Although glyphosate is a widely used non-toxic herbicide, its detection in the field is challenging due to the lack of portable equipment. Despite the presence of this herbicide in surface water, farmers’ urine, and crop residues, there are currently no easy-to-use, rapidly deployable sensors in the field, requiring transport of samples to laboratories.
Study: Enzymatic laser-induced graphene biosensor for the electrochemical detection of the herbicide glyphosate. Image credit: FrankHH/Shutterstock.com
In a paper recently published in the journal Global Challenges, a platinum-decorated laser-induced graphene (LIG) biosensor with immobilized glycine oxidase (GlyOx) flavoenzyme was developed and used to detect the herbicide glyphosate, as it is a substrate for to GlyOx. Thus, this graphene biosensor provided a scaffold for enzyme attachment.
The results revealed that the graphene biosensor exhibited a detection range of 10–260 micromoles with a limit of detection (LOD) of 3.03 micromoles and a sensitivity of 0.991 nanoamps per micrometer. The graphene biosensor showed minimal interference from other insecticides and herbicides, including 2,4-dichlorophenoxyacetic acid, atrazine, parathion-methyl, dicamba, and thiamethoxam.
In addition, the developed graphene biosensor was also tested on crop waste fluids and complex river water, validating the current platform as a selective method to detect glyphosate for food analysis and herbicide mapping.
Graphene biosensor for the detection of herbicide glyphosate
Glyphosate, N-(phosphonomethyl)glycine, is a broad-spectrum systemic herbicide and crop desiccant. Despite the non-toxicity of this herbicide to humans and animals, its movement into surface water and underground accumulation after heavy rainfall are problems affecting the environment and human health. Exposure to the herbicide glyphosate can lead to several health hazards, including non-Hodgkin’s lymphoma, heart disease, Parkinson’s disease, and infertility in women.
The current detection method for glyphosate includes laboratory techniques such as mass spectroscopy and liquid/gas chromatography, which are expensive equipment with complex protocols and require transport of samples to the laboratory. Therefore, a cost-effective field sensor is needed to overcome the drawbacks of transporting samples to the laboratory.
Although detection modalities include field-effect transistors (FETs) and chemiluminescence for monitoring glyphosate herbicide beyond the laboratory, these sensors require cleanroom conditions, making them unsuitable for use in the countryside.
Detection of the herbicide glyphosate based on electrochemical detection is a cost-effective and field-deployable method that facilitates the monitoring and mapping of contamination of this herbicide over large areas of the field. These electrochemical sensors allow detection of the herbicide even in turbid samples and provide a digital readout of the concentration of the target marker.
Carbon-based biomaterials such as graphene biosensors are low-cost materials with promising electrical properties, large specific surface area/porosity, and are suitable for field environmental sensing. LIG graphene biosensors involve a laser etching process that avoids the need for graphene synthesis, printing, solution-phase inks, and post-printing annealing.
For pesticides, graphene biosensors were previously used to detect neonicotinoids, which were combined with horseradish peroxidase to detect organophosphate hydrolase, atrazine, and acetylcholinesterase. Thus, graphene biosensors are viable pesticide sensors.
Enzymatic laser-induced graphene biosensor for glyphosate herbicide detection
In the present study, LIG, a graphene biosensor, was used to detect the herbicide glyphosate. Platinum (Pt) nanoparticles decorated the LIG circuit and improved its electrochemical reactivity. In addition, its biofunctionalization with the GlyOx enzyme facilitated the selective monitoring of the herbicide glyphosate. Thus, a Pt-GlyOx-LIG sensor was developed, demonstrating a linear detection 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 showed minimal interference due to commonly used neonicotinoids, organophosphates and herbicides. In addition, recovery tests in complex fluids were performed to validate the field usability of this graphene biosensor. Here, the sensor was exposed to soybean and corn residues and river water samples collected from the South Skunk River in Iowa.
Results revealed slightly higher recoveries for soybean and corn residues, attributed to oxidation of the innate glycine composition in each crop. Thus, it was demonstrated that this cost-effective graphene biosensor can be deployed on a large scale to monitor and map the herbicide glyphosate in agricultural watersheds.
conclusion
To conclude, the present work demonstrated the use of GlyOx and a laser-induced graphene biosensor to detect the herbicide glyphosate. This method involved the development of Pt-decorated LIG sensors, revealing the scalability of this fabrication method to avoid graphene synthesis, exfoliation, thermal annealing, and ink formulation.
The excellent electrical properties, large electrochemical surface area, electrocatalytic sites, and functional groups of LIG were favorable for the biosensing properties in developed graphene biosensors. The Pt-GlyOx-LIG sensor showed a detection range of 10–260 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.
reference
Johnson, ZT, Jared, N., Peterson, JK, Li, J., Smith, EA, Walper, SA, Hooe (2022). Enzymatic laser-induced graphene biosensor for electrochemical detection of the herbicide glyphosate. global challenges https://doi.org/10.1002/gch2.202200057
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