Quantitative detection of glyphosate by simultaneous analysis of UV spectroscopy and fluorescence using DNA-labeled gold nanoparticles

An on-off-on fluorescent probe for the detection of glyphosate based on a Cu2+-assisted squaraine dye sensor

The herbicide glyphosate, N-(phosphonomethyl)glycine, has been widely used in the past 40 years, and has had many adverse effects on human health. Here, we constructed a convenient "on-off-on" fluorescent platform for detection of glyphosate via Cu2+ modulated squaraine dye fluorescence quenching. The squaraine dye F-0 exhibited strong fluorescence, which could be quenched by the addition of Cu2+. However, the addition of glyphosate restored the fluorescence intensity of F-0 due to the formation of a Cu2+-glyphosate complex. F-0 was utilized as a fluorescent probe for the quantitative detection of glyphosate, with the lowest detection limit of 13.16 nmol L-1. Furthermore, this method demonstrated high selectivity and anti-interference capabilities. The successful monitoring of glyphosate in real samples was achieved using this detection strategy.

Pesticide biosensors: trends and progresses

Pesticides, chemical substances extensively employed in agriculture to optimize crop yields, pose potential risks to human and environmental health. Consequently, regulatory frameworks are in place to restrict pesticide residue concentrations in water intended for human consumption. These regulations are implemented to safeguard consumer safety and mitigate any adverse effects on the environment and public health. Although gas chromatography- and liquid chromatography-mass spectrometry (GC-MS and LC-MS) are highly efficient techniques for pesticide quantification, their use is not suitable for real-time monitoring due to the need for sophisticated laboratory pretreatment of samples prior to analysis. Since they would enable analyte detection with selectivity and sensitivity without sample pretreatment, biosensors appear as a promising alternative. These consist of a bioreceptor allowing for specific recognition of the target and of a detection platform, which translates the biological interaction into a measurable signal. As early detection systems remain urgently needed to promptly alert and act in case of pollution, we review here the biosensors described in the literature for pesticide detection to advance their development for use in the field.

Advanced visual sensing techniques for on-site detection of pesticide residue in water environments

Pesticide usage has increased to fulfil agricultural demand. Pesticides such as organophosphorus pesticides (OPPs) are ubiquitous in world food production. Their widespread usage has unavoidable detrimental consequences for humans, wildlife, water, and soil environments. Hence, the development of more convenient and efficient pesticide residue (PR) detection methods is of paramount importance. Visual detecting approaches have acquired a lot of interest among different sensing systems due to inherent advantages in terms of simplicity, speed, sensitivity, and eco-friendliness. Furthermore, various detections have been proven to enable real-life PR surveillance in environment water. Fluorometric (FL), colourimetric (CL), and enzyme-inhibition (EI) techniques have emerged as viable options. These sensing technologies do not need complex operating processes or specialist equipment, and the simple colour change allows for visual monitoring of the sensing result. Visual sensing techniques for on-site detection of PR in water environments are discussed in this paper. This paper further reviews prior research on the integration of CL, FL, and EI-based techniques with nanoparticles (NPs), quantum dots (QDs), and metal-organic frameworks (MOFs). Smartphone detection technologies for PRs are also reviewed. Finally, conventional methods and nanoparticle (NPs) based strategies for the detection of PRs are compared.

Red-Emitting Polymerizable Guanidinium Dyes as Fluorescent Probes in Molecularly Imprinted Polymers for Glyphosate Detection

The development of methodologies to sense glyphosate has gained momentum due to its toxicological and ecotoxicological effects. In this work, a red-emitting and polymerizable guanidinium benzoxadiazole probe was developed for the fluorescence detection of glyphosate. The interaction of the fluorescent probe and the tetrabutylammonium salt of glyphosate was studied via UV/vis absorption and fluorescence spectroscopy in chloroform and acetonitrile. The selective recognition of glyphosate was achieved by preparing molecularly imprinted polymers, able to discriminate against other common herbicides such as 2,4-dichlorophenoxyacetic acid (2,4-D) and 3,6-dichloro-2-methoxybenzoic acid (dicamba), as thin layers on submicron silica particles. The limits of detection of 4.8 µM and 0.6 µM were obtained for the sensing of glyphosate in chloroform and acetonitrile, respectively. The reported system shows promise for future application in the sensing of glyphosate through further optimization of the dye and the implementation of a biphasic assay with water/organic solvent mixtures for sensing in aqueous environmental samples.

ElectrochemSENSE: A platform towards field deployable direct on-produce glyphosate detection

Glyphosate is an organophosphorus herbicide that is applied to the leaves of plants and crops to kill broadleaf plants and grasses. In this paper, for the first time, a field deployable, user-friendly, portable and rapid electrochemical pesticide sensing system is presented that can screen for glyphosate in produce run-off/extract. ElectrochemSENSE comprises the following parts: A polymer based disposable substrate with metallized electrodes that are surface treated with polyclonal antibodies of glyphosate and a custom electronic reader capable of reporting pesticide contamination. Utilizing the principles of capacitive current changes due to selective binding of glyphosate to its capture probe, reporting was achieved rapidly (in under 5 min). ElectrochemSENSE was tested to screen for glyphosate concentrations on produce samples above or below the globally accepted metric criterion, otherwise known as the Maximum Residue Level (MRL). Experiments were conducted on 4 produce types-apples (MRL: 0.2 ppm), strawberries (MRL: 0.2 ppm), bell peppers (MRL: 0.1 ppm) and carrots (MRL: 5 ppm). To further add functionality and increase prediction accuracy- a machine learning binary classifier was integrated with the device as a proof-of-concept so that sensor's response can be trained and characterized to perform with high accuracy, thereby serving as an analytics medium which minimizes error rate. Utilizing this system-the sensor's limit of detection has been determined to be 0.01 ppm (10 ng/mL) considering the permissible Field Operating Range (FOR) for glyphosate residue in various tested produce.

A sensitive fluorometric bio-barcodes immunoassay for detection of triazophos residue in agricultural products and water samples by iterative cycles of DNA-RNA hybridization and dissociation of fluorophores by Ribonuclease H

Although the toxicity of triazophos is high and it has been pulled from the market in many countries; it is still widely used and frequently detected in agricultural products. While conventional analyses have been routinely used for the quantification and monitoring of triazophos residues, those for detecting low residual levels are deemed necessary. Therefore, we developed a novel and sensitive fluorometric signal amplification immunoassay employing bio-barcodes for the quantitative analysis of triazophos residues in foodstuffs and surface water. Herein, monoclonal antibodies (mAbs) attached to gold nanoparticles (AuNPs) were coated with DNA oligonucleotides (used as a signal generator), and a complementary fluorogenic RNA was used for signal amplification. The system generated detection signals through DNA-RNA hybridization and subsequent dissociation of fluorophores by Ribonuclease H (RNase H). It has to be noted that RNase H can only disintegrate the RNA in DNA-RNA duplex, but not cleave single or double-stranded DNA. Hence, with iterative cycles of DNA-RNA hybridization, sufficient strong signal was obtained for reliable detection of residues. Furthermore, this method enables quantitative detection of triazophos residues through fluorescence intensity measurements. The competitive immunoassay shows a wide linear range of 0.01-100 ng/mL with a limit of detection (LOD) of 0.0032 ng/mL. The assay substantially meets the demand for the low residue detection of triazophos residues in agricultural products and water samples. Accuracy (expressed as spiked recovery %) and coefficient of variation (CV) were ranged from 73.4% to 116% and 7.04% to 17.4%, respectively. The proposed bio-barcodes immunoassay has the advantages of being stable, reproducible, and reliable for residue detection. In sum, the present study provides a novel approach for detection of small molecules in various sample matrices.

Fast, sensitive and selective determination of herbicide glyphosate in water samples with a White Light Reflectance Spectroscopy immunosensor

An optical immunosensor based on White Light Reflectance Spectroscopy is described for the determination of the herbicide glyphosate in drinking water samples. The biosensor allows for the label-free real-time monitoring of biomolecular interactions taking place onto a SiO₂/Si chip by transforming the shift in the reflected interference spectrum caused by the immunoreaction to effective biomolecular adlayer thickness. Glyphosate determination is accomplished by functionalizing the chip with a protein conjugate of the herbicide followed by a competitive immunoassay format. Prior to the assay, glyphosate derivatization in the calibrators and/or the samples was performed through reaction with succinic anhydride. Under the optimized assay protocol, a detection limit of 10 pg mL^-1 was achieved. Recovery values ranging from 90.0 to 110% were determined in spiked bottled and tap water samples, demonstrating the accuracy of the method. In addition, the sensor could be regenerated and re-used for at least 14 times without statistically significant effect on the assay sensitivity and accuracy. The excellent analytical performance and short analysis time (approx. 25 min), combined with the small sensor size, should be helpful for the fast on-site determination of glyphosate in drinking water samples.

Immunoassay for rapid on-site detection of glyphosate herbicide

Glyphosate is the most widespread herbicide and its global use is steadily increasing. Although glyphosate is considered to have low toxicity, its wide application has raised concerns about its effects on human health. The extensive use of glyphosate has risen a need of its continuous monitoring in drinking and surface waters to assure in accordance with the set standards. Within the present study, we have developed a novel assay for the on-site detection of glyphosate by combining flow-through technology with the high specificity of immunorecognition. The proposed biosensing system was based on the detection of fluorescence signal generated by the quantitative replacement of glyphosate in antigen-antibody complex with IgY-type anti-glyphosate antibodies on microbeads by synthetic 5-carboxytetramethylrhodamine (5-TAMRA) conjugated glyphosate. The working range of this assay was in low millimolar range and the time required for glyphosate detection around 0.5 h. The applicability of the immunoassay for glyphosate detection in surface water was tested and the biosensor results were validated with high-performance liquid chromatography.

What are the Main Sensor Methods for Quantifying Pesticides in Agricultural Activities? A Review

In recent years, there has been an increase in pesticide use to improve crop production due to the growth of agricultural activities. Consequently, various pesticides have been present in the environment for an extended period of time. This review presents a general description of recent advances in the development of methods for the quantification of pesticides used in agricultural activities. Current advances focus on improving sensitivity and selectivity through the use of nanomaterials in both sensor assemblies and new biosensors. In this study, we summarize the electrochemical, optical, nano-colorimetric, piezoelectric, chemo-luminescent and fluorescent techniques related to the determination of agricultural pesticides. A brief description of each method and its applications, detection limit, purpose—which is to efficiently determine pesticides—cost and precision are considered. The main crops that are assessed in this study are bananas, although other fruits and vegetables contaminated with pesticides are also mentioned. While many studies have assessed biosensors for the determination of pesticides, the research in this area needs to be expanded to allow for a balance between agricultural activities and environmental protection.

Trends and Perspectives in Immunosensors for Determination of Currently-Used Pesticides: The Case of Glyphosate, Organophosphates, and Neonicotinoids

Pesticides, due to their intensive use and their peculiar chemical features, can persist in the environment and enter the trophic chain, thus representing an environmental risk for the ecosystems and human health. Although there are several robust and reliable standard analytical techniques for their monitoring, the high frequency of contamination caused by pesticides requires methods for massive monitoring campaigns that are capable of rapidly detecting these compounds in many samples of different origin. Immunosensors represent a potential tool for simple, rapid, and sensitive monitoring of pesticides. Antibodies coupled to electrochemical or optical transducers have resulted in effective detection devices. In this review, the new trends in immunosensor development and the application of immunosensors for the detection of pesticides of environmental concern-such as glyphosate, organophosphates, and neonicotinoids-are described.

Glyphosate Determination by Coupling an Immuno-Magnetic Assay with Electrochemical Sensors

Glyphosate (N-(phosphonomethyl)glycine) is the most frequently used broad-spectrum herbicide worldwide. Its mechanism of action is based on the inhibition of an enzyme that is essential to plant growth. Its intensive use has caused global contamination to occur, which has not only affected the ecosystems, but even food and other objects of common use. Thus, there is a pronounced need for developing analytical methods for glyphosate determination in different matrices. Here, an electrochemical competitive immunoassay, based on the use of antibody-modified magnetic particles, has been developed. Tetramethylbenzidine (TMB) has been used as an enzymatic substrate. The extent of the affinity reaction has been achieved by monitoring the current value, due to the reduction of the enzymatic product. A disposable screen-printed electrochemical cell has been used. The calibration curve has been recorded in the 0⁻10,000 ng/L concentration range, with a detection limit of 5 ng/L and quantification limit of 30 ng/L. The electrochemical immunoassay has also been applied to the analysis of spiked beer samples.

Glyphosate analysis using sensors and electromigration separation techniques as alternatives to gas or liquid chromatography

Since its introduction in 1974, the herbicide glyphosate has experienced a tremendous increase in use, with about one million tons used annually today. This review focuses on sensors and electromigration separation techniques as alternatives to chromatographic methods for the analysis of glyphosate and its metabolite aminomethyl phosphonic acid. Even with the large number of studies published, glyphosate analysis remains challenging. With its polar and depending on pH even ionic functional groups lacking a chromophore, it is difficult to analyze with chromatographic techniques. Its analysis is mostly achieved after derivatization. Its purification from food and environmental samples inevitably results incoextraction of ionic matrix components, with a further impact on analysis derivatization. Its purification from food and environmental samples inevitably results in coextraction of ionic matrix components, with a further impact on analysis and also derivatization reactions. Its ability to form chelates with metal cations is another obstacle for precise quantification. Lastly, the low limits of detection required by legislation have to be met. These challenges preclude glyphosate from being analyzed together with many other pesticides in common multiresidue (chromatographic) methods. For better monitoring of glyphosate in environmental and food samples, further fast and robust methods are required. In this review, analytical methods are summarized and discussed from the perspective of biosensors and various formats of electromigration separation techniques, including modes such as capillary electrophoresis and micellar electrokinetic chromatography, combined with various detection techniques. These methods are critically discussed with regard to matrix tolerance, limits of detection reached, and selectivity.

Mg2+ ion as a tuner for colorimetric sensing of glyphosate with improved sensitivity via the aggregation of 2-mercapto-5-nitrobenzimidazole capped silver nanoparticles

The sensitivity of MNBZ-Ag NPs was greatly improved by integrating Mg²⁺ ion as trigger that can capture the glyphosate at nanomolar concentration with high selectivity.

Efficient fluorescence resonance energy transfer between oppositely charged CdTe quantum dots and gold nanoparticles for turn-on fluorescence detection of glyphosate

We designed a turn-on fluorescence assay for glyphosate based on the fluorescence resonance energy transfer (FRET) between negatively charged CdTe quantum dots capped with thioglycolic acid (TGA-CdTe-QDs) and positively charged gold nanoparticles stabilized with cysteamine (CS-AuNPs). Oppositely charged TGA-CdTe-QDs and CS-AuNPs can form FRET donor-acceptor assemblies due to electrostatic interactions, which effectively quench the fluorescence intensity of TGA-CdTe-QDs. The presence of glyphosate could induce the aggregation of CS-AuNPs through electrostatic interactions, resulting in the fluorescence recovery of the quenched QDs. This FRET-based method has been successfully utilized to detect glyphosate in apples with satisfactory results. The detection limit for glyphosate was 9.8 ng/kg (3σ), with the linear range of 0.02-2.0 μg/kg. The attractive sensitivity was obtained due to the efficient FRET and the superior fluorescence properties of QDs. The proposed method is a promising approach for rapid screening of glyphosate in real samples.