title: Iridium Oxide-reduced Graphene Oxide Nanohybrid Thin Film Modified Screen-printed Electrodes as Disposable Electrochemical Paper Microfluidic pH Sensors.
abstract: A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use integrated paper microfluidic electrochemical pH sensor for resource-limited settings. Taking advantages from both pH meters and strips, the pH sensing platform is composed of hydrophobic barrier-patterned paper micropad (µPAD) using polydimethylsiloxane (PDMS), screen-printed electrode (SPE) modified with IrO2-graphene films and molded acrylonitrile butadiene styrene (ABS) plastic holder. Repetitive cathodic potential cycling was employed for graphene oxide (GO) reduction which can completely remove electrochemically unstable oxygenated groups and generate a 2D defect-free homogeneous graphene thin film with excellent stability and electronic properties. A uniform and smooth IrO2 film in nanoscale grain size is anodically electrodeposited onto the graphene film, without any observable cracks. The resulting IrO2-RGO electrode showed slightly super-Nernstian responses from pH 2-12 in Britton-Robinson (B-R) buffers with good linearity, small hysteresis, low response time and reproducibility in different buffers, as well as low sensitivities to different interfering ionic species and dissolved oxygen. A simple portable digital pH meter is fabricated, whose signal is measured with a multimeter, using high input-impedance operational amplifier and consumer batteries. The pH values measured with the portable electrochemical paper-microfluidic pH sensors were consistent with those measured using a commercial laboratory pH meter with a glass electrode.
authors.affiliation: Department of Biological Systems Engineering, University of Wisconsin-Madison; Environment, Energy and Natural Resources Center, Department of Environmental Science and Engineering, Fudan University.
authors.forename: Jiang
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Mechanical Engineering, University of Wisconsin-Milwaukee.
authors.forename: Tae-Joon
authors.initials: TJ
authors.lastname: Kwak
authors.affiliation: Department of Physics, School of Science, Tianjin University.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison.
authors.forename: Robert
authors.initials: R
authors.lastname: McClain
authors.affiliation: Department of Mechanical Engineering, University of Wisconsin-Milwaukee; School of Freshwater Sciences, University of Wisconsin-Milwaukee; wjchang@uwm.edu.
authors.forename: Woo-Jin
authors.initials: WJ
authors.lastname: Chang
authors.affiliation: Department of Biological Systems Engineering, University of Wisconsin-Madison; guna@wisc.edu.
authors.forename: Sundaram
authors.initials: S
authors.lastname: Gunasekaran
mesh_terms: D004566:Electrodes; D006108:Graphite; D006863:Hydrogen-Ion Concentration; D007495:Iridium; D044085:Microfluidics; D010087:Oxides; D015203:Reproducibility of Results
chemical_list: D010087:Oxides; D007495:Iridium; D006108:Graphite