Fabrication of Heavy Metal Ion FET Based Sensor for Detecting Arsenite

Abstract

Arsenic is one of the toxic chemical among heavy metals. It is mostly present in ground waters at higher levels. The long term exposure of food or water to arsenic leads to cancer and heart diseases. Arsenic occurs in two oxidation states, Arsenite (As2O3, As (III)) a trivalent form and Arsenate (As2O5, As (V)) a pentavalent form. As (III) is an inorganic form which is more toxic than As (V). The detection of arsenic ion in drinking water or in any liquid form of food can be done with several laboratory equipments such as ICP-MS. The detection limit of ICP-MS for Arsenic is 0.05μg/L (10^-10M). Though these laboratory methods can be used for detecting the arsenic ion but it is very complex, costly and time consuming. In this research, we developed a methodology for detecting Arsenite ion (As2O3, As (III)). FET based ion sensor is fabricated where the gate pulse is characterized with 1500 μs pulse width and amplitude of 1 V is connected to one electrode. A steady DC bias of 2 V is applied as the drainsource voltage. The Ion Selective Membrane(ISM) is used which is immobilized on the sensing areas. This ISM contains Ionophore, Potassium tetra phenyl borate, Poly vinyl chloride, 2-Nitrophenyl octyl ether and this ISM components mixture is dissolved in Tetrahydrofuran. Sodium Arsenite (NaAsO2) is the inorganic compound which is used for detection of As (III). This solution is dropped on the sensing area which covers both ISM and gate. When Vd is supplied, we temporarily apply Vg of 0V and 1V which causes a change in current level, we define it as gain and is used as our measurement signal. The concentration range from 10^-10 M to 10^-4 M of arsenite ion can be detected. This sensor is easy to fabricate, smaller in size, high sensitivity and takes less time for detecting Arsenite. This FET based ion sensor has same detection limit comparable to ICP-MS and this sensor shows higher sensitivity than the Nernstian slope. The sensing characteristics are not affected by the interfering ions. Figure 1