Graphene Based Electrochemical Sensing of Harmful Herbicides

Although glyphosate is a widely used non-toxic herbicide, its detection in the field is challenging due to the lack of portable equipment. Although these herbicides are present in surface water, farmer urine, and crop residues, fast, easy-to-use field sensors are not currently available, requiring transport of samples to the laboratory.

YouStudy: Enzymatic Laser Induced Graphene Biosensor for Electrochemical Sensing of Glyphosate Herbicides. Image Credit: FrankHH/Shutterstock.com

In an article recently published in the journal Global Challenges, a platinum-decorated graphene (LIG) biosensor was developed with the immobilized flavoenzyme glycine oxidase (GlyOx) and used to detect the herbicide glyphosate, as it is a substrate for GlyOx. Thus, this graphene biosensor provides a scaffold for enzyme attachment.

The results reveal that the graphene biosensor exhibits a detection range of 10 to 260 micromoles with a detection limit (LOD) of 3.03 micromoles and a sensitivity of 0.991 nanoamperes per micrometer. The graphene biosensor showed minimal interference by other insecticides and herbicides, including 2,4-dichlorophenoxyacetic acid, atrazine, paration-methyl, dicamba, and thiamethoxam.

Furthermore, the developed graphene biosensor was also tested against complex plant residue fluids and river water, validating the current platform as a selective method for detecting glyphosate for food analysis and herbicide mapping.

Graphene Biosensor for Detection of Glyphosate Herbicides

Glyphosate, N-(phosphonomethyl)glycine, is a broad-spectrum systemic herbicide and plant desiccant. Although this herbicide is non-toxic to humans and animals, its movement into surface water and underground accumulation after heavy rains is a cause for concern for the environment and human health. Exposure to the herbicide glyphosate can cause a variety of health hazards, including non-Hodgkin’s lymphoma, heart disease, Parkinson’s disease, and female infertility.

Current methods of glyphosate detection include laboratory-based techniques such as mass spectroscopy and liquid/gas chromatography, which are expensive equipment with complex protocols and require transport of the sample to the laboratory. Therefore, a cost-effective field sensor is needed to overcome the drawbacks of transporting samples to the laboratory.

Although sensing modalities include field-effect transistors (FET) and chemiluminescence for out-of-laboratory monitoring of the glyphosate herbicide, these sensors require clean room conditions, making them unsuitable for use in the field.

Detection of the herbicide glyphosate based on electrochemical sensing is a cost-effective and fieldable method that facilitates monitoring and mapping of contamination of this herbicide over a large field area. This electrochemical sensor allows detection of herbicides even in cloudy samples and provides digital readings of target marker concentrations.

Carbon-based biomaterials such as graphene biosensors are low-cost materials with promising electrical properties, large specific surface area/porosity, and are suitable for environmental sensing in the field. The graphene LIG biosensor involves a laser engraving process that avoids the need for graphene synthesis, printing, solution-phase ink and post-print annealing.

In the case of pesticides, graphene biosensors were previously used to detect neonicotinoids, which were further combined with horseradish peroxidase to detect organophosphate hydrolase, atrazine, and acetylcholinesterase. Thus, the graphene biosensor is a viable pesticide sensor.

Enzymatic Laser Induced Graphene Biosensor for Glyphosate Herbicide Detection

In this study, LIG, a graphene biosensor, was used to detect the herbicide glyphosate. Platinum (Pt) nanoparticles decorate the LIG circuit and enhance their electrochemical reactivity. In addition, its biofunctionalization with the enzyme GlyOx facilitates selective monitoring of the herbicide glyphosate. Thus, a Pt-GlyOx-LIG sensor was developed, exhibiting a linear sensing range of glyphosate between 10 and 260 micromoles with a response time of 150 seconds, a sensitivity of 0.991 nanoamps per micrometer, and an LOD of 3.03 micromoles.

The developed graphene biosensor shows minimal disturbance due to neonicotinoids, organophosphates, and commonly used herbicides. Subsequently, recovery tests were carried out in complex liquids to validate the usefulness of this graphene biosensor in the field. Here, sensors are exposed to soy and prickly corn residues and river water samples collected from the South Skunk River in Iowa.

The results revealed slightly higher recoveries for soybean and maize residues, which was attributed to the oxidation of the innate glycine composition in each plant. Thus, this cost-effective graphene biosensor has proven to be used on a large scale to monitor and map the herbicide glyphosate in agricultural watersheds.

Conclusion

In conclusion, this study demonstrates the use of GlyOx and a laser-induced graphene biosensor to detect the herbicide glyphosate. This method involves the development of a Pt-decorated LIG sensor, which reveals the scalability of this fabrication method to prevent graphene synthesis, exfoliation, thermal annealing, and ink formulation.

The excellent electrical properties, large electrochemical surface area, electrocatalytic sites, and LIG functional groups are conducive to biosensing properties in the developed graphene biosensor. The Pt-GlyOx-LIG sensor exhibits a detection range of 10 to 260 micromoles with a response time of 150 seconds, and an LOD of 3.03 micromoles. Furthermore, this graphene biosensor shows minimal interference with other insecticides and herbicides due to the presence of the GlyOx enzyme.

Reference

Johnson, ZT, Jared, N., Peterson, JK, Li, J., Smith, EA, Walper, SA, Hooe (2022). Enzymatic Laser Induced Graphene Biosensor for Electrochemical Sensing of Glyphosate Herbicides. Global Challenge. https://doi.org/10.1002/gch2.202200057

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