Synthesis and characterization of monodisperse chitosan nanoparticles with embedded quantum dots

Luminescent semiconductor quantum dots (QDs) have ideal optical properties and have been used to tag biomolecules for bio-detection and bio-imaging. Some efforts have been made to incorporate QDs into polymer microbeads in order to render them water soluble, chemically stable, and biocompatible in physiological media. While these microbeads are generally very useful for multiplexed immunoassays, they are not suitable for the staining or labelling of subcellular components or intracellular measurements as they are relatively large in size. In this paper, we present a novel and easy way to encapsulate QDs into chitosan nanoparticles. The nanoparticles formed are very monodisperse, spherical in shape, and about 102 nm in size with embedded QDs dispersed within chitosan nanoparticles. The fluorescence quantum yield of the QDs in chitosan is found to be 11.8% higher than that of free QDs. In addition, as chitosan is present on the outermost layer of the nanoparticles, biomolecules can be further attached to the amine and hydroxyl groups on chitosan through chemical bonding. The QD based chitosan nanoparticles will be very useful for either multiplexed bioassays or intracellular study due to their very small sizes. Use of this approach can be extended to the encapsulation of multiple-colour QDs and other colloidal nanocrystals.