The electrowetting-on-dielectric enhancement of the reduced and bamboo-like layered TiO2 nanotube array and the visual sensor application

Abstract

Based on the space charge polarization theory, the reduced and bamboo-like layered TiO2 nanotube arrays were designed and prepared by the voltage pulse anodization technique including reduction process of negative voltage. The reduction process synchronously introduces amount of oxygen vacancies, and the bamboo-like layered structure provides a plenty of interfaces to accumulate large amounts of free charges in the TiO2 nanotube arrays, which greatly enhance the space charge polarization in the TiO2 nanotube arrays. Thus, the capacitances of the reduced and layered TiO2 nanotube arrays are clearly increased, which further lead to the obvious enhancement of the electrowetting-on-dielectric (EWOD) responses. Furthermore, the reduced TiO2 nanotube arrays with bamboo-like layered structure were successfully used as the visual sensor to detect the NaCl and glucose concentration. Especially, it has higher sensitivity for the detection of the NaCl and glucose solution with low concentration.