Green engineering for large-scale synthesis of water-soluble and bio-taggable CdSe and CdSe–CdS quantum dots from microemulsion by double-capping

A novel green stabilization and recovery technique is developed to prepare highly fluorescent, water-soluble, and bio-taggable CdSe and CdSe–CdS quantum dots (QDs) at room temperature, from AOT/water/n-heptane microemulsion. The two versions of the technique, Post-Synthesis Stabilization (PostSS) and Pre-Synthesis Stabilization (PreSS) achieve about 80% recovery of n-heptane and, about 40% recovery of surfactant AOT, both of which are recycled, thus making the process green and attractive for larger batches of synthesis. Both PostSS and PreSS methods employ a double-capping mechanism for high stability of nanoparticles in aqueous dispersion. The QDs have been characterized in both microemulsion and aqueous phases, with UV–visible spectroscopy, fluorescence spectroscopy, transmission electron microscopy, X-ray diffraction, small-angle X-ray scattering and X-ray photoelectron spectroscopy. These MAA (mercaptoacetic acid)-capped QDs, dispersed in TSC (trisodium citrate) buffer, are ready for standard bio-coupling reactions. Further, the MAA-capped QDs are encapsulated in phospholipid liposomes and, studied with laser scanning confocal Microscopy, for possible application in drug/gene delivery.