Development of carbon dot based microplate and microfluidic chip immunoassay for rapid and sensitive detection of HIV-1 p24 antigen

A highly sensitive, precisely specific, environmentally friendly, high-throughput, microwell-plate and microchip-based sandwich assay was developed to detect HIV-1 p24 antigen, a protein biomarker using fluorescent carbon dots. High quantum yield carbon dots were synthesized using citric acid and ethylenediamine as carbon and nitrogen sources by a single-step hydrothermal reaction. The desired amine groups confirmed by FTIR on the carbon dots were coupled to streptavidin by amine–amine coupling reaction using glutaraldehyde. The detection range of the carbon dot based immunoassay (CDIA) was found to be between 20 and 1000 pg/mL in a linear dose-dependent manner. CDIA tested for HIV negative plasma samples showed no false positive results in the detection of HIV-1 p24 antigen. The CDIA was extended to develop a microfluidic carbon dot immunoassay (μCDIA) which exhibited analytical sensitivity in the range of 30–1000 pg/mL. The CDIA and μCDIA can easily be adapted to a lab-on-a-chip platform for use in resource limited settings and can also be multiplexed for the detection of other pathogens like TB and Hepatitis.     

Microfluidic platforms for discovery and detection of molecular biomarkers

Microfluidics has emerged as a promising platform for discovery and detection of molecular biomarkers recently. With this approach, the discovery of these biomarkers could be more efficient in time and consumes less samples and reagents. Furthermore, the entire discovery process could be automated since all the functional microfluidic devices such as micropumps and microvalves could be integrated on a single chip. Similarly, the detection of the discovered molecular biomarkers is also promising. Detection of nucleic acid biomarkers, protein biomarkers, and metabolite biomarkers has been demonstrated on microfluidic platforms recently. When compared with their large-scale counterparts, the miniature system can perform the detection of these biomarkers within less analysis time while a multiplexed detection scheme could be easily achieved. Furthermore, the entire detection process could be automated on the single chip as well. This review paper is therefore to review the recent development of microfluidic devices and systems for the discovery and detection of the molecular biomarker. Techniques for biomarker discovery, verification, and detection that have been adapted into microfluidics were first reviewed, and their advantages were highlighted. The new approach of biomarker screening based on in vitro-generated affinity reagents such as nucleic acid aptamers and peptide affinity reagents was then reviewed. Finally, in the biomarker detection section, this review placed a special emphasis on commercialized microfluidic-based diagnostics for molecular biomarkers.     

Microfluidic aptameric affinity sensing of vasopressin for clinical diagnostic and therapeutic applications

We present a microfluidic aptameric biosensor, or aptasensor, for selective detection of clinically relevant analytes with integrated analyte enrichment, isocratic elution and label-free detection by mass spectrometry. Using a microfluidic platform that is coupled to matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS), we demonstrate specific purification, enrichment, and label-free detection of trace amounts of arginine vasopressin (AVP), a peptide hormone that is responsible for arterial vasoconstriction. During extreme physical trauma, in particular immunological shock or congestive heart failure, AVP is excreted abnormally and is hence a biomarker for such conditions. The device uses an aptamer, i.e., an oligonucleotide that binds specifically to an analyte via affinity interactions, to achieve highly selective analyte capture and enrichment. In addition, via thermally induced reversible disruption of the aptamer-analyte binding, the device can be easily regenerated for reuse and allows isocratic analyte elution, i.e., release and collection of analytes using a single aqueous solution. Furthermore, the device is coupled to MALDI-MS using a microfluidic flow gate, which directs the eluted analyte onto a MALDI sample plate for mass spectrometry. We first perform systematic characterization of kinetic and thermal release properties, as well as the overall timescale of the assay, using fluorescently labeled AVP. We then demonstrate MALDI-MS detection of unlabeled AVP at clinically relevant concentrations approaching 1 pM.     

Fluorescence-profile pre-definable quantum-dot barcodes in liquid-core microcapsules

Microparticles incorporated with quantum-dot (QD) barcodes for multiplexed bioassays attract a great attention due to their potential applications in drug discovery, gene profiling and clinic diagnostics. However, the existing QD barcodes lack a necessary optical stability to ambient fluids or a repeatability of fluorescent profiles. We developed a new QD barcode by loading an aqueous QD mixture as a liquid core into a monodispersed polymer microcapsule by a microfluidic method to avoid those problems. We found that the QDs in the liquid cores were able to maintain their original characteristics, especially the linear relation between photoluminescence intensity and concentration. In addition, we found that the fluorescent profiles of the QD-loaded liquid cores were the same as those of the QD mixtures before being loaded inside the microcapsules. With these two properties, the QD barcodes can be predefined directly by multiplexing the emission peaks and concentrations of the QDs in the liquid cores. Furthermore, the graphical information from fluorescent images of the microcapsules, such as the sizes and numbers of the QD-loaded liquid cores, offers another dimension for barcoding to increase the coding capacity. We also presented a microfluidic method to manufacture the QD-barcoded microcapsules of size ~30?μm. These pre-definable QD barcodes with stable fluorescent profiles can be used as a platform for various high-throughput screening applications in different bioassay buffers.     

High color purity emission from quantum dots by optimizing the full width at half the maximum and optical density to blue light

In this paper, we got wide color gamut of quantum dot (QD) films by optimizing the spectra width and optical density (OD) of quantum dots. The specific methods to achieve the following: QD R: one layer of color filter R film was coated below the QD R layer. QD G: one layer of yellow‐green film was coated below the QD G film. By a structure optimal design, we got wide color gamut up to 99.2% BT2020 (equal to 132.86% NTSC) in Cd‐based QD and 93.6% BT2020 (equal to 125.35% NTSC) in Cd‐free QD. Furthermore, the gamut of QD display will continue to be improved by continuous refining the structure of QD display.     

A novel integrated microfluidic platform based on micro-magnetic sensor for magnetic bead manipulation and detection

We present a novel integrated microfluidic platform based on micro-magnetic sensor for manipulating and detecting magnetic beads (MB). A micro-spiral planar coil in MB manipulating system microfabricated by micro-electro-mechanical system technology is implemented to manipulate MB, and a giant magnetoimpedance (GMI) based micro-magnetic sensor is employed to detect the trapped MB. In our work, MB can be efficiently trapped by trapping force generated from micro-coil in microchannel. Next, trapped MB are detected by the changing ratio of impedance, as well as the variation of resistance and reactance in GMI sensor for trapped MB induce weak stray magnetic field under the magnetization by external magnetic field. The maximum difference of GMI ratio between with beads condition and without beads condition is 4.0% at the optimum driving frequency of 20 MHz under the external magnetic field of 15 Oe, and resistance ratio varies more significantly than reactance ratio. In comparison with traditional MB detecting methods by GMI sensor, the integrated microfluidic platform based on GMI sensor can not only manipulate and detect MB signal sensitively, but also enhance detection efficiency and decrease the experiment errors. Furthermore, this platform avoids contamination from the solutions in chemically reactive layers and reduces assay time in future biomarker detection. In our work, the microfluidic platform based on GMI sensor has potential applications in biomarker detection via MB manipulation and detection.     

Toward high‐resolution,inkjet‐printed,quantum dot light‐emitting diodes for next‐generation displays

We have investigated the possibility of fabricating quantum dot light‐emitting diodes (QLEDs) using inkjet printing technology, which is the most attractive method for the full‐color patterning of QLED displays. By controlling the quantum dot (QD) ink formulation and inkjet printing condition, we successfully patterned QLED pixels in the 60‐in ultrahigh definition TV format, which has a resolution of 73 pixels per inch. The inkjet‐printed QLEDs exhibited a maximum luminance of 2500 cd/m². Although the performance of inkjet‐printed QLEDs is low compared with that of QLEDs fabricated using the spin‐coating process, our results clearly indicate that the inkjet printing technology is suitable for patterning QD emissive layers to realize high‐resolution, full‐color QLED displays.     

分子信标研究进展

分子信标是一种新型核酸探针,它在核酸检测中具有高特异性、高选择性和高灵敏度,取得了广泛的应用.该文主要介绍了分子信标的原理,一些新型的分子信标的结构及其优缺点和潜在的应用前景,并对分子信标的应用领域做了一个简单的介绍.     

High‐efficiency quantum dot light‐emitting diodes with blue cadmium‐free quantum dots

We report outstanding electroluminescence properties of high‐efficiency blue cadmium‐free quantum dot light‐emitting diodes (QD‐LED). External quantum efficiency (EQE) of 14.7% was achieved for QD‐LED emitting at 428 nm. Furthermore, we developed high‐efficiency and narrow wavelength emission zinc selenide (ZnSe) nanocrystals emitting at 445 nm and achieved QD‐LED with an EQE of 10.7%. These new QDs have great potential to be used in next‐generation QD‐LED display with wide color gamut.     

Sensitive electrochemical immunosensor for the detection of cancer biomarker using quantum dot functionalized graphene sheets as labels

Quantum dot (QD) functionalized graphene sheets (GS) were prepared and used as labels for the preparation of sandwich-type electrochemical immunosensors for the detection of a cancer biomarker (i.e., prostate specific antigen (PSA)). The primary anti-PSA antibody was also immobilized onto the GS. The immunosensor displayed a wide range of linear response (0.005-10 ng/mL), low detection limit (3 pg/mL), and good reproducibility, selectivity and stability. The immunosensor was used to detect PSA in patient serum samples with satisfactory results. Thus, this unique immunosensor may provide many applications in clinical diagnosis.     

Heat‐ and water‐proof quantum dot/siloxane composite film: Effect of quantum dot–siloxane linkage

We report on the effect of linkage between quantum dot (QD) and siloxane matrix by preparing two different QD/siloxane films. One has chemical linkages between QD and siloxane matrix, and the other has no chemical linkages between QD and siloxane matrix. The QD/siloxane (methacryl) film, which has the chemical linkages, exhibits no degradation of photoluminescence (PL) quantum yield (QY) under heat or moisture condition for over 1 month, while the QD/siloxane (epoxy) film, which has no linkages, shows drastic decreased of PL QY. The chemical linkages between QD and siloxane matrix that makes effective siloxane passivation layer intact on the surface of QDs in QD/siloxane (methacryl) film. Given its exceptional stability with the help of linkages between QD and siloxane matrix, we expect that the QD/siloxane (methacryl) film is best fitted in PL‐type down‐conversion layer for display applications.     

Phonon Dephasing of the Exciton in InAs/GaAs Quantum Dots

The interaction of a exciton confined in a semiconductor quantum dot (QD) with bulk phonons (acoustical and optical) responsible for the exciton dephasing is studied. The decoherence of the exciton due to the creation of a polaron with long-living or decaying phonons is described. Characteristic dephasing times for an InAs/GaAs QD are estimated using Green function methods in order to determine fundamental time limitations for use of the QD exciton in quantum information processing.Presented at the 36th Symposium on Mathematical Physics, ‘Open Systems & Quantum Information’, Toruń, Poland, June 9-12, 2004.     

The effect of electric field on an asymmetric quantum dot qubit

On the condition of strong electron–LO phonon coupling in an asymmetric quantum dot (QD), we study the eigenenergies and eigenfunctions of the ground and the first excited states under an applied electric field by using variational method of Pekar type. This QD system may be used as a two-level qubit. When the electron is in the superposition state of the ground and the first excited states, we obtain the time evolution of the electron probability density, which oscillates in the QD. It is found that due to the presence of the 3-D anisotropic harmonic potentials in the transverse and longitudinal directions of the QD, the electron probability density shows double-peak configuration, whereas there is only one peak if the confinement is 2-D symmetric in the x- and y-directions. The oscillation period is an increasing function of the transverse and longitudinal effective confinement lengths of the QD, and decreases with respect to the electron–phonon coupling strength and the electric field.     

Maskless formation of chromatic-pattern barcodes in two-component microcapsules

We developed a microfluidic method to form chromatic-pattern barcodes without using photomasks as photolithography methods. Two different aqueous quantum dot solutions were loaded as liquid-state cores to form two-component microcapsules, which present as chromatic patterns under UV illumination for barcoding. This microfluidic method highly simplifies the formation of patterns without using any expensive alignment instruments and allows creating the easily discernible pattern-type barcodes with a high coding capacity up to tens of thousands. The easily discernible chromatic-pattern barcodes with a small size down to 40 μm are very promising to conduct multiplexed biomolecular assays under microscopes in general labs.     

A microfluidic based differential plasmon resonance sensor

A new type of differential surface plasmon (SPR) sensor integrated with a microfluidic system is presented. The working principle of the microfluidic device is based on hydrodynamic modulation of two laminar streams inside a microchannel to provide periodic changes of the environment on the SPR sensor. The modulated reflectance is then demodulated using a lock-in amplifier. The presented sensor provides sensitivities of index of refraction about 4 × 10⁻⁸ RIU together with a 4 orders of magnitude dynamic range. This method demonstrates a sensitive detection scheme which could be used for label-free detection.     

Active matrix QD‐LED with top emission structure by UV lithography for RGB patterning

We have developed full colour top emitting quantum dot light‐emitting diode (QD‐LED) display driven by a 176‐ppi active matrix of metal oxide thin‐film transistors. Red, green and blue (RGB) QD‐LED subpixel emission layers are patterned by our original UV photolithography process and materials. We also demonstrate the potential to achieve high resolution such as 528 ppi using this process.     

Spin-Based Quantum Information Processing in Magnetic Quantum Dots

We define the qubit as a pair of singlet and triplet states of two electrons in a He-type quantum dot (QD) placed in a diluted magnetic semiconductor (DMS) medium. The molecular field is here essential as it removes the degeneracy of the triplet state and strongly enhances the Zeeman splitting. Methods of qubit rotation as well as two-qubit operations are suggested. The system of a QD in a DMS is described in a way which allows an analysis of the decoherence due to spin waves in the DMS subsystem.on leave from Institute of Physics, Odessa UniversityPresented at the 36th Symposium on Mathematical Physics, “Open Systems & Quantum Information”, Toruń, Poland, June 9–12, 2004.     

Color tuning of indium phosphide quantum dots for cadmium‐free quantum dot light‐emitting devices with high efficiency and color saturation

Semiconductor quantum dots (QDs) promise facile color tuning and high color saturation in quantum‐dot light‐emitting devices (QD‐LEDs) by controlling nanoparticle size and size distribution. Here, we demonstrate how this promise can be practically realized for the cadmium‐free InP/ZnSe/ZnS multishell quantum dots. We developed a set of synthesis conditions and core/shell compositions that result in QDs with green, yellow, and red emission color. The QD‐LEDs employing these QDs show efficient electroluminescence (EL) with luminance up to 1800 cd/m² and efficiency up to 5.1 cd/ A . The color coordinates calculated from the EL spectra clearly demonstrate the outstanding color saturation as an outcome of the narrow particle size distribution. These results prove that the performance gap between cadmium‐free and cadmium‐based QDs in QD‐LEDs is shrinking rapidly.     

微流控芯片技术在心肌标志物检测中的应用综述

心肌标志物的检测异常,是急性心肌梗死的重要诊断指标之一。对心肌标志物的监测可直接影响心血管疾病患者的临床诊断、危险分层、治疗方案选择和预后判断。微流控芯片集进样、预处理、分离和检测于一体,具有样品需求量小、便携、分析快速等特点,是理想的心肌标志物检测平台。文章根据检测方法的不同,综述了近年来利用微流控芯片平台对心肌标志物的检测。已有检测方法中主要是光学和电学方法。随着传感器技术的发展,更多检测方法被采用。通过及时的综述概括,既可对已有技术和方法起到归纳作用,又可促进微流控芯片在心肌标志物即时诊断领域的发展。     

A numerical method for exact diagonalization of semiconductor quantum dot model

An approach to the exact diagonalization of many-electron Hamiltonian in semiconductor quantum dot (QD) structures is proposed. The QD model is based on 3D finite hard-wall confinement potential and nonparabolic effective-mass approximation (EMA) that render analytical basis functions such as Laguerre polynomials inaccessible for the numerical treatment of this kind of models. In this approach, the many-electron wave function is expanded in a basis of Slater determinants constructed from numerical wave functions of the single-electron Hamiltonian with the nonparabolic EMA which results in a cubic eigenvalue problem from a finite difference discretization. The nonlinear eigenvalue problem is solved by using the Jacobi-Davidson method. The Coulomb matrix elements in the many-electron Hamiltonian are obtained by solving Poisson's problems via GMRES. Numerical results reveal that a good convergence can be achieved by means of a few single-electron basis states.