(3dq) Nanoparticles for Biomedicine: Development of a Family of Novel Nanocomposites and Fundamental Research Into Bio-Transport Phenomena

            The potential of nanomaterials with special optical, magnetic, electronic and thermal properties for biomedical applications has been extensively demonstrated. My independent research program has two thrusts: (1) developing a new generation of nanomaterials, which could be loosely defined as nanoscale materials with properties beyond those currently in use. These novel nanomaterials would overcome current challenges (e.g. aggregation, loss in performance over time), or/and exhibit enhanced performance (e.g. greater brightness), or/and integrate functions from individual nano-species as well as micro-devices; (2) investigating fundamental behaviors of nanomaterials in biological systems. A focus is given to how nanomaterials are transported in cells (“transport phenomena” in biological systems). The knowledge obtained would be applied for design of new nanomaterials and new strategies of tackling diseases.   

            In addition to helping to build the groundwork for an emerging field, i.e. bionanotechnology, my work also contributes to the ongoing transformation of a traditional discipline, i.e. chemical engineering. The following are some highlights of my research accomplishments, which also serve as preliminary results for the two research thrusts of my independent research program described above.

 Nanocomposites: from tracking single molecules to delivering drugs

            A major recent development in bio-nanomaterials research is the emergence of composite nanomaterials, which combine the functions of individual nanomaterials. I have developed a family of novel nanocomposites based on micelle-templated self-assembly for a wide spectrum of biomedical applications.

            First, a composite nanoparticle that changes fluorescent color continuously was created by co-encapsulating several quantum dots (semiconductor nanocrystals with extraordinary fluorescent brightness and photostability) of different colors into a micelle. This novel nanocomposite, also known as alternating-color quantum dot nanocomposite, simultaneously solved two seemingly irreconcilable problems in quantum dot-based single particle/molecule tracking, namely blinking-caused interruptions in particle trajectory and difficulty to check single particle status in situ without blinking (Ruan et al. Nano Letters 11, 941-945 (2011)).

            Second, quantum dots (QDs) and superparamagnetic iron oxide nanoparticles (SPIONs) were co-encapsulated into a micelle, resulting in a composite nanoparticle that posses both fluorescent and magnetic properties. Compared with commercial magnetic beads, QD-SPION-micelles have the advantages of small size (less than 50 nm) and bright fluorescence for imaging. Combining QD-SPION-micelles with magnetic microarrays led to a novel nano-conveyor belt technology, which achieved the first simultaneous magnetic manipulation and fluorescent tracking of multiple individual sub-100 nm nanostructures (Ruan et al. Nano Letters 10, 2220-2224 (2010)). Preliminary results with biomolecules and cells indicate that the nano-conveyor belt technology could become a platform technology for new methods in molecular diagnostics, cell separation, and nano-fabrication.

            Third, poly (lactic-co-glycolic acid) (PLGA), which is the most commonly used biodegradable polymer for drug delivery, was encapsulated into a micelle, resulting in a novel drug delivery vehicle. Compared with previous techniques, which are essentially top-down approaches, this bottom-up approach offers a facile and robust method to fabricate sub-100 nm PLGA-based drug delivery vehicles. Compared with micelles alone (without PLGA), PLGA-micelles offer a way to control drug release without significantly changing particle size (Ruan et al. patent pending, patent no. 61/433,794).

            Further, a process to produce the micelle-based family of nanocomposites in continuous mode was developed. 300 times scale-up from the original batch production process was achieved (Doug et al. manuscript in preparation).

Probing intracellular transport of nanoparticles

            As numerous types of nanomaterials are being developed for biomedical applications, it is of fundamental importance to understand how nanomaterials interact with biological systems. In particular, transport processes of nanomaterials inside cells have been poorly understood, to a large extent due to lack of fluorescent probes that are sufficiently photostable and bright to track these dynamic processes. I have used quantum dots (QDs), which are fluorescent nanoparticles with extraordinary brightness and photostability, coupled with spinning disk confocal microscopy to image and track intracellular transport.

            First, QDs were conjugated with Tat peptide, which is being widely investigated for its potential as a delivery vehicle and is also the peptide sequence responsible for invasion of cells by HIV virus, to probe the mechanism of Tat-mediated intracellular delivery of nanoparticles. It was found that, in stark contrast to what was previously thought, Tat-QDs did not enter cell nucleus, but were trapped in intracellular vesicles. The motions of Tat-QD-vesicles along cytoskeletons were tracked and the velocities were determined. Furthermore, Tat-QD-vesicles were observed just outside cells. This discovery indicates that Tat-QDs can leave the cells via a process known as vesicle shedding (Ruan et al. Journal of the American Chemical Society 129, 14759-14766 (2007)).

            Second, single QDs were directly delivered into cytoplasm via a bacteria toxin streptolysin O (SLO). The single (or near single) status of the intracellular QDs was confirmed by their blinking behavior. In cytoplasm single QDs gradually formed aggregates, with the aggregation rate dependent on QD surface chemistry and cell type. Surprisingly, it was found that most of the single QDs were bound with dynein, the motor protein responsible for transporting cargos along microtubules towards the microtubule organizing center (just outside cell nucleus), by non-specific binding. Further, the binding of single QDs with dynein was exploited to track the dynein motion in live cells (Agrawal et al. manuscript in preparation).