Microelectrophoresis of semiconductive quantum dots

Abstract

Semiconductive quantum dots (QDs) with superior optical properties, have been used as unique fluorescent probes in biological sensing and labelling. The effective intracellular delivery of QDs is critical to those biological applications. Microelectrophoresis is a promising technique to precisely deliver monodispersed nanoparticles into target cells with negligible cell membrane damage and cell distortion. In addition, it can record the intracellular electrical activities of target cells at the same time. This thesis aims to achieve for the first time the intracellular delivery of QDs via microelectrophoresis technique. Microelectrophoresis technique has been well established to eject charged substances from fine-tipped glass micropipettes into tissue and cells via electrical currents. However, few studies have paid any attention to exploring standard experimental protocols for the intracellular microelectrophoretic ejection of biocompatible nanoparticles. The success of microelectrophoresis is largely limited by the aggregation of nanoparticles and subsequent blockages in the tip of micropipettes during ejection, which is caused by the colloidal instability of nanoparticles when the attractive van der Waals forces between them prevail over the repulsive electrostatic forces. Thus, successful microelectrophoresis requires optimized suspensions with monodispersed nanoparticles within micropipettes to avoid blockage. To improve the delivery, the tip size, current magnitude and ejection duration should be screened in parallel for the optimal parameters. To address the above-mentioned requirements, Chapter 2 provides an effective experimental protocol for the preparation of QDs suspensions for filling micropipettes, which has balanced the stability of QDs against the electrolytic conductivity of suspensions. In Chapter 3, micropipettes have been designed and manufactured with suitable tip inner diameters (IDs) for the size distribution of QDs suspensions, which has been demonstrated in Chapter 4 via microinjection technique. Finally, in Chapter 5, QDs have been successfully ejected out of micropipettes via microelectrophoresis and observed under a fluorescence microscope. The success of microelectrophoresis technique in ejecting semiconductive QDs described in this thesis has paved the way for managing a variety of other biocompatible nanoparticles with proper surface functional groups in either intracellular or extracellular delivery for various biological research.