Xueji Zhang

Highly Sensitive Multiple microRNA Detection Based on Fluorescence Quenching of Graphene Oxide and Isothermal Strand-Displacement Polymerase Reaction

A simple, highly sensitive, and selective multiple microRNA (miRNA) detection method based on the graphene oxide (GO) fluorescence quenching and isothermal strand-displacement polymerase reaction (ISDPR) was proposed. The capability to discriminate ssDNA and double-stranded nucleic acid structure coupled with the extraordinary fluorescence quenching of GO on multiple organic dye allows the proposed strategy to simultaneously and selectively detect several miRNA labeled with different dyes in the same solution, while the ISDPR amplification endows the detection method with high sensitivity. The strong interaction between ssDNA and GO led to the fluorescent ssDNA probe exhibiting minimal background fluorescence. Upon the recognition of specific target miRNA, an ISDPR was triggered to produce numerous massive specific DNA-miRNA duplex helixes, and a strong emission was observed due to the weak interaction between the DNA-miRNA duplex helix and GO. A miRNA biosensor down to 2.1 fM with a linear range of 4 orders of magnitude was obtained. Furthermore, the large planar surface of GO allows simultaneous quenching of several DNA probes with different dyes and produces a multiple biosensing platform with high sensitivity and selectivity, which has promising application in profiling the pattern of miRNA expression and biomedical research.

Trace and Label-Free MicroRNA Detection Using Oligonucleotide Encapsulated Silver Nanoclusters as Probes

A simple, sensitive, and label-free method for microRNA (miRNA) biosensing was described using oligonucleotide encapsulated silver nanoclusters (Ag-NCs) as effective electrochemical probes. The functional oligonucleotide probe integrates both recognition sequence for hybridization and template sequence for in situ synthesis of Ag-NCs, which appears to possess exceptional metal mimic enzyme properties for catalyzing H(2)O(2) reduction. The miRNA assay employs gold electrodes to immobilize the molecular beacon (MB) probe. After the MB probe subsequently hybridizes with the target and functional probe, the oligonucleotide encapsulated Ag-NCs are brought to the electrode surface and produce a detection signal, in response to H(2)O(2) reduction. An electrochemical miRNA biosensor down to 67 fM with a linear range of 5 orders of magnitude was obtained. Meanwhile, the MB probe allows the biosensor to detect the target with high selectivity. The Ag-NCs-based approach provides a novel avenue to detect miRNA with high sensitivity and selectivity while avoiding laborious label and signal amplification. It is convinced that rational introduction of signal amplification strategy to the Ag-NCs-based bioanalysis can further improve the sensitivity. To our best knowledge, this is the first application of the electrocatalytic activity of Ag-NCs in bioanalysis, which would be attractive for genetic analysis and clinic biomedical application.

Nanomedicine: Magnetic Nanoparticles and their Biomedical Applications

During this past decade, science and engineering have seen a rapid increase in interest for nanoscale materials with dimensions less than 100 nm, which lie in the intermediate state between atoms and bulk (solid) materials. Their attributes are significantly altered relative to the corresponding bulk materials as they exhibit size dependent behavior such as quantum size effects (depending on bulk Bohr radius), optical absorption and emission, coulomb staircase behavior (electrical transport), superparamagnetism and various unique properties. They are active components of ferrofluids, recording tape, flexible disk recording media along with potential future applications in spintronics: a new paradigm of electronics utilizing intrinsic charge and spin of electrons for ultra-high-density data storage and quantum computing. They are used in a gamut of biomedical applications: bioseparation of biological entities, therapeutic drugs and gene delivery, radiofrequency-induced destruction of cells and tumors (hyperthermia), and contrast-enhancement agents for magnetic resonance imaging (MRI). The magnetic nanoparticles have optimizable, controllable sizes enabling their comparison to cells (10-100 µm), viruses (20-250 nm), proteins (3-50 nm), and genes (10-100 nm). Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) provide necessary characterization methods that enable accurate structural and functional analysis of interaction of the biofunctional particles with the target bioentities. The goal of the present discussion is to provide a broad review of magnetic nanoparticle research with a special focus on the synthesis, functionalization and medical applications of these particles, which have been carried out during the past decade, and to examine several prospective directions.

Solid-state pH nanoelectrode based on polyaniline thin film electrodeposited onto ion-beam etched carbon fiber

Abstract An ultramicro pH sensor has been constructed based on a thin polyaniline film that was electrochemically deposited onto a carbon fiber nanometer-size electrode. The substrate nanoelectrodes were fabricated using ion-beam conically etched carbon fibers with tip diameters ranging ca. from 100 to 500xa0nm. The polyaniline film was deposited from HCl solution containing the aniline monomer by cycling the potential between −0.2 and +1.0xa0V. The electromotive force (emf) signal between the pH sensitive polyaniline-coated nanoelectrode and an Ag/AgCl reference electrode was linear over the pH range of 2.0–12.5 with a slightly super-Nernstian slope of ca. −60xa0mV/pH unit. Response times ranged from several sec at pHs around 7 up to 2xa0min at pH 12.5. The proposed pH nanoelectrode displayed high ion selectivity with respect to K + , Na + , Ca 2+ , and Li + , with logxa0 K H,M values around −12 and has a working lifetime of about 20 days. Key parameters important for the pH nanoelectrode performance, including polyaniline film preparation, selectivity, response time, temperature dependence, relative coating thickness, stability, and reproducibility, have been characterized and optimized. The performance of the pH nanoelectrode was examined by measuring the pH of several real samples including body fluids (serum, urine) and low ionic strength water samples (rain, deionized and tap water). The results agreed very well with those obtained by using commercial glass pH electrodes. The proposed pH nanoelectrode demonstrated attractive properties and seems particularly promising for use under physiological conditions.

Reversible Swarming and Separation of Self-Propelled Chemically Powered Nanomotors under Acoustic Fields

The collective behavior of biological systems has inspired efforts toward the controlled assembly of synthetic nanomotors. Here we demonstrate the use of acoustic fields to induce reversible assembly of catalytic nanomotors, controlled swarm movement, and separation of different nanomotors. The swarming mechanism relies on the interaction between individual nanomotors and the acoustic field, which triggers rapid migration and assembly around the nearest pressure node. Such on-demand assembly of catalytic nanomotors is extremely fast and reversible. Controlled movement of the resulting swarm is illustrated by changing the frequency of the acoustic field. Efficient separation of different types of nanomotors, which assemble in distinct swarming regions, is illustrated. The ability of acoustic fields to regulate the collective behavior of catalytic nanomotors holds considerable promise for a wide range of practical applications.

An Integrated Nitric Oxide Sensor Based on Carbon Fiber Coated with Selective Membranes

In vivo measurement of nitric oxide (NO) in a biological matrix is very difficult because of its assumed low stability and fugacity, in addition to the complexity of such matrix, limited space and volume of biological samples. Among different NO detection strategies, electrochemical NO sensors are still widely used by NO researchers. Though many kinds of NO sensors are commercial available from World Precision Instruments, Inc. and other companies, the small NO sensors still are needed for the NO detection, especially in single cell levels. In this article a NO-selective ultramicrosensor was developed as an easily applicable tool for real time nitric oxide (NO) detection. The sensor consists of a 7u2005µm carbon fiber working electrode coated with cation exchanger (Nafion), then covered with NO-selective gas permeable polymeric membranes, and Ag/AgCl micro-reference/counter electrode. Compared with other reported NO sensors, the sensor described herein offers several advantages: i) high selectivity against ascorbate (>104:1), dopamine (>103:1) and nitrite (104:1); ii) detection limit to low nanomolar concentration; iii) rapid, inexpensive and reproducible fabrication; iv) wide linear calibration range from 10u2005nM to 5u2005µM with R2=0.995; v) integrated ultramicrosensor eliminating the need of an external reference electrode, accordingly, experiments in small volume are possible with an integrated ultramicrosensor, even at single cell levels.

Ultrasound-Modulated Bubble Propulsion of Chemically Powered Microengines

The use of an ultrasound (US) field for rapid and reversible control of the movement of bubble-propelled chemically powered PEDOT/Ni/Pt microengines is demonstrated. Such operation reflects the US-induced disruption of normal bubble evolution and ejection, essential for efficient propulsion of catalytic microtubular engines. It offers precise speed control, with sharp increases and decreases of the speed at low and high US powers, respectively. A wide range of speeds can thus be generated by tuning the US power. Extremely fast changes in the motor speed (<0.1 s) and reproducible On/Off activations are observed, indicating distinct advantages compared to motion control methods based on other external stimuli. Such effective control of the propulsion of chemically powered microengines, including remarkable braking ability, holds considerable promise for diverse applications.

Size-dependent electrochemiluminescence behavior of water-soluble CdTe quantum dots and selective sensing of L-cysteine

Water-soluble CdTe quantum dots (QDs) with five sizes (2.25, 2.50, 2.77, 3.12, and 3.26nm) were synthesized with the hydrothermal method. The electrochemiluminescence (ECL) of CdTe QDs was investigated in detail in air-saturated solution without adding foreign oxidant. It was found that the ECL of CdTe QDs displayed a size-dependent property. With the increasing in the particle size of the CdTe QDs, the ECL intensity was gradually increased, in addition, both ECL peak potentials and ECL onset potentials of CdTe QDs were shifted positively. Influences of some factors on the ECL intensity were investigated. Under the optimal conditions, the ECL intensity had a linear relationship with the concentration of l-cysteine (l-Cys) in the range from 1.3 x 10(-6) to 3.5 x 10(-5) molL(-1) (R(2) 0.996) with a detection limit of 8.7 x 10(-7) molL(-1) (S/N=3). The proposed method was applied to the determination of l-Cys in real samples with satisfactory results. Compared with previous reports, it has better selectivity for the determination of l-Cys.

Amperometric sensor for ethanol based on one-step electropolymerization of thionine-carbon nanofiber nanocomposite containing alcohol oxidase

Thionine had strong interaction with carbon nanofiber (CNF) and was used in the non-covalent functionalization of carbon nanofiber for the preparation of stable thionine-CNF nanocomposite with good dispersion. With a simple one-step electrochemical polymerization of thionine-CNF nanocomposite and alcohol oxidase (AOD), a stable poly(thionine)-CNF/AOD biocomposite film was formed on electrode surface. Based on the excellent catalytic activity of the biocomposite film toward reduction of dissolved oxygen, a sensitive ethanol biosensor was proposed. The ethanol biosensor could monitor ethanol ranging from 2.0 to 252 microM with a detection limit of 1.7 microM. It displayed a rapid response, an expanded linear response range as well as excellent reproducibility and stability. The combination of catalytic activity of CNF and the promising feature of the biocomposite with one-step non-manual technique favored the sensitive determination of ethanol with improved analytical capabilities.

Novel Calibration Method for Nitric Oxide Microsensors by Stoichiometrical Generation of Nitric Oxide from SNAP

Calibration of nitric oxide (NO) sensor is a key step to measurement of NO. Currently there are three methods to calibrate electrochemical NO sensors. However, there are many problems associated with these techniques, especially for calibration of microsensors. This article describes a novel method for calibration of NO microsensors, which has the advantage of being simple, reproducible, wide range and suitable for all kind of NO electrochemical sensors, especially for the commercial available integrated NO microsensors such as ISO-NOP30. This method is based on quantitative release of NO from decomposition of SNAP trigged by Cu+. Using of monovalant copper, as described in the present study, represents a major methodological advancement in the quantitative release of NO from SNAP. The kinetic decomposition of SNAP, effect of Cu+ concentration, pH of the solution, temperature and oxygen concentration in the solution on the release of NO are discussed. Compared with other calibration methods, this method is simple, convenient, reliable, accurate.