functionalized gold nanofilms based on surface-enhanced Raman spectroscopy

Dual trace detection of hazardous substances by aptamer-functionalized gold nanofilms based on surface-enhanced Raman spectroscopy

Enhanced SERS signal in the hybrid substrate through electronic modulation of CVD grown single-layer graphene

The ever-growing demand for sensitive and reliable detection of hazardous material in the food chain and trace detection of chemical entities in a variety field attracted advanced Surface Enhanced Raman Spectroscopy (SERS) active material such as graphene-based hybrid SERS. The graphene‑silver nanostructures (AgNS) based hybrid SERS substrates are explored to understand the critical role of pristine graphene grown by chemical vapor deposition (CVD) on SERS signal and its possible mechanism. A lithography-free fabrication process has been developed for growth of uniform array of AgNS with varying both particle sizes and inter-particle gaps. The optimal AgNS with feature size ~40 nm and inter-particle spacing of ~13 nm demonstrated the maximum SERS enhancement with Rhodamine 6G (R6G). The single-layer graphene (SLG) grown by CVD with the aid of controlling the reaction geometry with growth under a free molecular regime leads to the highest quality graphene with I2D/IG ratio of ~3.58 and ID/IG ratio of 0.1539. The flow regime-controlled CVD-grown SLG integrated with AgNS and its SERS enhancement mechanism is explored for trace detection of R6G. The graphene with its ability to modulate the electronic structure and tune it relative to the highest occupied molecular orbital-lowest occupied molecular orbital (HOMO-LUMO) levels of R6G molecules resulted in improved SERS signal by about an order for graphene-AgNS hybrid structure as compared to bare AgNS. The obtained findings paved the way for the futuristic and reliable hybrid SERS substrate for trace-level detection of a wide range of chemical entities.

“Dandelion” magnetic bead-driven CDs@CeO2 based-multifunctional nanoplatform for tri-modal ultrasensitive detection and efficient eradication of pathogenic bacteria

To address the challenge of foodborne pathogens, we have developed an ultra-sensitive tri-modal detection and effective pathogen eradication strategy utilizing a “dandelion” magnetic bead-driven cerium dioxide doped with carbon dots (CDs@CeO2) multifunctional nanoplatform. Aptamer (Apt) modification CDs@CeO2 specifically recognizes and binds to the outer membrane proteins of Salmonella typhimurium (S. typhimurium). Concurrently, mannose-functionalized dandelion-like magnetic beads selectively recognize adhesins of S. typhimurium, avoiding competition with Apt for binding sites and leveraging the strong bacterial capture capability for high-sensitivity detection. The prepared CDs@CeO2 has been demonstrated to exhibit favourable fluorescence characteristics. In the presence of H2O2, CDs@CeO2 is capable of oxidising colourless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxide, displaying exceptional photothermal properties. CDs@CeO2 have the potential to generate •OH through a Fenton-like reaction, which could directly damage cells. Notably, coupling the photosensitizer Ce6 to CDs@CeO2 and subsequent illumination generates 1O2, which synergistically eradicates bacteria with •OH. Detection limits of the fluorescence, colorimetry, and photothermal methods were 3.85 cfu/mL, 9.44 cfu/mL, and 5.00 cfu/mL, respectively. The platform successfully achieves precise detection of S. typhimurium in actual pre-prepared food samples through fluorescence, colorimetry, and photothermal tri-modal signals, and effectively kills bacteria, achieving trace detection and source control.

Recent Progress in Nanomaterial-Based Surface-Enhanced Raman Spectroscopy for Food Safety Detection.

Food safety has recently become a widespread concern among consumers. Surface-enhanced Raman scattering (SERS) is a rapidly developing novel spectroscopic analysis technique with high sensitivity, an ability to provide molecular fingerprint spectra, and resistance to photobleaching, offering broad application prospects in rapid trace detection. With the interdisciplinary development of nanomaterials and biotechnology, the detection performance of SERS biosensors has improved significantly. This review describes the advantages of nanomaterial-based SERS detection technology and SERS's latest applications in the detection of biological and chemical contaminants, the identification of foodborne pathogens, the authentication and quality control of food, and the safety assessment of food packaging materials. Finally, the challenges and prospects of constructing and applying nanomaterial-based SERS sensing platforms in the field of food safety detection are discussed with the aim of early detection and ultimate control of foodborne diseases.

Mechanically Flexible, Large-Area Fabrication of Three-Dimensional Dendritic Au Films for Reproducible Surface-Enhanced Raman Scattering Detection of Nanoplastics.

The escalating crisis of nanoplastic pollution in water and food products demands the development of novel methodologies for detection and recycling. Despite various techniques available, surface-enhanced Raman scattering (SERS) is emerging as a highly efficient technique for the trace detection of micro/nanoplastics. However, the development of highly reproducible and stable, flexible SERS substrates that can be used for sensitive detection in environmental medium remains a challenge. Here, we report a fabrication of large-area, three-dimensional (3D), and highly flexible SERS substrate based on porous dendritic Au films onto a flexible indium tin oxide (ITO) substrate via facile, thermal evaporation of Au over the vacuum-compatible deep eutectic solvent (DES)-coated glass substrate and subsequent direct transfer process. The as-fabricated 3D dendritic Au/ITO flexible substrates can be used for ultrasensitive SERS detection of crystal violet (CV) as probe analyte molecules with the limit of detection (LOD) as low as 6.4 × 10-15 M, with good signal reproducibility (RSD of 11.3%). In addition, the substrate showed excellent sensitivity in detecting nanoplastics such as poly(ethylene terephthalate) (200 nm) and polystyrene (100 nm) with LODs reaching up to 0.051 and 8.2 μg/mL, respectively. This work provides a facile approach for the preparation of highly flexible plasmonic substrates, showing great potential for the SERS detection of a variety of environmental pollutants.

Lateral Flow Immunoassay for the Rapid Detection of Thiamethoxam in Tea Based on a SERS Tag Constructed by Phenolic-Mediated Coating Engineering.

Sensitive and accurate detection of thiamethoxam in tea is significant to ensuring consumer health. In this study, surface-enhanced Raman scattering (SERS) tags were prepared by using a polyphenol-mediated coating engineering strategy. This approach involved the self-assembly of tannic acid (TA) and self-polymerization of benzene-1,4-dithiol (BDT) on the surface of gold nanoparticles, resulting in the formation of Au@pBDT-TA. The SERS tags possess high Raman signals and antibody adsorption properties, avoiding the complex decoration or label steps of SERS reporters. We discovered that Au@pBDT-TA, composed of gold nanoparticles at 40 nm and a pBDT-TA thickness of 10 nm, was optimal for the development of the SERS lateral flow immunoassay (LFIA). In comparison to the gold nanoparticle-based LFIA, the SERS-LFIA demonstrated 4-fold and 720-fold enhancements in visual and quantitative limits of detection in buffer solution. The SERS-LFIA demonstrated quantitative limits of detection of 0.06 and 0.1 ng/g for black and green tea, respectively, with a broader linear range spanning over 2 orders of magnitude and a short detection time of 20 min. The proposed SERS-LFIA not only offers a sensitive and reliable method for monitoring thiamethoxam in tea but also possesses a versatile potential that can be easily adapted for the trace detection of various other targets.

Quantitative analysis of acetamiprid and thiacloprid in green tea using enhanced SERS and neural networks

Neonicotinoids (NEOs) are widely used in agricultural cultivation, and the presence of residual NEOs poses a serious threat to consumer health. Therefore, trace detection of NEOs is particularly important. In this study, a response surface experimental design was employed to develop AgNP with high enhancement factor and surface height anisotropy, effectively enhancing the Raman signals of acetamiprid (ACE) and thiacloprid (THI) through densely populated hotspots on the surface. Gaussian simulation calculations were used to assign peaks in the ACE and THI spectra. Subsequently, convolutional neural network, backpropagation neural network, and AlexNet neural network were employed to identify the ACE, THI, and mixed component spectra, successfully distinguishing the spectra of the three compounds and achieving qualitative analysis of unknown spectra. Furthermore, genetic algorithm-partial least squares was used to model the spectral data, achieving a correlation coefficient of 0.97. The method was applied for the detection of spiked tea samples, achieving a precision RSD of 4.84 %. Therefore, this sensor combined with intelligent algorithms can be used for spectral identification and trace detection of mixed pesticide samples with structurally similar compounds.

Convenient Au@Ag Double‐Layer Nanoarray Fabricated by Rapid Thermal Annealing and Chemical Replacement Method for Surface‐Enhanced Raman Spectroscopy Sensing

Surface‐enhanced Raman spectroscopy (SERS) has a wide range of applications in molecular recognition, environmental pollutant detection, and other fields. However, the intensity and number of “hot spots” in 1D and 2D nanostructures are limited due to the scale‐dependent localized plasmonic effect of nanostructures, making it difficult to increase the detection limit. Herein, a kind of 3D substrate called Au@Ag double‐layer nanoarray (Au@Ag DLA) is prepared using rapid thermal annealing and chemical replacement methods. The energy‐dispersive spectrometer spectra confirm the successful growth of AgNPs on the gold nanoarray (Au SLA) by showing no presence of the copper element, indicating complete replacement of the Cu film deposited on Au SLA by Ag atoms. The detection limit of malachite green in Au@Ag DLA is 10−8 mol L−1, four and three orders of magnitude higher than that of Au SLA and AgNPs, respectively. This stronger SERS effect of Au@Ag DLA arises from the larger number of intense hot spots generated not only on the horizontal surface but also in the vertical direction. This finding provides a method for developing efficient and stable 3D SERS substrate, which can be utilized for the trace detection of water pollutants and pesticide residue.

Raspberry-Like Plasmonic Nanoaggregates with Programmable Hierarchical Structures for Reproducible SERS Detection of Wastewater Pollutants and Biomarkers.

Conventional solid-based SERS substrates often face challenges with inconsistent sample distribution, while liquid-based SERS substrates are prone to aggregation and precipitation, resulting in irreproducible signals in both cases. In this study, we tackled this dilemma by designing and synthesizing raspberry-like plasmonic nanoaggregates that exhibit a high density of hotspots and are colloidally stable at the same time. In particular, the nanoaggregates consist of a core made of functionalized polystyrene (PS) microspheres, which act as a template for rapid self-assembly of Au@Ag core-shell nanoparticles to form raspberry-like hierarchical nanoaggregates within 5 min of mixing. The optimized nanoaggregates can be used as reproducible and stable SERS substrates for a range of wastewater pollutants (e.g., rhodamine 6G (R6G) and malachite green (MG)) and nucleobases (e.g., adenine and uracil), with the detection limits as low as 1 × 10-10, 1 × 10-16, 3 × 10-8, and 3 × 10-7 M, respectively. Additionally, the trace detection of adenine in clinical urine samples has been successfully demonstrated. Our modular assembly approach opens up new possibilities in SERS substrate design and advanced trace-chemical detection technologies.

Large-scale medieval urbanism traced by UAV-lidar in highland Central Asia.

Aerial light detection and ranging (lidar) has emerged as a powerful technology for mapping urban archaeological landscapes, especially where dense vegetation obscures site visibility1,2. More recently, uncrewed aerial vehicle/drone lidar scanning has markedly improved the resolution of three-dimensional point clouds, allowing for the detection of slight traces of structural features at centimetres of detail across large archaeological sites, a method particularly useful in areas such as mountains, where rapid deposition and erosion irregularly bury and expose archaeological remains3. Here we present the results of uncrewed aerial vehicle-lidar surveys in Central Asia, conducted at two recently discovered archaeological sites in southeastern Uzbekistan: Tashbulak and Tugunbulak. Situated at around 2,000-2,200 m above sea level, these sites illustrate a newly documented geography of large, high-altitude urban centres positioned along the mountainous crossroads of Asia's medieval Silk Routes (6th-11th centuryCE (Common Era)4,5. Although hidden by centuries of surface processes, our pairing of very-high-resolution surface modelling with semiautomated feature detection produces a detailed plan of monumental fortifications and architecture spanning 120 ha at Tugunbulak, thereby demonstrating one of the largest highland urban constellations in premodern Central Asia. Documentation of extensive urban infrastructure and technological production among medieval communities in Central Asia's mountains-a crucial nexus for Silk Road trade networks6-provides a new perspective on the participation of highland populations in the economic, political and social formation of medieval Eurasia.

Light-Sheet Skew Ray-Based Microbubble Chemical Sensor for Pb2+ Measurements

A multimode fiber-based sensor is proposed and demonstrated for the detection of lead traces in contaminated water. The sensing mechanism involves using a light sheet to excite a specific group of skew rays that optimizes light absorption. The sensing region features an inline microbubble structure that funnels the skew rays into a tight ring, thereby intensifying the evanescent field. The sensitivity is further refined by incorporating gold nanoparticles, which amplify the evanescent field strength through localized surface plasmon resonance. The gold nanoparticles are functionalized with oxalic acid to improve specificity for lead ion detection. Experiment results demonstrated the significantly enhanced absorption sensitivity of the proposed sensing method for large center offsets, achieving a detection limit of 0.1305 ng/mL (the World Health Organization safety limit is 10 ng/mL) for concentrations ranging from 0.1 to 10 ng/mL.

Near-Infrared Dual-Range Methane Sensor Using the OAIC-HC Mode Based on VMD-SG-Assisted Optical Noise Suppression.

Based on tunable diode laser absorption spectroscopy and off-axis integrated cavity output spectroscopy, a dual-range methane hybrid sensor was constructed utilizing the overtone absorption band of CH4 gas molecules at 1653.7 nm. By simultaneously utilizing an off-axis integrated cavity and Herriott cell with an effective absorption path of 11 and 405 m, respectively, the two received photoelectric signals are decomposed into different frequency components by VMD and then reconstructed after SG filtering. Applying the global optimization algorithm DA-ELM to CH4 concentration inversion, the correlation coefficient R2 is as high as 0.9995. Through long-term stability verification, the instrument's standard deviation at 1 ppm is 27 ppb. After Allan-Werle deviation analysis, the sensor's limit of detection is 2.298 ppb at an integration time of 138 s. Using the self-developed sensor, the detection of dual-range trace CH4 gas is achieved, enabling a dynamic detection range of trace CH4 gas ranging from 400 ppb to 1000 ppm. The sensor realizes dual-range methane trace detection and actively controls methane emissions to improve environmental quality while taking into account the safety benefits of reducing production accidents.