Fluorescence Of CdSe Quantum Dots Research Articles

Fluorescence Imaging of E. coli using CdSe Quantum Dots

Rapid and reliable method for the selective detection of pathogenic bacteria is critical in environmental monitoring, disease control, food safety and for the diagnosis of infectious diseases. In this study, we have synthesized hydrophilic fluorescent CdSe Quantum dots (CDSe QDs) and characterized using UV-Vis, IR and fluorescence spectroscopy. Crystallinity of the synthesized Qdots were analysed using XRD. As synthesized CdSe QDs were used for the imaging of buccal epithelial cells and pathogenic bacteria. Selectivity of CdSe QDs to detect E. coli was improved by the functionalization of QDs with glycerol. Easy imaging steps and decreased imaging time with the current procedure shows the potential for biomedical imaging.

Surface plasma enhanced fluorescence of CdSe quantum dots induced by laser on a grating surface

The fluorescence enhancement effect of CdSe quantum dots (QDs) was measured by using a picosecond pulsed laser with a 532 nm excitation wavelength to induce surface plasmon (SP) on a gold nanograting surface. A layered thin film was prepared on the gold film surface of silicon fund by atomic force microscope (AFM) etching and self-assembly method, respectively. The fluorescence spectrum of CdSe QDs was measured by adjusting the power of picosecond pulsed laser on a micro-Raman measuring platform. The results showed that the structure of the gold nanograting and CdSe QDs could greatly enhance the far-field fluorescence of CdSe QDs, the maximum fluorescence intensity was up to 7.80 times, and it had been saturated rapidly at the point of reaching the maximum intensity. The results of this study could be widely used in fields of the optoelectronic devices, biomedical detection.

Investigation of trypsin–CdSe quantum dot interactions via spectroscopic methods and effects on enzymatic activity

The paper presents the interactions between trypsin and water soluble cadmium selenide (CdSe) quantum dots investigated by spectrophotometric methods. CdSe quantum dots have strong ability to quench the intrinsic fluorescence of trypsin by a static quenching mechanism. The quenching has been studied at three different temperatures where the results revealed that electrostatic interactions exist between CdSe quantum dots and trypsin and are responsible to stabilize the complex. The Scatchard plot from quenching revealed 1 binding site for quantum dots by trypsin, the same has been confirmed by making isothermal titrations of quantum dots against trypsin. The distance between donor and acceptor for trypsin–CdSe quantum dot complexes is calculated to be 2.8nm by energy transfer mechanisms. The intrinsic fluorescence of CdSe quantum dots has also been enhanced by the trypsin, and is linear for concentration of trypsin ranging 1–80μl. All the observations evidence the formation of trypsin–CdSe quantum dot conjugates, where trypsin retains the enzymatic activity which in turn is temperature and pH dependent.

Fluorescence enhancement of cadmium selenide quantum dots assembled on silver nanoparticles and its application to glucose detection.

In this work, a new assembled glucose sensor based on the Ag nanoparticle (AgNP)-enhanced fluorescence of CdSe quantum dots (QDs) was developed. The mercaptoglycerol-modified AgNPs and aminophenylboronic acid-functionalized CdSe QDs are assembled into AgNP-CdSe QD complexes through the formation of a boronate ester bond. As compared to that of bare CdSe QDs, up to a 9-fold fluorescence enhancement and a clear blue shift of the emission peak for AgNP-CdSe QD complexes were observed, which is attributed to the surface plasmon resonance of AgNPs. In addition, the as-formed complexes are gradually disassembled in the presence of glucose molecules because they can replace the AgNPs by competitive binding with boronic acid groups, resulting in the weakening of fluorescence enhancement. The decrease in fluorescence intensity presents a linear relationship with glucose concentration in the range from 2 to 52 mM with a detection limit of 1.86 mM. Such a metal-enhanced QDs fluorescence system may have promising applications in chemical and biological sensors.

Uniform fluorescent nanobioprobes for pathogen detection.

Manipulating biochemical reactions in living cells to synthesize nanomaterials is an attractive strategy to realize their synthesis that cannot take place in nature. Yeast cells have been skillfully utilized to produce desired nanoparticles through spatiotemporal coupling of intracellular nonrelated biochemical reaction pathways for formation of fluorescent CdSe quantum dots. Here, we have successfully transformed Staphylococcus aureus cells into cellular beacons (fluorescing cells), all of which are highly fluorescent and photostable with perfect uniformity. Importantly, on the basis of such cells, we efficiently fabricated fluorescent nanobioprobes by a specific interaction between the protein A expressed on the S. aureus surface and the Fc fragment domain of antibodies, avoiding the use of other common methods for cell surface modifications, such as molecular covalent connection or more difficult genetic and metabolic engineering. Coupled with immunomagnetic beads, the resulting fluorescent-biotargeting bifunctional cells, i.e., biotargeting cellular beacons, can be employed as nanobioprobes for detection of viruses, bacteria, and tumor cells. With this method, H9N2 AIV can be detected specifically with a limit of 8.94 ng/mL (based on protein content). Furthermore, diverse probes for detection of different pathogens or for other biomedical applications can be easily obtained by simply changing the antibody conjugated to the cell surface.

Enhancement of emission efficiency of colloidal CdSe quantum dots on silicon substrate via an ultra-thin layer of aluminum oxide

We demonstrate that an ultra-thin layer of aluminum oxide can significantly enhance the emission efficiency of colloidal quantum dots on a Si substrate. For an ensemble of single quantum dots, our results show that this super brightening process can increase the fluorescence of CdSe quantum dots, forming well-resolved spectra, while in the absence of this layer the emission remains mostly at the noise level. We demonstrate that this process can be further enhanced with irradiation of the quantum dots, suggesting a significant photo-induced fluorescence enhancement via considerable suppression of non-radiative decay channels of the quantum dots. We study the impact of the Al oxide thickness on Si and interdot interactions, and discuss the results in terms of photo-induced catalytic properties of the Al oxide and the effects of such an oxide on the Coulomb blockade responsible for suppression of photo-ionization of the quantum dots.

Surface plasmon coupled fluorescence in deep-ultraviolet excitation by Kretschmann configuration

We report the experimental demonstration of fluorescence of CdSe quantum dots with surface plasmon excitation in deep-ultraviolet (deep-UV) region. Surface plasmon resonance in deep-UV is excited by aluminum thin film in the Kretschmann-Raether geometry. Considering the oxidation thickness of aluminum, the experimental results of incident angle dependence of reflectance show good agreement with Fresnel theory. Surface plasmon resonance with 19 nm-thick aluminum and 5 nm-thick alumina was excited at the incident angle of 48 degrees for 266 nm excitation. Fluorescence of CdSe quantum dots coated on this aluminum film was observed by the surface plasmon excitation.

Mechanism-Oriented Controllability of Intracellular Quantum Dots Formation: The Role of Glutathione Metabolic Pathway

Microbial cells have shown a great potential to biosynthesize inorganic nanoparticles within their orderly regulated intracellular environment. However, very little is known about the mechanism of nanoparticle biosynthesis. Therefore, it is difficult to control intracellular synthesis through the manipulation of biological processes. Here, we present a mechanism-oriented strategy for controlling the biosynthesis of fluorescent CdSe quantum dots (QDs) by means of metabolic engineering in yeast cells. Using genetic techniques, we demonstrated that the glutathione metabolic pathway controls the intracellular CdSe QD formation. Inspired from this mechanism, the controllability of CdSe QD yield was realized through engineering the glutathione metabolism in genetically modified yeast cells. The yeast cells were homogeneously transformed into more efficient cell-factories at the single-cell level, providing a specific way to direct the cellular metabolism toward CdSe QD formation. This work could provide the foundation for the future development of nanomaterial biosynthesis.

Synthesis and characterization of fluorescent CdSe quantum dots

Synthesis and characterization of fluorescent CdSe quantum dots

The enhanced two-photon-excited fluorescence of CdSe quantum dots on the surface of au island films from surface Plasmon resonance

CdSe quantum dots (QDs) are synthesized in an aqueous solution. A significant enhancement in fluorescence intensity is observed from the CdSe QDs on the Au island thin film (AIF) as compared to that on glass excited by 800nm femto second laser. On the other hand, the fluorescence intensity decay of CdSe QDs on AIF shows a faster decay decrease in average fluorescence lifetime. Fluorescence spectroscopy, transmission electron microscope, atomic force microscope and fluorescence decay are employed to analyze fluorescence enhancement of CdSe QDs. The spectrum change of the CdSe QDs on AIF is dependent on surface plasmon resonance. The enhanced two-photon-excited fluorescence of CdSe QDs on the surface of AIF could be utilized in a variety of chemical and biological detection from a practical point of view.

Seed-mediated synthesis, properties and application of γ-Fe 2O 3–CdSe magnetic quantum dots

Seed-mediated growth of fluorescent CdSe quantum dots (QDs) around γ-Fe 2O 3 magnetic cores was performed at high temperature (300 °C) in the presence of organic surfactants. Bi-functional magnetic quantum dots (MQDs) with tunable emission properties were successfully prepared. The as-synthesized MQDs were characterized by high-resolution transmission electron microscopy (HRTEM) and dynamic light scattering (DLS), which confirmed the assembly of heterodimers. When a longer growth period was employed, a homogeneous dispersion of QDs around a magnetic nanoparticle was obtained. The magnetic properties of these nanocomposites were examined. The MQDs were superparamagnetic with a saturation magnetization of 0.40 emu/g and a coercivity of 138 Oe at 5 K. To demonstrate their potential application in bio-labeling, these MQDs were coated with a thin silica shell, and functionalized with a polyethylene glycol (PEG) derivative. The functionalized MQDs were effectively used for the labeling of live cell membranes of 4T1 mouse breast cancer cells and HepG2 human liver cancer cells.

GABAC Receptor Binding of Quantum-Dot Conjugates of Variable Ligand Valency

Highly fluorescent CdSe quantum dots (qdots) can serve as a platform for tethering multiple copies of a receptor-targeted ligand, affording study of how the level of multivalency affects receptor binding. We previously showed that qdots conjugated with long PEG chains terminated by muscimol, a known GABA(C) agonist, exhibit specific binding to the surface membrane of GABA(C) receptor-expressing Xenopus oocytes. The present report addresses the effect of varying the number, i.e., valency, of muscimol- (M-) terminated PEG chains attached to the qdot on binding of the resulting conjugate to GABA(C) receptors. M-PEG-qdots of differing muscimol valency were prepared by conjugating AMP-CdSe/ZnS qdots with muscimol-terminated and methylamine-terminated PEG chains in proportions designed to yield varying percentages of muscimol-terminated chains among the total approximately 150-200 chains bound to the qdot. The investigated valencies represented 0%, approximately 25%, approximately 50%, and 100% loading with muscimol (preparations termed M-PEG-qdot0, M-PEG-qdot25, M-PEG-qdot50, and M-PEG-qdot100, respectively. Binding of a given conjugate to surface membranes of GABA(C) receptor-expressing oocytes was analyzed by quantitative fluorescence microscopy following defined incubation with approximately 30 nM of the conjugate. With 5-20 min incubation, the fluorescence signal resulting from incubation with M-PEG-qdot25 exceeded, by approximately 6-fold, the fluorescence level obtained with M-PEG-qdot preparations that lacked muscimol-terminated chains (M-PEG-qdot0). M-PEG-qdot50 yielded a net signal roughly similar to that of M-PEG-qdot25, and that produced by M-PEG-qdot100 exceeded, by approximately 30-50%, those for M-PEG-qdot25 and M-PEG-qdot50. The time course of changes in oocyte surface membrane fluorescence resulting from the introduction of and removal of M-PEG-qdots in the medium bathing the oocyte indicated only a modest dependence of both binding and wash-out kinetics on muscimol valency. The results demonstrate a dependence of the binding activity of the M-PEG-qdot conjugates on muscimol valency, presumably reflecting higher GABA(C) avidity and/or affinity of the muscimol at high valency, and provide insight on the interactions of membrane receptor proteins with qdot conjugates containing multiple copies of a receptor-targeting ligand.

Visualization of spontaneous aggregates by diblock poly(styrene)‐b‐poly(L‐lactide)/poly(D‐lactide) pairs in solution with new fluorescent CdSe quantum dot labels

AbstractSpontaneous stereocomplex aggregation of diblock poly(styrene)‐b‐poly(L‐lactide) PS‐b‐PLLA/poly(D‐lactide) PDLA pairs has been investigated under ambient temperature in tetrahydrofuran solution. First, diblock PS260‐b‐PLLA165 and PS260‐b‐PDLA162 bearing similar lengths of respective PLLA and PDLA blocks were synthesized through controlled atom‐transfer radical polymerization of styrene, and a subsequent living ring‐opening polymerization of optically pure lactides, and their structures were further characterized by nuclear magnetic resonance spectroscopy (NMR) and gel‐permeation chromatography (GPC). Subsequently, new enantiomeric poly(D‐lactide) stabilized core‐shell fluorescent CdSe quantum dots (CdSe/PDLA QD) were designed and prepared as sensitive fluorescence labels to shed new lights on the spontaneous stereocomplex aggregation in THF, which was mediated by stereocomplexation of the PLLA and PDLA chains. Upon simply mixing two individual THF solution of diblock PS260‐b‐PLLA165 and HO‐PDLA30‐SH, spontaneous stereocomplex aggregation was studied, and the aggregated uniform spherical particles were observed by scanning electronic microscopy (SEM) to exhibit average particle diameters of 2.0 μm. Finally, utilizing the prepared CdSe/PDLA QDs as new fluorescent labels, morphologies of the spontaneous aggregates by new diblock PS260‐b‐PLLA165/HO‐PDLA30‐SH pair were for the first time directly visualized by a confocal laser scanning fluorescence microscopy (CLSFM). These results might suggest alternative ways to simply prepare functional fluorescent particles with tunable diameter sizes and would be helpful to understand the mechanism of stereocomplex particle aggregation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1393–1405, 2009

CdSe quantum dots as luminescent probes for spironolactone determination

Based on the quenching of the fluorescence of CdSe quantum dots (QDs) by spironolactone, a simple, rapid and specific method for spironolactone determination was proposed. In the optimum conditions, spironolactone concentration versus quantum dot fluorescence gave a linear response with an excellent 0.997 correlation coefficient, between 2.5 and 700 mg/mL (6.0–1680 μmol/L) and the limit of detection (S/N = 3) was 0.2 μg/mL (0.48 μmol/L). The contents of spironolactone in pharmaceutical tablets were determined by the proposed method and the results agreed with the claimed values. The possible mechanism for the reaction was also discussed.