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Spectrally Barcoding Polymer Microbeads Using Quantum Dots
Achievement/Results
Fluorescently labeled polymer microbeads (10-100 microns in diameter) are promising platforms for implementing high-throughput screening assays of the binding interactions of proteins with different ligands for applications particularly in drug discovery. In this approach, ligands are first bound or synthesized directly to the bead surface and chromophores, fluorescing at a different wavelengths, are embedded in the beads to form a fluorescent spectral label.
A library of microbeads with different ligands and identifying labels are incubated with a protein of interest (usually fluorescently labeled), and the beads which bind the protein are identified by detecting the protein fluorescence. The binding ligands are identified simultaneously by recording the spectral label. In this way, large numbers of binding interactions can be assayed in one step. Quantum dot nanocrystals fluorescing at different wavelengths are ideal materials for forming a spectral label since they all can be excited at a common wavelength and their emission spectrum is characterized by sharp, symmetrical peaks. However, the usual aggegation of the nanocrystals in the beads gives rise to energy transfer which obscures the clarity of the spectral label.
City College of New York PhD students Shyam Vaidya and NSF IGERT Trainee Gerson Aguirre, together with CCNY faculty Alex Couzis (Chemical Engineering), Lane Gilchrist (Chemical Engineering and Biomedical Engineering), and Charles Maldarelli (Chemical Engineering and Levich Instititue), have solved this problem by using suspension polymerization of a high crosslinking polymer to encode the beads with the Qds during the polymerization step. The high crosslinking effectively isolates the nanocrystals, and the group has demonstrated a significant reduction in the energy transfer.
Address Goals
The spectrally barcoded microbeads developed in this study are essential in implementing methods which screen, in one step, the binding interactions of a protein with many different molecular ligands. As such, the microbeads will find applications in cell biology, in elaborating the complex web of binding interactions with which proteins direct and orchestrate cell activity. Thus this research has the potential to advance the understanding of the molecular basis of cell function.
In addition, the high throughput screening technologies implemented by these beads can be used to develop drug molecules which bind specifically to intended protein receptors – particularly those located on the surfaces of cell membranes – to achieve a therapeutic effect. Drugs that bind to cell membrane receptors are among the most promising in developing effective drug therapies. Hence the development of these beads, and the high-throughput screening protocols which they enable, stand to improve health care in the Nation.
