Detection of pH and Enzyme-Free H(2)O(2) Sensing Mechanism by Using GdO(x) Membrane in Electrolyte-Insulator-Semiconductor Structure

A 15-nm-thick GdO(x) membrane in an electrolyte-insulator-semiconductor (EIS) structure shows a higher pH sensitivity of 54.2 mV/pH and enzyme-free hydrogen peroxide (H(2)O(2)) detection than those of the bare SiO(2) and 3-nm-thick GdO(x) membranes for the first time. Polycrystalline grain and higher Gd content of the thicker GdO(x) films are confirmed by transmission electron microscopy (TEM) and X-ray photo-electron spectroscopy (XPS), respectively. In a thicker GdO(x) membrane, polycrystalline grain has lower energy gap and Gd(2+) oxidation states lead to change Gd(3+) states in the presence of H(2)O(2), which are confirmed by electron energy loss spectroscopy (EELS). The oxidation/reduction (redox) properties of thicker GdO(x) membrane with higher Gd content are responsible for detecting H(2)O(2) whereas both bare SiO(2) and thinner GdO(x) membranes do not show sensing. A low detection limit of 1 μM is obtained due to strong catalytic activity of Gd. The reference voltage shift increases with increase of the H(2)O(2) concentration from 1 to 200 μM owing to more generation of Gd(3+) ions, and the H(2)O(2) sensing mechanism has been explained as well.