Jianyuan Dai

Hierarchically porous nickel oxide nanosheets grown on nickel foam prepared by one-step in situ anodization for high-performance supercapacitors.

Porous NiO nanosheets are successfully grown on nickel foam substrate through an in situ anodization by using molten KOH as the electrolyte. High-purity NiO is directly obtained by this one-step method without any subsequent treatment. The obtained NiO supported on nickel foam is used as a binder-free electrode for a supercapacitor and its pseudocapacitive behavior has been investigated by cyclic voltammetry and galvanostatic charge-discharge tests in a 6 M aqueous solution of KOH. Electrochemical data demonstrates that this binder-free electrode possesses ultrahigh capacitance (4.74 F cm(-2) at 4 mA cm(-2)), excellent rate capability, and cycling stability. After 1000 cycles, the areal capacitance value is 9.4 % lower than the initial value and maintains 85.4 % of the maximum capacitance value.

Unusual sequence length-dependent gold nanoparticles aggregation of the ssDNA sticky end and its application for enzyme-free and signal amplified colorimetric DNA detection

It is known that the adsorption of short single-stranded DNA (ssDNA) on unmodified gold nanoparticles (AuNPs) is much faster than that for long ssDNA, and thus leads to length-dependent AuNPs aggregation after addition of salt, the color of the solutions sequentially changed from red to blue in accordance with the increase of ssDNA length. However, we found herein that the ssDNA sticky end of hairpin DNA exhibited a completely different adsorption behavior compared to ssDNA, an inverse blue-to-red color variation was observed in the colloid solution with the increase of sticky end length when the length is within a certain range. This unusual sequence length-dependent AuNPs aggregation might be ascribed to the effect of the stem of hairpin DNA. On the basis of this unique phenomenon and catalytic hairpin assembly (CHA) based signal amplification, a novel AuNPs-based colorimetric DNA assay with picomolar sensitivity and specificity was developed. This unusual sequence length-dependent AuNPs aggregation of the ssDNA sticky end introduces a new direction for the AuNPs-based colorimetric assays.

Target-catalyzed autonomous assembly of dendrimer-like DNA nanostructures for enzyme-free and signal amplified colorimetric nucleic acids detection.

Self-assembly of DNA nanostructures is of great importance in nanomedicine, nanotechnology and biosensing. Herein, a novel target-catalyzed autonomous assembly pathway for the formation of dendrimer-like DNA nanostructures that only employing target DNA and three hairpin DNA probes was proposed. We use the sticky-ended Y shape DNA (Y-DNA) as the assembly monomer and it was synthesized by the catalyzed hairpin assembly (CHA) instead of the DNA strand annealing method. The formed Y-DNA was equipped with three ssDNA sticky ends and two of them were predesigned to be complementary to the third one, then the dendrimer-like DNA nanostructures can be obtained via an autonomous assembly among these sticky-ended Y-DNAs. The resulting nanostructure has been successfully applied to develop an enzyme-free and signal amplified gold nanoparticle (AuNP)-based colorimetric nucleic acids assay.

Target-triggered autonomous assembly of DNA polymer chains and its application in colorimetric nucleic acid detection

A novel target-triggered DNA autonomous assembly pathway for the formation of one-dimensional DNA polymer chains was proposed based on the catalyzed hairpin assembly and sticky end self-assembly, which led to an enzyme-free and signal amplified gold nanoparticle (AuNP) based colorimetric nucleic acid assay with picomolar sensitivity and specificity.

Nucleotide base analog pyrrolo-deoxycytidine as fluorescent probe signal for enzyme-free and signal amplified nucleic acids detection

In the present work, an enzyme-free and signal amplified nucleic acids detection method based on the fluorescent nucleotide base analog pyrrolo-deoxycytidine (P-dC) and catalyzed hairpin assembly (CHA) has been developed. In the CHA signal amplification system, two hairpin auxiliary probes, H1 and H2, which containing a fluorescent P-dC at the end of the stem, respectively, were used as the fluorescent probes. The fluorescence of P-dC in H1 and H2 was quenched owing to the stacking interaction among the bases in the stem. In the presence of the target DNA, the catalytic assembly of H1 and H2 was triggered and the target could be released during the helix DNA H1-H2 complex formation process, then the released target was used to trigger another reaction cycle. In the H1-H2 complex, P-dC was located in the flexible single-stranded DNA (ssDNA) sticky ends instead of the rigid stem, thus resulting in the increase of fluorescence. The cycling use of the target in the CHA system amplified the fluorescence signal, and the detection limit of this method was obtained as 19pM, which is 3 orders of magnitude sensitive than the conventional fluorescent nucleotide base analogs based approach without CHA signal amplification.

N-Doped carbon dots: green and efficient synthesis on a large-scale and their application in fluorescent pH sensing

A green and efficient anhydrous strategy was developed for one-step synthesis of nitrogen-doped carbon dots (N-CDs) using sucrose and urea as carbon and nitrogen source, respectively. The reaction was carried out at ambient pressure by directly adding the mixture of sucrose and urea powder into heated edible oil. N-CDs could be generated in several minutes and were obtained by facile separation of the edible oil, which could be reused. This is therefore a green method and suitable for the synthesis of N-CDs on a large-scale. The as synthesized N-CDs possessed higher photostability, excellent optical properties and ultra-low cytotoxicity. Noticeably, the N-CDs exhibited a distinct pH-sensitive feature, and their fluorescent intensity increased linearly in the pH range from 6.75 to 11.0. Therefore, the as synthesized N-CDs can be used to construct pH fluorescent sensor, and the successful pH monitoring of environmental water samples demonstrates their applicability in complex matrixes. Our work would open up a new avenue for the green and convenient synthesis of high-performance heteroatom-doped materials on a large-scale.

Surfactant-free gold nanoparticles: rapid and green synthesis and their greatly improved catalytic activities for 4-nitrophenol reduction

It is highly desired but still remains a key challenge to develop a simple and green strategy for greatly improving the catalytic activity of catalysts. In this communication, surfactant-free gold nanoparticles (sf-AuNPs) were quickly synthesized (<30 s) using reductive carbon dots (r-CDs) instead of traditional surfactants; this is the fastest strategy for sf-AuNP synthesis based on r-CDs without using a strong reductant and protective agent. Whats more, the catalytic activity of sf-AuNPs/r-CDs for the 4-nitrophenol reduction is greatly improved due to the surfactant-free properties and the synergistic effects of AuNPs and r-CDs. Our work would open up a new avenue for the design of catalyst materials with high performance and catalytic activity.

Self-assembly of DNA nanoparticles through multiple catalyzed hairpin assembly for enzyme-free nucleic acid amplified detection

It is known that DNA molecules can be used to build a various of complicated geometrical DNA nanostructures with programmable sequence design, and these DNA nanomaterials show a promising application in biotechnology and biomedicine. However, the construction of large-sized three dimensional DNA-based nanomaterials still remains a challenge. In this work, we propose a new strategy that only employs one target DNA to trigger multiple catalyzed hairpin assembly (CHA) reactions and sticky ends self-assembly to prepare hundreds of nanometer-sized DNA nanoparticles. Moreover, the obtained DNA nanoparticles can be served as efficient biosensors for sensitive colorimetric nucleic acids detection with a detection limit of 7.7pM.

Rapid DNA detection based on self-replicating catalyzed hairpin assembly using nucleotide base analog pyrrolo-deoxycytidine as fluorophore

A rapid signal amplified DNA detection method based on self-replicating catalyzed hairpin assembly (SRCHA) has been proposed. In this SRCHA system, two split target DNA sequences were respectively integrated into hairpin auxiliary probes H1 and H2. H2 was used as fluorescent probe which containing a fluorescent nucleotide base analog pyrrolo-deoxycytidine (P-dC) at the end of the stem. Target DNA can be circularly used in this SRCHA system to form the helix DNA H1-H2 complex, the structure change of H2 will move P-dC from hairpin stem to flexible ssDNA sticky end, leading to fluorescence increase due to the less stacking interaction. Meanwhile, the two spilt target DNA sequence was reunited and the target DNA replicate was obtained, which also can be circularly used as new activator to trigger additional CHA reaction and fluorescence signal was then rapidly and significantly enhanced. This SRCHA system has been successfully employed for DNA detection with picomolar within around 15min, and provides a potential technology for the real-time rapid bioanalysis.

Self-Replicating Catalyzed Hairpin Assembly for Rapid Signal Amplification

A rapid signal amplification system based on the self-replicating catalyzed hairpin assembly is reported in which two hairpins, H1 and H2, were well-designed in which two split target/trigger DNA and two split G-quadruplex sequences were respectively integrated into H1 and H2. Target/trigger DNA can be cyclically used in this system to form the duplex DNA assemblies (H1-H2), which will bring the two G-quadruplex fragments into close-enough proximity to induce the formation of intact G-quadruplex as a colorimetric signal readout. Similarly, the two split target/trigger DNA sequences will reunite into a DNA sequence that is identical to the target/trigger DNA; then, the obtained replica can also be cyclically used as a new activator unit to trigger the CHA reaction, leading to the rapidly and significantly enhanced formation of target/trigger DNA replicas with the concomitant generation of a higher signal. This self-replication-based autocatalytic signal amplified approach has been successfully used to develop a rapid and visual assay for DNA and small molecule detection.