Facile labeling of lipoglycans with quantum dots

Bacterial endotoxins or lipopolysaccharides (LPS) are among the most potent activators of the innate immune system, yet mechanisms of their action and in particular the role of glycans remain elusive. Efficient non-invasive labeling strategies are necessary for studying interactions of LPS glycans with biological systems. Here we report a new method for labeling LPS and other lipoglycans with luminescent quantum dots. The labeling is achieved by partitioning of hydrophobic quantum dots into the core of various LPS aggregates without disturbing the native LPS structure. The biofunctionality of the LPS-Qdot conjugates is demonstrated by the labeling of mouse monocytes. This simple method should find broad applicability in studies concerned with visualization of LPS biodistribution and identification of LPS binding agents.     

简述量子点与抗体的偶联方法

量子点是一种具有独特光学性质的半导体纳米材料,表面带有功能基团的水溶性量子点可与抗体偶联,作为荧光探针用于多种生物学研究。根据量子点表面所修饰的物质不同,偶联方法可分为共价偶联与非公价偶联两大类。本研究主要对量子点与抗体的偶联方法进行简单介绍。     

荧光量子点探针及其标记技术

量子点作为一种新型荧光标记物,与有机染料和荧光蛋白质相比,它们具有可调谐且宽的吸收光谱,激发可产生多重荧光颜色、强荧光信号、抗光漂白能力强等独特的光学特性,使其广泛应用在生物和医学领域。该文就量子点探针的表面修饰和功能化及其标记技术的研究进展进行了阐述。     

Magnetic quantum dots in biotechnology – synthesis and applications

Quantum dots (QDs) have great promise in biological imaging, and as this promise is realized, there has been increasing interest in combining the benefits of QDs with those of other materials to yield composites with multifunctional properties. One of the most common materials combined with QDs is magnetic materials, either as ions (e.g. gadolinium) or as nanoparticles (e.g. superparamagnetic iron oxide nanoparticles, SPIONs). The fluorescent property of the QDs permits visualization, whereas the magnetic property of the composite enables imaging, magnetic separation, and may even have therapeutic benefit. In this review, the synthesis of fluorescent–magnetic nanoparticles, including magnetic QDs is explored; and the applications of these materials in imaging, separations, and theranostics are discussed. As the properties of these materials continue to improve, QDs have the potential to greatly impact biological imaging, diagnostics, and treatment.     

Studies on quantum dots synthesized in aqueous solution for biological labeling via electrostatic interaction

3-Mercaptopropyl acid-stabilized CdTe nanoparticles synthesized in aqueous solution are effectively bound to a biomacromolecule, papain, via electrostatic interaction. The conjugation between the nanoparticles and the papain is demonstrated by UV-Vis absorption, photoluminescence spectroscopy, transmission electron microscopy, and fluorescence micrographs. The biological activity of papain is maintained after the conjugation. The effects of the quantity of papain and the size of nanoparticles on the fluorescence characteristics of the CdTe-papain bioconjugates were studied.     

Water-soluble quantum dots for biomedical applications

Semiconductor nanocrystals are 1-10nm inorganic particles with unique size-dependent optical and electrical properties due to quantum confinement (so they are also called quantum dots). Quantum dots are new types of fluorescent materials for biological labeling with high quantum efficiency, long-term photostability, narrow emission, and continuous absorption spectra. Here, we discuss the recent development in making water-soluble quantum dots and related cytotoxicity for biomedical applications.     

Development of magnetic separation and quantum dots labeled immunoassay for the detection of mercury in biological samples

A rapid and sensitive immunoassays of mercury (Hg) in biological samples was developed using quantum dots (QDs) and magnetic beads (MBs) as fluorescent and separated probes, respectively. A monoclonal antibody (mAb) that recognizes an Hg detection antigen (BSA-DTPA-Hg) complex was produced by the injection of BALB/c mice with an Hg immunizing antigen (KLH-DTPA-Hg). Then the ascites monoclonal antibodies were purified. The Hg monoclonal antibody (Hg-mAb) is conjugated with MBs to separate Hg from biological samples, and the other antibody, which is associated with QDs, is used to detect the fluorescence. The Hg in biological samples can be quantified using the relationship between the QDs fluorescence intensity and the concentration of Hg in biological samples following magnetic separation. In this method, the detection linear range is 1–1000 ng/mL, and the minimum detection limit is 1 ng/mL. The standard addition recovery rate was 94.70–101.18%. The relative standard deviation values were 2.76–7.56%. Furthermore, the Hg concentration can be detected in less than 30 min, the significant interference of other heavy metals can be avoided, and the simultaneous testing of 96 samples can be performed. These results indicate that the method could be used for rapid monitoring Hg in the body.     

“Use of acidophilic bacteria of the genus Acidithiobacillus to biosynthesize CdS fluorescent nanoparticles (quantum dots) with high tolerance to acidic pH”

The use of bacterial cells to produce fluorescent semiconductor nanoparticles (quantum dots, QDs) represents a green alternative with promising economic potential. In the present work, we report for the first time the biosynthesis of CdS QDs by acidophilic bacteria of the Acidithiobacillus genus. CdS QDs were obtained by exposing A. ferrooxidans, A. thiooxidans and A. caldus cells to sublethal Cd²⁺ concentrations in the presence of cysteine and glutathione. The fluorescence of cadmium-exposed cells moves from green to red with incubation time, a characteristic property of QDs associated with nanocrystals growth. Biosynthesized nanoparticles (NPs) display an absorption peak at 360 nm and a broad emission spectra between 450 and 650 nm when excited at 370 nm, both characteristic of CdS QDs. Average sizes of 6 and 10 nm were determined for green and red NPs, respectively. The importance of cysteine and glutathione on QDs biosynthesis in Acidithiobacillus was related with the generation of H₂S. Interestingly, QDs produced by acidophilic bacteria display high tolerance to acidic pH. Absorbance and fluorescence properties of QDs was not affected at pH 2.0, a condition that totally inhibits the fluorescence of QDs produced chemically or biosynthesized by mesophilic bacteria (stable until pH 4.5–5.0). Results presented here constitute the first report of the generation of QDs with improved properties by using extremophile microorganisms.     

Electrochemiluminescence of CdSe quantum dots for immunosensing of human prealbumin

We describe a non-labeled electrochemiluminescence (ECL) immunosensor based on CdSe quantum dots (QDs) for the detection of human prealbumin (PAB, antigen). The immunosensor was fabricated by layer by layer coupled with nanoparticle-amplification techniques. After two gold nanoparticle layers were self-assembled onto the gold electrode surface through cysteamine, anti-PAB (antibody) were conjugated with -COOH groups of both the CdSe QDs and cysteine, which were linked to the gold nanoparticle-modified electrode. The principle of ECL detection was that the immunocomplex inhibited the ECL reaction between CdSe QDs and K(2)S(2)O(8), which resulted in the decrease of ECL intensity. On the one hand, the immunocomplex increased the steric hindrance. On the other hand, the immunocomplex maybe inhibit the transfer of K(2)S(2)O(8) to the surface of the CdSe QD-electrode. The PAB concentration was determined in the range of 5.0 x 10(-10) to 1.0 x 10(-6) g mL(-1), and the detection limit was 1.0 x 10(-11) g mL(-1). The developed CdSe QD-based ECL immunosensor provides a rapid, simple, and sensitive immunoassay protocol for protein detection, which could be applied in more bioanalytical systems.     

荧光量子点的生物合成方法研究进展

作为一种新型纳米材料,荧光量子点的合成方法大致可分为物理法、化学法和生物合成法。生物合成方法因其绿色、环保、产物生物相容性好而备受关注。本文通过对国内外荧光量子点生物合成方法的资料研究,以细菌、真菌、其它生物机体、生物辅助等角度对生物合成荧光量子点的方法进行归纳总结,并着重对基于微生物的合成方法进行了分类。在探讨微生物合成机理的基础上,对生物合成法的未来方向提出展望。     

量子点对细菌的标记及抗菌作用

目的量子点是近年来发展起来的一种新型的荧光纳米材料,与传统的材料相比具有独特的性质,所以在生物传感器、实时追踪、多色标记及成像等方面有着广泛的应用。本文主要对量子点在细菌标记和抗菌等方面的应用进行了综述。     

Synchrotron-based X-ray fluorescence imaging of human cells labeled with CdSe quantum dots

Synchrotron-based X-ray fluorescence (S-XRF) is a powerful technique for imaging the distribution of many biologically relevant elements as well as of “artificial” elements deliberately introduced into tissues and cells, for example, through functionalized nanoparticles. In this study, we explored the potential of S-XRF for chemical nanoimaging (100 nm spatial resolution, nanoXRF) of human cells through the use of functionalized CdSe/ZnS quantum dots (QDs). We used a commercially available QD-secondary antibody conjugate to label the cancer marker HER2 (human epidermal growth factor receptor 2) on the surface of SKOV3 cancer cells and β-tubulin, a protein associated with cytoskeleton microtubules. We set up samples with epoxy inclusion and intracellular labeling as well as samples without epoxy inclusion and with surface labeling. Epoxy inclusion, also used in electron microscopy, has the advantage of preserving cell morphology and guaranteeing long-term stability. QDs proved to be suitable probes for nanoXRF due to the Se emission band, which is not in close proximity to any other emission band, and the signal specificity, which is preserved in both types of labeling. Therefore, nanoXRF using QD-based markers can be very effective at colocalizing specific intracellular targets with elements naturally present in the cell and may complement confocal fluorescence microscopy in a synergistic fashion.     

Biomedical applications of glyconanoparticles based on quantum dots

Background

Quantum dots (QDs) are outstanding nanomaterials of great interest to life sciences. Their conjugation versatility added to unique optical properties, highlight these nanocrystals as very promising fluorescent probes. Among uncountable new nanosystems, in the last years, QDs conjugated to glycans or lectins have aroused a growing attention and their application as a tool to study biological and functional properties has increased.

Tunable excitation properties of ZnCdS:Mn/ZnS quantum dots for cancer imaging

Water‐soluble ZnS:Mn quantum dots (QDs) were synthesized using a hydrothermal method with 3‐mercaptopropionic acid as stabilizer. The optical properties of ZnS:Mn QDs were thoroughly investigated by tuning the doping concentration of Mn²⁺ and the Zn/S precursor ratio, to obtain an optimal parameter for QDs with excellent fluorescence characteristics. ZnS:Mn QDs excited at only one wavelength, however, which seriously limited their further application. Here, a trace Cd ion was doped into a ZnS host, resulting in QD excitation covering a wide adjustable waveband. Furthermore, when a ZnS shell was coated onto the surface of the ZnCdS:Mn QDs, photoluminescence intensity and stability were further enhanced. After coupling with an anti‐CK 19 antibody, the ZnCdS:Mn/ZnS core/shell QDs were able to function by labeling cancer cells, indicating that they could be considered as a suitable bio‐probe for cells and tissue imaging.     

Intracellular imaging of targeted proteins labeled with quantum dots

We developed a new method for imaging the movement of targeted proteins in living cancer cells with photostable and bright quantum dots (QDs). QDs were conjugated with various molecules and proteins, such as phalloidin, anti-tubulin antibody and kinesin. These bioconjugated QDs were mixed with a transfection reagent and successfully internalized into living cells. The movements of individual QDs were tracked for long periods of time. Phalloidin conjugated QDs bound to actin filaments and showed almost no movement. In contrast, anti-tubulin antibody conjugated QDs bound to microtubules and revealed dynamic movement of microtubules. Kinesin showed an interesting behavior whereby kinesin came to be almost paused briefly for a few seconds and then moved once again. This is in direct contrast to the smoothly continuous movement of kinesin in an in vitro assay. The maximum velocity of kinesin in cells was faster than that in the in vitro assay. These results suggest that intracellular movement of kinesin is different from that in the in vitro assay. This newly described method will be a powerful tool for investigating the functions of proteins in living cells.     

Novel fluoroimmunoassays for detecting ochratoxin A using CdTe quantum dots

Novel direct and indirect competitive fluorescence‐linked immunosorbent assays (c FLISA and ic FLISA) for detection of ochratoxin A (OTA) were described using CdTe quantum dots (QDs) as fluorescent label. CdTe QDs were successfully synthesized, which had an emission wavelength of 615 nm. The high purity monoclonal antibody against OTA was prepared through cell thawing and the octylic acid‐ammonium sulfate method. The OTA MAbs were successfully coupled with CdTe QDs, and which also retained the original biological activity. The 50% inhibition values (IC₅₀) of the c FLISA and ic FLISA were 0.630 ng/mL, 0.234 ng/mL, the limits of detection (LOD) were 7.06 × 10^–3 and 4.15 × 10^–3 ng/mL, and detection ranges were 7.06 × 10^–3 ? 18.34 ng/mL and 4.15 × 10^–3 ? 4.88 ng/mL, in‐order. The recoveries were 96.0–104.7% along with coefficients of variation (CVs) below 10%. The FLISA provided novel method for determination of OTA and the potential of MAb–CdTe QDs for the establishment of fluorescent immunochromatographic test strip.

     

Direct and indirect immunolabelling of HeLa cells with quantum dots

With excellent optical properties, quantum dots (QDs) have been made as attractive molecular probes for labelling cells in biological research. In this study high‐quality CdSe QDs prepared in a paraffin–oleic acid system were used as fluorescent labels in direct and indirect detection of carcinoembryonic antigen (CEA), a cancer marker expressed on the surface of HeLa cells. The primary antibody (Ab) (rabbit anti‐CEA8) and secondary Ab (goat anti‐rabbit IgG) were covalently linked to carboxyl‐functioned CdSe QDs, and both the QDs–antibody and QDs–IgG probes were successfully used to label HeLa cells. The present study demonstrates the practicability of CdSe QDs as an attractive type of fluorescent labels for biological applications such as protein probes and cell imaging. Copyright © 2008 John Wiley & Sons, Ltd.     

Immunofluorescent labeling of cancer cells with quantum dots synthesized in aqueous solution

Thioglycolic-acid-stabilized CdTe quantum dots, synthesized directly in aqueous solution, are successfully conjugated with biotin and polyethylene glycol. Using these conjugates, we report the development of this kind of water-soluble quantum dot for immunofluorescent labeling of cancer cells. The results show that these conjugates have very low nonspecific binding and good stability against photobleaching, enabling them to be applied in many biological fields, such as cellular labeling, intracellular tracking, and other imaging applications.     

Synthesis of CdSe quantum dots with luminescence in the violet region of the solar spectrum

We have designed a simple, one‐step synthesis of CdSe quantum dots with photoluminescence frequencies ranging from the red through to the violet region of the solar spectrum. The photoluminescence peaks have FWHM of 30 nm indicating absorption over a narrow range of wavelengths. The effect of solvent type and solvent boiling point on the physical and photoluminescence properties of the quantum dots has been studied. High boiling point, non‐polar solvents shift the photoluminescence peak to longer wavelengths and low boiling point, polar solvents shift the photoluminescence peak to shorter wavelengths. Copyright © 2009 John Wiley & Sons, Ltd.