(545d) Biocompatible Silicon Quantum Dots

Silicon quantum dots (QDs) have great potential for use in biological imaging and diagnostic applications, as an alternative to fluorescent organic dyes or potentially toxic heavy metal containing quantum dots. For quantum dots to be useful in biological systems they must remain stably dispersed in water and biological fluids, over a wide range of pH and salt concentration. There have been many challenges in creating such stable, water-dispersible quantum dots, including instability of photoluminescence due to oxidation in an aqueous environment and difficulty in attaching hydrophilic molecules to silicon surfaces without inducing oxidation. Here, a highly stable aqueous suspension of silicon QDs has been prepared, that maintains all of the desirable optical properties of Si nanocrystals dispersed in nonpolar solvents. These QDs are prepared by first grafting styrene to the surface of bare silicon nanocrystals, followed by suspension in a chloroform solution containing phospholipids. The solvents are evaporated and the particles are then dispersed in water, prompting the encapsulation of the silicon nanocrystals by phospholipid micelles. Phospholipids with different functional groups including carboxylic acid, biotin, and amine groups can be used in this process, providing built-in surface functionalization. This will allow silicon quantum dots to be useful for a variety of biological applications. The QD stability and optical properties are characterized in biologically relevant environments.