(427a) Dispersion of Semiconductor Nanoparticles In a Polymer Matrix:a Fluorescence Energy Transfer Study

The focus of this presentation is the development of optically barcoded polymer beads for use in high-throughput, multiplexed screening applications such as protein microarrays or flow cytometry. Luminescent semiconductor nanoparticles (or quantum dots (QDs)) with different emission wavelengths (colors), and incorporated in different compositions in polystyrene (PS) beads are used to define an optical barcode. The incorporation is undertaken by copolymerizing the PS beads with hydrophobically capped, core-shell, CdSe/ZnS QDs, using a spraying suspension polymerization procedure. Confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM) images of the beads indicate that the QDs are segregated into inclusions distributed throughout the bead. The segregation of the QDs inside the polymer beads is due to enthalpy and entropy-driven rejection of the QDs from polymerizing loci as the polymerization proceeds. CLSM and fluorimeter measurements of the emission spectra of PS beads embedded with multicolored QDs in varying concentrations are reported which verify that distinguishable optical ratio-metric barcodes, derived from the spectral scans of the barcoded beads, can be obtained by this technique.

Comparison of the emission profiles of the barcoded beads with that of the same QDs dispersed in styrene indicates Electronic Luminescence Energy Transfer from the lower wavelength QDs to the higher wavelength QDs, providing evidence that the QDs are situated within nanometers of each other in the inclusions. The energy transfer limits our ability to obtain significant number of ratio-metric barcodes for use in multiplexing applications. Therefore, we obtained a reduction in the energy transfer by separation of the segregating QDs from one another during the polymerization process. This separation was achieved by highly cross-linking the PS beads using divinylbenzene (DVB) as one of the monomer units. A diffused luminescence from the CLSM luminescence images of the beads containing DVB confirms the non-aggregation of the QDs in presence of DVB during the polymerization. TEM images of the bead interiors also indicate that the QDs are uniformly distributed in the polymer matrix. CLSM emission profiles of these barcoded beads in comparison with that of the beads without DVB show a significant reduction in the energy transfer.