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. 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.