Rapid detection of norovirus from fresh lettuce using immunomagnetic separation and a quantum dots assay

Current molecular methods that include PCR have been used to detect norovirus in many food samples. However, the protocols require removing PCR inhibitors and incorporate time-consuming concentration steps to separate virus from analyte for rapid and sensitive detection of norovirus. We developed an immunomagnetic separation (IMS) and a quantum dots (QDs) assay to detect norovirus eluted from fresh lettuce with Tris buffer containing 1% beef extract (pH 9.5). IMS facilitated viral precipitation with a 10-min incubation, whereas virus concentration using polyethylene glycol (PEG) requires more than 3 h and an additional high-speed centrifugation step to precipitate virus before reverse transcription PCR (RT-PCR) analysis. The fluorescence intensity of QDs was detected qualitatively on norovirus dilutions of 10(-1) to 10(-3) in a stool suspension (100 RT-PCR units/ml). The results suggest that a fluorescence assay based on IMS and QDs is valid for detecting norovirus qualitatively according to fluorescent signal intensity within the same virus detection limit produced by IMS-RT-PCR and PEG-RT-PCR.