Ratio Of Quantum Dots Research Articles

Structure-Controlled Preparation of Multicompartment Micelles with Tunable Emission through Hydrodynamics-Dependent Self-Assembly in Microfluidic Chips

Multicompartment micelles (MCMs) attracted much attention since they have subdivided domains that could be employed to encapsulate and transport diverse compounds simultaneously. Usually, preparation of MCMs relied on precise synthesis of block copolymers (BCPs) and elegant control of assembly kinetics, making it difficult to successively produce MCMs. Herein, we report a facile yet effective method for preparing MCMs by adjusting the hydrodynamics in microfluidic channels. It was found that well-defined MCMs were formed through hydrodynamics-dependent secondary assembly in microfluidic chips. By adjusting the flow diffusion process by varying the flow rate ratio and total flow rate, both the internal structure and size of MCMs could be effectively changed. A product diagram of micellar morphologies associated to the initial polymer concentration and flow rate ratio of water/BCPs solution was constructed. More interestingly, quantum dots (QDs) could be selectively loaded into different domains of the MCMs. Consequently, the Förster resonance energy transfer among QDs could be effectively suppressed. Thus, the emission spectrum of MCMs/QDs hybrid particles could be easily tuned by changing the ratio of QDs, showing great potential application in photonics and sensors.

Highly sensitive and rapid responding humidity sensors based on silver catalyzed Ag2S-TiO2 quantum dots prepared by SILAR.

We developed a resistive humidity sensor based on a heterojunction of silver sulfide (Ag2S) quantum dots (QDs) and TiO2 because of its specificity to water vapor adsorption and its insensitivity to environmental gases. The QDs were grown on a mesoporous TiO2 layer using the successive ionic layer adsorption and reaction (SILAR) method. The boundary condition between TiO2 and Ag2S provides a tunable energy gap by adjusting the number of SILAR cycles. Besides, the large surface-to-volume ratio of QDs provides a strong water vapor adsorption ability and electron transfer. Nano-silver precipitated during the SILAR process provides free electrons and lowers the Fermi level to between n-type TiO2 and p-type Ag2S. The resistance response increased significantly to 4600 and the reaction equilibrium time decreased greatly to 7 seconds due to the presence of nano-silver. Finally, the Ag2S QDs possess a best sensing range of 13–90%. To sum up, Ag2S QDs are high sensitivity and selectivity humidity sensors.

Quantum dot clusters as self-assembled antennae with phycocyanine and phycobilisomes as energy acceptors.

In this study, we investigated an experimental and Monte-Carlo computational characterization of self-assembled antennae built using CdTe colloidal quantum dots (QDs). These clusters provide efficient excitation of phycocyanine (PC) or phycobilisomes (PBSs). PBSs are light-harvesting complexes (LHCs) of cyanobacteria, made of several PC units, organized in disks and rods. Each PC contains three separate cofactors. Therefore, we analyzed variations in multi-donor and multi-acceptor systems. The self-assembled QD clusters were formed mostly by electrostatic interactions, possibly due to the introduction of a positive charge on an originally negatively charged nanoparticle surface. Our results suggest that PC may accept energy from multiple nanoparticles localized at a distance significantly longer than the Förster radius. The excitation transfers between particular nanoparticles with possible delocalization. The maximal energy transfer efficiency was obtained for the PC/PBS : QD ratio from 1 to 20 depending on the QD size. This cannot be fully explained using computational simulations; hence, we discussed the hypothesis and explained the observations. Our self-assembled systems may be considered for possible applications in artificial light-harvesting systems because absorption spectra of QDs are different from the absorption characteristics of PC/PBS. In addition, huge clusters of QDs may effectively increase the optical cross-section of so-created nanohybrids.

Triplexed CEA-NSE-PSA Immunoassay Using Time-Gated Terbium-to-Quantum Dot FRET

Time-gated Förster resonance energy transfer (TG-FRET) between Tb complexes and luminescent semiconductor quantum dots (QDs) provides highly advantageous photophysical properties for multiplexed biosensing. Multiplexed Tb-to-QD FRET immunoassays possess a large potential for in vitro diagnostics, but their performance is often insufficient for their application under clinical conditions. Here, we developed a homogeneous TG-FRET immunoassay for the quantification of carcinoembryonic antigen (CEA), neuron-specific enolase (NSE), and prostate-specific antigen (PSA) from a single serum sample by multiplexed Tb-to-QD FRET. Tb–IgG antibody donor conjugates were combined with compact QD-F(ab’)2 antibody acceptor conjugates with three different QDs emitting at 605, 650, and 705 nm. Upon antibody–antigen–antibody sandwich complex formation, the QD acceptors were sensitized via FRET from Tb, and the FRET ratios of QD and Tb TG luminescence intensities increased specifically with increasing antigen concentrations. Although limits of detection (LoDs: 3.6 ng/mL CEA, 3.5 ng/mL NSE, and 0.3 ng/mL PSA) for the triplexed assay were slightly higher compared to the single-antigen assays, they were still in a clinically relevant concentration range and could be quantified in 50 µL serum samples on a B·R·A·H·M·S KRYPTOR Compact PLUS clinical immunoassay plate reader. The simultaneous quantification of CEA, NSE, and PSA at different concentrations from the same serum sample demonstrated actual multiplexing Tb-to-QD FRET immunoassays and the potential of this technology for translation into clinical diagnostics.

Visible-Light-Induced Nanoparticle Assembly for Effective Hydrogen Photogeneration

Visible-light-induced nanoparticle assembly consisting of quantum dots (QDs) and Pt nanoparticles (NPs) has been achieved. The assembled nanoparticle joined a single Pt nanoparticle and multiple QDs together through controllable oxidation of thiol ligands on QDs under aerobic visible light irradiation and sonication. With an optimal ratio of QDs to Pt NPs (ca. 475:1), the assembly could achieve consecutive electron transfer from photoexcited QDs to Pt NP and evolve H2 gas with a constant rate of ∼13.9 μmol h–1 from triethylamine (TEA) during 70 h, corresponding to a turnover number (TON) of 1.4 × 107 mol H2 per mol Pt NPs. Our work shows that the assembled architecture of semiconducting QDs is a promising strategy for effective and durable H2 photogeneration.

Ultrasensitive lateral-flow assays based on quantum dot encapsulations with signal amplification

Lateral-flow assays (LFAs), with its convenience and low cost, promise to become the in-home test format for early diagnosis and monitoring of tumor marker. However, the insufficient signal intensity was generated by signal reporters reducing the sensitivity of this format. In this study, a novel nanoscale signal reporter capable of amplifying the fluorescence signal is fabricated by encapsulating quantum dots (QDs) into modified tri-copolymer (poly(tert-butyl acrylate-co-ethyl acrylate-co-methacrylic acid)) (ODA-g-tri-copolymer). The amplified signal varied by simply adjusting the ratio of QDs to the ODA-g-tri-copolymer for obtaining QD nanospheres with high QD loading. They exhibits outstanding stability compared to the individual QDs both in the biological buffer and strong acid solutions. Here, human chorionic gonadotrophin (HCG) is employed as the model protein of LFAs. The results show that the detection limit of the QD nanospheres is pushed down to 0.016 IU/L, which is about ~ 38.5 times enhanced compared to the individual QD-based LFAs without any signal amplifying. The ultrasensitive LFAs were attributed to the signal amplification strategy, and their efficiency and robustness demonstrated the great potential in clinical applications.

Multichannel Discriminative Detection of Explosive Vapors with an Array of Nanofibrous Membranes Loaded with Quantum Dots.

The multichannel fluorescent sensor array based on nanofibrous membranes loaded with ZnS quantum dots (QDs) was created and demonstrated for the discriminative detection of explosives. The synergistic effect of the high surface-to-volume ratio of QDs, the good permeability of nanofibrous membranes and the differential response introduced by surface ligands was played by constructing the sensing array using nanofibrous membranes loaded with ZnS QDs featuring several surface ligands. Interestingly, although the fluorescence quenching of the nanofibrous membranes is not linearly related to the exposure time, the fingerprint of each explosive at different times is very similar in shape, and the fingerprints of the three explosives show different shapes. Three saturated vapors of nitroaromatic explosives could be reliably detected and discriminated by the array at room temperature. This work is the first step toward devising a monitoring system for explosives in the field of public security and defense. It could, for example, be coupled with the technology of image recognition and large data analysis for a rapid diagnostic test of explosives. This work further highlights the power of differential, multichannel arrays for the rapid and discriminative detection of a wide range of chemicals.

Thermal characteristics of graphene nanosheet with graphane domains of varying morphologies

In this paper, thermal characteristics of graphene nanosheet embedded with graphane quantum dots (QDs) are investigated using Non-Equilibrium Molecular Dynamics (NEMD) method. Thermal conductivity of nanoribbon is demonstrated to be tunable by manipulating the geometrical characteristics of graphane QDs without changing the amount of hydrogenation. Graphane QDs of larger circumferences cause more deterioration in heat transfer due to the scattering of phonons occurred at the graphene-graphane interface. As a result, nanoribbon with graphane QDs possesses higher thermal conductivity than that with random hydrogenation of same amount. Under fixed circumferences, the length-to-width ratio of QD is revealed to be the most important causes of deterioration in thermal conductivity. Graphane QDs of high length-to-width ratio have smaller deterioration effect on thermal conductivity. Combing the effect of circumference and length-to-width ratio, the thermal difference between nanoribbons with graphane QDs of different shapes can be sufficiently interpreted. The demonstrated mechanism can be applied for the optimization of nanodevices fabricated from hydrogen functionalized graphene.

Enhanced normal-direction excitation and emission of dual-emitting quantum dots on a cascaded photonic crystal surface.

Large normal-direction excitation and emission of dual-emitting quantum dots (QDs) are essential for practical application of QD sensors based on the ratiometric fluorescence response. We have numerically demonstrated an all-dielectric four-layer cascaded photonic crystal (CPC) structure (alternating TiO2 and SiO2/SU8 layers with two dimensional nanoscale patterns in each layer) which is capable of providing normal-direction high Q-factor leaky modes at excitation wavelengths of QDs and two low Q-factor leaky modes coinciding with the two emission peaks of a dual-emitting QD. Normal-direction excitation and far-field emission of the dual-emitting QDs are enhanced significantly when QDs are distributed on/in the top TiO2 layer of the CPC structure, especially in the spatial distribution areas of the resonant leaky modes. QDs can be positioned differently depending on the applications. Positioning QDs on the top TiO2 layer will improve the signal-to-noise ratios of QD biomedical/chemical/temperature sensors, while embedding QDs in the top TiO2 layer will increase the light extraction from the QD light emitting device, making our CPC a versatile optical coupling structure. Our CPC-QD structure is experimentally feasible and robust against the parameter perturbation in real fabrication.

A Facile Strategy to Fabricate Thermoresponsive Polymer Functionalized CdTe/ZnS Quantum Dots: Assemblies and Optical Properties

Novel thermoresponsive CdTe/ZnS quantum dots (QDs) decorated with a copolymer ligand (CPL) containing 8-hydroxyquinoline and NIPAM units are prepared through coordinate bonding in aqueous solution. The dependence of the morphology and optical properties of the QDs/CPL assemblies formed via coordinate bonding on the experimental conditions is studied. The coordinate induced self-assemblies are observed by controlling the molar ratio of QDs and CPL. The self-organized structure of QDs/CPL proceeds through a first step of QDs-chains, followed by a necklace-like single annular chain, and subsequently increases its annular chain structure, forming a network. The CPL functionalized QDs can emit multiple colors from the cooperating interaction between the inherent emission (606 nm) of the QDs and the surface-coordinated emission (517 nm) of the CPL complex formed on the QD surface. For QDs-CPL systems, both Förster resonance energy transfer (FRET) and a high rate of photoinduced electron transfer (PET) are simultaneous, the latter mainly contributing to PL quenching. The thermoresponsive QDs/CPL assemblies also exhibit dual reversible PL properties between the inherent emission of QDs and surface-coordinated emission.

Enhancement of the Stabilization in White Organic Light-Emitting Diodes Utilizing a Color Conversion Layer Containing CdSe/ZnS Quantum Dots

White organic light emitting diodes (WOLEDs) were fabricated utilizing blue emitting organic light emitting diodes and color conversion layers containing CdSe/ZnS quantum dots (QDs). The best color purity of the WOLEDs was achieved by using the red and green QDs ratio of 1:9.5. Commission Internationale de l'Eclairage coordinates of the WOLEDs slightly shifted from (0.35, 0.33) to (0.35, 0.32) with increasing applied voltage from 9 to 14 V, indicative of a deep stabilized white color. Color tunable mechanisms of WOLEDs with a color conversion layer containing CdSe/ZnS QDs are described on the basis of the experimental results.

Quantum dot-based, quantitative, and multiplexed assay for tissue staining.

The excellent optical properties of quantum dots (QDs), such as high brightness, high photostability, continuous absorption, and narrow emission bandwidth, make them ideal as optical labels to develop QD-based immunohistofluorescence (IHF) imaging for multiplexing cancer biomarker detection on formalin-fixed and paraffin-embedded (FFPE) tissues. IHF is very important for the prediction of a patient's response to cancer chemotherapy or radiotherapy. QD-based IHF faces several challenges that differ from those encountered by organic dye based IHF for clinical assays. The current work addresses some of these issues. Initially, the chemical stability of QDs and organic dyes were compared. The results showed that QDs were stable for at least 5 months on FFPE tissue, whereas organic dyes were photobleached shortly after exposure to light. Various staining methods were also studied. QD fluorescence intensity on the tissue stained with primary antibody (Ab, p16, survivin, EF1α) conjugated QDs from our company was comparable to the signal from a commercially available method in which the tissue was stained with a primary p16 Ab and a QD-labeled secondary goat anti mouse Ab respectively. Finally, the effect of the amount of Ab conjugated to QD on tissue imaging was also studied. There was no significant increase in the QD fluorescence signal on tissues when the Ab:QD ratio increased from 5 to 30. In addition, protein G was tested as an adaptor protein to link Ab to QDs for IHF staining. However, the proper blocking of the protein G on QDs was necessary to reduce crosstalk. The biomarker quantification in QD-based IHF was validated by conventional Western blot and immunohistochemistry. The results contained herein demonstrate a promising application of QDs in multiplex detection and quantification of biomarkers.

Targeted quantum dots fluorescence probes functionalized with aptamer and peptide for transferrin receptor on tumor cells

Quantum dots (QDs) fluorescent probes based on oligonucleotide aptamers and peptides with specific molecular recognition have attracted much attention. In this paper, CdSe/ZnS QDs probes for targeted delivery to mouse and human cells using aptamer GS24 and peptide T7 specific to mouse/human transferrin receptors were developed. Capillary electrophoresis analyses indicated that the optimal molar ratios of QDs to aptamer or peptide were 1:5. Fluorescence and confocal microscope imaging revealed QD-GS24 and QD-T7 probes were able to specifically recognize B16 cells and HeLa cells respectively. Quantitative flow cytometry analysis indicated the transportation of QD-GS24 or QD-T7 into cells could be promoted by corresponding free transferrin. Transmission electron microscopy confirmed the uptake of probes in cells and the effective intracellular delivery. MTT assay suggested the cytotoxicity of probes was related to the surface ligand, and aptamer GS24 (or peptide T7) could reduce the cytotoxicity of probes to a certain degree. The study has great significance for preparing QDs fluorescent probes using non-antibody target molecules.

Fabrication of quantum dots-encoded microbeads with a simple capillary fluidic device and their application for biomolecule detection

Monodispersed quantum dots (QDs)-encoded polymer microbeads were generated using a simple capillary fluidic device (CFD). The polymer and QDs solution was emulsified into monodispersed microdroplets by the CFD and obtained droplets were solidified via solvent evaporation. Polymer microbeads can be fabricated in a range of different sizes through changing the flow rates of the two immiscible phases, and have a highly narrow size distribution and uniform shape. QDs-encoding capacity of the microbeads was investigated through adjusting the concentrations and ratios of QDs in the polymer solution. Mono-color encoded microbeads with five intensities and a dual-color QDs-encoded 5×5 microbeads array were obtained, and the spectral profiles of the microbeads were examined by a fluorescent microscope coupled with a spectral imaging system. QDs-tagged microbeads prepared with this method were more stable than the porous beads swollen with QDs in the buffer with various pH and crosslinking chemicals. Finally, the application of such microbeads for biomolecule detection was demonstrated by conjugation of rabbit IgG molecules on the surface of the microbeads via carboxyl groups, which were then detected by fluorophores-labeled goat-anti-rabbit IgG antibodies.

Development of smart nanoparticle–aptamer sensing technology

Quantum dots (QDs) are excellent donors in Förster resonance energy transfer (FRET) based sensors because of their broad absorption and narrow symmetric emission. However, the strict requirement of a short donor-acceptor distance to achieve high FRET (hence sensitivity) has posed a significant challenge for QD-FRET-based sensors due to challenges associated with the preparation of QD conjugates that are both compact and highly stable. Consequently, most robust QD-FRET sensors are often too bulky to produce FRET efficiently, especially at low target-to-QD copy numbers. They have largely relied on increasing the target:QD ratio to achieve high FRET, making them undesirable and inefficient in situations of low target:QD copy numbers. Herein we report our work on the preparation of stable, compact and water-soluble QDs and their subsequent use in making compact, functional QD-DNA-based smart nanoparticle sensors for labelled and label-free DNA and protein detection. We have developed two strategies to prepare QD-DNA sensors: 1) via QD-thiolated DNA self-assembly, and 2) via covalent coupling between DNA and a QD surface ligand functional group. We found that thiolated DNA (fluorophore labelled) can self-assemble onto a 3-mercaptopropionic acid-capped QDs to produce highly efficient FRET (~80%) at a DNA:QD ratio of 1 : 1. However, this system suffers from strong non-specific adsorption and the self-assembled single-stranded (ss) DNA target is unable to hybridise to its complementary probe. More recently, we found that a dihydrolipoic acid-capped QD-ssDNA self-assembled system can hybridise to a labelled complementary probe to produce efficient FRET that can be exploited for labelled DNA probe quantification. Further, incorporating an anti-thrombin DNA aptamer to this system leads to a QD-DNA aptamer sensor that can specifically detect a 10 nM unlabelled protein probe (thrombin). The non-specific adsorption problem can be eliminated by introducing a poly(ethylene glycol) (PEG) linker to the QD capping ligands or by capping the QD with a chelating dendritic ligand. The resulting QD-DNA sensors can specifically detect 1 nM unlabelled or 35 pM labelled DNA probes using QD-sensitised dye FRET signals on a conventional fluorimeter. Extension of the DNA target to other functional DNAs or DNA/RNA aptamers should allow the development of a multi-functional QD-DNA platform suitable for biosensing, disease diagnosis and therapeutic applications.

Preparation and Characterization of Biocompatible Quaternized Chitosan Nanoparticles Encapsulating CdS Quantum Dots

Nanoparticles were produced by encapsulating CdS quantum dots (QDs) with quaternized chitosan (N-(2- hydroxyl) propyl-3-trimethyl ammonium chitosan chloride, HTCC), in order to improve general biocompatibility and stability of pure QDs. The properties of CdS QDs encapsulated HTCC nanoparticles (HTCC/CdS QDs) can be controlled by changing the mass ratios of QD to HTCC (16:1, 8:1, 4:1, 2:1, 1:1, 1:2, 1:4, 1:8). Characterizations of HTCC/CdS QDs nanoparticles were performed using ultraviolet-visible, fluorescence spectrometry, and sizezeta analysis. As compared with nonencapsulated QDs, these HTCC/CdS QDs nanoparticles would keep their original optical properties, and greatly improve the quantum yield and stability in room temperature. The quantum yield can be improved from 9% to 23%. When the mass ratio of QD and HTCC was 1.0, the nanoparticles had the highest quantum yield (23%). After being stored for a week, the nanoparticles could still keep stable and high fluorescence intensity, while that of non-encapsulated QDs almost disappeared. In vitro 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) cytotoxicity tests on primary myoblast cells suggested that the cytotoxicity of the QDs was greatly reduced after HTCC encapsulation. Therefore, due to the increase of biocompability, HTCC/ CdS QDs nanoparticles can be potentially used in biological applications and labeling of biomolecules.

Quantum dots labeling using octa-arginine peptides for imaging of adipose tissue-derived stem cells

Quantum dots (QDs) have been used to study the effects of fluorescent probes for biomolecules and cell imaging. Adipose tissue-derived stem cells, which carry a relatively lower donor site morbidity, while yielding a large number of stem cells at harvest, were transduced with QDs using the octa-arginine peptide (R8) cell-penetrating peptide (CPP). The concentration ratio of QDs:R8 of 1 × 10 4 was optimal for delivery into ASCs. No cytotoxicity was observed in ASCs transduced with less than 16 nM of QDs655. In addition, >80% of the cells could be labeled within 1 h and the fluorescent intensity was maintained at least for 2 weeks. The ASCs transduced with QDs using R8 could be differentiated into both adipogenic and osteogenic cells, thus suggesting that the cells maintained their stem cell potency. The ASCs labeled with QDs using R8 were further transplanted subcutaneously into the backs of mice or into mice through the tail vein. The labeled ASCs could be imaged with good contrast using the Maestro in vivo imaging system. These data suggested that QD labeling using R8 could be utilized for the imaging of ASCs.

Quantum dot-based theranostics

Luminescent semiconductor nanocrystals, also known as quantum dots (QDs), have advanced the fields of molecular diagnostics and nanotherapeutics. Much of the initial progress for QDs in biology and medicine has focused on developing new biosensing formats to push the limit of detection sensitivity. Nevertheless, QDs can be more than passive bio-probes or labels for biological imaging and cellular studies. The high surface-to-volume ratio of QDs enables the construction of a "smart" multifunctional nanoplatform, where the QDs serve not only as an imaging agent but also a nanoscaffold catering for therapeutic and diagnostic (theranostic) modalities. This mini review highlights the emerging applications of functionalized QDs as fluorescence contrast agents for imaging or as nanoscale vehicles for delivery of therapeutics, with special attention paid to the promise and challenges towards QD-based theranostics.

Molecular beacon–quantum dot–Au nanoparticle hybrid nanoprobes for visualizing virus replication in living cells

Here we describe a new hybrid fluorescent nanoprobe composed of a nuclease-resistant molecular beacon (MB) backbone, CdSe-ZnS core-shell quantum dots (QDs) as donors, and gold nanoparticles (Au NPs) as quenchers, for the real-time visualization of virus replication in living cells. By using a Au NP-MB to QD ratio of 6 : 1, a 7.3-fold increase in fluorescent signal was achieved upon target binding. For living cell experiments, a hexahistidine-appended Tat peptide was self-assembled onto the QD surface to provide nearly 100% non-invasive delivery of the QD-MB-Au NP probes within 2 h. By directly visualizing the fluorescent complexes formed with the newly synthesized viral RNA, this QD-MB-Au NP probe provided sensitive and real-time detection of infectious viruses as well as the real-time visualization of cell-to-cell virus spreading.

MULTIPLEX DETECTION OF ESCHERICHIA COLI AND SALMONELLA ENTERITIDIS BY USING QUANTUM DOT‐LABELED ANTIBODIES

ABSTRACT In this study, we demonstrated the simultaneous detection of Escherichia coli and Salmonella enteritidis, by coupling immunomagnetic separation (IMS) with quantum dots (QDs) labeling. QDs having different emission wavelengths were conjugated with anti‐E. coli and anti‐Salmonella antibodies. QD–antibody conjugates were used to label immunomagnetically separated bacteria and the fluorescence intensities were measured for enumerations of both species. The concentrations of primary antibodies used in IMS, the ratio of QDs to antibodies during the conjugation and the concentration of QD–antibody conjugates used in labeling were optimized to enhance the sensitivity of the assay. After labeling bacteria with QDs, the quenching observed between bead–bacteria complex and QDs was eliminated by separating QDs from the complex using sodium dodecyl sulfate solution. The fluorescence intensities due to the capturing of different concentrations of bacteria were measured and the working ranges were found to be 5 × 102 to 5 × 105 cfu/mL for E. coli and 4 × 102 to 4 × 105 cfu/mL for S. enteritidis.PRACTICAL APPLICATIONSIn this study, antibody‐conjugated multicolor quantum dots (QDs) were used for simultaneous detection of Escherichia coli and Salmonella enteritidis. The results of this study indicate that QD labels can be used in multiplex, rapid and selective detection of bacteria with detection limits comparable with those of many novel methods in cases where the assay conditions are optimized. Furthermore, the assay can be modified for the simultaneous detection of more than two species through using QD labels having different emission wavelengths.