Journal
ACS SENSORS
Volume 1, Issue 10, Pages 1235-1243Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acssensors.6b00385
Keywords
iridium oxide; graphene; paper-fluidic; potentiometric sensor; pH sensor; electrochemistry; programmed flow rate; hydrophobic patterning
Funding
- Hjalma r D. and Janet W. Bruhn Fellowship
- Louis and Elsa Thomsen Wisconsin Distinguished Graduate Fellowship at UW-Madison
- UW-Milwaukee Research Growth Initiative awarded grant (RGI)
- Water Equipment & Policy NSF Industry/University Cooperative Research Centers Grant
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While pH test strips are not decimally accurate and only semiquantitative, the more accurate and automated laboratory-based pH meters lack disposability and portability. Benefiting from advantages of both sides and filling the gap of unmet needs in between, we integrated a miniaturized paper-fluidic electrochemical pH platform coupled with a portable pH device powered by consumer batteries to make digital pH test strips for truly in-field measurements. To overcome the inability to form the smooth and uniform pH-sensitive functionality on screen-printed carbon, i.e., anodically electrodeposited iridium oxide thin films (AEIROFs), reduced graphene oxide was used as substrate for synthesis of homogeneous metal oxide-nanocarbon hybrid thin films, IrO2-reduced graphene oxide (IrO2-rGO), as the sensing moiety with strong substrate adhesion. A hydrophobic barrier patterned paper micropad (mu PAD) with programmed flow rates can locally accelerate linear wicking speed to boost delivery and response time. IrO2-rGO shows slightly super-Nernstian linear responses from pH 2 to 12 with small hysteresis, fast response time, reproducible performances, and low sensitivities to interfering ionic species and dissolved oxygen. A miniaturized portable pH device made of high-impedance buffer amplifier and off-the-shelf digital multimeter provides results consistent with those of a commercial pH meter equipped with a glass electrode. Our system combines the accuracy of pH meters with the low-cost and convenience of pH strips, making it ideal for resource limited settings.
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