We developed the smaller sized quantum dots covered with sodium 2-mercaptoethanesulfonate which has a sulfonyl group (QDs-SO<sub>3</sub>-), and compared its stability in acid, salt and buffer solutions with that of the quantum dots covered with the mercaptoundecanoic acid (QDs-MUA) and covered with the NH<sub>2</sub> group (QDs-NH<sub>2</sub>). We found that the QD-SO<sub>3</sub>- well disperses in these solutions without quenching and this stability holds on 24 hours. Next, we observed the cell damage caused by the quantum dots. In the evaluation of cell damage, QD-SO<sub>3</sub>- did not show noticeable cell damage in the 0.2mg/mL by the comet assay as well as QD-MUA and QD-NH<sub>2</sub> in the same concentration. All these results could suggest that SO<sub>3</sub>- might be useful for the biomedical engineering.
Silicon quantum dots have been synthesized in micelles. Particle sizes have been ascertained by transmission electron microscopy and UV-Vis absorption and photoluminescence spectroscopy. The surface of the silicon and germanium particles produced have been modified to produce hydrophobic and hydrophilic particles by reaction with either with 1-heptene or allylamine respectively. For biological applications control of the surface character of the nanocrystals is essential. FTIR spectra show the surface modification of the particles by 1-heptene or allylamine.