Semiconductor Quantum Dot-Labeled Microsphere Bioconjugates Prepared by Stepwise Self-Assembly

Biologically active semiconductor quantum dot (QD)-labeled polystyrene (PS) beads with tailored QD loading and luminescence have been prepared via the layer-by-layer (LbL) assembly approach. PS beads of 925 nm diameter were used as templates for the deposition of CdTe nanocrystal/polyelectrolyte (PE) multilayers, formed via electrostatic interactions, followed by an outermost layer of anti-immunoglobulin G (anti-IgG) to render the particles biospecific. The beads formed were characterized by transmission electron microscopy (TEM) as well as absorption and luminescence spectroscopy. TEM demonstrated the formation of a uniform coating on the PS beads, while the optical spectra confirmed the deposition of CdTe nanocrystals with each CdTe QD/PE coating cycle, and the deposition of fluorescently labeled anti-IgG. The beads were shown to be immunologically active through agglutination assays with the biospecific partner IgG, leading to the formation of bead aggregates and increased light scattering of the dispe...