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 dispersions. Utilization of the LbL assembly method to prepare QD-tagged beads with increased complexity (e.g., several types of QDs and multiple biofunctionality) is expected to open new opportunities in a range of biotechnological applications where designer particles are required.