Light Addressable Potentiometric Sensor as Cell-Based Biosensors for Biomedical Application

One of most enduring topics in the field of biosensors and bioelectronics is cell-based biosensors, which are able to convert cellular biological effects to electrical signals, via living cells. As the archetypal interface between a biological and an electronic system, the research and development of cell-based biosensors are essentially dependent on the combined knowledge of engineers, physicists, chemists and biologists. In recent years, the miniaturization and expanding applications of cell-based biosensors in biology, environment and medicine fields, have drawn extensive attention. Light addressable potentiometric sensor (LAPS) is a semiconductor device proposed by Hafeman in 1988, and it is now as commonly used as ISFET (Hafeman et al., 1988). LAPS indicates a heterostructure of silicon/silicon oxide/silicon nitride, excited by a modulated light source to obtain a photocurrent. The amplitude of this light induced photocurrent is sensitive to the surface potential and thus LAPS is able to detect the potential variation caused by an electrochemical even. Therefore, in principle, any event that results in the change of surface potential can be detected by LAPS, including the change of ion concentration (Parce et al., 1989), redox effect (Piras et al., 1996), etc. LAPS shows some advantages comparing to ISFET while constructing cell-based biosensor. The easier fabrication process of LAPS is fully compatible with the standard microelectronics facilities. The encapsulation of LAPS is much less critical since no metal contact is formed on the surface. Besides, the extremely flat surface makes it compatible to incorporate into very small volume chamber, which is important for small dose measurement. Therefore, LAPS seems promising for biomedical application. Due to the spatial resolving power, LAPS also has an advantage for array sensing application (Shimizu et al., 1994). Usually, no additional sensor structure is needed to realize the LAPS array sensing. In fact, LAPS is an integrated sensor itself, whose integration level is defined by the spatial resolution and the illuminating system. Thus, miniaturization with high integration level can be achieved. Many efforts have been drawn on the integration of LAPS (Men et al., 2005; Wang et al., 2005). Among these attempts, most are focused on the