Electrochemical pH Sensing Techniques and Applications

Electrochemical pH sensing exploits the relationship between proton activity and electrical signals to measure acidity or alkalinity in a wide range of media. Traditional glass electrodes, although well established, are bulky and fragile, which has driven the development of solid-state platforms. Ion-sensitive field-effect transistors (ISFETs) and extended-gate FETs (EGFETs) replace the glass membrane with a semiconductor sensing interface, enhancing miniaturisation and integration with electronics. Potentiometric sensors based on metal oxides, conducting polymers and nanostructured materials deliver rapid response, near-Nernstian sensitivity and compatibility with flexible substrates. Chemiresistive devices, in which surface protonation alters resistance, offer reference-electrode-free operation. Advances in nanofabrication have yielded porous silicon, ZnO nanotubes, polyaniline nanofibres and iridium-oxide films with super-Nernstian behaviour, enabling wearable biosensors, implantable devices and in-line water-quality monitors. The global significance spans environmental surveillance, precision agriculture, biomedical diagnostics and industrial process control, where real-time, low-cost, robust pH monitoring is essential.

Research from Nature Portfolio

Recent studies have demonstrated a solid-state, wireless chemiresistor composed of oxidised single-walled carbon nanotubes functionalised with a conductive polymer. This device achieves a near-ideal (Nernstian) voltage response across the full pH range, retains performance over several months and operates without a conventional reference electrode. Integration with a passive radio-frequency identification tag allows battery-less, transdermal data transmission, laying the groundwork for implantable sensors capable of early detection of local acidosis around medical implants.

Research from all publishers

A comprehensive review of metal-oxide-based sensors highlights how materials such as ruthenium, iridium and titanium dioxides can be engineered to provide fast (<10 s) potentiometric response, high stability and wide pH coverage. Strategies to mitigate ionic interference and toxicity issues have focused on composite films and thin-film deposition techniques compatible with flexible electronics. In parallel, polyaniline nanofibre arrays printed onto flexible substrates exhibit near-Nernstian sensitivity (~62 mV/pH), rapid response (<15 s) and excellent mechanical resilience, enabling on-surface monitoring of food spoilage and fruit decay. Another development is a miniaturised multi-parameter chip combining an iridium-oxide pH electrode, conductivity sensor and temperature probe on a single MEMS platform, achieving super-Nernstian sensitivity (−67.6 mV/pH) and high linearity, thereby facilitating real-time water-quality assessment in distributed networks.

Electrochemical pH Sensing Techniques and Applications publication trend

The graph below shows the total number of articles in electrochemical ph sensing techniques and applications across all publications each year (not limited to Nature Index journals).

Technical terms

Potentiometric: Measurement of electrode potential relative to a reference electrode as a function of analyte concentration.

Ion-sensitive field-effect transistor (ISFET): Semiconductor device in which gate potential is modulated by ionic activity in solution, producing a current change correlated with pH.

Chemiresistor: Sensor where a chemical interaction at the sensing surface induces a change in electrical resistance proportional to analyte concentration.

Nernstian response: Ideal sensor sensitivity defined by the Nernst equation, corresponding to approximately 59 mV per pH unit at 25 °C.

Extended-gate field-effect transistor (EGFET): Configuration in which the sensing membrane is physically separated from the transistor gate and linked by a conductive wire, improving modularity and durability.

References

1. Metal oxides based electrochemical pH sensors: Current progress and future perspectives. Progress in Materials Science (2020).
2. Potentiometric performance of flexible pH sensor based on polyaniline nanofiber arrays. Nano Convergence (2019).
3. Carbon Nanotube Chemiresistor for Wireless pH Sensing. Scientific Reports (2014).
4. Fabrication of a Miniature Multi-Parameter Sensor Chip for Water Quality Assessment. Sensors (2017).
5. High Sensitivity pH Sensor Based on Porous Silicon (PSi) Extended Gate Field-Effect Transistor. Sensors (2016).
6. Miniaturized pH Sensors Based on Zinc Oxide Nanotubes/Nanorods. Sensors (2009).