Li Zaijun

Nickel–cobalt double hydroxides microspheres with hollow interior and hedgehog-like exterior structures for supercapacitors

Nickel–cobalt double hydroxide microspheres (Ni–Co-DHM) have been synthesized by a facile and cost-effective in situ method. The obtained Ni–Co-DHM displays a three-dimensional architecture with hollow interior and hedgehog-like exterior structures. The unique architecture greatly improves the faradaic redox reaction and mass transfer. The Ni–Co-DHM electrode offers an excellent pseudocapacitance performance, including high specific capacitance and rate capability, good charge–discharge stability and long-term cycling life. Its maximum specific capacitance was found to be 2275.5 F g−1 at current density of 1 A g−1, which is more than 3-fold that of common nickel–cobalt double hydroxides and 2-fold that of the mechanical mixture of Co(OH)2 and Ni(OH)2 microspheres. The specific capacitance can remain at 1007.8 F g−1 when the current density increases to 25 A g−1. The capacitance can keep at least 92.9% at current density of 10 A g−1 after 5000 cycles. Therefore, this work provides a promising approach for the design and synthesis of structure tunable materials with largely enhanced supercapacitor behavior, which can be potentially applied in energy storage/conversion devices.

An ultrasensitive hydrogen peroxide biosensor based on electrocatalytic synergy of graphene–gold nanocomposite, CdTe–CdS core–shell quantum dots and gold nanoparticles

We first reported an ultrasensitive hydrogen peroxide biosensor in this work. The biosensor was fabricated by coating graphene-gold nanocomposite (G-AuNP), CdTe-CdS core-shell quantum dots (CdTe-CdS), gold nanoparticles (AuNPs) and horseradish peroxidase (HRP) in sequence on the surface of gold electrode (GE). Cyclic voltammetry and differential pulse voltammetry were used to investigate electrochemical performances of the biosensor. Since promising electrocatalytic synergy of G-AuNP, CdTe-CdS and AuNPs towards hydrogen peroxide was achieved, the biosensor displayed a high sensitivity, low detection limit (S/N=3) (3.2×10(-11) M), wide calibration range (from 1×10(-10) M to 1.2×10(-8) M) and good long-term stability (20 weeks). Moreover, the effects of omitting G-AuNP, CdTe-CdS and AuNP were also examined. It was found that sensitivity of the biosensor is more 11-fold better if G-AuNP, CdTe-CdS and AuNPs are used. This could be ascribed to improvement of the conductivity between graphene nanosheets in the G-AuNP due to introduction of the AuNPs, ultrafast charge transfer from CdTe-CdS to the graphene sheets and AuNP due to unique electrochemical properties of the CdTe-CdS, and good biocompatibility of the AuNPs for horseradish peroxidase. The biosensor is of best sensitivity in all hydrogen peroxide biosensors based on graphene and its composites up to now.

Synergistic contributions of fullerene, ferrocene, chitosan and ionic liquid towards improved performance for a glucose sensor

The paper describes an ingenious approach for the fabrication of a promising glucose sensor, GOx/C(60)-Fc-CS-IL, that exploits the synergistic beneficial characteristics of fullerene (C(60)), ferrocene (Fc), chitosan (CS) and ionic liquid (IL) for glucose oxidase (GOx). Cyclic voltammetry, impedance spectroscopy and chronoamperometry were used to evaluate performance of the biosensor, respectively. Since efficient electron transfer between GOx and the electrode was achieved, the biosensor exhibits a high sensitivity (234.67 nA nM(-1) cm(-2)), low detection limit (S/N=3) (3x10(-9) M), fast response time (0.752 s), wide calibration range (from 1x10(-8) M to 1x10(-5) M) and excellent long-term stability (30 weeks). The apparent Michaelis-Menten constant (K(M)) of GOx on the composite medium, 0.03 mM, shows high bioelectrocatalytic activity of immobilized enzyme toward glucose oxidation. Due to low operating potential (100 V), the biosensor is relatively insensitive to electroactive interfering species in human blood such as ascorbic acid, and uric acid, which are commonly found in blood samples. Excellent electrochemical reversibility, high sensitivity and stability, technically simple and possibility of preparation at short period of time are of great advantages of these glucose biosensors.

Synthesis of nitrogen-doped activated graphene aerogel/gold nanoparticles and its application for electrochemical detection of hydroquinone and o-dihydroxybenzene.

Graphene aerogel materials have attracted increasing attention owing to their large specific surface area, high conductivity and electronic interactions. Here, we report for the first time a novel strategy for the synthesis of nitrogen-doped activated graphene aerogel/gold nanoparticles (N-doped AGA/GNs). First, the mixture of graphite oxide, 2,4,6-trihydroxybenzaldehyde, urea and potassium hydroxide was dispersed in water and subsequently heated to form a graphene oxide hydrogel. Then, the hydrogel was dried by freeze-drying and reduced by thermal annealing in an Ar/H2 environment in sequence. Finally, GNs were adsorbed on the surface of the N-doped AGA. The resulting N-doped AGA/GNs offers excellent electronic conductivity (2.8 × 10(3) S m(-1)), specific surface area (1258 m(2) g(-1)), well-defined 3D hierarchical porous structure and apparent heterogeneous electron transfer rate constant (40.78 ± 0.15 cm s(-1)), which are notably better than that of previous graphene aerogel materials. Moreover, the N-doped AGA/GNs was used as a new sensing material for the electrochemical detection of hydroquinone (HQ) and o-dihydroxybenzene (DHB). Owing to the greatly enhanced electron transfer and mass transport, the sensor displays ultrasensitive electrochemical response to HQ and DHB. Its differential pulse voltammetric peak current linearly increases with the increase of HQ and DHB in the range of 5.0 × 10(-8) to 1.8 × 10(-4) M for HQ and 1 × 10(-8) to 2.0 × 10(-4) M for DHB. The detection limit is 1.5 × 10(-8) M for HQ and 3.3 × 10(-9) M for DHB (S/N = 3). This method provides the advantage of sensitivity, repeatability and stability compared with other HQ and DHB sensors. The sensor has been successfully applied to detection of HQ and DHB in real water samples with the spiked recovery in the range of 96.8-103.2%. The study also provides a promising approach for the fabrication of various graphene aerogel materials with improved electrochemical performances, which can be potentially applied in biosensors, electrocatalysis, and energy storage/conversion devices.

A sensitive and highly stable electrochemical impedance immunosensor based on the formation of silica gel–ionic liquid biocompatible film on the glassy carbon electrode for the determination of aflatoxin B1 in bee pollen

The paper describes a sensitive and highly stable label-free electrochemical impedance immunosensor for the determination of aflatoxin B(1) (AFB(1)), which is based on the formation of silica gel-ionic liquid biocompatible film on the glassy carbon electrode. The electrochemical performances of the sensor were investigated by electrochemical impedance spectroscopy using a Fe(CN)(6)(3-/4-) phosphate buffer solution as base solution for test. As new ionic liquid, 1-amyl-2,3-dimethylimidazolium hexafluorophosphate, offers a very biocompatible microenvironment for AFB(1) antibody, the sensor exhibits good repeatability (RSD=1.2%), sensitive electrochemical impedance response to AFB(1) in the range of 0.1-10 ng ml(-1) and lowers the detection limit of AFB(1) (0.01 ng ml(-1)). The electron-transfer resistance change of the sensor after and before incubation with AFB(1) of 2.0 ng ml(-1) can retain 95% over a 180-day storage period at 4 degrees C. The results present a remarkable improvement of sensitivity (2-fold) and long-term stability (190-fold) when compared to classical silica gel sensor. Moreover, proposed sensor has a high selectivity to AFB(1) alone with no significant response to AFB(2), AFG(1), AFG(2) and AFM(1) as single substrates, it has been successfully applied to the determination of trace AFB(1) in bee pollen samples with a spiked recovery in the range of 96.0-102.5%.

Nitrogen-doped multiple graphene aerogel/gold nanostar as the electrochemical sensing platform for ultrasensitive detection of circulating free DNA in human serum

Graphene aerogel has attracted increasing attention due to its large specific surface area, high-conductivity and electronic interaction. The paper reported a facile synthesis of nitrogen-doped multiple graphene aerogel/gold nanostar (termed as N-doped MGA/GNS) and its use as the electrochemical sensing platform for detection of double stranded (dsDNA). On the one hand, the N-doped MGA offers a much better electrochemical performance compared with classical graphene aerogel. Interestingly, the performance can be enhanced by only increasing the cycle number of graphene oxide gelation. On the other hand, the hybridization with GNS further enhances the electrocatalytic activity towards Fe(CN)6(3-/4-). In addition, the N-doped MGA/GNS provides a well-defined three-dimensional architecture. The unique structure make it is easy to combine with dsDNA to form the electroactive bioconjugate. The integration not only triggers an ultrafast DNA electron and charge transfer, but also realizes a significant synergy between N-doped MGA, GNS and dsDNA. As a result, the electrochemical sensor based on the hybrid exhibits highly sensitive differential pulse voltammetric response (DPV) towards dsDNA. The DPV signal linearly increases with the increase of dsDNA concentration in the range from 1.0×10(-)(21) g ml(-)(1) to 1.0×10(-16) g ml(-1) with the detection limit of 3.9×10(-22) g ml(-1) (S/N=3). The sensitivity is much more than that of all reported DNA sensors. The analytical method was successfully applied in the electrochemical detection of circulating free DNA in human serum. The study also opens a window on the electrical properties of multiple graphene aerogel and DNA as well their hybrids to meet the needs of further applications as special nanoelectronics in molecule diagnosis, bioanalysis and catalysis.

Fast synthesis of copper nanoclusters through the use of hydrogen peroxide additive and their application for the fluorescence detection of Hg2+ in water samples

Copper nanoclusters (CuNCs) have become promising nanomaterials due to their high electronic conductivity and low cost. This study reports the fast synthesis of CuNCs through the use of hydrogen peroxide (H2O2) additive and their application for the fluorescent detection of Hg2+ in water samples. Cu2+ was rapidly reduced into Cu0 in the presence of H2O2 and bovine serum albumin (BSA), further leading to the production of CuNCs. Under optimized conditions, the synthesis needs 1 h to achieve a high conversion rate of Cu2+ (more than 99%). In the resulting CuNCs, no Cu2+ can be found by the sodium sulfide test. Research on resonance light scattering, synchronous fluorescence and circular dichroism spectroscopy reveals that H2O2 may play two important roles in the synthesis of CuNCs. One role as a ligand is to combine with BSA–Cu complex to form BSA–Cu–H2O2 complex, which diminishes the reduction potential of Cu2+ and leads to the fast reduction of Cu2+ into Cu0. Another role as an oxidizing agent is to partly destroy disulfide bonds in BSA, which increases the degree of exposure of free amino groups. This results in an enhanced reduction ability of BSA towards Cu2+. Interestingly, the as-prepared CuNCs display better fluorescence intensity and optical stability when compared with the CuNCs prepared by the conventional method. The nanosensor based on the CuNCs was developed for the rapid, reliable, sensitive and selective sensing of Hg2+ with a detection limit of 4.7 × 10−12 M (S/N = 3) and a dynamic range of 1 × 10−5−1 × 10−11 M. It has been successfully used for the detection of Hg2+ in water samples.

Synthesis of double gold nanoclusters/graphene oxide and its application as a new fluorescence probe for Hg2+ detection with greatly enhanced sensitivity and rapidity

Gold nanoclusters possess outstanding physical and chemical attributes that make them excellent scaffolds for construction of chemical and biological sensors. The paper reported synthesis of double gold nanoclusters/graphene oxide (D-GNCs/GO) and its application as a new fluorescence probe for Hg2+ detection. In the study, the amine group was introduced into GO sheets through the EDC/NHS mediated reaction to form positively charged GO sheets (GO-NH3+). After GNC@Lys was mixed with GNC@BSA to form negatively charged D-GNCs, the D-GNCs was assembled on the surface of GO-NH3+ with electrostatic interaction. The study demonstrated that the interaction between GNC@Lys and GNC@BSA increases fluorescence intensity of the GNC@BSA and leads to more sensitive fluorescence response towards Hg2+, for which the sensitivity is more than 3-fold that of single GNC@BSA. The interaction between GO and GNCs accelerates the reaction of D-GNCs/GO with Hg2+, for which the reaction rate is more than 3-fold that of single D-GNCs. Owing to prominent synergistic effects between GNC@Lys, GNC@BSA and GO, the nanosensor based on the D-GNCs/GO displays a surprisingly enhanced sensitivity and rapidity for Hg2+ detection. The fluorescence peak intensity linearly decreases with increasing Hg2+ concentration in the range of 1.0 × 10−5 to 5.0 × 10−13 M with a detection limit of 1.8 × 10−13 M (S/N = 3). The analytical method presents an obvious advantage of sensitivity, rapidity and repeatability when compared with present Hg2+ optical sensors. It has been successfully applied to detection of Hg2+ in water samples. The study also opens a new avenue for fabrication of fluorescent hybrids, which holds great potential applications in sensing, spectral encoding, bioimaging and catalysis.

A free template strategy for the fabrication of nickel/cobalt double hydroxide microspheres with tunable nanostructure and morphology for high performance supercapacitors

We report a free template strategy for the fabrication of nickel/cobalt double hydroxide microspheres (Ni/Co-DHMs) in a tertbutanol–water (TBA–H2O) medium. This study demonstrates that the nanostructure and morphology of the Ni/Co-DHMs can be easily tuned by altering the ratio of TBA/H2O. When the reaction is performed in a solvent mixture with a low water content, the as-synthesized Ni/Co-DHMs form as pure nanoflakes with a good hydrotalcite structure, but increasing the ratio of water leads first to a mixture of nanoflakes and nanorods, and then increasing it further gives rise to a mixture of pure α-Co(OH)2 and α-Ni(OH)2 nanorods. In this work, three typical Ni/Co-DHM materials were prepared using TBA/H2O ratios of 9 : 1, 8 : 2 and 6 : 4. Since the unique architecture of the synthesised Ni/Co-DHM materials leads to greatly improved faradaic redox reaction and mass transfer, these Ni/Co-DHM electrodes offer high electrochemical performance for application in supercapacitors. Their specific capacities are 1800.4 F g−1, 1603.2 F g−1 and 1430.8 F g−1 at a current density of 1 A g−1, and 98.7%, 95.1% and 90.1% of these specific capacities are retained at a current density of 10 A g−1 after 3000 cycles, respectively. This study also provides a promising approach for the design and synthesis of structure tunable materials with largely enhanced electrochemical characteristics, which can be potentially applied in various energy storage/conversion devices.

Ionic Liquid as Novel Solvent for Extraction and Separation in Analytical Chemistry

Direct analysis of samples, regardless their origin, is desirable although for the majority of cases unfeasible on account of the complexity of the sample matrix, inadequate concentration of the target analytes, or even incompatibility with the detector. In these cases, a sample pretreatment step is required for interference removal and analytes separation/preconcentration. Despite valuable advances developed in separation science, the traditional solvent extraction is widely used for samples preparation. Main drawback of the solvent extraction is the requirement of large amounts of high-purity solvents that are expensive and toxic and result in the production of hazardous waste. Therefore, the search for new solvent is a key trend in solvent extraction evolution. In this sense, ionic liquid, which is ionic media resulting from the combination of organic cations and various anions, has attracted much attention taking into account their special features like: low-vapor pressure, high viscosity, dual natural polarity, good thermal stability and a wide range of miscibility with water and other organic solvents, hence many environmental and safety problems associated with organic solvents are avoided. As a result of their unique chemical and physical properties, the ionic liquid has aroused increasing interest for their promising role as alternative medium for classical solvent extraction [1-7] and organic synthesis [8-10]. Recently, ionic liquids were rapidly developed as environment-friendly acceptor phase for various microextraction to sample preparation in analytical chemistry such as liquid phase microextraction, single drop liquid phase microextraction, solid phase microextraction, dispersive liquid phase microextraction and cold induced aggregation microextraction. The microextraction with ionic liquid often exhibited better extraction efficiency and enrichment factor than that with conventional solvent extractions. Among the microextractions, dispersive liquid phase microextraction is very rapid and effective. Since the ionic liquid is dispersed completely into aqueous phase and the analytes will more easily migrate into the ionic liquid phase because of the much large contact area, the procedure for dispersive liquid phase microextraction may be complete within several minutes. In recent years, the ionic liquid extraction coupled with different analytical technology has widely been applied to determination of ultra trace analytes in water or other samples such as high performance liquid chromatography (HPLC) and gas chromatography mass spectrometry (GC-MS) for organic compounds, and flame atomic absorption spectrometry (AAS) and graphite furnace atomic absorption spectrometry (ETAAS) for metal ions. In general, the extractions with