The presence of pathogenic bacteria is a worldwide health concern; therefore, rapid identification is crucial to prevent widespread outbreaks of disease. Exhibiting size-dependent optical and electronic properties, semiconductor quantum dots (QDs) are progressing as improved fluorophores for biological labeling because they provide many advantages over the typical organic dyes used in current assays: broader absorption spectra for simultaneous excitation, narrower emission spectra for simultaneous detection, and increased photostability. CdSe QDs are the best understood quantum-confined systems to date and are the most popular choice for biolabeling because their fluorescence can span the entire visible region of the electromagnetic spectrum.
My work is focused on developing modified QDs that will selectively label the common pathogenic bacterium Escherichia coli O157:H7. Attaching streptavidin-functionalized CdSe/ZnS QDs to E. coli O157:H7 cells that are labeled with biotinylated anti-E. coli O157:H7 antibodies results in selective binding to the pathogenic cells over benign E. coli DH5α cells. Determined using fluorometry and epifluorescence microscopy, this simple assay is 2 orders of magnitude more sensitive and more photostable than an analogous method using a traditional dye, fluorescein isothiocyanate (FITC). These same QDs have also surpassed their FITC counterpart in the realm of flow cytometry of bacterial cell mixtures: QDs exhibit better accuracies (factor of 2); brighter fluorescence intensities (order of magnitude); and lower detection limits (1% E. coli O157:H7 cells) when mixed with overwhelming amounts of E. coli DH5α cells. Therefore, semiconductor QDs are vastly improved fluorophores for selective and sensitive labeling of a pathogenic bacterium and have no deleterious effects on the biological molecules or the antibody–antigen and streptavidin–biotin interactions utilized in these studies.
Currently, I am a postdoctoral research associate working in collaboration with the Eastman Kodak Company on a light-emitting diode (LED) constructed entirely of inorganic nanocrystal components.
