Bovine serum albumin-directed synthesis of biocompatible CdSe quantum dots and bacteria labeling

Abstract

A simple method was developed for preparing CdSe quantum dots (QDs) using a common protein (bovine serum albumin (BSA)) to sequester QD precursors (Cd 2+) in situ. Fluorescence (FL) and absorption spectra showed that the chelating time between BSA and Cd 2+, the molar ratio of BSA/Cd 2+, 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.