Lipid-specific labeling of enveloped viruses with quantum dots for single-virus tracking

Quantum dots (QDs) possess optical properties of superbright fluorescence, excellent photostability, narrow emission spectra, and optional colors. Labeled with QDs, single molecules/viruses can be rapidly and continuously imaged for a long time, providing more detailed information than labeled with other fluorophores. While they are widely used to label proteins in single-molecule tracking studies, QDs have rarely been used to study virus infection, mainly due to lack of accepted labeling strategies. Here, we report a general method to mildly and readily label enveloped viruses with QDs. Lipid-biotin conjugates were used to recognize and mark viral lipid membranes, and streptavidin (SA)-QD conjugates were used to light them up. Such a method allowed enveloped viruses to be labeled in 2 hours with specificity and efficiency up to 99% and 98%. The intact morphology and the native infectivity of viruses could be furthest preserved. With the aid of this QD labeling method, we lit wild-type (WT) and mutant Japanese encephalitis virus (JEV) up, tracked their infection in living Vero cells, and found that H144A and Q258A substitutions in the envelope (E) protein didn9t affect the virus intracellular trafficking. The lipid-specific QD labeling method described in this study provides a handy and practical tool to readily “see” the viruses and follow their infection, facilitating the widespread use of single-virus tracking and the uncovering of complex infection mechanisms.