Labeling the nucleocapsid of enveloped baculovirus with quantum dots for single-virus tracking

Utilization of quantum dots (QDs) for single-virus tracking is highly important for understanding virus infection mechanism. However, QD labeling site of real enveloped viruses has been confined to the external envelope so far, causing the impossibility to monitor the late infection events after the loss of envelope. Herein, a strategy to label the internal nucleocapsid of enveloped virus with QDs was proposed. The nucleocapsid of enveloped baculovirus was self-biotinylated during virus replication process in host cells and subsequently labeled with streptavidin-conjugated QDs (SA-QDs). Such host cell-assisted QD labeling was proved to be reliable, specific, efficient and capable of maintaining virus infectivity. Based on such labeling, critical infection events before and after the envelope loss were monitored in real time, including single virus interacting with late endosomes and the subsequent nucleocapsid transporting into cell nucleus. Thus our established QD labeling of enveloped virus nucleocapsid with QDs enables the comprehensive single-virus tracking for deeply understanding virus infection mechanism.