Design and rapid prototyping of printed graphene electrochemical biosensors for sensitive monitoring of pesticide levels for agricultural use

While the use of pesticides (herbicides and insecticides) are critically important to meet the current and future food demands (increases crop yield by up to 40%), their overuse has shown long-term detrimental impacts on the environment from polluting watersheds used for drinking water to eutrophic “dead zones”. Current pesticide soil measurement methods (chromatography) are costly, require trained technicians, and take days to analyze; thus, farmers are taking an “over-application approach” which is pollution the environment and waterways. A disposable pesticide soil sensor would provide farmers the opportunity of precisely regulating the application of pesticides in an independent and economical fashion. Electrochemical biosensors provide the unique ability to quickly detect analytes with low-cost sensors; however, the detection limit and sensitivity of these biosensors are inadequate for current applications. This dissertation addresses this issue with the following focus in mind: 1) Increasing the enzymatic efficiency of organophosphate hydrolase by strategically functionalizing to nanomaterials [e.g., 17-fold increase in Vmax when functionalized to gold nanoparticles vs free enzyme]. 2) Develop a low-cost, rapid, and high-resolution manufacturing method to pattern solution-phase graphene [i.e., inkjet maskless lithography (IML), line resolution ~20 µm, sheet resistance ~ 0.7 kΩ/sq]. 3) Enhance the electroactive surface area by nano/microstructuring the graphene surface [3D petal-like graphene morphology] using laser annealing. 4) Increase the electrochemical surface area by incorporating macro and micro pores [2.2x with the inclusion of macropores] in the graphene surface. This work demonstrates the manufacturing of simple, low-cost electrochemical biosensors which suitable for rapid in-field detection of organophosphates. The fabricated graphene biosensors demonstrate high sensitivity, high linear sensing range, and ultra-low detection limits. Additionally, while this work is tailored towards a disposable pesticide sensor, the manufacturing techniques, sensor designs, and biosensor principle are a platform technology that could be amenable to other applications such as healthcare screening, drinking water monitoring, and even bioterror agent detection