氮掺杂石墨烯量子点的激发波长依赖性发光研究

激发波长依赖发光是碳基荧光材料中有趣的光学性质之一,其在不同激发波长下呈现的多彩发光对某些实际应用很重要.本文以氧化石墨烯为碳源,采用酸氧化法制备了尺寸约为3~5nm的少层石墨烯量子点(GQDs),然后将其与乙二胺(EDA)在160℃下进行水热反应,得到了石墨烯边缘氮掺杂的石墨烯量子点(NGQDs).采用傅立叶变换红外光谱(FTIR)证实了N-GQDs中酰胺键和胺C-N键的形成.GQDs的吸收主要来自C=C的π-π*跃迁(265nm)和C-O相关的n-π*跃迁(340nm),而N-GQDs中出现了C(=O)NHR相关的新能级(386nm).GQDs荧光峰随着激发光波长的移动Δλem/Δλex呈现线性变化,斜率约为0.43,而N-GQDs的Δλ_(em)/Δλ_(ex)出现两段线性变化,激发波长在420nm以后斜率增大到0.78,表明C(=O)NHR相关的荧光偶极子具有更强的激发波长依赖性发光特性.     

Temperature-dependent photoluminescence of water-soluble quantum dots for a bioprobe

The photoluminescence of water-soluble CdSe/ZnS core/shell quantum dots is found to be temperature-dependent: as temperature arising from 280 K to 351 K, the photoluminescence declines with emission peak shifting towards the red at a rate of ∼0.11 nm K⁻¹. And the studies show that the photoluminescence of water-soluble CdSe/ZnS quantum dots with core capped by a thinner ZnS shell is more sensitive to temperature than that of ones with core capped by a thicker one. That is, with 50% decrement of the quantum yield the temperature of the former need to arise from 280 K to 295 K, while the latter requires much higher temperature (315.6 K), which means that the integrality of shell coverage is a very important factor on temperature-sensitivity to for the photoluminescence of water-soluble CdSe/ZnS quantum dots. Moreover, it is found that the water-soluble CdSe quantum dots with different core sizes, whose cores are capped by thicker ZnS shells, possess almost the same sensitivity to the temperature. All of the studies about photoluminescence temperature-dependence of water-soluble CdSe/ZnS core/shell quantum dots show an indispensable proof for their applications in life science.     

Core/shell quantum dots with high relaxivity and photoluminescence for multimodality imaging

A series of core/shell CdSe/Zn1-xMnxS nanoparticles were synthesized for use in dual-mode optical and magnetic resonance (MR) imaging techniques. Mn2+ content was in the range of 0.6-6.2% and varies with the thickness of the shell or amount of Mn2+ introduced to the reaction. These materials showed high quantum yield (QY), reaching 60% in organic solvent. Water-soluble nanoparticles were obtained by capping the core/shell particles with amphiphilic polymer, and the QY values in water reached 21%. These materials also demonstrated high relaxivity with r1 values in the range of 11-18 mM-1 s-1 (at room temperature, 7 T). Both optical and MR imaging were performed on nanoparticles in aqueous solution and applied to cells in culture. The results showed that the QY and manganese concentration in the particles was sufficient to produce contrast for both modalities at relatively low concentrations of nanoparticles.     

One-pot synthesis of concentration and excitation dual-dependency truly full-color photoluminescence carbon dots

The paper describes a kind of truly full-color photoluminescence (PL) CDs. The CDs were prepared by using one-pot hydrothermally heating citric acid and formamide at 200 °C for 2 h. The CDs have three fluorescent centers at blue, green, and red light region. Their color was regulated through two means, including changing excitation wavelengths or CDs concentrations. The emission maxima changed from blue to red with the increase of excitation wavelengths or CDs concentrations. The full-color PL behavior of the CDs was inherited and conserved in the solid polymer matrix, giving multicolor CDs/polymer films and light emitting diodes (LEDs). White-light LED (WLED) with the CIE coordinate approaching to (0.31, 0.32) were also achieved.     

Studies on optical absorption and photoluminescence of thioglycerol-stabilized CdS quantum dots

Nanoparticles of CdS were prepared at 303 K by aqueous precipitation method using CdSO4 and (NH4)2S in presence of the stabilizing agent thioglycerol. Adjustment of the thioglycerol (T) to ammonium sulphide (A) ratio (T:A) from 1:25 to 1:3.3 was done during synthesis and nanoparticles of different size were obtained. The prepared colloids were characterized by UV-vis and photoluminescence (PL) spectroscopic studies. Prominent first and second excitonic transitions are observed in the UV-vis spectrum of the colloid prepared with a T:A ratio of 1:3.3. Particle size analysis was done using XRD, high resolution TEM and dynamic light scattering and found to be approximately 3 nm. UV-vis and PL spectral features also agree with this particle size in colloid with T:A of 1:3.3. The band gap of CdS quantum dots has increased from the bulk value 2.4-2.9 eV. PL spectra show quantum size effect and the peak is shifted from 628 to 556 nm when the ratio of T:A was changed from 1:25 to 1:3.3. Doping of CdS with Zn2+ and Cu2+ is found to enhance the PL intensity. PL band shows blue-shift and red-shift on doping with Zn2+ and Cu2+, respectively. UV and PL spectral features of the CdS/Au hybrid nanoparticles obtained by a physical mixing of CdS and Au nanoclusters in various volume ratios is also discussed. Au red-shifts and rapidly quenches the PL of CdS. An additional low energy band approximately 650 nm is observed in the UV visible spectrum of the hybrid nanoparticles.     

Porous phosphate heterostructures containing CdS quantum dots: assembly, characterization and photoluminescence

The synthesis and characterization of cadmium sulphide (CdS) quantum dots, conjugated in a porous phosphate heterostructure functionalized with aminopropyl groups is described. The resulting material has fluorescence properties with maximum emission intensity at 575 nm. The fluorescent materials are not soluble in water and exhibit high stability in aqueous solution in the pH ranges from 2 to 9. Energy dispersive X-ray spectroscopy confirmed the qualitative elemental composition of the synthesized materials and X-ray photoelectron spectra showed a surface S/Cd atomic ratio of 1.09. SEM images show that the materials are amorphous, possessing porous with sizes of several tens nanometres, homogeneous and exhibit a layered morphology. The adsorption–desorption analysis by N₂ at 77 K showed the accessibility of the CdS quantum dots onto the pores of the structure. The CdS quantum dots were stabilized by mercaptopropionic acid and bounded to the host materials by amine groups.     

The preparation of glutathione-capped CdTe quantum dots and their use in imaging of cells

In this paper, different sizes of glutathione-capped CdTe (GSH/CdTe) quantum dots (QDs) have been prepared directly in aqueous solution. The QDs have tunable fluorescence in the range of 510-670 nm, and they also have high photoluminescence quantum yield (PLQY) without any postpreparative treatment. Furthermore, the QDs have strong resistance to photobleaching, and they also have to be considered as cytocompatible. In addition, for the first time, folic acid was covalently conjugated to the GSH/CdTe QDs for imaging of cancer cells, demonstrating their potentially broad application as biolabels.     

Quenching of photoluminescence in conjugates of quantum dots and single-walled carbon nanotube

Development of quantum dot (QD) based device components requires controlled integration of QDs into different photonic and electronic materials. In this regard, introduction of methods for regular arrangement of QDs and investigation of properties of QD-based assemblies are important. In the current work we report (1) controlled conjugation of CdSe-ZnS QDs to sidewall-functionalized single-walled carbon nanotube (SWCNT) templates (2) and the effect of conjugation of QDs to SWCNT on the photoluminescence (PL) properties of QDs. We identified that PL intensity and lifetime of QDs are considerably reduced after conjugation to SWCNT. The origin of the quenching of the PL intensity and lifetime was discussed in terms of F?rster resonance energy transfer (FRET). FRET involves nonradiative transfer of energy from a photoexcited QD (energy donor) to a nearby SWCNT (energy acceptor) in the ground state. This was examined by varying the density of QDs on SWCNT and conjugating smaller and bigger QDs to the same SWCNT. We estimated the FRET efficiency in QD-SWCNT conjugates from the quenching of the PL intensity and lifetime and identified that FRET is independent of the density and type of QDs on SWCNT but inherent to QD-SWCNT conjugates.     

In vitro and intracellular sensing by using the photoluminescence of quantum dots

Quantum dots (QDs) have attracted increasing attention due to their unique physical and chemical properties. This article introduces recent advances in using QDs’ photoluminescence (PL) for in vitro and intracellular sensing analytes, in particular ions, and biomolecules from the last 3 years. Different sensing strategies are demonstrated and compared for increasing the detecting/sensing selectivity. The perspectives for in vitro and intracellular sensing based on QDs’ PL are also discussed.     

Proton-sponge coated quantum dots for siRNA delivery and intracellular imaging

We report the rational design of multifunctional nanoparticles for short-interfering RNA (siRNA) delivery and imaging based on the use of semiconductor quantum dots (QDs) and proton-absorbing polymeric coatings (proton sponges). With a balanced composition of tertiary amine and carboxylic acid groups, these nanoparticles are specifically designed to address longstanding barriers in siRNA delivery such as cellular penetration, endosomal release, carrier unpacking, and intracellular transport. The results demonstrate dramatic improvement in gene silencing efficiency by 10-20-fold and simultaneous reduction in cellular toxicity by 5-6-fold, when compared directly with existing transfection agents for MDA-MB-231 cells. The QD-siRNA nanoparticles are also dual-modality optical and electron-microscopy probes, allowing real-time tracking and ultrastructural localization of QDs during delivery and transfection. These new insights and capabilities represent a major step toward nanoparticle engineering for imaging and therapeutic applications.     

Au:CdHgTe quantum dots for in vivo tumor-targeted multispectral fluorescence imaging

Near-infrared gold-doped CdHgTe quantum dots (QDs) with improved photoluminescence and biocompatibility were developed using an aqueous solution route with l-glutathione and l-cysteine as stabilizers. As-prepared Au:CdHgTe QDs were covalently linked to arginine–glycine–aspartic acid (RGD) peptide, anti-epidermal growth factor receptor (EGFR) monoclonal antibody (MAb), and anti- carcinoembryonic antigen-related cell adhesion molecule-1 (CEACAM1) MAb separately. Three Au:CdHgTe QD bioconjugates (QD800-RGD, QD820-anti-CEACAM1, and QD840-anti-EGFR) were successfully used as probes for in vivo tumor-targeted multispectral fluorescence imaging of xenografts. Fluorescence signals from the QD bioconjugates used to detect three tumor markers were spectrally unmixed, and their co-localization was analyzed. The results indicate that multiple tumor markers could be simultaneously detected by multispectral fluorescence imaging in vivo using QD bioconjugates as probes. This approach has excellent potential as an imaging method for the noninvasive exploration and detection of multiple tumor markers in vivo, thereby substantially aiding the diagnosis of cancer.     

Substrate- and time-dependent photoluminescence of quantum dots inside the ultrathin polymer LbL film

The photoluminescence of CdSe/ZnS quantum dots (QDs) in different configurations at solid surfaces (glass, silicon, PDMS, and metals) is considered for three types of organization: QDs directly adsorbed on solid surfaces, separated from the solid surface by a nanoscale polymer film with different thickness, and encapsulated into a polymer film. The complete suppression of photoluminescence for QDs on conductive metal surfaces (copper, gold) indicated a strong quenching effect. The temporal variation of the photoluminescent intensity on other substrates (glass, silicon, and PDMS) can be tuned by placing the nanoscale (3-50 nm) LbL polymer film between QDs and the substrate. The photooxidation and photobleaching processes of QD nanoparticles in the vicinity of the solid surface can be tuned by proper selection of the substrate and the dielectric nanoscale polymer film placed between the substrate and QDs. Moreover, the encapsulation of QD nanoparticles into the polymer film resulted in a dramatic initial increase in the photoemission intensity due to the accelerated photooxidation process. The phenomenon of enhanced photoemission of QDs encapsulated into the ultrathin polymer film provides not only the opportunity for making flexible, ultrathin, QD-containing polymer films, transferable to any microfabricated substrate, but also improved light emitting properties.     

The use of size-selective excitation to study photocurrent through junctions containing single-size and multi-size arrays of colloidal CdSe quantum dots

This paper describes a study of the generation and flow of photocurrent through junctions containing three-dimensional arrays of colloidal CdSe quantum dots (QDs) of either a single size or multiple sizes. The electrodes were indium tin oxide (ITO) covered with a thin layer of poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) and a eutectic alloy of Ga and In (EGaIn). We measured the current-voltage characteristics of the junctions in the dark and under illumination, with various sources and wavelengths of excitation, and their photocurrent action spectra. Size-selective photoexcitation of the arrays of multiple sizes of QDs helped to determine (i) the location of the interface at which photoinduced separation of charge occurred, (ii) whether the energy absorbed by the QDs was redistributed before separation of charge, and (iii) the dependence of the photovoltage on the locations of various sizes of QDs within the junction. This research is a step toward the use of QDs for harvesting light and for transporting energy and charge in devices-for example, solar cells and photodetectors-that operate at zero bias.     

Conjugation of quantum dots with graphene for fluorescence imaging of live cells

It is difficult to achieve fluorescent graphene-quantum dots (QDs) conjugation because graphene quenches the fluorescence of the QDs. In the present study, the conjugation of graphene (reduced graphene oxide, RGO) with QDs via a bridge of bovine serum albumin (BSA) provides a novel highly fluorescent nano probe for the first time. BSA capped QDs are firmly grafted onto polyethylenimine (PEI)/poly(sodium 4-styrenesulfonate) (PSS) coated RGO (graphene-QDs) via electrostatic layer by layer assembly. The strong luminescence of the graphene-QDs provides a potential for non-invasive optical in vitro imaging. The graphene-QDs are used for in vitro imaging of live human carcinoma (Hela) cells. Graphene-QDs could be readily up-taken by Hela cells in the absence of specific targeting molecules, e.g., antibodies or folic acid, and no in vitro cytotoxicity is observed at 360 μg mL(-1) of the graphene-QDs. The results for the imaging of live cells indicated that the cell-penetrating graphene-QDs could be a promising nano probe for intracellular imaging and therapeutic applications.     

Facile synthesis and step by step enhancement of blue photoluminescence from Ag-doped ZnS quantum dots

Our results pertaining to the step by step enhancement of photoluminescence (PL) intensity from ZnS:Ag,Al quantum dots (QDs) are presented. Initially, these QDs were synthesized using a simple co-precipitation technique involving a surfactant, polyvinylpyrrolidone (PVP), in de-ionised water. It was observed that the blue PL originated from ZnS:Ag,Al QDs was considerably weak and not suitable for any practical display application. Upon UV (365 nm) photolysis, the PL intensity augmented to ~170% and attained a saturation value after ~100 min of exposure. This is attributed to the photo-corrosion mechanism exerted by high-flux UV light on ZnS:Ag,Al QDs. Auxiliary enhancement of PL intensity to 250% has been evidenced by subjecting the QDs to high temperatures (200 °C) and pressures (~120 bars) in a sulphur-rich atmosphere, which is due to the improvement in crystallanity of ZnS QDs. The origin of the bright-blue PL has been discussed. The results were supported by X-ray phase analysis, high-resolution electron microscopy and compositional evaluation.     

Recent advances in the use of near-infrared quantum dots as optical probes for bioanalytical,imaging and solar cell application

Near-infrared quantum dots (NIR QDs) represent a powerful material and diagnostic tool owing to their long emission wavelength which extends into the near-infrared region where permeation depths are much larger and where the intrinsic absorbance and autofluorescence of tissue is much smaller compared to shortwave emitting QDs. We are reviewing here recent (2008–2013) methods for the preparation of NIR QDs, their (bio)chemical modifications, and their applications. The article is subdivided into the following sections: (a) Synthesis of NIR QDs; (b) modification of NIR QDs and probe preparation; (c) applications of NIR QDs (with subsections on fluorescence quenching and fluorescence enhancement-based bioanalytical detection, on fluorescence bioimaging, on uses in photovoltaic cells and solar cells, and on molecular detection based on electrogenerated chemiluminescence). We finally make conclusions and discuss current challenges, trends, and future applications. The review contains 119 references. Figure

This review systematically presents the development, preparation methods, modifications and bioapplications of Near-infrared quantum dots (NIR QDs). The review contains 126 references.     

131I-labeled PEG and folic acid co-functionalized graphene quantum dots for tumor-targeted imaging

Journal of Radioanalytical and Nuclear Chemistry - In this study, we successfully synthesized polyethylene glycol (PEG) and folic acid (FA) co-functionalized graphene quantum dots (GQDs) to improve...