J.A. Hondred, S.R. Das, J.C. Breger, S.A. Walper, I.L. Medintz, J.C. Claussen
Iowa State University,
Keywords: graphene, inkjet printing, enzymes, nanoparticles, pesticide, soil
Summary:This abstract needs to be submitted to the USDA Special Session - Nano-biosensors and Nanomaterials for Agriculture, Food and Diagnostics. This presentation will fulfill my obligation to the USDA annual grantees meeting (Program Manager: Hongda Chen) High resolution inkjet printed nanomaterials have shown tremendous promise towards the fabrication of low-cost, flexible electrical circuits. However, the utility of these inkjet printed nanomaterials in the biosensing domain has been relatively unexplored. This presentation demonstrates how the utility of inkjet printed graphene and enzyme-nanoparticle bioconjugates can be enabled for rapid, in field water and soil pesticide detection. Inkjet printed graphene uses low-cost exfoliated graphene/graphene oxide flakes (in lieu of high-cost chemical vapor deposition synthesized graphene) to form carbon-based electrical circuits. Inkjet printed graphene applications have been constrained due in part to post-print annealing steps, low electrochemical reactivity, and relatively smooth, planar surfaces. This presentation demonstrates how the utility of inkjet printed graphene can be expanded by welding/stitching the printed graphene flakes and nanostructuring the flakes into 3D nanopetals via pulsed laser processing and high-temperature thermal annealing (400-950C) in a nitrogen ambient. The laser processing and/or thermal annealing techniques change the electrically conductivity of the printed graphene from highly resistive (> 100 MΩ) to highly conductive (< 1 kΩ sheet resistance); the hydrophobicity of the graphene from hydrophilic (water contact angle ~ 45°C) to superhydrophobic (water contact angle ~ 155°C); the graphene electrochemical reactivity from a surface with slow, irreversible charge transport to fast, reversible charge transport; and finally a graphene surface roughness that changes from 2D planer to 3D nano/microstructured with stitched/welded graphene flakes. We demonstrate how these improvements in material properties enable highly sensitive and selective enzymatic biosensing. We also demonstrate how the performance of pesticide sensing enzymes such as phosphotriesterase trimer, can be improved via immobilization on gold nanoparticles. These results demonstrate a nearly 17-fold increase in the maximum enzymatic velocity (Vmax) of the phosphotriesterase trimer immobilized on gold nanoparticles versus the same enzyme without said conjugation. This work demonstrates an overall route to creating a sensitive and selective paper-test strip technology for low-cost, in-field pesticide sensing.