Preparation and characterization of novel fluorescent nanocomposite particles: CdSe/ZnS core-shell quantum dots loaded solid lipid nanoparticles.

Fluorescent quantum dots (QDs, semiconductor nanocrystals) have gained increasing attention in the past decade due to their unique optical properties. In this work, we synthesized highly luminescent lipophilic CdSe/ZnS core-shell QDs under mild conditions, and encapsulated the QDs into solid lipid nanoparticles (SLNs) to prepare fluorescent nanocomposite particles. The transmission electron microscopy image showed that the QDs were nearly monodispersed and uniform with an average diameter of about 4 nm. The fluorescence spectrum of the QDs was symmetric and narrow with an emission maximum at 556 nm. Characterized by photon correlation spectroscopy (PCS) and zeta potential measurement, the nanocomposite particles (QDs-loaded SLNs) exhibit an average particle size of about 90 nm and zeta potential of about -28 mV. Fluorescence measurements showed that the encapsulated QDs maintain their high fluorescence and narrow/symmetric emission spectra. Assembling many QDs in single nanocomposite particle significantly increases the fluorescence signal and the signal-to-background ratio compared to individual QDs. In vitro and in vivo imaging indicated that QDs-loaded SLNs were stable and slow to photobleach. These fluorescent QDs-loaded SLNs were biocompatible with fluorescence stability and had good potential in biological imaging applications. The approaches could also be used to encapsulate other optical nanocrystals or magnetic nanoparticles, and allow them to be used under aqueous biological conditions.