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Quantum dot encapsulated nanocolloidal bioconjugates function as bioprobes for in vitro intracellular imaging

Muralidhara, Soujanya, Malu, Krishnakumar, Gaines, Peter, Budhlall, Bridgette M.
Colloids and surfaces 2019 v.182 pp. 110348
X-ray photoelectron spectroscopy, antibodies, biotin, cell viability, colloids, confocal microscopy, cytotoxicity, encapsulation, epitopes, fluorescence, fluorescent dyes, image analysis, laponite, latex, monitoring, nanoemulsions, organelles, photostability, polystyrenes, quantum dots, scanning electron microscopy, streptavidin, transmission electron microscopy, zeta potential
Bioimaging probes incorporating quantum dots (QDs) are important for identifying organelles and monitoring their movement/location in living cells. Organelle specificity can be accomplished by functionalizing probe surfaces with chemical groups that can react with antibodies capable of targeting specific organelle-protein epitopes. Here, such a bioprobe is generated by encapsulating ZnS-capped CdSe QDs within polystyrene (PS) nanocolloids via Pickering miniemulsion using laponite nanoclay platelets as solid-stabilizers. The surfaces of these platelets are modified with aminopropyltriethoxysilane (APTES), and biotinylated by reacting sulfo-NHS-Biotin via the APTES amine group. Surface functionalization and bioconjugation are confirmed using X-ray photoelectron spectroscopy. The number of sites available on Streptavidin for Biotin binding is determined using a competitive HABA assay to optimize the bioconjugation protocol. The PS-encapsulated QDs (PS-QDs) nanocolloids are 50–200 nm in diameter and colloidally stable, as evidenced by transmission electron microscopy and ζ-potential measurements, respectively. Spherical particle shape is confirmed by scanning electron microscopy. Transmission electron microscopy also showed the nanoclay platelets on the surface of QD-encapsulating latex particles. The PS-QDs particles are easily dispersed in water and exhibit long-term photostability over various conditions. Cell viability of >95% is observed for NIH-3T3 cells after 72-h exposure to PS-QDs nanocolloids, with no cytotoxicity to living cells, even at 0.1 mg mL−1. NIH-3T3 cellular uptake and internalization are confirmed by confocal microscopy, with PS-QDs fluorescence within cells remaining high even after 24-h exposure, demonstrating the applicability of PS-QDs nanocolloids as long-lived fluorescent bioprobes for in vitro intracellular imaging.