Nanocrystal quantum dots (QDs) have been applied to molecular biology because of their greater and longer fluorescence. Here we report the potential cytotoxicity of our characterized QDs modified with various molecules. Surface modification of QDs changed their physicochemical properties. In addition, the cytotoxicity of QDs was dependent on their surface molecules. These results suggested that the properties of QDs are not related to those of QD-core materials but to molecules covering the surface of QDs.

Affected mutation carriers with CTLA-4 insufficiency can present in any medical specialty. Family members should be counseled because disease manifestation can occur as late as 50 years of age. EBV- and cytomegalovirus-associated complications must be closely monitored. Treatment interventions should be coordinated in clinical trials.

The quantum confinement of excitons in semiconductor quantum dots leads to interesting optical properties that can be exploited in a range of photonic applications including biological fluorescence imaging [1][2][3][4][5][6] and optoelectronic devices. [7][8][9][10][11][12][13] Quantum dots are becoming popular as replacements for fluorescent dyes in biological fluorescence imaging because of their superior stability against photobleaching. To date, considerable emphasis has been placed on using CdSe quantum dots with a ZnS shell as biological chromophores since they emit light that can be tuned throughout the visible spectrum.[14] However, concerns have been raised about the toxicological issue of using cadmium in biological systems.[15] In particular, Derfus et al. showed that CdSe quantum dots without a ZnS shell were toxic to liver cells after exposure to UV light.[15] The potential biocompatibility of silicon makes photoluminescent silicon quantum dots an ideal candidate for biological fluorescence imaging and should eliminate any potential toxicology problems that might arise from having a CdSe core. [16,17] Strong quantum confinement in silicon increases the probability of radiative recombination through the direct band gap transitions and reduces phonon-assisted indirect band gap transitions. [18] In silicon, this requires the physical dimensions of the quantum dots to be on the order of or less than the bulk exciton Bohr radius of 4 nm. [19,20] Quantum dot sizes of less than 8 nm are easily achieved using wet chemistry techniques. [19][20][21][22] The remarkably successful advances in the synthesis of the semiconductor groups II/VI and III/V have not been applied to silicon as a consequence of the relatively high temperatures required to degrade the precursor and to produce highly crystalline quantum dots. The greatest success in producing silicon quantum dots with strong quantum confinement to date has been by the solution-phase reduction of silicon salts. [19,21,22] The solution-phase synthesis of silicon quantum dots has previously been reported by Kauzlarich and co-workers [21,22] through the use of a variety of reducing agents, by Korgel and co-workers [19,23] through the use of high temperatures and pressures, and by Wilcoxon et al. by using micelles. [20,24] The current problem associated with the simpler room-temperature syntheses [20][21][22] is the large size distribution produced. The large size distribution prevents a simple interpretation of the optical spectra. Post-synthesis treatments for narrowing the size distribution of the silicon quantum dots, such as highpressure gas chromatography (HPGC), have revealed sharp features in the absorption spectra and narrow photoluminescence spectra attributed to direct band gap transitions.[20] We have recently reported the synthesis of 1-2-nm silicon quantum dots that were surface-passivated by 1-heptene. These dots had a narrower size distribution than previously reported and gave a strong blue photoluminescence. [25] For silicon quantum dots to be ...

Quantum dots (QDs) such as CdSe QDs are nano-sized metal clusters. QDs have specific characteristics such as the quantum effect, which is a special photo quality caused by the widening of the band gap when the spatial dimension is reduced. Kubo et al. predicted the specific character of the quantum dot theoretically in 1962 (14-16). Since then, research concerning the applications of QDs has gained a great amount of interest. For example, in the field of Information Technology and optical-engineering (3, 10, 21, 29, 30), QDs have been proposed for use as a new material for memory, and as miniature laser-beam emitting devices. Furthermore , the biological applications of QDs conjugated with antibody have started to attract much attention, especially in immunostaining, separating cells, and diagnostics, because of their advantages such as longer lifetime and higher fluorescence over conventional organic fluorophores (1, 2, 8, 27). The first synthesized QDs are insoluble in biological solvents because non-polar groups of organic molecules are exposed on the surface of QDs. However the water-soluble QDs covered with mercapto-undecanoic acid (MUA) have been reported (2). In addition, the MUA-QD covered with sheep serum albumin (SSA) is well dispersed in water (2, 9). The advantages of MUA-QDs described above make it possible to consider the application of MUA-QDs to drug delivery systems (6, 20, 25, 28) as a drug-carrier and cell delivery system. Quantum dots have a longer lifetime compared to conventional organic fluo-rophores and thus make it easier to trace the drug delivered in living organisms. To make sure the application is feasible, an in-depth evaluation using MUA-QD in living organisms is needed. In fact cadmium (13) and selenium (24) are known to be toxic. Though the use of MUA-QDs for organisms has been known and some other studies about the actual injections into organisms have been conducted, the toxicity of MUA-QDs has not been reported in detail yet. Published works regarding Abstract: Quantum dots (QDs) such as CdSe QDs have been introduced as new fluorophores. The QDs conjugated with antibody are starting to be widely used for immunostaining. However there is still not sufficient analysis of the toxicity of QDs in the literature. Therefore we evaluated the cell damage caused by the quantum dots for biological applications. We performed cell viability assay to determine the difference in cell damage depending on the sizes and colors of mercapto-undecanoic acid (MUA) QDs and the cell types. The results showed that the cell viability decreased with increasing concentration of MUA-QDs. But in the case of Vero cell (African green monkey's kidney cell) with red fluorescence QD (QD640), the cell damage was less than for the others. Furthermore through the flow cytometry assay we found that this cell damage caused by MUA-QD turned out to be cell death after 4-6-hr incubation. From the two assays described above, we found that there is a range of concentration of MUA-QDs where the cell viability decreased wi...