Investigation on light-addressable potentiometric sensor as a possible cell  /semiconductor hybrid Abu Bakar Md. Ismail a,b, *, Tatsuo Yoshinobu b , Hiroshi Iwasaki b , Hirokazu Sugihara c , Tetsuo Yukimasa c , Isao Hirata d , Hiroo Iwata d a Department of Applied Physics and Electronics, Rajshahi University, Rajshahi 6205, Bangladesh b Department of Quantum Molecular Devices, The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki City, Osaka 567-0047, Japan c Health Care Development Office, Matsushita Electric Industrial Co., Soraku, Kyoto, Japan d Institute of Frontier Medical Sciences, Kyoto University, Shogoin, Sakyo-ku, Kyoto 619-0237, Japan Received 26 May 2002; received in revised form 25 February 2003; accepted 9 March 2003 Abstract This article reports an investigation on light-addressable potentiometric sensor (LAPS) to be used as a possible biological cell / semiconductor hybrid that will enable us to make an interface between the physical and biological system. To increase the surface potential sensitivity, we used a LAPS structure with single insulator (SiO 2 ) coated with poly-L-ornithine and laminin (PLOL) on Si. Efficient culturing of PC-12 and nerve cells of Lymnaea stagnalis on PLOL-coated Si 3 N 4 and SiO 2 was achieved. The thickness of the PLOL layer was found to be about 4 nm by the atomic force microscope (AFM) measurement. Using the advantage of this thin layer of PLOL, we compared the performance of a novel structure to the previously reported ‘‘PLOL-coated Si 3 N 4 /SiO 2 /Si’’ structure. Due to high insulating capacitance, the photocurrent response of the novel LAPS was found to be very steep. As a result, higher sensitivity was achieved. This steepness did not degrade during 10 days when the sensor surface was kept in contact with the cell culture medium and environment. The thickness of PLOL layer, its ability to improve the biological cell adhesion, enhanced sensitivity, and experiment with simulated neural action potential (AP) applied to the novel LAPS show a good promise for LAPS to be a biological cell  /semiconductor hybrid. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Light-addressable potentiometric sensor; Cell /semiconductor hybrid; Surface modification; Neural action potential 1. Introduction A biological cell-semiconductor hybrid that connects a cell to a semiconductor so that both the cell and the electronic device can take advantage of the best attri- butes of the other, can potentially bridge the wide communication gap between the biological system and electronics. This combination of organic molecules and cells with microelectronics and biochip technology could create new devices with new capabilities. These minia- turized cell /semiconductor hybrids are of great interest for a large variety of applications such as spatially resolved monitoring of electrical communication within neuronal networks, the development of neuronal pros- theses, and the use as biosensor to monitor pharmaceu- tical agents. In principle, they stand for noninvasive, spatially resolved multi-site detection with long-term stability. Due to some advantages such as selection of measurement point by a scanning light beam and spatial resolution, the light-addressable potentiometric sensors (LAPSs) have become popular in many chemical and biological applications (Yoshinobu et al., 1997; Tanaka et al., 1999; Uithoven et al., 2000; Ismail et al., 2002). So far, LAPS has been limited to the applications involving the modification of the surface potential due to the charge bound at the electrolyte  /insulator and in- sulator /semiconductor interfaces. However, LAPS re- sponds to any potential in series with the external bias * Corresponding author. Present address: Department of Applied Physics and Electronics, Rajshahi University, Rajshahi 6205, Bangladesh. Tel.:  /880-721-770701; fax:  /880-721-750064. E-mail address: ismail@librabd.net (A. Ismail). Biosensors and Bioelectronics 18 (2003) 1509 /1514 www.elsevier.com/locate/bios 0956-5663/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0956-5663(03)00129-5