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Although glyphosate is a widely used nontoxic herbicide, its in-field detection is challenging due to the lack of portable equipment. Despite the presence of this herbicide in surface waters, farmers’ urine, and crop residues, rapid field-deployable, and user-friendly sensors are currently unavailable, which necessitates the transportation of samples to laboratories.

​​​​​​​Study: Enzymatic Laser-Induced Graphene Biosensor for Electrochemical Sensing of the Herbicide Glyphosate. Image Credit: FrankHH/Shutterstock.com

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

The results revealed that the graphene biosensor exhibited a detection range of 10 to 260 micromoles with a limit of detection (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, parathion-methyl, dicamba, and thiamethoxam.

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

Glyphosate, N-(phosphonomethyl) glycine, is a broad-spectrum systemic herbicide and crop desiccant. Despite of nontoxicity of this herbicide to humans and animals, its movement into surface waters and underground accumulation after heavy rains are concerning issues impacting the environment and human health. Exposure to glyphosate herbicide may lead to various health hazards, including non-Hodgkin lymphoma, heart disease, Parkinson's disease, and infertility in females.

The current detection method for glyphosate includes laboratory-based techniques like mass spectroscopy and liquid/gas chromatography, which are expensive equipment with complex protocols and require the transportation of samples to the laboratory. Hence, there is a need for a cost-effective, in-field sensor to overcome the drawbacks of sample transportation to the laboratory.

Although sensing modalities include field-effect transistors (FETs) and chemiluminescence for glyphosate herbicide monitoring beyond the laboratory, these sensors require cleanroom conditions, making them unsuitable for in-field use.

The detection of glyphosate herbicide based on electrochemical sensing is a cost-effective and field deployable method that facilitates the monitoring and mapping of this herbicide contamination across large field areas. These electrochemical sensors allow detection of the herbicide even in turbid samples and provide a digital readout of the target marker’s concentration.

Carbon-based biomaterials like graphene biosensors are low-cost materials with promising electrical properties, large specific surface area/porosity, and are suitable for in-field environmental sensing. LIG graphene biosensors involve a laser engraving process that circumvents the need for graphene synthesis, print, solution-phase inks, and post-print annealing.

In terms of pesticides, the graphene biosensors were previously used to detect neonicotinoids, which were further coupled with horseradish peroxidase to detect organophosphorus hydrolase, atrazine, and acetylcholinesterase. Thus, the graphene biosensors are viable pesticide sensors.

In the present study, LIG, a graphene biosensor, was used to detect the glyphosate herbicide. The platinum (Pt) nanoparticles decorated LIG circuit and improved its electrochemical reactivity. Moreover, its biofunctionalization with the GlyOx enzyme facilitated selective monitoring of the glyphosate herbicide. Thus, a Pt-GlyOx-LIG sensor was developed, demonstrating a glyphosate linear sensing range between 10 and 260 micromoles with a response time of 150 seconds, a sensitivity of 0.991 nanoamperes per micrometer, and LOD of 3.03 micromoles.

The developed graphene biosensor showed minimal interference due to commonly used neonicotinoids, organophosphates, and herbicides. Furthermore, recovery tests were conducted in complex fluids to validate the in-field usability of this graphene biosensor. Here, the sensor was exposed to spiked soybean and corn residues and river water samples collected from the South Skunk River in Iowa. 

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

To conclude, the present work demonstrated the use of GlyOx and a laser-induced graphene biosensor to detect the glyphosate herbicide. This method involved the development of Pt-decorated LIG sensors, revealing the scalability of this fabrication method to prevent the graphene synthesis, exfoliation, thermal annealing, and formulation of the ink.

The excellent electrical properties, large electrochemical surface area, electrocatalytic sites, and functional groups of LIG were conducive to biosensing properties in developed graphene biosensors. The Pt-GlyOx-LIG sensor showed 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 showed minimal interference with other insecticides and herbicides due to the presence of the GlyOx enzyme.

Johnson, Z. T., Jared, N., Peterson, J. K., Li, J., Smith, E. A., Walper, S. A., Hooe (2022). Enzymatic Laser-Induced Graphene Biosensor for Electrochemical Sensing of the Herbicide Glyphosate. Global Challenges. https://doi.org/10.1002/gch2.202200057

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Bhavna Kaveti is a science writer based in Hyderabad, India. She has a Masters in Pharmaceutical Chemistry from Vellore Institute of Technology, India, and a Ph.D. in Organic and Medicinal Chemistry from Universidad de Guanajuato, Mexico. Her research work involved designing and synthesizing heterocycle-based bioactive molecules, where she had exposure to both multistep and multicomponent synthesis. During her doctoral studies, she worked on synthesizing various linked and fused heterocycle-based peptidomimetic molecules that are anticipated to have a bioactive potential for further functionalization. While working on her thesis and research papers, she explored her passion for scientific writing and communications.

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