Quantum dot-based near-infrared electrochemiluminescent immunosensor with gold nanoparticle-graphene nanosheet hybrids and silica nanospheres double-assisted signal amplification

Near-infrared electrochemiluminescence (NIR ECL) from quantum dots (QDs) has aroused particular attention. However, whether it is possible to achieve NIR ECL sensing has remained an open question. In this article, we reported a NIR ECL immunosensor with amplification techniques for ultrasensitive and selective determination of biomarker. In this sensing platform, NIR-emitting CdTe/CdS core(small)/shell(thick) QDs were first selected as NIR ECL emitters. The NIR ECL nanoprobe (SiO(2)-QD-Ab2) was designed by covalent assembly of goat antihuman IgG antibody (Ab2) on CdTe/CdS QDs tagged silica nanospheres. Gold nanoparticle-graphene nanosheet (Au-GN) hybrids were prepared by a sonication-induced self-assembly and served as an effective matrix for initial antibodies (Ab1) attachment. After a sandwich immunoreaction, the functionalized silica nanosphere labels were captured onto the glass carbon electrode surface. Integrating the dual amplification from the promoting electron transfer rate of Au-GN hybrids and the increasing QD loading of SiO(2)-QD-Ab2 labels, the NIR ECL response from CdTe/CdS QDs enhanced 16.8-fold compared to the unamplified protocol and successfully fulfilled the ultrasensitive detection of human IgG (HIgG) with a detection limit of 87 fg mL(-1). Moreover, as a practical application, the proposed immunosensor was used to monitor HIgG level in human serum with satisfactory results obtained.     

NIR‐Emitting Quantum Dot‐Encoded Microbeads through Membrane Emulsification for Multiplexed Immunoassays

NIR‐emitting CdSeTe/CdS/ZnS core/shell/shell QD‐encoded microbeads are combined with common flow cytometry with one laser for multiplexed detection of hepatitis B virus (HBV). A facile one‐pot synthetic route is developed to prepare CdSeTe/CdS/ZnS core/shell/shell QDs with high photoluminescence quantum yield and excellent stability in liquid paraffin, and a Shirasu porous glass (SPG) membrane emulsification technique is applied to incorporate the QDs into polystyrene–maleic anhydride (PSMA) microbeads to obtain highly fluorescent QD‐encoded microbeads. The relatively wide NIR photoluminescence full width half maximum of the CdSeTe/CdS/ZnS QDs is used to develop a ‘single wavelength’ encoding method to obtain different optical codes by changing the wavelengh and emission intensity of the QDs incorporated into the microbeads. Moreover, a detection platform combining NIR‐emitting CdSeTe/CdS/ZnS QD‐encoded microbeads and Beckman Coulter FC 500 flow cytometry with one laser of 488 nm is successfully used to conduct a 2‐plex hybridization assay for hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg), and a 3‐plex hybridization assay for hepatitis B surface antibody (HBsAb), hepatitis B e antibody (HBeAb), and hepatitis B core antibody (HBcAb), which suggests the promising application of NIR QD‐encoded microbeads for multiplex immunoassays.     

Cytotoxicity of cadmium-containing quantum dots based on a study using a microfluidic chip

There is a lack of reliable nanotoxicity assays available for monitoring and quantifying multiple cellular events in cultured cells. In this study, we used a microfluidic chip to systematically investigate the cytotoxicity of three kinds of well-characterized cadmium-containing quantum dots (QDs) with the same core but different shell structures, including CdTe core QDs, CdTe/CdS core–shell QDs, and CdTe/CdS/ZnS core-shell-shell QDs, in HEK293 cells. Using the microfluidic chip combined with fluorescence microscopy, multiple QD-induced cellular events including cell morphology, viability, proliferation, and QD uptake were simultaneously analysed. The three kinds of QDs showed significantly different cytotoxicities. The CdTe QDs, which are highly toxic to HEK293 cells, resulted in remarkable cellular and nuclear morphological changes, a dose-dependent decrease in cell viability, and strong inhibition of cell proliferation; the CdTe/CdS QDs were moderately toxic but did not significantly affect the proliferation of HEK293 cells; while the CdTe/CdS/ZnS QDs had no detectable influence on cytotoxicity with respect to cell morphology, viability, and proliferation. Our data indicated that QD cytotoxicity was closely related to their surface structures and specific physicochemical properties. This study also demonstrated that the microfluidic chip could serve as a powerful tool to systematically evaluate the cytotoxicity of nanoparticles in multiple cellular events.     

Visualizing resonance energy transfer in supramolecular surface patterns of β-CD-functionalized quantum dot hosts and organic dye guests by fluorescence lifetime imaging

Detection of an analyte via supramolecular host-guest binding and quantum dot (QD)-based fluorescence resonance energy transfer (FRET) signal transduction mechanism is demonstrated. Surface patterns consisting of CdSe/ZnS QDs functionalized at their periphery with β-cyclodextrin (β-CD) were obtained by immobilization of the QDs from solution onto glass substrates patterned with adamantyl-terminated poly(propylene imine) dendrimeric "glue." Subsequent formation of host-guest complexes between vacant β-CD on the QD surface and an adamantyl-functionalized lissamine rhodamine resulting in FRET was confirmed by fluorescence microscopy, spectroscopy, and fluorescence lifetime imaging microscopy (FLIM).     

Preparation,optical and thermal properties of CdSe–ZnS/poly(lactic acid) (PLA) nanocomposites

In this study, CdSe–ZnS/poly(lactic acid) (PLA) nanocomposite films, containing different concentrations of surface-modified CdSe–ZnS quantum dots (QDs), were prepared via a solution casting method. The optical microstructural and thermal properties of the as-prepared QDs/PLA films were investigated. The QDs/PLA films exhibited strong and stable photoluminescence (PL) intensity with concentration dependent amplitudes. The transmission electron microscopy (TEM) pictures revealed that QDs of ∼5 nm diameter were uniformly dispersed in the PLA matrix. According to the results of thermogravimetric analysis, the weight-loss onset temperature of PLA clearly decreased with the QD content. A combination of Fourier transform infrared (FT-IR) spectroscopy, X-ray diffractometry (XRD) and differential scanning calorimetry (DSC) results suggested that the QDs exhibit obvious nucleation activity on the crystallization behavior of the PLA matrix. This research provides useful information to the foundations of practical applications of QDs/PLA nanocomposites as fluorescent and biodegradable functionalized materials.     

Specific integrin labeling in living cells using functionalized nanocrystals

We present an integrin labeling method using functionalized quantum dots (QDs). Cyclic Arg-Gly-Asp (RGD) peptides and a biotin-streptavidin linkage are used to specifically couple individual QDs to integrins of living cells. The spacer distance between the RGD sequence and the QD surface is a crucial parameter to ensure specific binding to individual alpha(v)beta(3) integrins of osteoblast cells. Despite blinking, the position of single QDs is tracked with nanometer precision and localized diffusive behavior is observed. We show that blinking events do not prevent the acquisition of quantitative parameters from the QD trajectories.     

Energy transfer: Visualizing Resonance Energy Transfer in Supramolecular Surface Patterns of β‐CD‐Functionalized Quantum Dot Hosts and Organic Dye Guests by Fluorescence Lifetime Imaging (Small 24/2010)

Detection of an analyte via supramolecular host–guest binding and quantum dot (QD)‐based fluorescence resonance energy transfer (FRET) signal transduction mechanism is demonstrated. Surface patterns consisting of CdSe/ZnS QDs functionalized at their periphery with β‐cyclodextrin (β‐CD) were obtained by immobilization of the QDs from solution onto glass substrates patterned with adamantyl‐terminated poly(propylene imine) dendrimeric “glue.” Subsequent formation of host–guest complexes between vacant β‐CD on the QD surface and an adamantyl‐functionalized lissamine rhodamine resulting in FRET was confirmed by fluorescence microscopy, spectroscopy, and fluorescence lifetime imaging microscopy (FLIM).     

ATRP方法可控合成碳纳米管/PMMA纳米复合材料

通过多壁碳纳米管的表面改性合成了ATRP引发剂,利用合成的ATRP引发剂进行ATRP活性聚合,成功地在碳纳米管表面接枝聚合物PMMA。利用红外(IR)、透射电镜(TEM)、热重(TGA)以及核磁共振(NMR)表征接枝的碳纳米管,考察了碳纳米管用量对碳纳米管/PMMA纳米复合材料力学性能的影响,结果表明,碳纳米管表面成功接枝聚合物PMMA,PMMA的力学性能得到很大改善。     

Three dimensional hierarchy structures from self-assembly of quantum dots

We have reported first example of 3D hierarchy structure from self-assembly of water-soluble QDs followed by chemical reaction control. After addition of ethylenediaminetetraacetic acid, dipotassium salt dehydrate (EDTA) into L-cysteine-stabilized CdTe QD solution, the color of solution was observed to become lighter and shallower, and finally white precipitates appeared. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results confirm that the morphology transformation from zero dimensional (0D) QDs via two-dimensional (2D) nanoflakes to 3D microflowers occurs among those QD assemblies. Meanwhile, EDX results demonstrate that the as-formed QD-assemblies are not CdTe but CdS. The turnover of chemistry nature from CdTe to CdS after addition of EDTA is mainly due to the oxidation of Te followed by a series of chemical reactions. The photoluminescence (PL) spectroscopy and confocal laser scanning microscopy (CLSM) results reveal that such 3D hierarchy structure of CdS QDs have good optical property.     

Transfection of aqueous CdS quantum dots using polyethylenimine

In this study, we have examined the transfection of aqueous CdS quantum dots (QDs) in the cytoplasm of PC12 neuronal cells using polyethylenimine (PEI) as carrier. The CdS QDs were prepared using a unique aqueous synthesis method, at 5?nm in size and capped with 3-mercaptopropyltrimethoxysilane (MPS). They exhibited a quantum yield of 7.5% and a zeta potential of -25?mV. With PEI they formed complexes by electrostatic attraction. At PEI/QD number ratios of>100, the PEI-QD complexes obtained exhibited a saturated size of about 24?nm and a zeta potential of about 15?mV. Confocal microscopy showed that PEI-QD complexes of a PEI/QD number ratio of 200 were successfully internalized and uniformly distributed inside the cells, indicating that the PEI-QD complexes were able to rupture the vesicles to enter the cytoplasm without aggregation. In addition, we showed that the presence of the PEI did not reduce the photoluminescence of the QDs and only mildly reduced the mitochondrial activity of the transfected cells-with no apparent reduction at a PEI/QD ratio of <40 to about 30% reduction at a PEI/QD number ratio of 200.     

Silica fluorescent nanospheres containing a large amount of quantum dots prepared using liposomes as templates

Quantum dot (QD) fluorescent spheres have captivated many scientists because of their many potential applications in biomedical research. In this work, QD nanospheres were prepared using a novel method: incorporating QDs into nano-liposomes and then synthesising a silica shell using a lipid membrane as the template. The results showed that the nanocomposites obtained were spherical in shape, and each nanosphere contained a silica shell and the cores consisted of a large amount of QDs. Ultrathin sections of the spheres showed that the thickness of the silica shell was about 50–60?nm. Because the QD cores were coated with liposome and thick silica shell, the bright field of the silica sphere suspension was close to milk white in colour, which was different from that of the red-coloured QD solution. Although the quantum yield of the silica spheres (2.27%) was lower than that of the QDs (23.52%), these nanospheres still emitted a bright fluorescence, and there was no obvious difference between the fluorescent colour of the nanosphere suspension and the QD solution.     

Synthesis of Zn(1-x)Cd(x)S:Mn/ZnS quantum dots and their application to light-emitting diodes

3.6?nm sized Mn-doped Zn(1-x)Cd(x)S quantum dots (QDs) with the composition (x) of 1, 0.5, 0.2 and 0 were synthesized by a reverse micelle approach. The bandgap energy of Zn(1-x)Cd(x)S:Mn QDs was tuned to a higher energy by increasing the Zn content, and the actual composition of alloyed Zn(1-x)Cd(x)S:Mn QDs was found to be different from the solution composition. Consecutive overcoating of the Zn(1-x)Cd(x)S:Mn QD surface by a ZnS shell was done, and the core/shell structured QDs exhibited quantum yields of 14-30%, depending on the composition of the core QDs. Using CdS:Mn/ZnS QDs, orange and white light-emitting diodes (LEDs) pumped by a near-UV and blue LED chips, respectively, were fabricated and their optical properties are described.     

Fluorescence Lifetime Imaging and FRET‐Induced Intracellular Redistribution of Tat‐Conjugated Quantum Dot Nanoparticles through Interaction with a Phthalocyanine Photosensitiser

The interaction of Tat‐conjugated PEGylated CdSe/ZnS quantum dots (QD) with the amphiphilic disulfonated aluminium phthalocyanine photosensitiser is investigated in aqueous solution and in a human breast cancer cell line. In aqueous solution, the QDs and phthalocyanine form stable nanocomposites. Using steady‐state and time‐resolved fluorescence measurements combined with singlet oxygen detection, efficient Förster resonance energy transfer (FRET) is observed with the QDs acting as donors, and the phthalocyanine photosensitiser, which mediates production of singlet oxygen, as acceptors. In cells, the Tat‐conjugated QDs localise in lysosomes and the QD fluorescence lifetimes are close to values observed in aqueous solution. Strong FRET‐induced quenching of the QD lifetime is observed in cells incubated with the nanocomposites using fluorescence lifetime imaging microscopy (FLIM). Using excitation of the QDs at wavelengths where phthalocyanine absorption is negligible, FRET‐induced release of QDs from endo/lysosomes is confirmed using confocal imaging and FLIM, which is attributed to photooxidative damage to the endo/lysosomal membranes mediated by the phthalocyanine acceptor.     

碳纳米管/聚甲醛复合材料的结晶形态与力学性能

在对碳纳米管(CNT)进行表面修饰后,采用活性自由基聚合法(ATRP)在其表面接枝聚甲基丙烯酸甲酯(PMMA)。再将接枝上聚合物的碳纳米管添加到聚甲醛中熔融共混制得碳纳米管/聚甲醛纳米复合材料。通过偏光显微镜观察其结晶形态,并研究了功能化碳纳米管的含量对聚甲醛缺口冲击强度的影响,结果表明,CNT-PMMA的加入使聚甲醛球晶细化,复合材料的缺口冲击强度得到提高。     

Fast-grown CdS quantum dots: Single-source precursor approach vs microwave route

A cross-disciplinary protocol of characterization by joint techniques enables one to closely compare chemical and physical properties of CdS quantum dots (QDs) grown by single source precursor methodology (SSPM) or by microwave synthetic route (MWSR). The results are discussed in relation with the synthesis protocols. The QD average sizes, reproducible as a function of the temperatures involved in the growth processes, range complementarily in 2.8–4.5 nm and 4.5–5.2 nm for SSPM and MWSR, respectively. Hexagonal and cubic structures after X-ray diffraction on SSPM and MWSR grown CdS QDs, respectively, are tentatively correlated to a better crystalline quality of the latter with respect to the further ones, suggested by (i) a remarkable stability of the MWSR grown QDs after exposure to air during several days and (ii) no evidence of their fragmentation during mass spectrometry (MS) analyses, after a fair agreement between size dispersities obtained by transmission electron microscopy (TEM) and MS, in contrast with the discrepancy found for the SSPM grown QDs. Correlatively, a better optical quality is suggested for the MWSR grown QDs by the resolution of n > 1 excitonic transitions in their absorption spectra. The QD average sizes obtained by TEM and deduced from MS are in overall agreement. This agreement is improved for the MWSR grown QDs, taking into account a prolate shape of the QDs also observed in the TEM images. For both series of samples, the excitonic responses vs the average sizes are consistent with the commonly admitted empirical energy-size correspondence. A low energy PL band is observed in the case of the SSPM grown QDs. Its decrease in intensity with QD size increase suggests a surface origin tentatively attributed to S vacancies. In the case of the MWSR grown QDs, the absence of this PL is tentatively correlated to an absence of S vacancies and therefore to the stable behavior observed when the QDs are exposed to air.     

Quantum dot (QD)-modified carbon tape electrodes for reproducible electrochemiluminescence (ECL) emission on a paper-based platform

Stable and sensitive electrochemiluminescence (ECL) detection relies on successful immobilization of quantum dots (QDs) on working electrodes. Herein, we report a new technique to apply double-sided carbon adhesive tape as the working electrode to improve the stability and reproducibility of QD-based ECL emission. CdS QD-modified electrodes were prepared by dropping and drying CdS QD suspension on the carbon adhesive tape supported by indium tin oxide (ITO) glass. The ECL detection was performed with the prepared electrode on a paper-based platform. We tested our system using H(2)O(2) of various concentrations and demonstrated that consistent ECL emission could be obtained. We attribute stable and reproducible ECL emission to the robust attachment of CdS QDs on the carbon adhesive tape. The proposed method could be used to quantify the concentration of dopamine from 1 μM to 10 mM based on the quenching effect of dopamine on ECL emission of CdS QD system using H(2)O(2) as the coreactant. Our approach addressed the problem in the integration of stable QD-based ECL detection with portable paper-based analytical devices. The similar design offers great potential for low-cost electrochemical and ECL analytical instruments.     

Synthesis and enzymatic cleavage of dual-ligand quantum dots

Site directed therapy promises to minimize treatment-limiting systemic effects associated with cytotoxic agents that have no specificity for pathologic tissues. One general strategy is to target cell surface receptors uniquely presented on particular tissues. Highly specific in vivo targeting of an emerging neoplasm through a single molecular recognition mechanism has not generally been successful. Nonspecific binding and specific binding to non-target cells compromise the therapeutic index of small molecule, ubiquitous cancer targeting ligands. In this work, we have designed and fabricated a nanoparticle (NP) construct that could potentially overcome the current limitations of targeted in vivo delivery. Quantum dots (QDs) were functionalized with a poly(ethylene glycol) (PEG) modified to enable specific cleavage by matrix metalloprotease-7 (MMP-7). The QDs were further functionalized with folic acid, a ligand for a cell surface receptor that is overexpressed in many tumors, but also expressed in some normal tissues. The nanomolecular construct is designed so that the PEG initially conceals the folate ligand and construct binding to cells is inhibited. MMP-7 activated peptide cleavage and subsequent unmasking of the folate ligand occurs only near tumor tissue, resulting in a proximity activated (PA) targeting system. QDs functionalized with both the MMP-7 cleavable substrate and folic acid were successfully synthesized and characterized. The proteolytic capability of the dual ligand QD construct was quantitatively assessed by fluorometric analysis and compared to a QD construct functionalized with only the PA ligand. The dual ligand PA nanoparticles studied here exhibit significant susceptibility to cleavage by MMP-7 at physiologically relevant conditions. The capacity to autonomously convert a biopassivated nanostructure to a tissue-specific targeted delivery agent in vivo represents a paradigm change for site-directed therapies.     

Effect of filler functionalization on thermo-mechanical properties of polyamide-12/carbon nanofibers composites: a study of filler–matrix molecular interactions

The effect of carbon nanofiber (CNF) functionalization on the thermo-mechanical properties of polyamide-12/CNF nanocomposites was investigated. Three main different surface treatments were performed to obtain CNF-OH (OH rich), CNF-Silane (C₆H₅Si–O–), and CNF-peroxide. CNF modified with poly-(tert-butyl acrylate) chains grown from the surface via ATRP (atom transfer radical polymerization) were also prepared and tested. The modified CNFs and neat CNFs were used as fillers in polyamide-12 nanocomposites and the properties of the ensuing materials were characterized and compared. Universal tensile tests demonstrated a substantial increase (up to 20 %) of the yield strength, without reduction of the final elongation, for all functionalized samples tested within 1 wt% filler content. Further evidences of mechanical properties improvement were given by dynamic mechanical thermal analyses. CNFs functionalized with poly-(tert-butyl acrylate) and silane exhibited the best performance with stiffening and strengthening at low (≤1 wt%) filler loadings, via a partial decrease of the intensity of β-transitions attributed to favorable interactions between the functional groups on the surface of functionalized CNFs and polyamide-12. CNFs treated with peroxide proved to be the most simple preparation technique and the ensuing nanocomposites exhibited the highest storage modulus at high (5 wt%) filler content. Theoretical simulations using the micro-mechanics model were used to predict the Young modulus of the composites and compare them with experimental data. The results obtained suggest a synergistic effect between the matrix and the filler enhanced by surface functionalization.     

Bandgap Tuning with Thermal Residual Stresses Induced in a Quantum Dot

Lattice distortion induced by residual stresses can alter electronic and mechanical properties of materials significantly. Herein, a novel way of the bandgap tuning in a quantum dot (QD) by lattice distortion is presented using 4‐nm‐sized CdS QDs grown on a TiO₂ particle as an application example. The bandgap tuning (from 2.74 eV to 2.49 eV) of a CdS QD is achieved by suitably adjusting the degree of lattice distortion in a QD via the tensile residual stresses which arise from the difference in thermal expansion coefficients between CdS and TiO₂. The idea of bandgap tuning is then applied to QD‐sensitized solar cells, achieving ≈60% increase in the power conversion efficiency by controlling the degree of thermal residual stress. Since the present methodology is not limited to a specific QD system, it will potentially pave a way to unexplored quantum effects in various QD‐based applications.     

P(S-SS)/CdS核壳粒子的制备与表征

采用超声辐照乳液聚合得到聚(苯乙烯-苯乙烯磺酸钠)(P(S-SS))乳胶粒,用直接沉淀法在乳胶粒表面原位生成硫化镉(CdS)纳米粒子,得到P(S-SS)/CdS核壳粒子。用元素分析和XPS研究了共聚物的组成及磺酸基(-SO3-)的分布,结果表明,-SO3-主要分布在乳胶粒表面,有利于CdS纳米粒子在乳胶粒表面的沉积。用XRD、TEM及UV-v is表征了共聚物乳胶粒及P(S-SS)/CdS核壳粒子的结构及CdS的量子效应。结果表明,所制备的CdS纳米粒子为六方晶型,平均粒径为6 nm,在P(S-SS)乳胶粒外层形成多层包覆,P(S-SS)/CdS核壳粒子平均粒径为70 nm,CdS纳米粒子表现出明显的量子尺寸效应。