Imaging Escherichia coli using functionalized core/shell CdSe/CdS quantum dots

The internalization of a series of water-soluble CdSe/CdS quantum dots (QDs) stabilized by citrate, isocitrate, succinate, and malate by Escherichia coli is established by epifluorescence and confocal fluorescence scanning microscopy, fluorimetry, and UV–vis spectroscopy on whole and lysed bacterial cells. The organic-acid-stabilized QDs span a range in size from 3.8±1.1 to 6.0±2.4 nm with emission wavelengths from 540 to 630 nm. QDs of different sizes (i.e., 3.8–6 nm) can enter the bacterium and be detected on different fluorescence channels with little interference from other QDs as a result of the distinct emission profiles (i.e., 540–630 nm, respectively). Costaining QD-labeled E. coli with 4′,6-diamidino-2-phenylindole dihydrochloride (DAPI) demonstrates that the QDs and DAPI are colocalized within E. coli, whereas costaining QD-labeled E. coli with membrane dye FM4-64 shows that the FM4-64 is localized in the outer bacterial membrane and that the QDs are inside.Electronic Supplementary Material Supplementary material is available to authorized users in the online version of this article at .