Xinghu Ji

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 micromol/L) and the limit of detection (S/N=3) was 0.2 microg/mL (0.48 micromol/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.

Simultaneous Determination of Human Enterovirus 71 and Coxsackievirus B3 by Dual-Color Quantum Dots and Homogeneous Immunoassay

Human Enterovirus 71 (EV71) and Coxsackievirus B3 (CVB3) have high risks for morbidity and mortality. A virus quantitation immunoassay has been proposed by employing two colored quantum dots (QDs), antibodies of the virus, and graphene oxide (GO). The QDs are streptavidin-conjugated quantum dots (SA-QDs), and the antibodies are biotinylated antibodies. Biotinylated EV71 antibody (Ab1) was associated with 525 nm green colored SA-QDs via biotin-streptavidin interaction forming QDs-Ab1, whereas biotinylated CVB3 antibody (Ab2) was associated with 605 nm red colored SA-QDs via biotin-streptavidin interaction forming QDs-Ab2. GO was an excellent quencher to the fluorescence of both QDs-Ab1 and QDs-Ab2. The targets of EV71 and CVB3 can break up the complex of QDs-Ab and GO, recovering the fluorescence of QDs-Ab1 and QDs-Ab2, respectively. Using these two different colored QDs-Ab fluorescence recovery intensities upon the addition of targets EV71 and CVB3, the two enteroviruses can be simultaneously quantitatively determined with a single excitation light. The detection limits of EV71 and CVB3 are 0.42 and 0.39 ng mL(-1) based on 3 times signal-to-noise ratio, respectively. More importantly, this strategy can be further used as a universal method for any protein or virus determination by changing the conjugated antibodies in disease early diagnosis, which can provide a fast and promising clinical approach for virus differentiation and determination. In a word, a simple, fast, sensitive, and highly selective assay for EV71 and CVB3 has been developed. It could be applied in clinical sample analysis with a satisfactory result. It was notable that the sensor could not only achieve rapid and precise quantitative determination of protein/virus by fluorescent intensity but also could be applied in semiquantitative protein/virus determination by digital visualization.

Determination of glucose and uric acid with bienzyme colorimetry on microfluidic paper-based analysis devices

In this work, we first employ a drying method combining with the bienzyme colorimetric detection of glucose and uric acid on microfluidic paper-based analysis devices (μPADs). The channels of 3D μPADs are also designed by us to get better results. The color results are recorded by both Gel Documentation systems and a common camera. By using Gel Documentation systems, the limits of detection (LOD) of glucose and uric acid are 3.81 × 10(-5)M and 4.31 × 10(-5)M, respectively one order of magnitude lower than that of the reported methods on μPADs. By using a common camera, the limits of detection (LOD) of glucose and uric acid are 2.13 × 10(-4)M and 2.87 × 10(-4)M, respectively. Furthermore, the effects of detection conditions have been investigated and discussed comprehensively. Human serum samples are detected with satisfactory results, which are comparable with the clinical testing results. A low-cost, simple and rapid colorimetric method for the simultaneous detection of glucose and uric acid on the μPADs has been developed with enhanced sensitivity.

One-pot synthesized aptamer-functionalized CdTe:Zn2+ quantum dots for tumor-targeted fluorescence imaging in vitro and in vivo.

High quality and facile DNA functionalized quantum dots (QDs) as efficient fluorescence nanomaterials are of great significance for bioimaging both in vitro and in vivo applications. Herein, we offer a strategy to synthesize DNA-functionalized Zn(2+) doped CdTe QDs (DNA-QDs) through a facile one-pot hydrothermal route. DNA is directly attached to the surface of QDs. The as-prepared QDs exhibit small size (3.85 ± 0.53 nm), high quantum yield (up to 80.5%), and excellent photostability. In addition, the toxicity of QDs has dropped considerably because of the Zn-doping and the existence of DNA. Furthermore, DNA has been designed as an aptamer specific for mucin 1 overexpressed in many cancer cells including lung adenocarcinoma. The aptamer-functionalized Zn(2+) doped CdTe QDs (aptamer-QDs) have been successfully applied in active tumor-targeted imaging in vitro and in vivo. A universal design of DNA for synthesis of Zn(2+) doped CdTe QDs could be extended to other target sequences. Owing to the abilities of specific recognition and the simple synthesis route, the applications of QDs will potentially be extended to biosensing and bioimaging.

Determination of clenbuterol by capillary electrophoresis immunoassay with chemiluminescence detection.

A competitive immunoassay for clenbuterol (CLB) based on capillary electrophoresis with chemiluminescence (CL) detection was established. The method was based on the competitive reaction of horseradish peroxidase (HRP)-labeled CLB (CLB-HRP) and free CLB with anti-CLB antiserum. The factors affecting the electrophoresis and CL detection were systematically investigated with HRP as a model sample. Under the optimal conditions, the tracer CLB-HRP and the immunoassay complex were separated, and the linear range and the detection limit (S/N=3) for CLB were 5.0-40nmoll(-1) and 1.2nmoll(-1), respectively. The proposed method has been applied satisfactorily in the analysis of urine sample.

Droplet electric separator microfluidic device for cell sorting

A simple and effective droplet electric separator microfluidic device was developed for cell sorting. The aqueous droplet without precharging operation was influenced to move a distance in the channel along the electric field direction by applying dc voltage on the electrodes beside the channel, which made the target droplet flowing to the collector. Single droplet can be isolated in a sorting rate of ∼100 Hz with microelectrodes under a required pulse. Single or multiple mammalian cell (HePG2) encapsulated in the surfactant free alginate droplet could be sorted out respectively. This method may be used for single cell operation or analysis.

On-demand preparation of quantum dot-encoded microparticles using a droplet microfluidic system

Optical barcoding technology based on quantum dot (QD)-encoded microparticles has attracted increasing attention in high-throughput multiplexed biological assays, which is realized by embedding different-sized QDs into polymeric matrixes at precisely controlled ratios. Considering the advantage of droplet-based microfluidics, producing monodisperse particles with precise control over the size, shape and composition, we present a proof-of-concept approach for on-demand preparation of QD-encoded microparticles based on this versatile new strategy. Combining a flow-focusing microchannel with a double T-junction in a microfluidic chip, biocompatible QD-doped microparticles were constructed by shearing sodium alginate solution into microdroplets and on-chip gelating these droplets into a hydrogel matrix to encapsulate CdSe/ZnS QDs. Size-controllable QD-doped hydrogel microparticles were produced under the optimum flow conditions, and their fluorescent properties were investigated. A novel multiplex optical encoding strategy was realized by loading different sized QDs into a single droplet (and thus a hydrogel microparticle) with different concentrations, which was triggered by tuning the flow rates of the sodium alginate solutions entrapped with different-colored QDs. A series of QD-encoded microparticles were controllably, and continuously, produced in a single step with the present approach. Their application in a model immunoassay demonstrated the potential practicability of QD-encoded hydrogel microparticles in multiplexed biomolecular detection. This simple and robust strategy should be further improved and practically used in making barcode microparticles with various polymer matrixes.

One‐Pot Synthesized DNA–CdTe Quantum Dots Applied in a Biosensor for the Detection of Sequence‐Specific Oligonucleotides

In the past decade, as a new class of fluorescent probes, semiconductor quantum dots (QDs) have been widely applied in the area of biosensing, immunoassays, and biological imaging because of their unique optical characteristics and biocompatibility. In these applications, a number of biomolecule-labeled QDs were devoted to biospecific interactions, such as DNA-labeled QDs. These QDs can be usually used as a donor for molecular recognition mainly in fluorescence resonance energy transfer (FRET). The coupling reaction between streptavidin QDs and biotin–DNA is a common approach for DNA-labeled QDs for the streptavidin–biotin specific reaction. The method is convenient, but it has no advantage in FRET application, due to increasing the distance between the donor (the large size of the QD) and the acceptor. Furthermore, streptavidin QDs are expensive. DNA covalent bonding to QDs by reaction between the carboxy/amino group of QDs and amino/carboxy group modified DNA could overcome these flaws; however; the acidic coupling conditions may lead to the breakdown of the QDs, which limits its application. Zhou et al. directly coupled a dye-labeled DNA acceptor to a QD donor through a thiol linker. This method costs less, significantly reduces the donor–acceptor distance to increase the FRET efficiency, and at the same time retains the stability of the QDs . However, the process is multistep and complicated. A one-step synthesis of DNA-labeled QDs has been established in such an environment. Phosphorothiolate phosphate (ps–po) DNA compounds were used as ligands to obtain DNA-labeled QDs. Herein, we have synthesized nucleic acid functionalized CdTe nanocrystals with different emission wavelengths by a one-step synthesis. Recently, new emerging zero-bandgap carbon nanomaterials, graphene, and graphene oxide (GO) have attracted great interest in the fields of biology, chemistry, physics, and materials. Graphene and GO have p-systems, which allows them very easily to accept electrons. Inspired by the property, researchers have used graphene and GO as energy acceptors to develop many biosensors based on the FRET system. Importantly, graphene and GO possess a superquenching ability that is critical for the sensitivity of assays. In addition, graphene displays better conductivity than GO, because GO has many oxygen-containing groups, which destroy the conjugate structure. Thus, graphene was chosen as the energy acceptor in this paper. A biosensor, which is based on FRET from the DNA-functionalized CdTe nanocrystals to graphene, has been developed, that is, DNA–CdTe QDs prepared by a one-pot method, and its successful application in the analytical detection of the hepatitis B virus (HBV) surface–antigen gene is described for the first time. Scheme 1 shows the preparation of DNA–CdTe QDs by a one-pot method. Glutathione (GSH) and a specific-sequence DNA were used as a co-ligands to stabilize the QDs. The DNA ligand consisted of two domains: phosphorothio-

Valve-based microfluidic device for droplet on-demand operation and static assay

A valve-based microfluidic device was developed for droplet on-demand operation and static assay. Droplet generation with precise and expectant volume, transportation, fusion, and trapping was achieved by integration of microvalves with programed control. Based on this automatic unique function combination, a droplet team was created with a controllable proportion of components. A DNA sample was encapsulated into the aqueous droplets, selectively merged with probe droplet in the desired ratio, well mixed, and then trapped for the static fluorescence assay with a total reagent consumption of no more than 2 μl. This method would have a powerful potential for biochemical or chemical research.A valve-based microfluidic device was developed for droplet on-demand operation and static assay. Droplet generation with precise and expectant volume, transportation, fusion, and trapping was achieved by integration of microvalves with programed control. Based on this automatic unique function combination, a droplet team was created with a controllable proportion of components. A DNA sample was encapsulated into the aqueous droplets, selectively merged with probe droplet in the desired ratio, well mixed, and then trapped for the static fluorescence assay with a total reagent consumption of no more than 2 μl. This method would have a powerful potential for biochemical or chemical research.

Multifunctional Dumbbell-Shaped DNA-Templated Selective Formation of Fluorescent Silver Nanoclusters or Copper Nanoparticles for Sensitive Detection of Biomolecules.

In this work, a multifunctional template for selective formation of fluorescent silver nanoclusters (AgNCs) or copper nanoparticles (CuNPs) is put forward. This dumbbell-shaped (DS) DNA template is made up of two cytosine hairpin loops and an adenine-thymine-rich double-helical stem which is closed by the loops. The cytosine loops act as specific regions for the growth of AgNCs, and the double-helical stem serves as template for the CuNPs formation. By carefully investigating the sequence and length of DS DNA, we present the optimal design of the template. Benefiting from the smart design and facile synthesis, a simple, label-free, and ultrasensitive fluorescence strategy for adenosine triphosphate (ATP) detection is proposed. Through the systematic comparison, it is found that the strategy based on CuNPs formation is more sensitive for ATP assay than that based on AgNCs synthesis, and the detection limitation was found to be 81 pM. Whats more, the CuNPs formation-based method is successfully applied in the detection of ATP in human serum as well as the determination of cellular ATP. In addition to small target molecule, the sensing strategy was also extended to the detection of biomacromolecule (DNA), which illustrates the generality of this biosensor.