Layer-by-layer (LBL) assembly composed of liposome and membrane protein, bacteriorhodopsin (bR) was fabricated on quartz crystal microbalance (QCM) as a sensor element for bio-recognition. The LBL assembly was prepared by stacking of liposome/bR solutions alternately with a flowing system. By atomic force microscopy (AFM) and the QCM monitoring the bR and the liposome were found to be stacked regularly until the 8th layer of the liposome. The fabricated LBL assembly on the QCM was engaged to detect nonylphenol in solution, which is one of the endocrine disrupting chemicals. It was confirmed that the existence of nonylphenol in solution can be detected by a mass decrease of the LBL assembly on the QCM, which is caused by the disruption of the liposome through nonylphenol, in the low concentration range of 0.1-10 ppm. (C) 2009 Elsevier B.V. All rights reserved.