Original Quantum Dots Research Articles

SYNTHESIS OF A MULTIFUNCTIONAL COMB-TYPE AMPHIPHILIC POLYMER AND ITS USE FOR ENCAPSULATING LUMINESCENT QUANTUM DOTS

Solution polymerization and amidation reaction were used to synthesize the multifunctional combtype amphiphilic polymer,poly(stearyl methacrylate-co-methylacrylic acid)-(ethanolamine-ethanediamine-folic acid) ( PSM-EE-FA ). A study on structure and configurations was conducted through Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H-NMR). The molecular weight distribution was determined by gel-permeation chromatograpy ( GPC ). It was found that the polymer was synthesized successfully,and that the number-average molar mass and the polydispersity index were 28600 and 1. 375 respectively. Through the phase transfer process,the amphiphilic polymer was used to encapsulate hydrophobic CdSe /ZnS core-shell quantum dots ( QDs) in chloroform to get water-soluble,targeting quantum dots ( PSM-EE-FA-QDs). The water-soluble QDs solution was stable. The optical properties of PSM-QDs were determined by ultraviolet-visible (UV-Vis) and fluorescence emission spectrum. As shown in the results,the UV-Vis and fluorescence emission peaks were similar to those of the original hydrophobic QDs. However,because of the formation of the polymer layer on the surface of the QDs,the red-shifts of the peaks were observed. The resulting PSM-EE-FA-QDs retained 98% of the photoluminescence value of the original CdSe /ZnS QDs in chloroform. The quantum yield (QY) of the PSM-EE-FA-QDs was 95% of the original QDs. With the dynamic light scattering (DLS) and transmission electron microscopy ( TEM) results,it was indicated that the water-soluble QDs were well-dispersed within the polymer. In addition to good performance of PSM-EE-FA-QDs,the synthesis of the copolymer and the corresponding water-soluble QDs is relatively simple.

Special method to prepare quantum dot probes with reduced cytotoxicity and increased optical property

Quantum dots (QDs) are widely used in the life sciences because of their novel physicochemical properties. However, the cytotoxity of these nonoparticles have attracted great attention recently because this has not been well resolved. Four probes were synthesized by chemical coupling and protein denaturation with CdSeZnS, CdTe QDs, and transferrin. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and capillary electrophoresis were used to verify the conjugation of these luminescent probes. The cytotoxicity of these four luminescent probes and the original QDs were evaluated in HeLa cells. The results showed that over 92% of HeLa cells were still alive after being exposed to 3.2-microM CdSeZnS QDs capped with denatured transferrin for 72 h. Furthermore, while the probe preparation was very simple, the photoluminescence quantum yield of this probe was 7% higher than the original CdSeZnS QDs. This provides a new way for exploiting QD probes with low cytotoxicity, which will expand applications of nanocomposite assembly in biolabeling and imaging.

Biotinylated Glyco-Functionalized Quantum Dots: Synthesis, Characterization, and Cytotoxicity Studies

Quantum dots (QDs) containing surface carboxylic groups have been successfully modified using biotinylated glycopolymer and carbohydrate/biotin reagents via EDC coupling. The biotinylated glycopolymer was synthesized in controlled dimension via the reversible addition-fragmentation chain transfer (RAFT) polymerization of the three monomers containing biotin, sugar, and amine groups as pendent groups, respectively. The modified QDs were analyzed by dynamic light scattering and fluorescence spectrophotometry, and the data revealed no change in the physical properties of QDs after surface modification. Furthermore, the surface modified QDs showed excellent water solubility and colloidal stability. Subsequently, the availability of the biotin ligand on the surface of functionalized QDs was quantified using 4-hydroxyazobenzene 2-carboxylic acid (HABA)/avidin binding assay. Cell viability studies revealed that the cytotoxicity of QDs after surface functionalization is improved and that the biotinylated glycopolymer modified QDs showed an enhancement in biocompatibility as compared to that of the original QDs. The biotinylated glyco-functionalized quantum dots may act as new suitable fluorescent probes in biomedical applications.

Synthesis of cadmium selenide quantum dots modified with thiourea type ligands as fluorescent probes for iodide ions

Highly luminescent and stable CdSe quantum dots (QDs) modified with 4-substituted pyridine type ligands containing thiourea groups: 1-(4-fluorobenzoyl)-3-(5-(pyridin-4-yl)-1,3,4-thiadiazol-2-yl)thiourea (PyTU); were prepared through a ligand exchange process, and were characterized by transmission electron microscopy (TEM), fluorescence spectroscopy, UV-vis spectroscopy and FT-IR spectroscopy. The synthesized nanocomposites show higher fluorescence (FL) intensity and are more stable in comparison with original QDs. The PyTU–CdSe QDs allow a highly sensitive determination of iodidevia significant FL intensity quenching. Under optimal conditions, the relative FL intensity is decreased linearly with increasing iodide concentration in the range 0–50 μM with a detection limit of 1.5 × 10−9 M, while the FL intensity of PyTU–CdSe QDs to other anions including F−, Cl−, Br−, SCN−, HCOO−, CH3COO−, HSO3−, and C2O42− is negligible. It is found that the decreased luminescence intensity of the PyTU–CdSe QDs dependent on the concentration of iodide is best described by a Stern–Volmer equation. The possible mechanism is discussed.

Fluorescence Analysis with Quantum Dot Probes for Hepatoma Under One- and Two-Photon Excitation

A new class of fluorescent probe produced by conjugating semiconductor quantum dots (QDs) with protein molecule is proposed as an alternative to conventional organic labels. However the fluorescence characteristics of the QD bioconjugates are not clear while they are excitied with one- or two-photon laser pulse. We synthesized specific immunofluorescent probes by linking QDs to alpha fetoprotein (AFP) antibody for specific binding alpha-fetoprotein -an important marker for hepatocellular carcinoma cell lines, and archived specific fluorescence detection with the QDs-Anti-AFP in nude mice. Then, we have analyzed the fluorescence characteristics of QDs-Anti-AFP and original QDs both under one- and two-photon excitations. The results demonstrated that QDs-Anti-AFP's fluorescent spectral and lifetime haven't varied much from that of original QDs. Moreover, QDs-Anti-AFP have exhibited higher fluorescence efficiency than QDs under two-photon examination.