remove any
loosely bound species. The bacterial cells were covalently attached to the mercaptopropionic acid modified AuNPs by immersing the above eggshell membrane into a 0.020 M phosphate buffer (pH 7.0) containing of 20 mg cells for 1 h at ambient conditions. Then, it was washed with distilled water to remove unbound cells [30]. After washing, the membrane was positioned on the surface of an O
electrode and kept in steady position by an O-ring. The electrode was then exposed to a stirred 10-mL phosphate buffer solution (20 mM, pH 7.0). Various volumes of standard (0.10 mM) or sample methanol solution were injected into the phosphate buffer solution. The dissolved O
2
signal was captured and processed by a data logger system consisting of a Science Workshop 500 interface, serial cables, power supply and control software. The data were logged in a computer for real-time display and processing. When the methanol biosensor was not in use, the cells-immobilized eggshell membrane was removed from the O
2
sensor and stored in a pH 7.0 phosphate solution at 4
◦
2
C unless otherwise stated.