Silver nanoparticles-based colorimetric array for the detection of Thiophanate-methyl

Copper-based fluorescent nanozyme used to construct a ratiometric sensor for visual detection of thiophanate methyl

Although nanozyme has shown great potential in designing fluorescent assays for pesticide residue, most of them are based on single emission, thus affecting the detection accuracy. Herein, a copper-based fluorescent nanozyme (Cu-BH) synthesized with dual-ligand, integrating fluorescence and oxidase-mimic into one spherical nanomaterial, was used firstly to establish a ratiometric approach for visual detection of thiophanate methyl (TM). Cu-BH possesses excellent oxidase-like activities, triggering the oxidation of colorless o-phenylenediamine (OPD) into yellow luminescent products (oxOPD, λem = 564 nm). Besides, the ligand of 2-amino-1,4-benzene-dicarboxylic acid imparts Cu-BH blue fluorescence (λem = 425 nm), which is quenched by oxOPD via inner filtration effect (IFE). The introduction of TM can prevent not only the oxidase-like activity remarkably but also the intrinsic luminescence of Cu-BH slightly because of the complexation of TM with Cu2+. As a result, the fluorescence intensity at 564 nm and 425 nm presents a significant decrease and a slight increase, respectively, producing a ratiometric fluorescent signal (F425/F564). Therefore, a novel ratiometric fluorescent strategy has been proposed to detect TM ranging from 0.1 to 100 μM with detection limit of 0.03 μM (S/N = 3). Besides, visual detection of TM can be achieved by RGB reading with the assistance of smartphone owing to the color variation from yellow to blue. This fluorescent nanozyme-based ratiometric strategy provides a specific method for the detection of TM in food samples.

Sensitive and selective colorimetric detection of thiophanate-methyl based on a novel Ru-Fe3O4 nanozyme with enhanced peroxidase-like activity

A novel Ru-Fe3O4 nanozyme with enhanced peroxidase-like (POD-like) activity was synthesized through a hydrothermal method. Ru-Fe3O4 nanozyme was effectively utilized for the detection of thiophanate-methyl (TM) using a colorimetric technique. The POD-like activity of Ru-Fe3O4 was found to be superior compared to Fe3O4, Rh-Fe3O4, and Pd-Fe3O4. Ru-Fe3O4 provided excellent POD-like activity with Michaelis constants of 0.00645 mM and 0.66714 mM for substrates of 3,3',5,5'-tetramethylbenzidine and H2O2, respectively. The density functional theory calculation showed that Ru-Fe3O4 had better H2O2 decomposition reactivity compared to Fe3O4. Compared with Fe3O4, the adsorbed H2O2 molecules underwent decomposition more readily on the Ru-Fe3O4 catalytic surface facilitating the occurrence of the H2O2 catalytic reaction, further suggesting the excellent POD-like activity of Ru-Fe3O4. The coordination and electrostatic interactions of Ru-Fe3O4 and TM promoted their binding, contributing to TM covering Ru-Fe3O4 catalytic site and inhibiting the POD-like activity of Ru-Fe3O4. As a result, the sensitive and selective detection of TM using Ru-Fe3O4 by a colorimetric method was achieved. The Ru-Fe3O4 nanozyme displayed a good linear correlation, with a linear detection range and a detection limit of 0.1-100 and 0.03 μg/mL, respectively. The Ru-Fe3O4 nanozyme was used for the determination of TM in soil and water samples with success.

Ensuring food safety by artificial intelligence-enhanced nanosensor arrays

Current analytical methods utilized for food safety inspection requires improvement in terms of their cost-efficiency, speed of detection, and ease of use. Sensor array technology has emerged as a food safety assessment method that applies multiple cross-reactive sensors to identify specific targets via pattern recognition. When the sensor arrays are fabricated with nanomaterials, the binding affinity of analytes to the sensors and the response of sensor arrays can be remarkably enhanced, thereby making the detection process more rapid, sensitive, and accurate. Data analysis is vital in converting the signals from sensor arrays into meaningful information regarding the analytes. As the sensor arrays can generate complex, high-dimensional data in response to analytes, they require the use of machine learning algorithms to reduce the dimensionality of the data to gain more reliable outcomes. Moreover, the advances in handheld smart devices have made it easier to read and analyze the sensor array signals, with the advantages of convenience, portability, and efficiency. While facing some challenges, the integration of artificial intelligence with nanosensor arrays holds promise for enhancing food safety monitoring.

Smartphone-assisted carbon dots fluorescent sensing platform for visual detection of Thiophanate-methyl in fruits and vegetables

Trimesic acid and o-phenylenediamine (OPD) were employed as precursors to synthesize yellow-green fluorescent carbon dots (Y-G-CDs) by solvothermal synthesis for the sensitive detection of Thiophanate-methyl (TM) in real agricultural products. The Y-G-CDs probe could specifically recognize the TM primarily through π-π stacking. Moreover, the fluorescence quenching of the probe was ultimately dominated by the PET effect, based on the interaction between the abundant carboxyl groups on the surface of the Y-G-CDs and the amino group of TM. A strong linear relationship between the fluorescence quenching of the probe and TM concentration in the range of 0-10 µmol/L was observed and the limit of detection (LOD) was calculated to be 50.7 nmol/L. Compared to the interference pesticides, the Y-G-CDs probe demonstrated exceptional selectivity toward TM, with satisfactory recoveries of 96.3 % - 104.2 % in spiked food samples. The Y-G-CDs probe enables simple pretreatment, cost-effective, and on-site detection of TM in fruits and vegetables with visual detection of the TM employing a smartphone-assisted sensing platform.

MOF-based Ag NPs/Co3O4 nanozyme for colorimetric detection of thiophanate-methyl based on analyte-enhanced sensing mechanism

Silver nanoparticles supported on metal-organic framework (ZIF-67)-derived Co3O4 nanostructures (Ag NPs/Co3O4) were synthesized via a facile in situ reduction strategy. The resulting materials exhibited pH-switchable peroxidase/catalase-like catalytic activity. Ag NP doping greatly enhanced the catalytic activity of Ag NPs/Co3O4 towards 3,3',5,5'-tetramethylbenzidine (TMB) oxidation and H2O2 decomposition which were 59 times (A652 of oxTMB) and 3 times (A240 of H2O2) higher than that of ZIF-67, respectively. Excitingly, thiophanate-methyl (TM) further enhanced the peroxidase-like activity of Ag NPs/Co3O4 nanozyme due to the formation of Ag(I) species in TM-Ag NPs/Co3O4 and generation of more radicals resulting from strong interaction between Ag NPs and TM. The TM-Ag NPs/Co3O4 nanozyme exhibited lower Km and higher Vmax values towards H2O2 when compared with Ag NPs/Co3O4 nanozyme. A simple, bioelement-free colorimetric TM detection method based on Ag NPs/Co3O4 nanozyme via analyte-enhanced sensing strategy was successfully established with high sensitivity and selectivity. Our study demonstrated that hybrid noble metal NPs/MOF-based nanozyme can be a class of promising artificial nanozyme in environmental and food safety applications.

CuI-p-DPA coordination polymer isomers for "turn-on" fluorescence detection of thiophanate-methyl

Three copper iodide coordination polymer (CuI-p-DPA) isomers were prepared from the fluorescent organic ligand p-DPA and cuprous iodide (CuI) under different solvothermal conditions, which exhibited quenched fluorescence behaviors after forming coordination polymers (CPs). These CuI-p-DPA isomers showed discrepant fluorescence responses to thiophanate-methyl (TM). Among these CuI-p-DPA isomers, α-CuI-p-DPA exhibited the maximum fluorescence enhancement after its incubation with TM in aqueous solution. The fluorescence enhancement mechanism was that TM competed with the ligand p-DPA to coordinate with CuI clusters, and then α-CuI-p-DPA released p-DPA into the solution and induced fluorescence enhancement. The present detection method possesses the advantages of good selectivity, high sensitivity, short response time, and strong anti-interference ability with a linear range of 0.5-100 μM and a detection limit of 0.01 μM. This study not only reveals that the spatial structures of CPs play an important role in the fluorescence response ability, but also provide a new fluorescence signal-on analysis method to rapidly and sensitively determine the pesticide residue for TM.

Specific detection of fungicide thiophanate-methyl: A smartphone colorimetric sensor based on target-regulated oxidase-like activity of copper-doped carbon nanozyme

Nanozyme-based colorimetric assays have shown great potential in the rapid and sensitive determination of pesticide residue in environment. However, the non-specific enzyme inhibition makes the assays generally lack of selectivity. In this study, we proposed a colorimetric sensing platform for the specific detection of the agricultural fungicide thiophanate-methyl (TM) based on its distinctive inhibitory effect on the nanozyme activity. Since TM contains the symmetric ethylenediamine- and bisthiourea-like groups, it displays strong affinity to the metal site, leading to a loss of the catalytic activity. Accordingly, a Cu-doped carbon nanozyme with excellent oxidase-like properties was designed, and the oxidation process of chromogenic substrate is promoted by Cu-induced generation of reactive oxygen species. Interestingly, the nanozyme activity can be directly and strongly restrained by TM, rather than other probably coexistent pesticides. Consequently, the as-proposed analytical method exhibits specific response toward TM and good linear relationship in the range of 0.2-15 μg mL-1 with a low limit of detection of 0.04 μg mL-1 (S/N = 3). Besides, a smartphone-assisted rapid detection was achieved through identifying the RGB value of the chromogenic system. This work provides a new nanozyme inhibition strategy for the specific detection of TM in environmental sample.

Colorimetric Sensor Array for Identification of Proteins and Classification of Metabolic Profiles under Various Osmolyte Conditions

Rapid and efficient detection and identification of proteins hold great promise in medical diagnostics, treatment of different diseases, and proteomics. Here, we present a simple colorimetric sensor array for the differentiation of proteins in various osmolyte solutions. Osmolytes have different influences on the conformation of proteins, which have differential binding to silver nanoparticles, resulting in color changes. The sensor array shows unique color change patterns for each of the 19 proteins, allowing unambiguous identification. Very interestingly, the differentiation of 19 proteins is related to their molecular weight. Moreover, the sensor array can be used to identify protein mixtures, thermal denaturized proteins, and unknown protein samples. Finally, the sensor array can also analyze the plasma or liver samples of the four groups of salt-sensitive rats fed with different diets, indicating that it has the potential for the classification of metabolic profiles.

Copper-Modified Double-Emission Carbon Dots for Rapid Detection of Thiophanate Methyl in Food

The detection of food safety and quality is very significant throughout the food supply. Stable dual-emission copper-modified fluorescent carbon dots (Cu-CDs) were successfully synthesized by a simple and environment-friendly hydrothermal, which was used for the real-time detection of pesticide residues in agricultural products. By optimizing the reaction conditions, Cu-CDs showed two emission peaks, with the highest fluorescence intensities at 375 and 450 nm. The structure, chemical composition and optical properties of Cu-CDs were investigated by XRD, TEM and IR. The results showed that thiophanate methyl (TM) could induce fluorescence quenching of Cu-CDs with no other ligands by the electron transfer through π-π stacking. The synchronous response of the dual-emission sensor enhanced the specificity of TM, which showed remarkable anti-interference capability. The fluorescence quenching degree of Cu-CDs had a good linear relationship with the TM concentration; the low detection limit for a pear was 0.75 μM, and for an apple, 0.78 μM. The recoveries in the fruit samples were 79.70–91.15% and 81.20–93.55%, respectively, and the relative standard deviations (RSDs) were less than 4.23% for the pear and less than 3.78% for the apple. Thus, our results indicate the feasibility and reliability of our methods in detecting pesticide residues in agricultural products.

Carbon dots@Cu metal-organic frameworks hybrids for ratiometric fluorescent determination of pesticide thiophanate-methyl

A dual-emission fluorescent (FL) probe was constructed by coordinating Cu²⁺ of copper metal-organic frameworks (Cu-MOFs) with - COO^- group of carbon dots (CDs) for pesticide thiophanate-methyl (TM) determination. TM was recognized by organic ligands (H₂BDC and H₂BDC-NH₂) of Cu-MOFs via π stacking. Due to the higher affinity of Cu²⁺ to TM than ligands and CDs, TM chelated with Cu²⁺ to form TM-Cu complex. Thus coordination of Cu-MOFs was damaged and the ligands were released resulting in the FL intensity increase of Cu-MOFs (F₄₃₀). And also CDs were released from CDs@Cu-MOFs hybrids and electron transfer from CDs to CuMOFs was inhibited, leading to the FL intensity increase of CDs (F₆₀₀). The FL intensity ratio (F₄₃₀/F₆₀₀) showed a good linear relationship with TM concentrations of 0.0307-0.769 μmol L^-1 with a limit of detection (LOD) of ~ 3.67 nmol L^-1. The probe was successfully applied to detect TM in spiked food samples with satisfactory recoveries of 93.1-113%. Additionally, visual detection of TM was achieved according to the fluorescence color variation from blue to carmine, indicating promising application of CDs@Cu-MOFs probe.

Smart MOF-on-MOF Hydrogel as a Simple Rod-shaped Core for Visual Detection and Effective Removal of Pesticides

The immoderate use of pesticides in the modern agricultural industry has led to the pollution of water resources and ultimately threatens the human body. Herein, two metal-organic frameworks (MOFs), namely {[Zn(tpt)₂ ·2H₂ O]}_n (Zn1) and {[Zn₂ (tpt)₂ (bdc)]}_n (Zn2), (Htpt = 5-[4(1H-1,2,4-triazol-1-yl)]phenyl-2H-tetrazole), respectively, are constructed as smart materials for visual and on-site detection of pesticides and their removal from water. The exposed nitrogen-rich sites and high chemical stability make Zn2 a self-assembly core to further fabricate MOF-on-MOF-sodium alginate (ZIF-8-on-Zn2@SA) composite by wrapping ZIF-8 on the outside surface. Inheriting the excellent fluorescent emission of Zn2, the rod-like ZIF-8-on-Zn2@SA module exhibits naked-eye detection of thiophanate-methyl (TM) in real fruits and vegetables with a broad linear range (10-100 × 10^-6  m), a low limit of detection (LOD = 0.14 × 10^-6  m), and satisfactory recoveries (98.30-102.70%). In addition, carbendazim (CBZ), the metabolite of TM after usage in crops, can be efficiently removed from water by the ZIF-8-on-Zn2@SA (q_max  = 161.8 mg g^-1 ) with a high correlation coefficient (R²  > 0.99). Therefore, the portable ZIF-8-on-Zn2@SA sensing platform presents a promising candidate for monitoring and removal of pesticides, especially suitable for regions with serious pesticide environmental pollution.

Recent advances of nanomaterial-based optical sensor for the detection of benzimidazole fungicides in food: a review

The abuse of pesticides in agricultural land during pre- and post-harvest causes an increase of residue in agricultural products and pollution in the environment, which ultimately affects human health. Hence, it is crucially important to develop an effective detection method to quantify the trace amount of residue in food and water. However, with the rapid development of nanotechnology and considering the exclusive properties of nanomaterials, optical, and their integrated system have gained exclusive interest for accurately sensing of pesticides in food and agricultural samples to ensure food safety thanks to their unique benefit of high sensitivity, low detection limit, good selectivity and so on and making them a trending hotspot. This review focuses on recent progress in the past five years on nanomaterial-based optical, such as colorimetric, fluorescence, surface-enhanced Raman scattering (SERS), and their integrated system for the monitoring of benzimidazole fungicide (including, carbendazim, thiabendazole, and thiophanate-methyl) residue in food and water samples. This review firstly provides a brief introduction to mentioned techniques, detection mechanism, applied nanomaterials, label-free detection, target-specific detection, etc. then their specific application. Finally, challenges and perspectives in the respective field are discussed.

Recent Advances in (Bio)Chemical Sensors for Food Safety and Quality Based on Silver Nanomaterials

There is a continuing need for tools and devices which can simplify, quicken and reduce the cost of analyses of food safety and quality. Chemical sensors and biosensors are increasingly being developed for this purpose, reaping from the opportunities provided by nanotechnology. Due to the distinct electrical and optical properties of silver nanoparticles (AgNPs), this material plays a vital role in (bio)sensor development. This review is an analysis of chemical sensors and biosensors based on silver nanoparticles with application in food and beverage matrices. It consists of academic research published from 2015 to 2020. The paper is structured to separately explore the designs of two major (bio)sensor classes: electrochemical (including voltammetric and impedimetric sensors) and optical sensors (including colourimetric and luminescent), with special focus on the type of silver nanomaterial and its role in the sensor system. The review indicates that diverse nanosensors have been developed, capable of detecting analytes such as pesticides, mycotoxins, fertilisers, microorganisms, heavy metals, and various additives with exceptional analytical performance. Current trends in the design of such sensors are highlighted and challenges which need to be overcome in the future are discussed.

An OliGreen-responsive fluorescence sensor for sensitive detection of organophosphorus pesticide based on its specific selectivity towards T-Hg2+-T DNA structure

In this paper, it was found that OliGreen emitted much stronger fluorescence in rigid T-Hg²⁺-T DNA structure than that in the presence of poly T. Thus, an OliGreen-responsive label-free fluorescent sensor was proposed for sensitive detection of organophosphorus pesticides (OPs) by constructing T-Hg²⁺-T DNA structure. OliGreen emits strong fluorescence in T-Hg²⁺-T structures. The rigid DNA structure of T-Hg²⁺-T is prone to be destroyed by thiocholine (TCh) that hydrolyzed by acetylcholinesterase (AChE) because of the high affinity of TCh with Hg²⁺. As a result, T-Hg²⁺-T DNA structure broke down and the fluorescence intensity of OliGreen decreased greatly. With the inhibition of AChE by OPs, fluorescence intensity of OliGreen remained strong because of the rigid T-Hg²⁺-T DNA structure. Thus, a "turn-on" fluorescent sensor which avoids synthesis of nanomaterials and complex label procedures is proposed based on the fluorescence intensity of OliGreen. DDVP were detected with a wide linear range from 0.005 to 25.0 ng/mL and the detection limit was 2.9 pg/mL, which is more sensitive than previously reported methods.

Recent advances in functionalization of plasmonic nanostructures for optical sensing

This review summarizes the progress that has been made in the use of nanostructured SPR-based chemical sensors and biosensors. Following an introduction into the field, a first large section covers principles of nanomaterial-based SPR sensing, mainly on methods using noble metal nanoparticles (spheres, cubes, triangular plates, etc.). The next section covers methods for functionalization of plasmonic nanostructures, with subsections on functionalization using (a) amino acids and proteins; (b) oligonucleotides, (c) organic polymers, and (d) organic compounds. Several tables are presented that give an overview on the wealth of methods and materials published. A concluding section summarizes the current status, addresses current challenges, and gives an outlook on potential future trends. This review is not intended to be a comprehensive compilation of the literature in the field but rather is a systematic overview of the state of the art in surface chemistry of plasmonic nanostructures. The ability of various ligands and receptors for functionalization of nanoparticles as well as their sensing capability is discussed.

A novel thioctic acid-carbon dots fluorescence sensor for the detection of Hg2+ and thiophanate methyl via S-Hg affinity

Mercury ions and thiophanate methyl (TM), are common contaminants present in the environment and food products. These contaminants cause neurovirulence and carcinogenicity effect on the human body. Herein, thioctic acid-carbon dots (SCDs) was synthesized and applied in a fluorescent "turn-off-on" probe to detect Hg²⁺ and TM. The presence of other common metal ions and pesticides did not affect the response of the developed sensor. Further investigation revealed that the fluorescent "turn-off-on" model were static, wherein the "turn-off" was induced by an electron transfer effect, while the "turn-on" was caused by the formation of TM-Hg complexes. Under optimal conditions, the fluorescence sensor method exhibited limits of detection as low as 33.3 nmol/L and 7.6 nmol/L for Hg²⁺ and TM, respectively. The developed sensor was designed to detect Hg²⁺ and TM in real tap water, grape juice and Citri Reticulatae Pericarpium (CRP) water samples.

Use of silver nanoparticles to counter fungicide-resistance in Monilinia fructicola

The potential of Ag-NPs to suppress Monilia fructicola isolates and to broaden the effectiveness of fungicides to overcome resistance was tested in vitro and in vivo. Twenty-three M. fructicola isolates were subjected to fungitoxicity screening with a number of fungicides in vitro, which resulted in the detection of 18 isolates resistant to benzimidazoles (BEN-R) thiophanare methyl (TM) and carbendazim (CARB). DNA sequencing revealed the E198A resistance mutation in the β-tubulin gene, target site of the benzimidazole fungicides in all resistant isolates. Ag-NPs effectively suppressed mycelial growth in both sensitive (BENS) and resistant isolates. The combination of Ag-NPs with TM led to a significantly enhanced fungitoxic effect compared to the individual treatments regardless resistant phenotype (BEN-R/S) both in vitro and when applied on apple fruit. The above observed additive/synergistic action is probably associated with an enhanced Ag-NPs activity/availability as indicated by the positive correlation between Ag-NPs and TM + Ag-NPs treatments. No correlation was found between AgNO₃ and Ag-NPs suggesting that difference(s) exist in the fungitoxic mechanism of action between nanoparticles and their ionic counterparts. Synergy observed between Ag-NPs and the oxidative phosphorylation-uncoupler fluazinam (FM) against both resistance phenotypes indicates a possible role of energy (ATP) metabolism in the mode of action of Ag-NPs. Additionally, the role of released silver ions on the fungitoxic action of Ag-NPs against M. fructicola was found to be limited because the combination with NaCl revealed a synergistic rather than the antagonistic effect that would be expected from silver ion binding with chlorine ions. The results of this study suggested that Ag-NPs can be effectively used against M. fructicola and when used in combination with conventional fungicides they could provide the means for countering benzimidazole resistance and at the same time reduce the environmental impact of synthetic fungicides by reducing doses needed for the control of the pathogen.

Cu2+-Triggered Carbon Dots with Synchronous Response of Dual Emission for Ultrasensitive Ratiometric Fluorescence Determination of Thiophanate-Methyl Residues

Copper ion (Cu²⁺)-triggered carbon dots (CDs/Cu) with dual emissions were utilized to develop a ratiometric fluorescence sensor for ultrasensitive detection of inert thiophanate-methyl (TM). TM could be recognized by CDs/Cu through π-π stacking and could chelate Cu²⁺ of CDs/Cu through metal ion coordination, inducing synchronous fluoresent quenching of the dual emission of CDs/Cu based on the excited state intramolecular proton transfer and the ligand-to-metal charge transfer. The fluorescence ratio of CDs/Cu (F₄₁₆/F₄₈₁) linearly responded in a TM concentration of 0.10-20.00 μmol/L with an ultralow limit of detection of 2.90 × 10^-6 μmol/L. A synchronous response of the ratiometric sensor enhanced the specificity toward TM and presented remarkable capability of anti-interference in complex matrices. The sensor exhibited satifactory accuracy and precision for practical applications with recoveries of 88.33-101.09% and relative standard deviations of 1.61-5.06%, demonstrating an ultrasensitive ratiometric fluorescent nanosensor for detecting pesticides residues in complex matrices.