Conjugation of DNA to Streptavidin-coated Quantum Dots for the Real-time Imaging of Gene Transfer into Live Cells

We have developed the method for the conjugation of biotinylated DNA to streptavidin-coated quantum dots (QDs). QD-DNA conjugates and a highly sensitive fluorescence imaging technique are adopted to visualize gene transport across the membrane of the live cell in real time. Endocytotic cellular uptake of oligonucleotide is monitored by a real-time confocal imaging system. Longterm kinetic study enables us to reveal the unknown mechanisms and rate-limiting steps of extracellular and intracellular transport of DNA. Gel electrophoresis is used to verify the effect of incubation time and the molar ratio of QDs to DNA on the conjugation efficiency. It is possible to fractionate the QD-DNA conjugates according to the DNA concentration and obtain the purified conjugates by a gel extraction technique. QD-DNA conjugates have a potential to be nanoscale building blocks by self-assembly process as well as a versatile tool for fluorescence imaging and monitoring of biological systems.