Microbeads boast dual functions

Micrometer-sized beads arebecoming a popular format for performing biological assays. These beads must be both manipulatable and detectable. Shuming Nie and coworkers at Emory University and Georgia Institute of Technology report that they can embed quantum dots and iron oxide nanocrystals in the pores of mesoporous silica beads to create dual-function microcarriers that can be simultaneously encoded, enriched, and separated (Anal. Chem., DOI: 10.1021/ac0610309). The beads are doped by mixing the silica beads with solutions of quantum dots and iron oxide nanocrystals, either simultaneously or sequentially. The iron oxide nanocrystals reduce the fluorescence from the quantum dots, but this attenuation can be lessened by choosing longer excitation wavelengths and by incorporating only about 100,000 iron oxide nanocrystals per bead. Nie and coworkers show that they can separate magnetic beads encoded with red quantum dots from nonmagnetic beads encoded with green quantum dots. The method is "elegant, simple, and effective," comments Shawn P. Mulvaney of the Naval Research Laboratory. "They can potentially tune both the magnetic and optical properties."