The effect of quantum dot size and poly(ethylenimine) coating on the efficiency of gene delivery into human mesenchymal stem cells

Quantum dot (QDs) have been employed as bioimaging agents and delivery vehicles for gene therapeutics in several types of cells. In this study, we fabricated multiple QD bundled nanoparticles (NPs) to investigate the effect of QD size and poly(ethylenimine) (PEI) coating on the efficiency of gene delivery into human mesenchymal stem cells (hMSCs). Several types of QDs, which exhibit different ranges of particle size and fluorescence when employed, were coated with PEI to alter their negative charges and to enable them to be bundled into larger particles. Using specific wavelengths of QDs for bioimaging, gene-complexed QD bundled NPs were easily detected in the hMSCs using several different methods such as fluorescence-activated cell sorter, confocal laser scanning microscopy, and in vivo optical imaging. These PEI-coated, bundled QD NPs exhibited significantly higher gene transfection efficacy than single-type QDs. Particularly, the largest QD bundled NPs examined, QD655, had a much higher uptake capability and greater gene expression ability than the other QD NPs (QD525, QD565, and QD605). We believe that our findings help to enrich knowledge of design considerations that will aid in the engineering of QD NPs for stem cell application in the future.