Mercury is an extremely toxic metal that can cause irreversible damage to human, animal and plant life. Even a very low level exposure to mercury over a long period of time is detrimental. Monitoring mercury levels in drinking water, water bodies and other drinks are thus necessary.

A method which can detect mercury level instantly from the sample would be ideal, but traditional methods are really complex and time consuming, they also require bulky and costly apparatus and in some cases requires really high temperature up to 10000K.

Recently ion-selective electrodes have been quite popular due to their portability and selectivity also they are economical than the traditional methods. In our research, we utilize an AlGaN/GaN high electron mobility transistor by functionalizing the gate area with a polyvinyl chloride (PVC) based ion selective membrane. The functionalized HEMT device is applied with pulsed gate bias at reference gate electrode positioned at fixed distance from the membrane functionalized channel region. The gate bias drops across the test solution, influencing the membrane on the channel where specific ionophore captures the target heavy metal ion. Thus the liquid gated HEMT’s drain current response is a function of the concentration of the target heavy metal ion. The unique sensing structure design enables direct detection of target ions in a background matrix of high ionic concentration solution. Ionophores are added to the membrane which increases the affinity to the particular ion and promises high specificity and low affinity for other ions.

The sensing technique enables direct detection of target ions in the medium using GaN HEMT and innovative biosensor packaging methodology, a portable biosensor system has been designed and fabricated which can provide quantitative detection in 10 minutes with a 10 µl sample.

The sensor showed a rapid and stable response when introduced to solutions of varying Hg²⁺ concentrations. An interesting thing about the technique is that that the pH of the sample is between 6-7, which helps in real time testing and have a fast response time. ISFET sensors are portable and robust, they also show better selectivity and sensitivity when compared to traditional electrochemical ion selective electrodes and for AlGaN/GaN devices with other forms of functionalization. These devices have much greater possibilities for development and integration as they don't require a reference electrode which reduces the manufacturing costs of ISFET. The development of this sensor will help in providing real time monitoring of water quality in rivers or water bodies, tap water and even beverages which will be a great boon to humankind.