Synthesis And Application Of Low Toxicity Quantum Dots

Quantum dots (QDs) are novel fluorescent material aroused in recent years. Due to the excellent optical and electronic properties, QDs has the potential applications in biomarkers, drug delivery, sensors, solar cells etc. With advances in technology and broaden of application, higher resquest for QDs are proposed, such as, high FL intensity and quantum yields, stable to environment chang and low toxicity. Especially, after commercialization of QDs in vivo and in vitro, the biological toxicity of QDs has attracted much attention and excited postulation. This paper studies the synthesis, toxicity improvement and application of QDs and the findings are listed below:(1) β-cysteamine capped CdTe quantum dots (Cys-CdTe QDs) were synthesized through the reaction between freshly prepared NaHTe and Cd2+ ions. Then glucose was attached to the surface of CdTe QDs by a simple incubating glucose with CdTe QDs in water bath to promote the reaction between the amino groups on the CdTe NPs surface and the aldehyde groups of glucose. IR results indicated that glucose was attached to the surface of CdTe QDs. TEM images and XRD patterns of CdTe QDs showed that the particle size and crystalline form of CdTe QDs didn’t change evidently after incubation. UV-Vis and FL spectra showed that, FL intensity of Glu-CdTe QDs was 8 times stronger than the original QDs and the stability under illumination increased greatly. To find out the optimal incubation conditions, UV-Vis and FL spectra were also used to monitor the factors that can affect the intensity and stability of the resulting product, such as glucose content, incubation temperature and incubation time. After incubating with glucose, the sterilization rate of Glu-CdTe QDs drops obviously, indicating that the toxity of CdTe QDs das been effectively improved.(2) Cysteamine/glucose grafted CdTe quantum dots (QDs) were synthesized and subsequently, carbon chains wrapped around the surfaces were carbonized via further hydrothermal heat treatment to obtain raisin-bun-like carbon protected CdTe QDs nanocomposites (CdTe@C NCs). As shown in FTIR, TEM, FESEM, XPS and Raman spectrum, CdTe QDs was capped with carbon materials. The optical properties of the as-prepared products were carefully investigated by UV-Vis and PL, respectively. With the protection of carbon shell, as synthesized CdTe@C NCs are tolerate to both acidic and alkaline environment, NaCl solution as well as oxidative hydrogen peroxide. MTT assay also confirms the low cytotoxicity of CdTe@C NCs.(3) In this paper, bright and and uniformly distributed carbon dots (CNPs) were prepared by refluxing the membranous carbonized β-cyclodextrin in nitric acid. The structure and optical properties of CNPs were characterized by SEM, TEM, FT-IR, FL, XRD and Raman spectroscopy. The mechanism for the formation of CNPs is also discussed. As-prepared CNPs could be used as peroxidase mimics for the detection of H2O2. The results indicate that CNPs is capable of rapid and sensitive detection of H2O2. The linear range as well as detection limit was measured. More importantly, the peroxidase-like activity of CNPs is expanded to the detection of some oxidative ions (such as Fe3+ and Ag+). The linear ranges and detection limits for Fe3+ and Ag+ are measured respectively. MTT assay confirms the low cytotoxicity of CNPs. Most importantly, CNPs was successfully applied for fluorescent bio image of human liver cancer cells (HepG) cells.(4) β-Cysteamine(CA)-capped gold nanoparticles (Au NPs) were loaded to attapulgite(ATP) through electrostatic interactions, producing an attapulgite supported Au nanocompo sites (Au/ATP NCs) structure. Gold particle size and the loading amount can be easily tuned by adjusting ATP/Au ratio and the influence of the parameters were investigated by XRD and TEM. The Au/ATP NCs could be used as peroxidase mimics and the catalytic performance for the detection of H2O2 was examined. The results of quantitative experiments indicate that Au/ATP NCs is capable of rapid and sensitive detection of H2O2. The linear range as well as detection limit was measured. Besides, Au/ATP NCs could be collected after the reaction simply and more than 95% catalytic activity reserved after 8 round reactions. Based on the absorption spectrum and steady-state kinetics, a mechanism for peroxidase mimic reaction is proposed. We also discovered that Au/ATP NCs could be expanded for the detection of some oxidative ions (Fe3+ and Ag+). The linear ranges and detection limits for Fe3+ and Ag+ are measured respectively. Our result represents the first examples of detection of H2O2 (Fe3+ or Ag+) using Au/ATP NCs as peroxidase enzyme mimics and holds a great promise for future biomedical and analytical applications. Besides, Au/ATP NCs structure could also catalyse the Suzuki-Miyaura cross-coupling ceaction between chlorobenzene/bromobenzene and phenylboronic acid. After recycled for 7 times, the catalytic efficiency for chlorobenzene and bromobenzene maintained 78% and 53% respectively, indicating that as prepared structure also holds promise for industrial application of precious metal catalyst.