the unlabeled and modified , labeled oligonucleotides ( hplc - purified and lyophilized ) were obtained from iba gmbh . n - cyano imidazole ( nci ) was synthesized in - house according to previous protocols30 . 1-octadecene ( ode , sigma ) , oleylamine ( sigma ) , oleic acid ( sigma ) , trioctylphosphine ( top , cytec ) , cadmium oxide ( sigma ) , selenium pellets ( sigma ) , sulfur powder ( sigma ) and tetradecylphosphonic acid ( tdpa , pci synthesis ) were purchased from the indicated suppliers . the detailed procedures for synthesis , characterization and encapsulation of qds within dna icosahedron are provided in the supplementary information . the experiments on cells were carried out using qds provided by nexdot ( www.nexdot.fr ) . ia2.2 cell line is a chinese hamster ovary ( cho ) cell line that lacks endogenous transferrin receptors but stably expresses the human transferrin and folate receptors described in reference 43 . the cells were cultured in hams - f12 complete media ( hf-12 , himedia ) containing 10% heat - inactivated fbs , 100 g / ml streptomycin and 100 g / ml penicillin with 200 g / ml g418 and 100 g / ml hygromycin to ensure maintenance of the transferrin and folate receptors . hela ( source described in reference 44 ) , rab5-gfp expressing hela cells and mefs cells ( source described in ref 31 ) were cultured in dmem media supplemented with 10% fcs and ps mixture . for binding experiments , ia2.2 cells were pulsed for 30 min on ice with 100 nm concentrations of all probes ( iqd , tf or plb ) , washed 2 - 3 times with m1 media , and imaged under olympus fv1000 confocal microscope , using appropriate lasers and imaging conditions . for the uptake assay , cells were pulsed for 15 min at 37c with the indicated probes , washed and imaged . uptake and colocalization were quantified using the pearson colocalization coefficient application in imagej ( nih ) . cysteine engineered gal3 and stxb were conjugated to amine modified dna using sulfo - mbs or sm(peg)8 ( piercenet ) crosslinkers . labeled gal3/stxb and dna - gal3/dna - stxb were pulsed to cells at 50 or 100 nm concentrations in dmem media for the indicated periods of time . post incubation cells were washed with pbs , fixed in 4% pfa , and coverslips mounted on fluoromount mowiol for imaging . for fixed samples , imaging was performed using a leica epifluorescence microscope , and for live cell and single particle tracking , a1r confocal , tirf - frap and spinning disk sp7 microscopes from nikon were used . the unlabeled and modified , labeled oligonucleotides ( hplc - purified and lyophilized ) were obtained from iba gmbh . n - cyano imidazole ( nci ) was synthesized in - house according to previous protocols30 . 1-octadecene ( ode , sigma ) , oleylamine ( sigma ) , oleic acid ( sigma ) , trioctylphosphine ( top , cytec ) , cadmium oxide ( sigma ) , selenium pellets ( sigma ) , sulfur powder ( sigma ) and tetradecylphosphonic acid ( tdpa , pci synthesis ) were purchased from the indicated suppliers . the detailed procedures for synthesis , characterization and encapsulation of qds within dna icosahedron are provided in the supplementary information . the experiments on cells were carried out using qds provided by nexdot ( www.nexdot.fr ) . ia2.2 cell line is a chinese hamster ovary ( cho ) cell line that lacks endogenous transferrin receptors but stably expresses the human transferrin and folate receptors described in reference 43 . the cells were cultured in hams - f12 complete media ( hf-12 , himedia ) containing 10% heat - inactivated fbs , 100 g / ml streptomycin and 100 g / ml penicillin with 200 g / ml g418 and 100 g / ml hygromycin to ensure maintenance of the transferrin and folate receptors . hela ( source described in reference 44 ) , rab5-gfp expressing hela cells and mefs cells ( source described in ref 31 ) were cultured in dmem media supplemented with 10% fcs and ps mixture . for binding experiments , ia2.2 cells were pulsed for 30 min on ice with 100 nm concentrations of all probes ( iqd , tf or plb ) , washed 2 - 3 times with m1 media , and imaged under olympus fv1000 confocal microscope , using appropriate lasers and imaging conditions . for the uptake assay , cells were pulsed for 15 min at 37c with the indicated probes , washed and imaged . uptake and colocalization were quantified using the pearson colocalization coefficient application in imagej ( nih ) . cysteine engineered gal3 and stxb were conjugated to amine modified dna using sulfo - mbs or sm(peg)8 ( piercenet ) crosslinkers . labeled gal3/stxb and dna - gal3/dna - stxb were pulsed to cells at 50 or 100 nm concentrations in dmem media for the indicated periods of time . post incubation cells were washed with pbs , fixed in 4% pfa , and coverslips mounted on fluoromount mowiol for imaging . for fixed samples , imaging was performed using a leica epifluorescence microscope , and for live cell and single particle tracking , a1r confocal , tirf - frap and spinning disk sp7 microscopes from nikon were used . plasma membrane of hela cells visualized by total internal reflection microscopy ( tirf ) showing two dimensional diffusion of surface - bound iqd . single particle tracking of surface - bound iqd on hela cells . a collection of single particle tracks using the trackmate plugin of imagej on the region above , where individual tracks are colored differently for clarity . dynamics of single internalized iqd particles along microtubules of hela cells . spinning disc confocal image of early endosomes labeled with iqd ( white ) along the microtubule network ( green ) , movie s4 . zoomed region of movie s3 showing the movement of iqd loaded vesicles along microtubules showing back and forth motility , color coded for particle velocity in m / sec , with same scaling as figure 5c .
functionalization of quantum dots ( qds ) with a single biomolecular tag using traditional approaches in bulk solution has met with limited success . 
 dna polyhedra consist of an internal void bounded by a well - defined three - dimensional structured surface . 
 the void can house cargo and the surface can be functionalized with stoichiometric and spatial precision . here , we show that monofunctionalized qds can be achieved by encapsulating qds inside dna icosahedra and functionalizing the dna shell with an endocytic ligand . 
 we deployed the dna - encapsulated qds for real time imaging of three different endocytic ligands - folic acid , galectin-3 ( gal3 ) and the shiga toxin b - subunit ( stxb ) . 
 single particle tracking of gal3 or stxb - functionalized , qd - loaded dna icosahedra allows us to monitor compartmental dynamics along endocytic pathways . 
 these dna - encapsulated qds that bear a unique stoichiometry of endocytic ligands represent a new class of molecular probes for quantitative imaging of endocytic receptor dynamics .