High Field Modulated Field Effect Transistors Coated By Ion Selective Membrane for Cadmium Ion Detection in Water

Abstract

Cadmium is one among the most hazardous heavy metals. Heavy metal cannot be metabolized or digested by human body, therefore, heavy metal accumulates in our body through time. Cadmium in human body causes lung cancer, osteomalacia and even proteinuria. Mostly cadmium ions get in to human body by ingestion, so detecting cadmium ion in drinking water, tap water and liquid form of food is very important. However, traditional laboratory detection methods of cadmium ion are complex and time consuming and requires heavy and expensive machinery. Though the electrochemical ion selective electrode is easy to use, its poor stability and larger detection limit are huge disadvantages. In this research, we devised a small size, high sensitivity, low detection limit, short response time and easy to fabricate cadmium ion selective membrane field effect transistor (ISMFET). This device is easy to use and can measure the cadmium concentration in water quickly with the combination of ion-selective membrane and field effect transistor. The sensing mechanism depends on electrical double layer (EDL) gating coupled with high electric field to enhance the sensitivity of ISHEMT beyond the limit of ideal Nernst sensitivity. World Health Orgnization (WHO) suggests that cadmium ion in drinking water should be lower than 3 ppb, equal to 2.68 10-8 M. This device can detect cadmium ion concentration form 10-7 M to 10-11 M, covering the wide dynamic range according to WHO’s suggestion. Such high sensitivity and low detection limits devices are highly desirable for consumers who intend to regularly monitor the water quality, for food and environmental safety. In contrast, testing cadmium ion in water by ICP-MS takes several hours and the instrument occupies larger space. To improve the yield and sensitivity of our sensor, we are studying on different condition of ISM. With this cadmium, ISMFET, we can determine the cadmium concentration in water in 15 minutes and even higher sensitivity and lower detection limit, in comparison with conventional laboratory based techniques. Not only Cadmium, but also other heavy metals, for example lead and mercury, can use similar methodology to get better detection time and detection limit. This design makes quality monitoring of water we consume in daily life become much easier and convenient.