The optical properties of antiphotobleaching and the advantage of long-term fluorescence observation of quantum dots are fully adopted to study the effects of iron on the endocytosis of transferrin. Quantum dots are labeled for transferrin and endocytosis of transferrin in HeLa cells is observed under the normal state, iron overloading, and an iron-deficient state. In these three states, the fluorescence undergoes a gradual process of first dark, then light, and finally dark, indicating the endocytosis of transferrin. The fluorescence intensity analysis shows that a platform emerges when fluorescence changes to a certain degree in the three states. Experienced a same period of time after platform, the fluorescence strength of cells in the normal state is 1.2 times the first value, and the iron-deficiency state is 1.4 times, but the iron overloading state was 0.85 times. We also find that the average fluorescence intensity in cells detected by the spectrophotometer in the iron-deficiency state is almost 7 times than that in a high iron state. All this proves that iron overloading would slow the process, but iron deficiency would accelerate endocytosis. We advance a direct observational method that may contribute to further study of the relationship of iron and transferrin.
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 CdSe/ZnS, 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-µM CdSe/ZnS 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 CdSe/ZnS QDs. This provides a new way for exploiting QD probes with low cytotoxicity, which will expand applications of nanocomposite assembly in biolabeling and imaging.
A novel multiplex analysis technology based on quantum dot (QD) optical encoded beads was studied. Carboxyl functionalized polystyrene beads, about 100 µm in size, were precisely encoded by the various ratios of two types of QDs whose emission wavelengths are 576 and 628 nm, respectively. Then the different encoded beads were covalently immobilized with different probes in the existing of sulfo-NHS and 1-[3-(Dimethylamino) propyl]-3-ethylcarbodiimide methiodide, and the probe density could reach to 3.1 mmol/g. These probe-linked encoded beads were used to detect the target DNA sequences in complex DNA solution by hybridization. Hybridization was visualized using fluorescein isothiocynate–labeled DNA sequences. The results show that the QDs and target signals can be obviously identified from a single-bead-level spectrum. This technology can detect DNA targets effectively with a detection limit of 0.2 µg/mL in complex solution.
Microbeads with embedded encode characteristics are of considerable interest due to their potential use in multiplexed bioassays, high-throughput screening and combinatorial chemistry. Lots of encoding strategies for tagging or labeling microbeads have arisen in the past couple of years. Compared with the organic dye counterparts, the ideal optical properties of quantum dots (QDs) (e.g. characteristic narrow and symmetric spectra, size-tunable emission and simultaneous excitation) make it possible to tag microbeads in a quantitative way. In this paper, quantitative doping of commercial polystyrene microbeads with single color quantum dots was reported. A detailed analysis of the optical characteristics of the QD-tagged microbeads was presented based on the combination of fluorescent spectroscopy and microscope imaging.
A novel green synthesis of semiconductor nanoparticles was introduced and it was used as optical probes for bio-imaging. Quantum dots are known as <10nm scaled semiconductor nanoparticles, which could dramatically improve fluorescent imaging. Since these nanocrystals act as robust broadly tunable nano-emitters that can be excited by a single light source, they could pride significant advantages over current labels (e.g. traditional organic dyes, isotope and fluorescent proteins) in vitro and in vivo. As for a novel green synthesis, the usage of dangerous organic composites under rigorously air-free conditions was avoided, and ZnS-capped CdSe semiconductor nanoparticles was prepared economically. And the surface of as- synthesized nanoparticle would be modified by hydrophilic molecules for optical bio-probes. Moreover, such optical probes under aqueous biological conditions could maintain many characters: economy, photostability, colloidal stability, efficient fluorescence, low non-specific adsorption, biological compatibility and validity for multiplex assays.
The latest self-encoding resin bead is a novel technology for solid phase synthesis combinatorial library screening. A new encode-positional deconvolution strategy which was based on that technology been illustrated compared with positional scanning and iterative strategies. The self-encoding resin beads technology provides an efficient method for improving the high-throughput screening of combinatorial library.
The hybridization of probes on electrode surfaces with target sequences in solution was examined using DNA- covalently modified electrodes. It was found that the probes on electrode surfaces keep their activity of hybridization.
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