SV40 Capsid-based Fluorescent/Magnetic Micro-particles For Dual-modal Detection Of Single Cell

Background Life in the nature are mostly composed by a variety of cells with different functions.The stochastic average analysis from cell population will mask the cell-to-cell variations,leading a missing information about the vital molecular mechanism of life.Such as cancer stem cell theory,the metastasis and localization of tumor cells are related to very small subgroups.Hence,if we can accurately detect and monitor these small subpopulations of cells,it is possible to predict the tumor metastasis and organs co-localization,achieving better control of cancer and even cure of cancer.However,the spatial and temporal resolution of current imaging techniques is not sufficient for single cell detecting and tracking.Especially,single cell detection and tracing in vivo is rather challenged,and thereby the development of a high spatiotemporal resolutions method to achieve single cell monitoring in vivo is urgently demanded.Purpose To break through the bottleneck of single cell detection technique,we established a novel method to simultaneously deliver micro-sized magnetic iron oxide particles(MPIOs)and quantum dots(QDs)into cells by using SV40,which have self-assembly capacity and cell infection activity,to improve the labeling efficiency,magnetic/fluorescent signals,and finally realize a magnetic/fluorescent dual-mode detection at a single-cell resolution.Methods Firstly,we used virus-like particles(VLPs)of simian virus 40(SV40)to encapsulate QDs by in vitro self-assembly of the major capsid protein of SV40,termed VLP-QDs.Then the VLP-QDs were modified with biotin and further conjugated with streptavidin functionalized micro-sized iron oxide particles(SA-MPIOs),resulting in multifunctional magnetic and fluorescent micro-sized particles(MPIO-VLP-QDs).The as-obtained particles were incubated with living Vero cells to accomplish the labeling with high efficiency.The labeled cells were detected by fluorescent/magnetic dual-mode imaging using high resolution fluorescence microscope and MRI,and internalized mechanism of MPIO-VLP-QDs toward cells has been also investigated.Results The multifunctional MPIO-VLP-QDs has been constructed and succeeded in cell labeling with high efficiency.The single cell detection was realized in vitro by 9.4T MRI.The mechanism investigation demonstrated that MPIO-VLP-QDs were co-localized with VP1,caveolin-1 and endoplasmic reticulum,but not with golgi and clathrin.Conclusions The MPIO-VLP-QDs can be delivery into the Vero cell without obvious harmful effect on the cell viability.The labeled cells have strong magnetic signal and can be detected by MRI in single cell level.The MPIO-VLP-QDs enter the cells by caveolar endocytosis,travel along the microtubules,and accumulate in the endoplasmic reticulum.This process mimics the early infection steps of SV40.