Digital pH Test Strips for In-Field pH Monitoring Using Iridium Oxide-Reduced Graphene Oxide Hybrid Thin Films

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• 作者：Jiang Yang ; Tae Joon Kwak ; Xiaodong Zhang ; Robert McClain ; Woo-Jin Chang ; Sundaram Gunasekaran
• 刊名：ACS Sensor
• 出版年：2016
• 出版时间：October 28, 2016
• 年：2016
• 卷：1
• 期：10
• 页码：1235-1243
• 全文大小：780K
• ISSN：2379-3694

文摘

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 (μPAD) 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.