Huimin Deng

A Highly Sensitive and Selective Electrochemical Biosensor for Direct Detection of MicroRNAs in Serum

On the basis of hybridized target microRNA (miRNA) strand initiated cleavage of hybridized deoxyribonucleic acid (DNA) capture probes (CPs) by a duplex-specific nuclease (DSN), a highly sensitive and selective label-free miRNA biosensor is developed in this article. Briefly, thiolated DNA CPs are immobilized onto a gold electrode through self-assembly. The electrode is then hybridized to a sample solution containing the target miRNA. The hybridized CPs in the miRNA-CP duplexes are simultaneously cleaved by the DSN, releasing the target miRNA strands back to the sample solution. The released target miRNA strands again hybridize with the remaining CPs on the electrode, thus forming an isothermal amplification cycle. The distinct difference in electrochemical impedance between a control and the DSN cleaved biosensor allows label-free detection of miRNA down to femtomolar levels. The mismatch discrimination ability of the DSN permits miRNA expression to be profiled with high selectivity. The exceptional amplification power of the DSN along with the simple assay protocol makes direct miRNA expression profiling possible in real-world samples with minimal or no sample pretreatments. Attempts are made in direct profiling circulating miRNAs in serum and miRNAs in total RNA extracted from cancer cells.

Gold nanoparticle-enabled real-time ligation chain reaction for ultrasensitive detection of DNA.

A simple and ultrasensitive colorimetric DNA assay based on the detection of the product of a ligation chain reaction (LCR) and the use of gold nanoparticles (AuNPs) as signal generators has been developed. During LCR, the AuNPs were ligated together, resulting in a distinct color change in real time after a sufficient number of thermal cycles. The cumulative nature of the protocol produced a detection limit of 20 aM with a selectivity factor of 10(3).

Nanoparticulate Peroxidase/Catalase Mimetic and Its Application

Ru sitting comfortably: Ruthenium oxide nanoparticles show bienzyme-like activities, and are capable of catalyzing H(2)O(2) disproportionation at pH 7.0 and peroxidation at pH 4.0 in aqueous solutions (see scheme). Their specific activities are better than many natural catalases and peroxidases and far better than bifunctional catalase/peroxidases.

A real-time colorimetric assay for label-free detection of microRNAs down to sub-femtomolar levels.

A real-time colorimetric assay utilizing gold nanoparticle networks and a duplex-specific nuclease (DSN) for label-free detection of microRNAs is proposed. Excellent sensitivity and selectivity were accomplished through the engagement of the DSN and a cumulative signal amplification process.

A highly sensitive microRNA biosensor based on hybridized microRNA-guided deposition of polyaniline.

On the basis of hybridized microRNA (miRNA)-guided deposition of polyaniline (PAn), a highly sensitive impedimetric miRNA biosensor is developed in this report. Briefly, a gold electrode coated with charge neutral peptide nucleic acid (PNA) capture probes (CPs) is first hybridized to a target miRNA. After a very brief rinsing the hybridized electrode is incubated in pH 3.0 of 0.10 M potassium phosphate buffer-based cocktail containing aniline, H2O2, and a G-qudraplex-hemin DNAzyme. The DNAzyme catalyzes the polymerization of aniline and the hybridized miRNA strands guide the deposition of PAn, thus resulting in the formation of a thin PAn film on the biosensor surface. Electron-transfer impeding power of the PAn film in alkaline medium is utilized to determine the concentration of the target miRNA. Under optimized experimental conditions, 0.50 fM target miRNA is successfully detected. Excellent mismatch discrimination capability of the biosensor was observed largely due to the excellent hybridization selectivity of the PNA CPs. Attempts were made in profiling miRNAs in total RNA samples extracted from cancer cells and blood.

Colorimetric detection of single-nucleotide polymorphisms with a real-time PCR-like sensitivity

Coupling gold nanoparticle-based ligation to a ligation chain reaction enables colorimetric detection of single-nucleotide polymorphisms with a real-time PCR-like sensitivity. One mutant in 2000 copies of a wild-type gene can be detected in 20-100 pg of PCR-amplified genomic DNA samples.

An electronic sensor array for label-free detection of single-nucleotide polymorphisms.

A highly sensitive and selective electronic sensor array for label-free detection of single-nucleotide polymorphisms (SNPs) is described in this work. Its sensing mechanism relies on building target DNA-templated silver nanowires (conductive paths) across a nanogap. Following hybridization with a SNP target, a cocktail of nucleases is applied to the nanogap sensor array. Free capture probes (CPs) and imperfectly hybridized CPs are digested while the perfectly hybridized CPs are covalently joined together over the nanogap at the mutation site. Detection of SNPs down to 0.10 fM is realized by measuring the conductance of the nanogap after a simple DNA metallization step. The engagement of the nucleases grants the nanogap sensor excellent ability to discriminate against mismatched sequences and allows hybridization to be carried out at very low stringency (room temperature), enabling a highly selective approach for SNP genotyping. And hybridization at low stringency ensures that all targets will be preferably hybridized at equilibrium. A selectivity factor of 3000 is observed when a mixture of a wild-type and a mutated gene is analyzed by the sensor array. Attempts are made in applying the sensor array to the detection of SNPs in DNA samples extracted from tissues and cultured cells.

Synthesis of polyaniline via DNAzyme-catalyzed polymerization of aniline

In this report, a novel method for the synthesis of polyaniline in aqueous medium, based on a G-quadruplex DNAzyme-catalyzed oxidation and polymerization of aniline by hydrogen peroxide in the presence of a polyanionic template, is described. The synthesis is simple and the experimental conditions are mild. The polymerization of aniline is carried out in an acidic aqueous medium with a catalytic amount of the DNAzyme. It was found that aniline polymerization occurs in a pH range from 2.0 to 5.0 with an optimal pH of 3.0. The polymerization kinetics can be described by the classical Michaelis–Menten reaction mechanism. Comparing to the horseradish peroxidase-catalyzed polymerization of aniline, the advantages of using the DNAzyme as the catalyst in the polymerization of aniline are cost-effectiveness and greater tolerance to the acidity of the reaction solution and high concentrations of hydrogen peroxide.

pH-dependent selective ion exchange based on (ethylenediamintetraacetic acid-nickel)-layered double hydroxide to catalyze the polymerization of aniline for detection of Cu 2+ and Fe 3+

A pH-dependent selective ion exchange coupled with catalytic polymerization of aniline has been developed for sensitive detection of copper (Cu2+) and ferric ions (Fe3+). Ethylenediamintetraacetic acid (EDTA) chelated with nickel ion (Ni2+) were intercalated in a layered double hydroxide via a co-precipitation reaction. The product was subsequently applied as sorbent for the enrichment of Cu2+ at pH 6.5 and Fe3+ at pH 4.5. Since both Cu2+ and Fe3+ have stronger complex formation constants with EDTA, Ni2+ exchanges with Cu2+/Fe3+ selectively. The resulting sorbent containing Cu2+/Fe3+ was transferred to catalyze the aniline polymerization reaction, since Cu2+/Fe3+ could be released by the sorbent effectively at different pH values and have high catalytic abilities for the polymerization reaction. The resulting polyaniline with different colors were produced at different pH values, an observation that was utilized to distinguish between the colorimetric signals of Cu2+ and Fe3+. The extraction temperature, extraction time, catalysis time and pH were optimized. The results showed that this method provided low limits of detection of 0.1 nM (6.4 ng/L) for Cu2+, 1 nM (56 ng/L) for Fe3+, wide linear ranges (0.0005-2.5 µM, and 0.005-5 µM, respectively), and good linearities (r2 values of 0.9904, and 0.9965, respectively). The optimized method was applied to river water samples. Using Cu2+/Fe3+ as examples, this work provided a new and interesting approach for the convenient and efficient detection of metal ions in aqueous samples.

Synthesis and anticancer properties of a novel bis-intercalator.

A series of naphthalene diimide (ND)-based mono-, bis-, and tris-intercalators are synthesized and evaluated for their anticancer activities. All compounds show anticancer activities in the micromolar range. Among them the bis-intercalator is the most promising. Experimental results indicate that (i) target compounds intercalate DNA and (ii) the bis-intercalator with the optimal linker shows considerably more affinity to DNA than corresponding mono-and tris-intercalators. Spectroscopic measurements indicate that the ND groups bind to the double-stranded DNA (ds-DNA) in a classical threading intercalation mode, while the cationic linker reinforces the intercalation via electrostatic interaction with ds-DNA. In vitro cytotoxicity of the bis-intercalator towards a number of cancer cells, such as C6, HeLa, and MDA-435S, is tested and compared to that of normal cells. Attractive anticancer activity is observed with the bisintercalator, which provides a new lead in the anticancer drug design strategy.