Xingfen Liu

Unmodified gold nanoparticles as a colorimetric probe for potassium DNA aptamers

Unmodified gold nanoparticles effectively differentiate unfolded and folded DNA, thus providing a novel approach to colorimetrically probe aptamer-based recognition processes.

The synthesis of shape-controlled MnO2/graphene composites via a facile one-step hydrothermal method and their application in supercapacitors

Novel MnO2 petal nanosheet and nanorod/graphene composites are successfully fabricated by a facile one-step hydrothermal method through changing the content of the Mn source. The formation mechanism of different morphologies of MnO2/graphene composites have been studied. The structure of the MnO2/graphene is “sandwich”-like, with MnO2 petal nanosheets and nanorods homogeneously anchored on each side of the graphene. Furthermore, the MnO2/graphene composites with different shapes can be used for supercapacitor electrode materials. The experimental results show that the MnO2 petal nanosheet/graphene composite has better capacitance performance than that of the MnO2 nanorod/graphene composite. The MnO2 petal nanosheet/graphene composite shows excellent specific capacitance as high as 516.8 F g−1 at a scan rate of 1 mV s−1 in 1 M Na2SO4 electrolyte and good long-term cycle stability, indicating its potential application to act as a promising electrode material for high-performance supercapacitors. This study provides a facile and in situ method to prepare metal oxide/graphene composite materials and a novel scaffold to construct other metal oxides with graphene for energy storage.

Gold nanoparticle-decorated MoS2 nanosheets for simultaneous detection of ascorbic acid, dopamine and uric acid

An electrochemical sensor has been developed for simultaneous detection of dopamine (DA), uric acid (UA) and ascorbic acid (AA) based on a gold nanoparticle-decorated MoS2 nanocomposite (AuNPs@MoS2) modified electrode. The AuNPs@MoS2 nanocomposite has been synthesized by electrodeposition of AuNPs on the MoS2 nanosheets, which possesses better properties than pure AuNPs and MoS2. The AuNPs@MoS2 film modified electrode showed excellent electrocatalytic activity toward the oxidation of AA, DA and UA with three well-resolved oxidation peaks. The peak separation of AA–DA, DA–UA and AA–UA is 151 mV, 137 mV and 288 mV, respectively, which permits the modified electrode to individually or simultaneously analyze AA, DA and UA by differential pulse voltammetry (DPV). Under optimum conditions, the AuNPs@MoS2 modified electrode exhibits linear response toward AA, DA and UA in the range of 50–100 000 μM, 0.05–30 μM and 50–40 000 μM, respectively. Moreover, the MoS2-based modified electrode was successfully employed to determine DA in human serum samples with satisfactory results.

Creating SERS Hot Spots on MoS2 Nanosheets with in Situ Grown Gold Nanoparticles

Herein, a reliable surface-enhanced Raman scattering (SERS)-active substrate has been prepared by synthesizing gold nanoparticles (AuNPs)-decorated MoS2 nanocomposite. The AuNPs grew in situ on the surface of MoS2 nanosheet to form efficient SERS hot spots by a spontaneous redox reaction with tetrachloroauric acid (HAuCl4) without any reducing agent. The morphologies of MoS2 and AuNPs-decorated MoS2 nanosheet were characterized by TEM, HRTEM, and AFM. The formation of hot spots greatly depended on the ratio of MoS2 and HAuCl4. When the concentration of HAuCl4 was 2.4 mM, the as-prepared AuNPs@MoS2-3 nanocomposite exhibited a high-quality SERS activity toward probe molecule due to the generated hot spots. The spot-to-spot SERS signals showed that the relative standard deviation (RSD) in the intensity of the main Raman vibration modes (1362, 1511, and 1652 cm(-1)) of Rhodamine 6G were about 20%, which displayed good uniformity and reproducibility. The AuNPs@MoS2-based substrate was reliable, sensitive, and reproducible, which showed great potential to be an excellent SERS substrate for biological and chemical detection.

The self-assembly of shape controlled functionalized graphene–MnO2 composites for application as supercapacitors

Graphene–MnO2 nanocomposites with different morphologies were obtained by a facile self-assembly method. The formation mechanism of graphene–MnO2 composites with different shapes of MnO2 is discussed in detail. Nanostructured MnO2 with different morphologies was distributed on the surface of graphene uniformly. The prepared graphene–MnO2 composites could be used as electrode materials for supercapacitors. The graphene–MnO2 (flowerlike nanospheres) composite (405 F g−1) exhibited better capacitive performance than that of the graphene–MnO2 (nanowires) composite (318 F g−1) at a current density of 1.0 A g−1. The synergistic effect of graphene and MnO2 endowed the composite with high electrochemical capacitance. Moreover, the graphene–MnO2 (flowerlike nanospheres) composite showed a fast charge–discharge process and high cyclic stability.

DNA-conjugated quantum dot nanoprobe for high-sensitivity fluorescent detection of DNA and micro-RNA.

Herein, we report a convenient approach to developing quantum dots (QDs)-based nanosensors for DNA and micro-RNA (miRNA) detection. The DNA-QDs conjugate was prepared by a ligand-exchange method. Thiol-labeled ssDNA is directly attached to the QD surface, leading to highly water-dispersible nanoconjugates. The DNA-QDs conjugate has the advantages of the excellent optical properties of QDs and well-controlled recognition properties of DNA and can be used as a nanoprobe to construct a nanosensor for nucleic acid detection. With the addition of a target nucleic acid sequence, the fluorescence intensity of QDs was quenched by an organic quencher (BHQ2) via Förster resonance energy transfer. This nanosensor can detect as low as 1 fM DNA and 10 fM miRNA. Moreover, the QDs-based nanosensor exhibited excellent selectivity. It not only can effectively distinguish single-base-mismatched and random nucleic sequences but also can recognize pre-miRNA and mature miRNA. Therefore, the nanosensor has high application potential for disease diagnosis and biological analysis.

DNA biosensors based on water-soluble conjugated polymers.

Conjugated polymers (CPs) with large, delocalised molecular structures exhibit unique optical and electrochemical characteristics that can be used as excellent sensing elements. Recently, research on chemical and biological sensors that use water-soluble CPs as transducers has generated intense interest. Two main sensing mechanisms are used for the detection of DNA-related events, such as hybridisation, mismatch, single nucleotide polymorphism (SNP), SNP genotyping, conformational changes, and cleavage of the nucleic acids. One mechanism takes advantage of the fluorescence resonance energy transfer (FRET) between CPs and a chromophore label on the nucleic acid probes in which a series of cationic polyfluorene, polythiophene and polyarylene derivatives are frequently used. The other mechanism relies on the conformational effects of CPs, which is induced by combination of the specific targets in which cationic polythiophene derivatives are often used. The electron transfer property of CPs are always used to design high sensitive electrochemical DNA biosensors. Here we review recent progress in the development of optical and electrochemical DNA biosensors based on water-soluble CPs.

Optical study on the size effects in BaTiO3 thin films

To study the size effects in ferroelectric thin film, we measured the optical transmittance and Raman spectra in BaTiO3 thin films deposited by the rf-magnetron sputtering technique on fused quartz and (111) Si substrates. A variation in the energy gap and Raman peaks with film thickness and grain size was observed and the possible origin was analyzed.

Synthesis of a graphene/polyaniline/MCM-41 nanocomposite and its application as a supercapacitor

A ternary nanocomposite of graphene/polyaniline (PANI)/porous silica MCM-41 (MCM-41) was prepared by a hydrothermal method. The amount of graphene oxide (GO) in the graphene/PANI/MCM-41 nanocomposite had a strong effect on the supercapacitor performance. The experimental results showed that the specific capacitance of the graphene/PANI/MCM-41 nanocomposite could reach the highest value when the GO content was 50%. The specific capacitance of the nanocomposite was 405 F g−1 at a current density of 0.8 A g−1. Furthermore, over 91.4% of the original capacitance was retained after repeating the galvanostatic charge–discharge for 1000 cycles. The performance of the prepared supercapacitor containing different amounts of GO were studied in detail.

Monodispersed grafted conjugated polyelectrolyte-stabilized magnetic nanoparticles as multifunctional platform for cellular imaging and drug delivery

An anionic grafted conjugated polyelectrolyte was synthesized, and then magnetic nanoparticles stabilized with this material were successfully prepared by a convenient method and used for bioimaging and drug delivery. Grafted conjugated polymer (PFPAA) containing abundant carboxyl groups was attached to the surface of Fe3O4 nanoparticles through ligand exchange with oleic acid and anionic grafted conjugated polyelectrolyte-stabilized magnetic nanoparticles (MNPs@PFPANa) were then obtained by ionization with sodium carbonate. These as-synthesized nanoparticles showed good water solubility and stability, with no precipitation observed in 8 months, and had a narrow size distribution with a mean hydrodynamic diameter of 26 ± 2.4 nm. In addition, these nanoparticles exhibited superparamagnetic properties with a saturation magnetization (Ms) of 20 emu g-1, which sufficient for bioapplications. Upon 48 h incubation with macrophage cells, the obtained nanoparticles showed good biocompatibility of 2 pg Fe per cell as measured by ICP-OES. Furthermore, MNPs@PFPANa were low toxicity as confirmed by an MTT assay using NIH-3T3 fibroblasts. Confocal microscopy results revealed that MNPs@PFPANa can be retained in cytoplasm with high fluorescence. MNPs@PFPANa exhibited good DOX drug loading efficiency of about 10 wt% and showed good therapeutic efficiency for BGC-823 cancer cells. These results indicated such multifunctional nanoparticles would be useful in bioimaging and as drug carriers for cancer treatment.