Encapsulation of luminescent quantum nanodots in silica nanocapsules for biological labeling

Semiconductor quantum dots (QDs) have attracted considerable interest in biological labeling due to their unique optical properties. Compared with conventional organic fluorophores, QDs have a strong fluorescence emission and narrow, symmetric emission spectrum, and are photochemically stable. QDs also exhibit a wide range of size-tunable colors and a series of different-colored dots can be activated using a single laser. The ideal optical properties of QDs offers the possibility of using them to tag biomolecules in ultra-sensitive biological detection based on optical coding technology. Biological labels that can theoretically encode more than one million biomolecules can be produced by packing different combinations of QDs with different colors into the labeling materials. Furthermore, some technical problems relating to QDs' surface chemistry remain to be ironed out such as water solubility, biocompatibility, how to make QDs chemically stable in physiological media and how to couple biomolecules to QDs' surface. Efforts have been made to do some surface modifications on single QDs to solve the above problems, but the surface modification is very dependent on the surface chemistry of QDs and successful cases are limited to conjugation of thiols or TOPO to ZnS caped or uncapped CdSe. In this work, multiple quantum dots were incorporated into silica nanocapsules to produce bar coding nanocomposites as biological labels. The encapsulation of QDs in these silica nanocapsules will also solve the above mentioned problems of water solubility, biocompatibility, stability, and provides a possibility of further attaching biomolecules to these nanocapsules as well. The encapsulation was carried out in two steps as shown in Figure 1: the QDs were first encapsulated by a monolayer of polymerized 3-(trimethoxysilyl)-propyl methacrylate (MPS) using microemulsion method; (2) silica was subsequently coated through chemical bonding between silane and silanol groups of MPS. The samples were characterized by TEM, AFM, UV and Fluorescence spectrophotometers.