Graphene-based devices for measuring pH

pH measuring and monitoring is fundamental to understand or control many chemical processes in biological, industrial or environmental fields. Potentiometric measurements by a glass electrode is the most common method to measure pH, although single-use paper strips are also widely used. Other methods include the use of hydrogen, quinhydron, and antimony electrodes, the imaging using pH-sensitive indicators such as dyes or proteins, and the use of ion-selective field effect transistor (ISFET). Due to the chemical reactivity of both sides of its 2D structure, nanometer thickness, high electron mobility, high reactivity to oxygen groups such as OH-, and ultrafast optical response, graphene has the potential to be used for the fabrication of nanoscale, wide-range, high-sensitivity and flexible pH sensors. This review describes how graphene, graphene oxide and reduced graphene oxide can be used to fabricate pH-sensitive devices (e.g. solution-gated FETs, solid-gate FETs, electrochemical sensors, and pH-sensitive quantum dots). The various configurations are reported along with the advantages and current limitations.