We have developed small glass capsules incorporating multiple CdSe/ZnS quantum dots (QDs) that show bright photoluminescence (PL). The capsule can be used as a fluorescent reagent in a variety of bio-applications. Its brightness and durability could make it useful as a phosphor for electronics as well.

Among QDs, a CdSe/ZnS QD is advantageous in brightness, however, it easily agglomerates. To prevent this, polymer-coated QDs are commercially available. But it is difficult to further increase their brightness. It is advantageous to encapsulate the QDs in glass which is more durable than polymers.

We have worked to develop a QD-dispersed glass capsule with a diameter of less than 100 nm by the Stöber synthesis, a kind of sol-gel method using alkoxide, since the particle of this size is critical for easy endocytosis by cells. Utilizing the properties of alkoxides, we have succeeded in incorporating multiple QDs in a glass capsule. The 50-nm capsule has brightness of about 10 times, light resistance of about 100 times, and cadmium leaching in a buffer solution of less than one-tenth, when compared with those of polymer-coated QDs.