Porous Titanium Nitride electrodes on miniaturised pH sensor for foetal health monitoring application

Measuring pH level on foetal scalp is a common practice to prevent the risk of acidosis in monitoring foetal health during labour. However, the current technique of collecting capillary sample (blood gas analyser method) is not continuous and has high rate of failures. In this work, a prototype of miniaturized pH sensor based on porous Titanium Nitride (TiN) electrodes to get continuous measurement of pH has been developed, targeting foetal health monitoring. By exploiting wet etching techniques on flat TiN electrodes, porosity of the working surface area has been increased, exhibiting better properties and performances of our pH sensor. Precision of the developed TiN pH sensor is 0.03 in pH, which is close to the requirement of the application. The sensitivity is determined to be 67.06 mV/ pH within pH range of interest from 6 to 8. In addition, the Potentiostatic Electro Impedance spectroscopy (PEIS) and Cyclic Voltammetry (CV) were recorded, showing a 6.3-time smaller impedance at 100 Hz frequency and a better conductivity compared to the flat TiN electrode. This work is under the next step of fabrication to transfer the system from glass onto a flexible Polyimide substrate and to be integrated into a specific miniaturised packaged device for in-vivo testing.