Spectral Bar Coding of Polystyrene Microbeads Using Multicolored Quantum Dots

Abstract

This paper focuses on encoding polystyrene microbeads, 10-100 microm in diameter, with a luminescent spectral bar code composed of mixtures of quantum dots (QDs) emitting at different wavelengths (colors). The QDs are encapsulated in the bead interior during the bead synthesis using a suspension polymerization, and the bar code is constructed by varying both the number of colors included in the bead and, for each color, the number of QDs of that color. Confocal laser scanning microscopy images of the beads demonstrate that the multicolored QDs are pushed together into inclusions within the bead interior. The encoded bead emission spectrum indicates that the peak position of the included colors does not shift relative to the corresponding peaks of the spectra recorded for the nonaggregated QDs at identical loading concentrations. Due to the spatial proximity of the QDs in the inclusions, electronic energy transfer from the lower wavelength emitting QDs to the higher emitting QDs changes the relative intensities of the colors compared to the values in the nonaggregated spectra. We show that this energy transfer does not obscure the spectral uniqueness of the different codes. Ratiometric encoding, in which the bar code is read as relative color intensity, is shown to remove the dependence of the code on the bead size.

Quantum dot incorporated Bacillus spore as nanosensor for viral infection

“…Han et al were the first to apply QD-tagged 1.2 µm polymer microspheres to the multiplexed optical coding of DNA hybridization (Han et al, 2001). Fuelled by their studies, the following three preparation methods for optical QD-encoded microspheres were developed: (i) incorporation of QDs during microsphere synthesis (Joumaa et al, 2006;Li et al, 2005;Vaidya et al, 2007;Wang and Seo, 2008;Yang et al, 2006), (ii) deposition of QDs onto bead surfaces through layer-bylayer adsorption (Li et al, 2009a(Li et al, , 2009bRauf et al, 2009), and (iii) diffusion of hydrophobic QDs into polymeric microspheres. Encoded microspheres are usually prepared by embedding hydrophobic microspheres with hydrophobic QDs via porosity partitioning and entrapment or swelling (Bradley et al, 2005;Gao and Nie, 2004).…”

Hemoglobin‐CdTe‐CaCO3@Polyelectrolytes 3D Architecture: Fabrication, Characterization, and Application in Biosensing

“…[13] An alternative and promising strategy is to utilize a biofunctionalized ''host'' labeled with QDs. Currently, three methods have been tested for the incorporation of QDs into a ''host'': [14] a) QDs are incorporated in the beads during the bead synthesis; b) QDs are trapped or affinity-partitioned directly into a preformed bead; or c) coating of the bead surface with QDs. While the problem of the first approach lies in the drawback of phase separation between the beads and QDs during the synthesis, the second method suffers from the drawback of a non-uniform distribution of QDs inside the beads.…”

Fluorescent nanocrystal-encoded microbeads for multiplexed cancer imaging and diagnosis

“…Vaidya et al [60] has examined experimental parameters of the suspension polymerization method for incorporating quantum dots in the interior of polymer microbeads. The study examined two aspects of this encapsulation method, which are relevant for using the QD-loaded microbeads as a luminescent bar code.…”

“…constructing the code as the intensity of a particular colour divided by the total intensity removes the dependence of the code on the bead size. For each of the two scripts studied, tables of the ratiometric bar codes for beads of varying size were compiled, and the codes were shown to differ by less than 5% for a 10% or more variation in the bead size [60].…”