A simple method was developed for preparing CdSe quantum dots (QDs) using a common protein (bovine serum albumin (BSA)) to sequester QD precursors (Cd2+) in situ. Fluorescence (FL) and absorption spectra showed that the chelating time between BSA and Cd2+, the molar ratio of BSA/Cd2+, temperature, and pH are the crucial factors for the quality of QDs. The average QD particle size was estimated to be about 5 nm, determined by high-resolution transmission electron microscopy. With FL spectra, Fourier transform infrared spectra, and thermogravimetric analysis, an interesting mechanism was discussed for the formation of the BSA-CdSe QDs. The results indicate that there might be conjugated bonds between CdSe QDs and -OH, -NH, and -SH groups in BSA. In addition, fluorescence imaging suggests that the QDs we designed can successfully label Escherichia coli cells, which gives us a great opportunity to develop biocompatible tools to label bacteria cells. (C) 2010 Elsevier Inc. All rights reserved.