Detection of environmental microorganisms with a bead-based assay and quantum dots

Quantum dots (QDs) promise significant advantages in environmental and bead-based applications where the target cells need to be discriminated above background fluorescence. We examined the possible applications of QDs as markers for flow cytometric measurements. Paramagnetic beads were labelled with either QDs or some commonly-used fluorochromes and their fluorescence intensity was studied by flow cytometry after DNA capture or amplification. PCR amplicons were detected successfully when using a blue light excitation source for the QDs. Despite the low fluorescent signal of QDs compared to organic dyes found in this study, it is anticipated that the use of a UV laser instead of a blue laser would magnify the signal intensity significantly. We describe a bead-based method for identifying bacteria and archaea based on beads with an inherent fluorescent dye but applications of QDs may be reduced due to their large size relative to current fluorophores.