Fluorescent Tagging Of Cells Via Conjugation With CdTe Quantum Dot – TiO2 Nanotube Composite Nanostructures

Student: J. Spencer Morris
Department: Physics
Advisor: Latika Menon

Abstract

There exists a growing need for the tagging of individual cells in vitro, and ultimately cellular components and cells in vivo, as biologists and biochemists require increasingly fundamental data sets. A device for fluorescent cellular tagging is an excellent means of collecting such data. While quantum dots (QDs) have already been demonstrated to fulfill such a purpose, proposed systems lack the necessary interfacial stability and costs remain high. The fabrication of composite CdTe QD and TiO2 nanotube nanostructures may be an excellent mechanism for fluorescent cellular tagging.

Fluorescence as a Solution for Cellular Tracking

Nanocrystal-based technology has become increasingly sophisticated in recent years and, in particular, the application of QDs, due to their novel optical properties, to biological systems for cellular imaging (initially demonstrated in 1998) has been the source of intense research. Because QDs have finely tunable emission spectra and exhibit high photostability relative to traditional flourophores such as dyes, their potential as reliable cellular tags is unsurpassed, and whereas conventional biological imaging technologies often involve< radiation, QDs can be chemically modified for optimum biocompatibility. Once a safe and reliable method of QD-based fluorescent cell labeling has been established in vitro, more complex technologies can be developed such as intracellular modifications and in vivo uses such as targeted drug delivery. One of the primary difficulties facing the development of this technology is the coupling of QDs to cells, an obstacle I attempt to address by using the nanotube component of the functionalized nanocomposite structure as the QD-cell interface.
Principles of Nanocomposite Constituents and Nanocomposite Function

The proposed composite nanostructure is a CdTe QD interfaced with a TiO2 nanotube, which can be accomplished via the correct functionalization of the nanocrystal surface. CdTe is an ideal QD species for biofluorescent applications due to its inherent water-solubility, demonstrated biocompatibility, and emission range extending into the near infrared, thus eliminating background autofluorescence of cellular components. Like all QDs, CdTe emission can be directly controlled via growth conditions, and operates under the principle of photon-activated excitation and resultant redshifted emission. Likewise, TiO2, long known to be highly biocompatible, in a short nanotubular structure allows for close proximity of the QD-activated fluorescence to the cell of intended study, with the added benefit that such nanotubes are relatively inexpensive.

Methodology

The proposed experiment will involve first the synthesis of the CdTe QDs. Conjugation with TiO2 nanotubes will be accomplished by an initial study involving altering the functionalization of these QDs such that a stable QD-nanotube interface can be formed. Once the composite nanostructures are fabricated a culture test will ensue to verify the nanostructures are benign to live cells. These cells will then be grown on top of a composite nanostructure solution upon confirmation of this condition, and fluorescent signals will be monitored in vitro via fluorescent optical microscopy. Further modification and optimization of the composite nanostructures will commence as time permits.