Quantum Dots Conjugated E. coli Living Cells as Fluorescent Reporters to Detect Cytotoxicity of Chemicals

Abstract

Quantum dots (QDs) have attracted much of research interest in recent years for imaging, diagnostics, and therapy due to their unique optical properties, such as broad excitation spectra and long fluorescence stability. In this study, a controlled bioconjugation using CdTe QDs with gram negative E. coli cells was performed to develop QD-E. coli bioconjugates. These bioconjugates were used as whole cell living baits to determine cytotoxicity of model toxic chemicals, such as oxidative stress inducer (H₂O₂) and a pesticide (methyl viologen or paraquat). These chemicals over a wide concentration ranges were exposed to QD-E. coli bioconjugates that interacted with cells and the real time fluorescence responses, with QD-E. coli bioconjugates, were analyzed. The results showed that the fluorescent ability of QD-E. coli bioconjugates tend to diminish with increasing concentration of toxic chemicals. This stress is attributed to the damages occurred as a result of interaction of toxic chemicals to the cell-wall or membrane of cells that resulted in the loss of fluorescence signal. This loss in the fluorescence (signal off phenomena) of QD-E. coli bioconjugates can be used as probes to develop a variety of fluorescence-based detection kits for the rapid determination of toxic drugs or food sample testing.