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High-frequency quartz crystal microbalance biosensing platforms were constructed using an aptamer and antibody as bioreceptors for fast and label-free SARS-CoV-2 RBD assay.

Highly sensitive and selective microRNA (miRNA) assay is of great significance for disease diagnosis and therapy. Herein, a magnetic-assisted electrochemistry (EC)-photoelectrochemistry (PEC) dual-mode biosensing platform was developed for miRNA-210 detection based on dual-signaling EC and photocurrent-polarity-switching PEC strategies. Porous magnetic Fe3O4 octahedra with a large surface area were synthesized by calcining Fe-based metal-organic frameworks. Subsequently, the magnetic photoelectric materials (Fe3O4@CdS) were developed by the successive ionic layer adsorption and reaction method in Cd2+ and S2- solutions. Then, the self-assembled DNA nanoprisms contained three thiols/hanging arms that could capture miRNA-210 efficiently and were anchored to the Fe3O4@CdS octahedra via the Cd-S bond. When miRNA-210 was present, the double-stranded DNA concatemers [the self-assembled duplex helixes based on a pair of methylene blue (MB)-labeled single-stranded DNAs (AP1 and AP2) through the hybridization chain reaction and then intercalated with adriamycin (Dox) into their grooves] were connected with the Fe3O4@CdS-DNA nanoprisms. MB and Dox not only acted as the electrochemical probes but also synergistically switched the photocurrent polarity of the Fe3O4@CdS octahedra. Thus, miRNA-210 was assayed sensitively and selectively via the proposed EC-PEC dual-mode biosensing platform. Additionally, the abovementioned recognition steps occurred in a homogeneous system, and the effects of the impurities and interferences on the miRNA-210 assay could be easily avoided by magnetic separation due to the good magnetic properties of Fe3O4 octahedra. The proposed EC-PEC dual-mode biosensing platform showed a wide range of potential applications in bioanalysis and early diagnosis of disease.

Herein, an electrochemical (EC)-photoelectrochemical (PEC) dual-mode biosensor was constructed for cytokeratin 19 fragment 21-1 (CYFRA21-1) assay based on the dual-signaling electrochemical ratiometric strategy and "on-off-on" PEC method. The indium tin oxide (ITO) electrode was modified by 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA)@C60 and gold nanoparticles (Au NPs), and the double-stranded DNA composed of thiol/methylene blue (MB)-labeled single-stranded DNA (ssDNA) (S0-MB) and antibody/ferrocene (Fc)-labeled ssDNA (Ab1-S1-Fc) was immobilized on the Au NPs/PTCDA@C60/ITO electrode via the Au-S bond between Au NPs and thiol of S0-MB. With the help of another antibody-labeled ssDNA (Ab2-S2), the presence of CYFRA21-1 triggered a typical antigen-antibody sandwich immune reaction (Ab1, CYFRA21-1, and Ab2) and proximity hybridization between Ab1-S1-Fc and Ab2-S2. This caused the release of Ab1-S1-Fc from the modified electrode and the change of S0-MB to a hairpin structure, resulting in a decrease (an increase) of the oxidation peak current of Fc (MB) and an increase of the photocurrent due to the enhancing (inhibiting) effect of MB (Fc) on the photoelectric performance of the Au NPs/PTCDA@C60/ITO electrode. Thus, CYFRA21-1 was detected by the developed EC-PEC dual-mode sensing platform sensitively, and the linear response ranges of 0.001-40 ng/mL with a detection limit of 0.3 pg/mL for the EC technique and 0.0001-4 ng/mL with a detection limit of 0.03 pg/mL for the PEC method were obtained. Furthermore, by changing the specific antibodies of disease-related biomarkers, the developed dual-mode biosensing platform could be readily extended to detect other antigens, implying its great potential applications in biological analysis and early disease diagnosis.

As a significant biomarker of prion diseases, ultrasensitive assay of infectious isoform of prion (PrPSc) is highly desirable for early diagnostics of prion diseases. Herein, taking normal cellular form of prion (PrPC) as a model owing to a high risk of pathogenicity of PrPSc, a new photoelectrochemical immunosensor has been developed based on hemin-induced switching of photocurrent direction. In the presence of PrPC, nitrogen-doped porous carbon-hemin polyhedra labeled with secondary antibody were introduced onto the CdS-chitosan (CS) nanoparticles-modified indium–tin oxide (ITO) electrode via the antigen–antibody specific recognition. Because of the matched energy level between CdS and hemin, the high-efficiency switch of photocurrent direction of the ITO/CdS-CS photoelectrode from anodic to cathodic photocurrent was observed even at very low concentration (0.4 aM) of PrPC. Through changing the specific antibody, this method can be easily expanded to PrPSc assay. Such low detectable limit is very useful in the early diagnosis and screening of prion diseases. The developed method has also promising applications in bioanalysis, disease diagnostics, and clinical biomedicine.

N-enriched porous carbon materials represent a kind of effective electrocatalysts for oxygen reduction reaction (ORR), which have received extensive attention owing to their low-cost, advantageous catalytic activity and stability. However, exploring non-noble-metal catalysts for replacing high-cost notable metal catalysts remains a major challenge. Herein, iron and sulfur co-doped N-enriched hierarchical porous carbon polyhedron (NC) derived from metal-organic framework (Fe/S-NC) was successfully prepared by a facile strategy, including a direct pyrolyzation of zeolitic imidazolium framework (ZIF-8) and a further pyrolysis of the impregnated NC with Fe(SCN)3 solution. Electron microscopic studies showed that Fe/S co-doping has not changed the polyhedron morphology of NC. The resulted Fe/S-NC demonstrated obviously enhanced ORR activity, excellent durability and methanol tolerance in both alkaline and acidic media. The half-wave potential of the Fe/S-NC exhibited 32 mV positive shift in 0.1 M KOH, and only 25 mV negative shift in 0.5 M H2SO4, respectively, as compared to that of the commercial Pt/C (20% Pt loading) catalyst. The superior performance is attributable to the combined roles of the unique hierarchical porous structure of NC and the Fe/S co-doping by endowing Fe/S-NC with great specific surface area, rich active sites, excellent conductivity and synergistic effect between Fe-Nx-C active sites and a thiophene-like structure (C-S-C).

In this paper, we demonstrate a two-step method to transform Co-Co Prussian blue analogue (PBA) nanocubes into porous and hollow CoS2 nanocubes. The morphology and microstructures of the synthesized CoS2 hollow nanocubes were investigated by scanning electron microscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, X-ray diffraction, and automatic micropore physisorption analyzer. Electrochemical capacitive properties of the synthesized CoS2 hollow nanocubes were characterized by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge tests in alkaline aqueous solution (2 M KOH). Results show that the porous CoS2 nanocubes have hollow and mesoporous structure with high specific surface area (113.9 m2 g−1), and show a high specific capacitance of 936 F g−1 at the current density of 1 A g−1. Also, the CoS2 hollow nanocubes possess good power characteristics (the capacitance retention is 73.3% from 1 A g−1 to 20 A g−1) and good long-term cycling life with 83% specific capacitance retention after 5000 cycles at 5 A g−1. Additionally, an asymmetric supercapacitor (ACS) was assembled by using CoS2 on carbon cloth and activated carbon (AC) on carbon cloth as the positive and negative electrodes, respectively. The prepared ACS shows a high energy density of 34.68 Wh kg−1 at the power density of 356.9 W kg−1, 25.74 Wh kg−1 remained at a power density of 7336.8 W kg−1, and excellent rate performance (the capacitance retention is 74.2% from 0.5 to 10 A g−1). These indicate that the CoS2 hollow nanocubes are good candidates for the next-generation high performance supercapacitor electrode materials.

Nitrogen doped porous carbon nanopolyhedra (N-PCNPs) were prepared from direct carbonization of ZIF-8 nanopolyhedra. The N-PCNPs showed uniform morphology, narrow pore-size distribution centered at 3.7 nm, high surface area (2221 m2 g−1) and good electrochemical properties and were used to modify a glassy carbon electrode to electrochemically detect ascorbic acid (AA), dopamine (DA) and uric acid (UA). Compared with the bare GC electrode and reduced graphene oxide modified glassy carbon (rGO/GC) electrode, the N-PCNPs modified GC electrode (N-PCNPs/GC) was found to perform better toward electrocatalytic oxidation of AA, DA and UA. For simultaneous sensing of three analytes, three well-separated voltammetry peaks were obtained using the N-PCNPs/GC electrode in differential pulse voltammetry measurements, and the corresponding peak separations between AA and DA, DA and UA were 228 mV, 124 mV respectively. The linear response ranges for the determination of AA, DA and UA were 80–2000 μM, 0.5–30 μM and 4–50 μM, respectively, and the detection limits (S/N = 3) were 740 nM, 11 nM and 21 nM, respectively. Furthermore, the N-PCNPs/GC electrode showed good reproducibility and stability. The attractive features of N-PCNPs provided potential applications in the simultaneous determination of UA, AA and DA.

In this work, a simple and “signal-off” photoelectrochemical (PEC) immunosensor for prion protein detection was developed taking 3‑Mercaptopropionic acid (MPA)-capped CdTe quantum dots as photocathodic materials and support for the immobilization of antibody (Ab 1 ) of prion protein. In the presence of prion protein, the bioconjugates of secondary antibody (Ab 2 )-gold nanoparticles-glucose oxidase (Ab 2 -AuNPs-GOx) was introduced to the electrode surface due to the specific interaction between prion and its antibodies (Ab 1 and Ab 2 ). Under the addition of glucose, GOx catalyzed the oxidation of glucose and the reduction of the dissolved oxygen to in-situ generates hydrogen peroxide which could deteriorate the PEC properties of MPA-CdTe quantum dots. The consumption of the dissolved oxygen and the deterioration of the PEC properties of the photocathodic materials (MPA-CdTe quantum dots) result in the decrease of the photocurrent of the PEC platform. Under the optimal conditions, the developed PEC immunosensor could be used for sensitive assay of prion protein and showed two linear response ranges from 1 pg mL −1 to 50 pg mL −1 and from 50 pg mL −1 to 1000 pg mL −1 with the detection limit of 0.73 pg mL −1 (3σ). Moreover, this method could be easily generalized for the assay of other proteins by altering the related antibodies, implying its promising applications in bioanalysis and disease diagnostics.

In this work, high-performance non-enzymatic catalysts based on 3D hierarchical hollow porous Co3O4 nanododecahedras in situ decorated on carbon nanotubes (3D Co3O4-HPND/CNTs) were successfully prepared via direct carbonizing metal-organic framework-67 in situ grown on carbon nanotubes. The morphology, microstructure, and composite of 3D Co3O4-HPND/CNTs were characterized by scanning electron microscopy, transmission electron microscopy, micropore and chemisorption analyzer, and X-ray diffraction. The electrochemical characterizations indicated that 3D Co3O4-HPND/CNTs present considerably catalytic activity toward glucose oxidation and could be promising for constructing high-performance electrochemical non-enzymatic glucose sensors and glucose/O2 biofuel cell. When used for non-enzymatic glucose detection, the 3D Co3O4-HPND/CNTs modified glassy carbon electrode (3D Co3O4-HPND/CNTs/GCE) exhibited excellent analytical performance with high sensitivity (22.21 mA mM−1 cm−2), low detection limit of 0.35 μM (S/N = 3), fast response (less than 5 s) and good stability. On the other hand, when the 3D Co3O4-HPND/CNTs/GCE worked as an anode of a biofuel cell, a maximum power density of 210 μW cm−2 at 0.15 V could be obtained, and the open circuit potential was 0.68 V. The attractive 3D hierarchical porous structural features, the large surface area, and the excellent conductivity based on the continuous and effective electron transport network in 3D Co3O4-HPND/CNTs endow 3D Co3O4-HPND/CNTs with the enhanced electrochemical performance and promising applications in electrochemical sensing, biofuel cell, and other energy storage and conversion devices such as supercapacitor.

Taking ZnO nanorods as a template, N-doped and porous carbon sheets (NPCS) were obtained by high-temperature carbonization and KOH activation of ZIF-8@ZnO hybrids. The morphology, structure and elemental composition of the as-obtained NPCS were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and N2 adsorption analyzer. The NPCS showed a large specific surface area (1190 m2 g− 1), high specific capacitance of 290 F g− 1 at current density of 1 A g− 1, and superior charge–discharge cycle stability (the capacitance retains 94% after 10,000 cycles at a high current density of 20 A g− 1). Furthermore, the NPCS//NPCS two-electrode symmetric supercapacitor also showed high energy density and power density, and excellent rate performance of 81.9% capacitance retention when the current density was increased from 0.5 to 50 A g− 1. These suggested the great potential applications of NPCS in high-performance electrochemical supercapacitors.

Herein, a new electrochemical aptamer-based biosensor for highly sensitive assay of thrombin has been developed based on the dual-signaling electrochemical ratiometric method and the DNA walker strategy, and shows a low detection limit of about 56 fM.

The sensitive and specific determination of nucleic acids is very important in clinical diagnosis and biological studies. In this work, an ultrasensitive photoelectrochemical (PEC) biosensor has been developed for DNA detection based on a "signal-on" sensing strategy and a three-stage cascade signal amplification method (catalytic hairpin assembly (CHA), hybridization chain reaction (HCR) and alkaline phosphatase (ALP)-triggered in situ generation of ascorbic acid (AA)). Here, CHA hairpin 1 (CHA-HP1) is opened by the target DNA (T-DNA) owing to the hybridization between T-DNA and CHA-HP1, and then the opened CHA-HP1 hybridizes with CHA hairpin 2 (CHA-HP2) to displace the T-DNA, generating a CHA-HP1/CHA-HP2 complex. The displaced T-DNA triggers the next cycle of CHA, resulting in the generation of numerous CHA-HP1/CHA-HP2 complexes. Subsequently, one end of the CHA-HP1/CHA-HP2 complex hybridizes with the capture DNA immobilized on the indium tin oxide/TiO2/CdS : Mn electrode. After the introduction of dual-biotin labeled HCR hairpin 1 (HCR-HP1-Bio) and dual-biotin labeled HCR hairpin 2 (HCR-HP2-Bio), the other end of the CHA-HP1/CHA-HP2 complex opens HCR-HP1-Bio. The opened HCR-HP1-Bio triggers the HCR reaction between HCR-HP1-Bio and HCR-HP2-Bio, leading to the formation of long nicked duplex DNA structures. The dual-biotin modified HCR-hairpins can anchor more streptavidin-ALP to catalyze 2-phospho-l-ascorbic acid trisodium salt to yield more AA, leading to a larger PEC response. The proposed PEC biosensor shows superior analytical performance for T-DNA detection with a linear response ranging from 0.1 fM to 100 pM and a detection limit of 0.052 fM, and may provide a powerful biosensing platform for bioanalysis and early disease diagnosis.

Herein, a photocurrent polarity switching platform for highly selective assay of mucin 1 (MUC1) was developed based on target-induced hemin transfer from ZrO2 hollow spheres (ZrO2 HSs) to G-quadruplex nanowires (G wires). In this system, SiO2 spheres were used as templates to synthesize the uniform and mesoporous ZrO2 HSs. As nanocontainers, ZrO2 HSs could load hemin in its cavity via pores. Then, the aptamers of MUC1, as bio-gates, blocked the pores of ZrO2 HSs based on the specific binding of Zr4+ and the phosphate groups of aptamer. In the presence of MUC1, the aptamer could specifically recognize and bind with MUC1, and then leave away from the surface of ZrO2 HSs, which resulted in the opening of the bio-gates and releasing of hemin. Assisted with the G wires formed on the Au NPs/In2S3/ITO, the released hemin was captured on the electrode through the formation of hemin/G-quadruplex structure, leading to the switch of the photocurrent polarity of the electrode from anodic photocurrent to cathodic photocurrent. The proposed photoelectrochemical biosensor showed outstanding performance for MUC1 assay with high selectivity, wide linear response range (1 fg mL−1 -10 ng mL−1) and lower detection limit (0.48 fg mL−1). And the strategy could be easily extended to a triple-mode detection of MUC1 because the hemin/G-quadruplex structure was widely used in electrochemical and colorimetric methods as a hydrogen peroxide mimetic enzyme, which might provide wide applications in biological or clinical studies.

In this work, we developed a sensitive electrochemical immunosensor for prion detection based on poly- β -cyclodextrin (P β -CD)/gold nanoparticles (AuNPs) modified electrode. Here, P β -CD film provided lots of β -CD units to capture the prion antibody by host-guest interaction. In the presence of prion, the specific interaction between prion and its antibody brought prion protein to the electrode surface to block the electron transfer channel of [Fe(CN) 6 ] 3−/4− ions provided by the inner cavity of β -CD, resulting in the decrease of the redox currents of [Fe(CN) 6 ] 3−/4− ions. Based on this kind of “blocking effect”, prion protein was detected sensitively. Under the optimal conditions, the developed immunosensor showed a linear response range from 15 fM to 1500 fM with a low detection limit of 2.1 fM (3 σ ). By changing the specific antibody, this strategy could be easily extended to detect the infectious isoform of prion (PrP Sc ) and other proteins. Based on its low cost (second antibody-free and label-free) and high sensitivity, the developed method shows great potential applications in diagnosis of prion diseases at presymptomatic stage and bioanalysis.

Herein, we report a template-engaged strategy to fabricate urchin-like ternary metal phosphide (Ni0.5Co0.5P-300) as catalyst for hydrogen evolution reaction. The morphology and microstructure of Ni0.5Co0.5P-300 and its precursors were examined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and micropore and chemisorption analyzer. Electrochemical properties were characterized by typical electrochemical methods, such as linear sweep voltammetry, cyclic voltammetry, chronoamperometry, chronopotentiometry and electrochemical impedance spectroscopy on a standard three-electrode system. Results show that the developed porous hierarchical 3D Ni0.5Co0.5P-300 catalyst has excellent electrocatalytic activity for hydrogen evolution in alkaline aqueous solution with onset overpotential of 26 mV and Tafel slope of 58 mV at the loading mass of 0.28 mg cm−2. It only needs 87 mV to reach the current density of 10 mA cm−2 and can hold the nearly unchanged current density for 25 h amperometric test. Meanwhile, the Ni0.5Co0.5P-300 catalyst also exhibits good electrocatalytic properties for hydrogen evolution in 1 M PBS solution (pH = 7). These indicate that the Ni0.5Co0.5P-300 catalyst with urchin-like structure, bimetallic merit, and low cost may be a good candidate as electrocatalyst in practical application of hydrogen evolution.

In this work, Au NPs decorated porous hollow tubular carbon materials (PHTCs@Au) by direct carbonization of zeolitic imidazolate framework-8 (ZIF-8) derived from ZnO nanorods were prepared and used as enzyme immobilizing matrix to construct a bioanode for glucose/O 2 biofuel cells (BFCs). Due to high surface area, good electric conductivity and extraordinary porous-hollow tubular structure of PHTCs@Au, the resulted enzyme electrode (PHTCs@Au/GOD (glucose oxidase)-GA (glutaraldehyde)/glassy carbon (GC) electrode) exhibited excellent catalytic capacity towards glucose oxidation and good stability. For the assembled glucose/O 2 BFC with the PHTCs@Au/GOD-GA/GC electrode as the bioanode and a commercial Pt plate electrode as the cathode, the maximum power density of 310 μW cm − 2 can be obtained at 0.23 V, and the open circuit potential is 0.63 V. The attractive features of PHTCs also provide potential applications in energy storage and conversion devices such as supercapacitor and fuel cells, etc.

Taking Prussian blue analogue (Co3[Co(CN)6]2) nanocubes as precursor, mesoporous Co(OH)2 nanocubes were synthesized by simply reacting Co3[Co(CN)6]2 nanocubes with NaOH aqueous solution. Their morphology and microstructures were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and micropore and chemisorption analyzer. Electrocapacitive properties of mesoporous Co(OH)2 nanocubes were characterized by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge method. Results show that the mesoporous Co(OH)2 nanocubes have mainly mesoporous structure with the specific surface area as high as 297 m2 g− 1, a high specific capacitance of 420 F g− 1 at 1 A g− 1 and excellent rate performance (80.9% retention from 1 A g− 1 to 10 A g− 1). In addition, the capacitance of the mesoporous Co(OH)2 nanocubes retained 82.4% of the initial value after 5000 cycles even at a high current density of 10 A g− 1. These indicates that the mesoporous Co(OH)2 nanocubes are good candidates for supercapacitor electrode material.

In this work, a new electrochemical method for rapid and sensitive evaluation of DNA methyltransferase (MTase) activity based on DNA strand displacement reaction (SDR) recycling signal amplification strategy was developed. Briefly, DNA adenine methyltransferase (Dam MTase) can catalyze the methylation of adenine into N6-methyladenine adenine (m6A) in the specific 5′-GATC-3′ of the hairpin DNA probe 1 (H1). Methylated H1 can be specifically recognized and cleaved by the restriction endonuclease DpnI, which releases a unstable loop DNA and quickly converted to a single-stranded DNA (S1). Then S1 can hybridize with hairpin DNA probe 2 (H2) on the electrode and open the hairpin structure of H2, and hairpin DNA probe 3 (H3) in the solution would hybridize with H2 to form a double-strand DNA (dsDNA), freeing S1 to trigger another reaction cycle and generating a significant response signal. The results demonstrated that the developed method could be used in highly sensitive detection of Dam MTase with a low detection limit of 0.03 U mL− 1. Furthermore, the proposed method suggested that 5-Fluorouracil could inhibit the Dam MTase activity with the half maximal inhibitory concentration (IC50) of 0.6 μM, implying its promising application in screening of suitable inhibitors for Dam MTase.

Prion proteins, as an important biomarker of prion disease, are responsible for the transmissible spongiform encephalopathies (a group of fatal neurodegenerative diseases). Hence, the sensitive detection of prion protein is very essential for biological studies and medical diagnostics. In this paper, a novel label-free and cascaded dual-signaling amplified electrochemical strategy was developed for sensitive and selective analysis of cellular prion protein (PrP(C)). The recognition elements included double-stranded DNA consisted of PrP(C)-binding aptamer (DNA1) and its partially complementary DNA (DNA2), and ordered mesoporous carbon probe (OMCP) fabricated by sealing the electroactive ferrocenecarboxylic acid (Fc) into its inner pores and then using single-stranded DNA (DNA3) as the gatekeeper. In the presence of PrP(C), DNA1 could bind the target protein and free DNA2. More importantly, DNA2 could hybridize with DNA3 to form a rigid duplex DNA and thus triggered the exonuclease III (Exo III) cleavage process to realize the DNA2 recycling, accompanied by opening more biogates and releasing more Fc. The released Fc could be further used as a competitive guest of β-cyclodextrin (β-CD) to displace the Rhodamine B (RhB) on the electrode. As a result, an amplified oxidation peak current of Fc (RhB) increased (decreased) with the increase of PrP(C) concentration. When "ΔI=ΔIFc+|ΔIRhB|" (ΔIFc and ΔIRhB were the change values of the oxidation peak currents of Fc and RhB, respectively.) was used as the response signal for quantitative determination of PrP(C), the detection limit was 7.6fM (3σ), which was much lower than that of the most reported methods for PrP(C) assay. This strategy provided a simple and sensitive approach for the detection of PrP(C) and has a great potential for bioanalysis, disease diagnostics, and clinical biomedicine applications.

Owing to the hydrophobic inner cavity and hydrophilic exterior of cyclodextrins (CDs), CDs molecules could exhibit excellent properties in water solubility, molecular recognition and enrichment capability, and CDs-based materials attracted considerable attentions in electrochemical sensing. This review shows the unique advantages and detecting mechanism of electrochemical sensors based on CDs functionalized materials, and recent advances for CDs-based materials (including CDs/carbon nanotubes, CDs/graphene, CDs/conducting polymers and other CDs-based nanomaterials) in electrochemical sensing. Finally, we also discussed some critical challenges and prospects in this field.

In this communication, 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) funtionalized graphene nanoribbons (HP-β-CD/GNRs) were prepared for the first time by using a simple wet chemical strategy, and then, the HP-β-CD/GNRs were applied for constructing electrochemical sensors for three representative analytes (p-aminophenol, p-AP; l-tyrosine, Tyr; rhodamine B, RhB). Owing to the synergetic effects of GNRs (excellent electrochemical properties and large surface area) and HP-β-CD (high host–guest recognition and enrichment capability), the highly sensitive electrochemical sensing platforms of three analytes were established by using HP-β-CD/GNRs modified electrode, and the detection limits were 0.0008, 0.003, and 0.001 μM for p-AP, Tyr, and RhB, respectively. Keywords: Graphene nanoribbon, Cyclodextrin, Electrochemical sensor, p-Aminophenol, l-Tyrosine, Rhodamine B

DNA methylation catalyzed by M.SssI methyltransferases (MTase) has important roles in gene expression and other cellular activities, and relates to some diseases, especially cancers. Therefore, it is important to develop a sensitive sensing platform for M.SssI MTase activity assay. Here, taking zeolitic imidazolate framework-8 (ZIF-8) polyhedra as the carriers of graphene quantum dots (GQDs), GQDs-embedded ZIF-8 polyhedra (denoted as GQDs@ZIF-8 polyhedra) were successfully prepared and used as the multi-functional signal quencher to construct a novel signal-off photoelectrochemical (PEC) biosensor for M.SssI MTase activity assay. Firstly, the indium tin oxide (ITO) slice was modified with TiO2, poly(diallyldimethylammonium chloride) and CdTe quantum dots (QDs). The obtained electrode was used as the photoelectrode and labeled as ITO/TiO2/CdTe QDs. Then, single-stranded DNA (S1) was anchored on the photoelectrode surface via S-Cd bond. After hybridization between S1 and biotinylated single-stranded DNA (S2), the streptavidin (SA)-labeled GQDs@ZIF-8 polyhedra were introduced to the modified electrode via the specific reaction between biotin and SA. As the signal quencher, GQDs@ZIF-8 polyhedra could not only inhibit the photocurrent signal of the ITO/TiO2/CdTe QDs electrode due to the steric hindrance effect, but also act as peroxidase mimetics to catalyze precipitation reaction of 4-chloro-1-naphthol, resulting in the evident depression of the photocurrent signal. For the specially designed S1/S2 double-strand DNA, the decreased photocurrent was quantitatively correlated with the M.SssI MTase activity (linear response range, 0.005-150 U mL-1; detection limit, 0.004 U mL-1). The developed GQDs@ZIF-8 polyhedra and related PEC biosensor may have potential applications in clinical research and disease diagnosis.

Searching for efficient and durable electrocatalysts toward hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) is highly desirable for the development of sustainable energy conversion technologies, but still remains a great challenge. Here, high-dispersed Rh nanoparticles are successfully encapsulated in the pores of N-doped porous carbon polyhedrons (NPCP) derived from ZIF-8 to avoid their aggregation and detachment, which makes the electrocatalyst (Rh@NPCP) have high activity and good stability. With an accepted metal loading (9.84 wt% Rh), Rh@NPCP exhibits excellent activity for HER electrocatalysis with ultralow overpotentials of 20, 23 and 45 mV to reach a current density of 10 mA cm−2 in alkaline, acidic and neutral media. Besides, remarkable ORR electrocatalytic activity with a half-wave potential of 0.84 V in alkaline media is achieved. Compared to the commercial Pt/C catalyst (20 wt% Pt), the prepared Rh@NPCP catalyst demonstrates significantly superior electrocatalytic performance toward pH-universal HER and alkaline ORR, especially in stability. This work provides a highly efficient, durable and affordable electrocatalyst for HER and ORR, which may have practical applications in water splitting and fuel cells.

Taking the advantages of the excellent electron transfer ability of gold nanoparticles (AuNPs) and their unique interaction with aptamer, a novel electrochemical aptasensor has been developed and used to sensitively detect a target model, adenosine triphosphate (ATP). Briefly, because of the interaction between AuNPs and nitrogen-containing bases, the ATP-binding aptamer (ABA) which is immobilized on the gold electrode can directly adsorb AuNPs. Thus, the electron transfer of the redox probe [Fe(CN) 6 ] 3 −/4 − to electrode can be greatly promoted. In the presence of ATP, the formed ABA-ATP complex has poor affinity with AuNPs and results in a large electron-transfer resistance (R et ) owing to the negatively charged ATP and the phosphate backbones of ABA. Here, the change of the interfacial feature of the electrode was characterized by the electrochemical impedance spectroscopy and AuNPs without any modification were employed as the signal amplifiers. The results demonstrated that the developed label-free aptasensor could detect ATP as low as 0.54 nM with a wide linear range from 1.0 nM to 100.0 μM, and has great promising applications in sensitive assays of other small molecules and proteins.

A ratiometric electrochemical sensor has been developed for highly sensitive and selective detection of bisphenol A. The assay strategy was based on the competitive host–guest interaction between poly- β -cyclodextrin/electroreduced graphene (P β -CD/EG) and Rhodamine B (RhB) probe or bisphenol A (BPA) target molecules. RhB can enter into the hydrophobic inner cavity of β -CD and shows an obvious oxidation peak on the P β -CD/EG modified glassy carbon electrode. In the presence of BPA, the RhB molecules are displaced by BPA because the host–guest interaction between β -CD and BPA is stronger than that between β -CD and RhB. As a result, the oxidation peak current of RhB ( I RhB ) decreases and the oxidation peak current of BPA ( I BPA ) increases correspondingly. The logarithmic value of I BPA / I RhB is linear with the logarithm of BPA concentration in the range of 1–6000 nM and the detection limit is 52 pM (S/N = 3). This strategy provides a new approach for sensitive detection of BPA, and has promising applications in the detection of organic pollutants in real environmental samples.

Based on the superior electrocatalytic property of graphene (GN) toward ascorbic acid (AA) oxidation, a new electrochemical aptasensor has been developed. Here, adenosine triphosphate (ATP) is used as the model to demonstrate the performance of the developed aptasensor. Briefly, GN is attached to the thiolated ATP binding aptamer (ABA) modified gold electrode through π-π stacking interaction, resulting in a significant oxidation signal of AA. In the presence of ATP, the formation of ATP-ABA complex leads to the release of GN from sensing interface, resulting in a sharp decrease of the oxidation peak current of AA and an obviously positive shift of the related peak potential. Taking both the change values of the peak current and peak potential of AA oxidation as the response signals, ATP can be detected sensitively. This is the first time to demonstrate the application of GN as the nanocatalyst in an amplified aptasensor. It can be expected that GN, as nanocatalyst, should become the very promising amplifying-elements in DNA-based electrochemical biosensors.

In this paper, a simple, selective and reusable electrochemical biosensor for the sensitive detection of mercury ions (Hg 2+ ) has been developed based on thymine (T)-rich stem–loop (hairpin) DNA probe and a dual-signaling electrochemical ratiometric strategy. The assay strategy includes both “signal-on” and “signal-off” elements. The thiolated methylene blue (MB)-modified T-rich hairpin DNA capture probe (MB-P) firstly self-assembled on the gold electrode surface via Au–S bond. In the presence of Hg 2+ , the ferrocene (Fc)-labeled T-rich DNA probe (Fc-P) hybridized with MB-P via the Hg 2+ -mediated coordination of T–Hg 2+ –T base pairs. As a result, the hairpin MB-P was opened, the MB tags were away from the gold electrode surface and the Fc tags closed to the gold electrode surface. These conformation changes led to the decrease of the oxidation peak current of MB ( I MB ), accompanied with the increase of that of Fc ( I Fc ). The logarithmic value of I Fc / I MB is linear with the logarithm of Hg 2+ concentration in the range from 0.5 nM to 5000 nM, and the detection limit of 0.08 nM is much lower than 10 nM (the US Environmental Protection Agency (EPA) limit of Hg 2+ in drinking water). What is more, the developed DNA-based electrochemical biosensor could be regenerated by adding cysteine and Mg 2+ . This strategy provides a simple and rapid approach for the detection of Hg 2+ , and has promising application in the detection of Hg 2+ in real environmental samples.

Taking phenylboronic acid as a boron source and ZIF-11 as a carbon template, boron and nitrogen co-doped porous carbon polyhedra (BN-PCPs) were prepared through a simple procedure for the first time. The as-prepared BN-PCPs were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and typical electrochemical methods. The results show that the developed BN-PCPs possess 10.68 atom% B and 8.1 atom% N with uniform distribution, and excellent electrochemical capacitive properties with high specific capacitance of 262 F g−1 at 20 mV s−1 in 1.0 M H2SO4 aqueous solution and excellent long-term charge–discharge stability (no obvious degradation during 40 000 charge–discharge cycles at 20 A g−1).

Platinum nanoparticles (Pt NPs) encapsulated in nitrogen-doped mesoporous carbons (NMCs) are prepared by direct carbonization of zeolitic imidazolate framework-8 (ZIF-8)-encapsulated Pt NPs, and used as a methanol-tolerant oxygen reduction electrocatalyst. ZIF-8 is used as the carbon and nitrogen precursors and as a matrix for Pt NPs. The obtained Pt NP–NMC hybrids are characterized in detail. The results show that the Pt NP–NMC hybrids possess high surface area (1226 m2 g−1), abundant mesopores with narrow pore size distribution (centered at 3.9 nm), nitrogen doping (5.13 at %), and small and well-dispersed encapsulated Pt NPs (3.7 nm). Furthermore, the prepared Pt NP–NMC catalyst exhibits high electrocatalytic activity, high stability and excellent methanol tolerance in the oxygen reduction reaction.

Based on Co-Co Prussian blue analogue (Co-Co PBA), a novel immunosensor has been developed for sensitive detection of prion protein (PrPC). Gold nanoparticles (AuNPs)-modified Co-Co PBA nanocubes (PBA-AuNPs) worked as a support of the antibody (Ab2) of PrPC to obtain Ab2-PBA-AuNPs composite and also as the signal source for PrPC assay. When PrPC existed, Ab2-PBA-AuNPs could be introduced to the surface of another antibody of PrPC (Ab1) modified AuNPs/GC electrode (the gold nanoparticles-modified glassy carbon electrode) through specific antigen-antibody interaction between PrPC and its antibodies to form the Ab1-PrPC-Ab2 sandwich structure. With the help of KOH aqueous solution, PBA generated a large DPV response. The response peak currents were linear with the logarithmic values of the concentration of PrPC in the range from 0.075 pg mL−1 to 100 pg mL−1 with the detection limit of 0.014 pg mL−1. Also, the immunosensor showed good selectivity and reproducibility. Based on the simple sensing structure and good analytical performance, the developed immunosensor may have promising applications in practical assay of infectious isoform of prion (PrPSc) and other proteins by simply changing the related antibody.

Biomolecular receptors such as nucleic acids that switch between two or more conformations upon binding to a specific target can be used to build specific and sensitive biosensors. In this work, based on the electrochemical dual-signaling ratiometric strategy and triple-helix molecular switch, we developed a selective, reusable, and simple electrochemical DNA (E-DNA) biosensor for target DNA (T-DNA) detection. A hairpin DNA capture probe labeled with methylene blue (MB-DNA) self-assembles on the surface of a gold electrode (GE) through Au-S bond, and then a single-strand DNA modified with two ferrocenes (Fc-DNA) on each end to enhance the oxidation signal hybridizes with the MB-DNA to form a triple-helix conformation. When T-DNA exists, the Fc-DNA hybridizes with T-DNA disassembling the triple-helix stem and allowing the MB-DNA to revert to its hairpin structure. Hence, the Fc tags diffuse away from the GE surface while the MB tags remain affixed close to it, resulting in a decrease in the peak current of Fc (I

Based on the ultrasonic cavitation assisted hydrogen implosion method, Pt nanoparticles (NPs)/nitrogen-doped graphene nanohybrid scrolls (Pt NPs/N-GNSs) were synthesized. As the results of the N-doping and high reduction degree of graphene, and scroll structure of the nanohybrids, the Pt NPs/N-GNSs electrocatalyst shows excellent performance in the direct oxidation of methanol: low onset and peak potentials, high oxidation current, and good long-term cycle stability. The Pt NPs/N-GNSs should have great promising applications in heterogeneous catalysis and fuel cells.

A novel ratiometric electrochemical aptasensor for sensitive and selective analysis of thrombin has been developed based on aptamer–target–aptamer sandwich structure. In the absence of thrombin, the methylene blue (MB) tagged thrombin aptamer (MB-TBA) was introduced on the electrode through the hybridization with the immobilized DNA sequences, thereby observing an oxidation signal of MB due to the flexible, single-stranded element of 5′ end of MB-TBA. After the addition of thrombin, the specific thrombin–aptamer interaction drove the conformational change of MB-TBA (from the unfolded conformation to the G-quadruplex), resulting in the MB tag far from the electrode surface. The second thrombin aptamer with ferrocene (Fc) tagged on both chain ends (Fc-TBA-Fc) interacted with thrombin to form another G-quadruplex conformation. Such sandwich structure and the G-quadruplex conformation acted cooperatively to allow the two Fc tags to be close to the electrode surface. These conformational changes resulted in a decrease of the oxidation peak current of MB ( I MB ) and an increase of that of Fc ( I Fc ), and the logarithmic value of I Fc / I MB was linear with the logarithm of thrombin concentration. The developed aptasensor shows good response toward the target with a wide linear range from 1 nM to 600 nM and a low detection limit of 170 pM.

In this paper, a facile electrodeposition method without any additive has been successfully adopted to fabricate dendritic gold nanostructure (DenAu) on glassy carbon (GC) electrode and the prepared DenAu/GC electrode has large surface area. A sensitive third-generation superoxide radical (O 2 − ) biosensor was then constructed by assembled l -cysteine (cys) onto the DenAu/GC electrode to immobilize large amounts of superoxide dismutase (SOD). The direct electron transfer of SOD was successfully realized and a pair of quasi-reversible redox peaks of SOD was observed at the SOD/cys/DenAu/GC electrode in the phosphate buffer solution (25 mM, pH 7.2). Due to the high loading of SOD on the electrode, the resulted biosensor exhibited good analytical performance for O 2 − detection, such as a low detection limit of 2.1 nM, a good stability and reproducibility, especially a wide linear range up to 540 μM.

A simple, label-free electrochemical biosensor based on a dopamine (DA) DNA aptamer immobilized on a Au electrode through the Au–S bond was developed. Methylene blue (MB) was used as the intercalating probe, and DA was sensitively and selectively detected. The developed electrochemical DA aptasensor showed a good linear response to DA from 5–150 nmol L−1 as well as having a low detection limit of 1.0 nM (S/N = 3). The biosensor also exhibited satisfactory selectivity and could be successfully used to detect DA in human blood, suggesting that the aptasensor is a promising application for the analysis of DA in real clinical samples.

A sensitive electrochemical method for the detection of hydroxyl radical ( OH) was successfully developed based on magnetic beads (MBs)–DNA–Ag nanoparticles (AgNPs) (MBs–DNA–AgNPs) nanocomposite. MBs were utilized for bioseparation and AgNPs as signal indicator. When OH broke the DNA strands, AgNPs were detached from the surface of the MBs–DNA–AgNPs nanocomposite. Magnetic particles could be easily removed from the solution and the detached AgNPs were collected. Therefore, the anodic stripping voltammetry (ASV) signal of dissolved silver on glassy carbon (GC) electrode depended on the amounts of OH. The results show that the ASV signal linearly increases with the increase of the concentration of OH in the range of 0.05–4 μM, and the detection limit is as low as 10 nM, which is much lower than the detection limit obtained on the recently developed electrochemical and photoelectrochemical methods. In addition, the developed method has potential application in the screening of antioxidants.

Based on the competitive host-guest interaction between a β-cyclodextrin/poly(N-acetylaniline)/electrogenerated-graphene (β-CD/PNAANI/EG) film and probe or target molecules, a new dual-signalling electrochemical sensing method has been developed for the sensitive and selective determination of organic pollutants. As a model system, rhodamine B (RhB) and 1-aminopyrene (1-AP) were adopted as the probe and target molecules, respectively. Due to the host-guest interaction, RhB molecules can enter into the hydrophobic inner cavity of β-CD, and the β-CD/PNAANI/EG-modified glassy carbon electrode displays a remarkable oxidation peak due to RhB. In the presence of 1-AP, competitive association to β-CD occurs and the RhB molecules are displaced by 1-AP. This results in a decreased oxidation peak current of RhB and the appearance of an oxidation peak current for 1-AP, and the changes of these signals correlate linearly with the concentration of 1-AP. When the value ΔI(1-AP)+∣ΔI(RhB)∣ (ΔI(1-AP) and ΔI(RhB) are the change values of the oxidation peak currents of 1-AP and RhB, respectively) is used as the response signal to quantitatively determine the concentration of 1-AP, the detection limit is much lower than that given by using ΔI(1-AP) or ΔI(RhB) as the response signal. This dual-signalling sensor can provide more sensitive target recognition and will have important applications in the sensitive and selective electrochemical determination of electroactive organic pollutants.

Taking TdT-mediated hemin/G-quadruplex DNAzyme nanowires as NADH oxidase and HRP-mimicking DNAzyme, a novel DNA-based electrochemical method has been developed for sensitive and selective assay of alkaline phosphatase (AP) activity. The double-stranded DNA (dsDNA) probe consisted of thiol-functionalized DNA1 and 3'-phosphorylated DNA2, was immobilized on a gold nanoparticles (AuNPs) modified glassy carbon (GC) electrode. In the presence of AP, 3'-phosphoryl end of DNA2 was dephosphorylated. Terminal deoxynucletidyl transferase (TdT) catalyzed the sequential addition of deoxynucleotides (dTTPs) at 3'-OH end of DNA2 to extend DNA2 with a poly-T sequence. Then, G-rich DNA3 strand hybridized with the poly-T sequence of DNA2. Upon addition of hemin, the hemin/G-quadruplex DNAzyme was formed. In the presence of NADH, the hemin/G-quadruplex DNAzyme oxidased NADH to NAD+, accompanied by the formation of H2O2 which was further catalyzed by hemin/G-quadruplex DNAzyme (served as a HRP-mimicking DNAzyme) with the thionine (Thi) as electron transfer mediator, leading to the amplified electrochemical signal. Under optimized conditions, the response peak current was linear with the concentration of AP in the range from 0.1UL-1 to 5UL-1 with the detection limit of 0.03UL-1. Also, the developed biosensor possessed good selectivity, reproducibility and stability, and simple sensing structure, showing promising practical applications in AP activity assay.

In this work, a simple, signal-on and label-free electrochemical biosensor for ultrasensitive DNA detection is reported on the basis of an autocatalytic and exonuclease III (Exo III)-assisted cascade signal amplification strategy. In the presence of target DNA (T-DNA), the hybridization between the 3′-protruding DNA fragment of hairpin DNA probe (HP1) and T-DNA triggered the Exo III cleavage process, accompanied by the releasing of T-DNA and autonomous generation of new DNA fragment which was used for the successive hybridization with the another hairpin DNA (HP2) on the electrode. After the Exo III cleavage process, numerous quadruplex-forming oligomers which caged in HP2 were liberated on the electrode surface and folded into G-quadruplex-hemin complexes with the help of K+ and hemin to give a remarkable electrochemical response. As a result, a low detection limit of 4.83 fM with an excellent selectivity toward T-DNA was achieved. The developed electrochemical biosensor should be further extended for the detection of a wide spectrum of analytes and has great potential for the development of ultrasensitive biosensing platform for early diagnosis in gene-related diseases.

Due to awfully harmful to the environment and human health, the qualitative and quantitative determinations of naphthols [1-naphthol (1-NAP) and 2-naphthol (2-NAP)] are of great significance and receive great attention. In this paper, gold nanoparticles (AuNPs)/hollow nitrogen-doped carbon microspheres (HNCMS) hybrids (AuNPs/HNCMS) were prepared and functionalized with thiolated-β-cyclodextrin (HS-β-CD) for the first time, and then applied successfully in sensitive and simultaneous electrochemical detection of naphthols. The results show that the oxidation peak currents of naphthols obtained on the HS-β-CD/AuNPs/HNCMS modified glassy carbon (GC) electrode are much higher than that on the AuNPs/HNCMS/GC, HNCMS/GC and bare GC electrodes. Additionally, compared with other electrochemical sensors developed previously, the proposed electrode results in improved detection limits of about four times for 1-NAP (1.0 nM) and two orders of magnitude for 2-NAP (1.2 nM). The linear response ranges of both 1-NAP and 2-NAP are 2–150 nM.

The direct electropolymerization of pyrrole in [BMIM]PF6 microemulsion was investigated for the first time. The H2O/TX-100/[BMIM]PF6 (W/IL), bicontinuous (BC), [BMIM]PF6/TX-100/H2O (IL/W) subregions can be used as electrolytes for pyrrole electropolymerization. The use of IL microemulsion remarkably reduces the amount of IL. Furthermore, electrochemical measurements indicated that W/IL microemulsion was the optimal medium and its polymerization rate was the fastest. Compared with molecular solvent system (0.25 mol L−1 [BMIM]PF6/acetonitrile) and neat [BMIM]PF6, the resultant films electrodeposited in W/IL microemulsion possessed excellent electrochemical activity and uniform morphology. All the results indicated that the H2O/TX-100/[BMIM]PF6 microemulsion as electrolyte medium is the most suitable for electropolymerization of pyrrole. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

A facile method for one-pot synthesis of highly dispersed palladium nanoparticles on acetylenic ionic liquid polymer functionalized carbon nanotubes (PdNPs-AILP-CNTs) has been developed in this paper. The nanohybrids are prepared by polymerization of acetylenic ionic liquid monomers catalyzed by PdCl2, which is further reduced to PdNPs by NaBH4 on CNTs in one pot and characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and transmission electron microscopy. The electrocatalytic oxidation of glucose on the PdNPs-AILP-CNT nanohybrids is also investigated by cyclic voltammetry and chronoamperometry. The results show that the PdNPs with a particle size of around 3.5 nm disperse uniformly on CNTs, and PdNPs-AILP-CNT nanohybrids have good electrocatalytic performance for glucose oxidation.

The heavy metal (HM) ion-enzyme interaction is an important research topic in many areas. Using glucose oxidase (GOx) as an example, a comprehensive experimental platform based on quartz crystal microbalance and electroanalysis techniques is developed here to quantitatively study the HM ion-enzyme interactions and amperometric inhibitive assays of HM ions. The effects of some common HM ions on the bioactivities of solution-state GOx (GOx(s)), electrode surface-adsorbed GOx (GOx(ads)), and polymer-entrapped GOx (GOx(e)) are comparatively examined on the basis of anodic amperometric detection of enzymatically generated H(2)O(2). Ag(+) shows the strongest inhibition effect among the HM ions examined, and the inhibitive assays of Ag(+) based on GOx(s), GOx(ads), and GOx(e) entrapped in poly(l-noradrenalin) (PNA) give limits of detection (LOD) of 2.0, 8.0, and 5.0 nM (S/N = 3), respectively. Inhibition effects of Hg(2+), Cu(2+), and Co(2+) are detectable only at 15 μM or higher concentrations, and the other HM ions show undetectable inhibition even at 1.0 mM. The developed experimental platform allows one to quantify the number of the bound HM ions per GOx(ads) molecule at various inhibition percentages. In addition, the electrosynthesized PNA matrix to entrap GOx for an inhibitive assay of Ag(+) shows the lowest competitive affinity to HM ions and gives the highest sensitivity, as compared with several other polymer matrixes commonly used for the inhibitive assay. The suggested experimental platform is recommended for wide applications in enzymatic inhibitive assays and quantitative studies of the inhibition effects of HM ions on many other redox-event-relevant enzymes.

A novel one-dimensional (1-D) caterpillar-like manganese dioxide-carbon (MnO(2)-C) nanocomposite has been synthesized by a direct redox reaction between carbon nanotubes (CNTs) and permanganate ions for the first time. The as-prepared nanostructured MnO(2)-C composite mainly consisting of ε-MnO(2) nanoflakes had a unique microstructure, high specific surface area (200 m(2) g(-1)) and favourable conductivity. The nanostructured MnO(2)-C composite, added as a modification to the glassy carbon (GC) electrode via a direct electrochemical co-deposition process with a chitosan hydrogel, was found to exhibit excellent catalytic activity toward L-cysteine electro-oxidation because the specific interaction between the -SH group of L-cysteine and solid MnO(2) occurred to form surface complexes. A determination of L-cysteine at the MnO(2)-C/chitosan/GC (MnO(2)-C/chit/GC) electrode was carried out by amperometric measurement. Under the optimum experimental conditions, the detection response for L-cysteine was fast (within 7 s). The logarithm of catalytic currents shows a good linear relationship with that of the L-cysteine concentration in the range of 0.5-680 μM (R = 0.9986), with a low detection limit of 22 nM. The MnO(2)-C/Chit/GC electrode exhibited excellent stability (without any decrease of the response signal after 1 month) and admirable resistance against interference like glutathione and other oxidizable amino acids (tryptophan, tyrosine, L-lysine and methionine).

NiO nanoparticles have been prepared by thermal decomposition of the nickel acetate/starch precursor in air. N2 adsorption-desorption analysis show that the resultant NiO samples possess nanoporous structures and large BET surface areas. The Brunauer-Emmet-Teller (BET) surface area of NiO increases from 17 to 38 m2·g−1 because of the use of the starch template. The surface area decreases and the average pore diameter increases for the NiO products with increasing heat treatment temperature. The formation mechanism of the NiO nanoparticles was proposed. Furthermore, the electrochemical measurements indicate that the NiO nanoparticles have favorable faradaic pseudocapacitive behavior. The method has also been demonstrated for nickel nitrate.

A new kind of supercapacitor by using chemical reduced graphene (CRG) as electrode material and ionic liquid with addition of acetonitrile as electrolyte is assembled and investigated. CRG materials with high surface area are prepared by chemical reduction of graphene oxide. The capacitive properties of the supercapacitor composed of the CRG and ionic liquid electrolyte are studied by electrical impedance spectroscopy, cyclic voltammetry and galvanostatic charge–discharge. With the combined advantages of graphene and ionic liquid, the supercapacitor shows perfect performance. The supercapacitor possesses wide cell voltage and good stability. The specific capacitance, energy density, and specific power density of the present supercapacitor are 132 Fg−1, 143.7 Wh kg−1, and 2.8 kW kg−1, respectively. The results demonstrate the potential application of electrical energy storage devices with high performance based on this new kind of supercapacitor.

Graphene oxide (GO) and Au(Ш) are electrochemically co-reduced in ionic liquid to prepare graphene/Au nanocomposites. The electrochemical reduction processes were recorded by I–t curves, which indicate that the simultaneous reduction of GO and Au(Ш) is favorable to each other. The X-ray diffraction patterns confirm the complete reduction of GO. The scanning electron microscopy and transmission electron microscopy results reveal that Au particles with a diameter of about 10 nm are dispersed uniformly on the electrochemically reduced graphene (ER-G). Furthermore, the electrochemical activity of ER-G/Au nanocomposites was evaluated and the ER-G/Au nanocomposites electrode demonstrates great electrochemical catalytic activity and stability.

P-octyl polyethylene glycol phenyl ether (Triton X-100) and cetyltrimethylammonium bromide (CTAB) were mixed to be used as surfactant for preparing reverse microemulsion with n-hexane, n-hexanol and water. Effects of weight ratio of the two surfactants, temperature, concentrations of water and cosurfactant on the conductivity were studied. The results indicate that the conductivity of the mixed surfactants reverse microemulsion is greatly higher than that of the single surfactant system. The reverse microemulsion has been modified to be with good conductivity. The weight ratio of the two surfactants, temperature, concentrations of water and cosurfactant have obvious effects on the conductivity of the reverse microemulsion. Furthermore, the electrochemical behavior of potassium ferricyanide [K3Fe(CN)6] in the mixed surfactants reverse microemulsion was investigated by cyclic voltammetry. The result shows that the redox processes of \( {{\text{Fe}}\left( {\text{CN}} \right)_{ 6}}^{ 3- } / {{\text{Fe}}\left( {\text{CN}} \right)_{ 6}}^{ 4-} \) present good reversibility and are controlled by diffusion in the system.