Semiconductor quantum dots (QDs) have emerged as a new class of fluorescent probes and labeling agents for biological samples. QDs are bright, highly photostable and allow simultaneous excitation of multiple emissions. Owing to these properties, QDs hold exceptional promise in enabling intracellular biochemical studies and diagnosis with unprecedented sensitivity and accuracy. However, use of QD probes inside living cells remains a challenge due to difficulties in delivery of nanoparticles without causing aggregation and imaging single nanoparticles inside living cells. In this dissertation, a systematic approach to deliver, image and locate single QDs inside living cells is presented and the properties of molecular motor protein driven QD transport are studied. First, spectroscopic and imaging methods capable of differentiating single nanoparticles from the aggregates were developed. These technologies were validated by differentiating surface protein expression on viral particles and by enabling rapid counting of single biomolecules. Second, controlled delivery of single QDs into living cells is demonstrated. A surprising finding is that single QDs associate non-specifically with the dynein motor protein complex and are transported to the microtubule organizing center. Accurate localization and tracking of QDs inside cell cytoplasm revealed multiple dynein motor protein attachment resulting in increased velocity of the QDs. Further, spectrin molecule which is known to recruit dynein motor protein complex to phospholipid micelles was found to associate with the QDs. These results may serve as a benchmark for developing new QD surface coatings suitable for intracellular applications. Since, nanoparticles are similar in size to viral pathogens; better understanding of nanoparticle-cell interactions should also help engineer nanoparticle models to study virus-host cell interactions. (Contains AVI format multimedia files)

Cellular internalization of large therapeutic agents such as proteins or nucleic acids is a challenging task because of the presence of the plasma membrane. One strategy to facilitate intracellular drug uptake is to induce transient pores in the cell membrane through physical delivery strategies. Physical approaches are attractive as they offer more generic applicability compared with viral or biochemical counterparts. Pulsed laser light can induce the endothermic carbon-steam reaction in carbon-nanoparticle suspensions to produce explosive photoacoustic effects in the surrounding medium. In this study, for the first time, these photoacoustic forces were used to transiently permeabilize the cell membrane to deliver macromolecules into cells. Intracellular delivery using this method was demonstrated in multiple cell types for uptake of small molecules, proteins and DNA. At optimized conditions, uptake was seen in up to 50% of cells with nearly 100% viability and in 90% of cells with ≥90% viability, which compared favorably with other physical methods of drug delivery. Cellular bioeffects were shown to be a consequence of laser-carbon interaction and correlated with properties of the carbon and laser, such as carbon concentration and size, laser pulse duration, wavelength, intensity and exposure time. Similar results were observed using two different lasers, a femtosecond Ti: Sapphire laser and a nanosecond Nd: YAG laser. Uptake was also shown in murine skeletal muscles in vivo with up to 40% efficiency compared to non-irradiated controls. This synergistic use of nanotechnology with advanced laser technology could provide an alternative to viral and chemical-based drug and gene delivery.