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Abstract: A label-free electrochemical DNA biosensor array was developed as a model system for simultaneous detection of multiplexed DNAs using microlitres of sample. A novel multi-electrode array was comprised of six gold working electrodes and a gold auxiliary electrode, which were fabricated by gold sputtering technology, and a printed Ag/AgCl reference electrode was fabricated by screen-printing technology. The DNA biosensor array for simultaneous detection of the human immunodeficiency virus (HIV) oligonucleotide sequences, HIV-1 and HIV-2, was fabricated in sequence by self-assembling each of two kinds of thiolated hairpin-DNA probes onto the surfaces of the corresponding three working electrodes, respectively. The hybridization events were monitored by square wave voltammetry using methylene blue (MB) as a hybridization redox indicator. The oxidation currents of MB accumulated on the array decreased with increasing the concentration of HIVs due to higher affinity of MB for single strand rather than double strands of DNA. Under the optimized conditions, the peak currents were linear over ranges from 20 to 100nM for HIV-1 and HIV-2, with the same detection limits of 0.1nM (S/N=3), respectively. The biosensor array showed a good specificity without the obvious cross-interference. Furthermore, single-base mutation oligonucleotides and random oligonucleotides can be easily discriminated from complementary target DNAs. This work demonstrates that different hairpin-DNA probes can be used to design the label-free electrochemical biosensor array for simultaneous detection of multiplexed DNA sequences for various clinical applications. [Copyright &y& Elsevier]

Abstract: A label-free and sensitive faradic impedance spectroscopy (FIS) aptasensor based on target-induced aptamer displacement was developed for the determination of lysozyme as a model system. The aptasensor was fabricated by self-assembling the partial complementary single strand DNA (pcDNA)–lysozyme binding aptamer (LBA) duplex on the surface of a gold electrode. To measure lysozyme, the change in interfacial electron transfer resistance of the aptasensor using a redox couple of [Fe(CN)6]3−/4− as the probe was monitored. The introduction of target lysozyme induced the displacement of the LBA from the pcDNA–LBA duplex on the electrode into the solution, decreasing the electron transfer resistance of the aptasensor. The decrease in the FIS signal is linear with the concentration of lysozyme in the range from 0.2nM to 4.0nM, with a detection limit of 0.07nM. The fabricated aptasensor shows a high sensitivity, good selectivity and satisfactory regeneration. This work demonstrates that a high sensitivity of the fabricated aptasensor can be obtained using a relatively short pcDNA. This work also demonstrates that the target-induced aptamer displacement strategy is promising in the design of an electrochemical aptasensor for the determination of lysozyme with good selectivity and high sensitivity. [Copyright &y& Elsevier]

Abstract: A novel multielectrode array modified with multiwall carbon nanotubes (MWCNTs) to simultaneous amperometric determination of dihydroxybenzene isomers was designed. The three oxidation peaks at the multielectrode array fabricated in 0.10M KCl–0.20M acetate buffer solution (pH 5.40) containing hydroquinone, catechol and resorcinol appeared at +0.192V, +0.301V and +0.683V, corresponding to the oxidation of hydroquinone, catechol and resorcinol, respectively. A simple electrochemical method for simultaneous determination of dihydroxybenzene isomers was developed by multiple linear regression (MLR) method. Under the optimized conditions, the amperometric currents were linear over ranges from 1.0×10−6 M to 1.0×10−4 M for hydroquinone, from 1.0×10−6 M to 1.0×10−4 M for catechol and from 6.0×10−6 M to 1.0×10−4 M for resorcinol, with the detection limits of 3.0×10−7 M, 2.0×10−7 M and 6.0×10−7 M, respectively. The developed method has been applied to simultaneous determination of dihydroxybenzene isomers in artificial wastewater with a satisfactory recovery from 97% to 101%. This work demonstrates that the MWCNTs-modified multielectrode array incorporating multiple linear regression method is a promising strategy for simultaneous electrochemical determination of isomers of organic compounds. [Copyright &y& Elsevier]

Molybdenum disulfide quantum dots (MoS2 QDs) are used in a fluorometric method for the determination of folic acid (FA) based on fluorescence quenching. The MoS2 QDs synthesized by a hydrothermal method possess bright blue fluorescence (with excitation/emission maxima of 325/415 nm), quantum yield of 3.7%, and excellent storage stability in solution (30 days in the refrigerator). Their fluorescence is quenched by FA, and intensity decreases linearly in the 0.1 to 125 μM FA concentration range. The detection limit is 0.1 μM (at S/N = 3), and the relative standard deviation (for n = 5) is 2.8% for 25 μM concentrations of FA. Studies on the quenching mechanism suggest that the effect is due to static quenching. The FA in commercial FA tablets was successfully determined. [ABSTRACT FROM AUTHOR]

Modular electrochemical production (MEP) system could decouple the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), and pairing with a redox mediator (RM), respectively. Herein, Mott–Schottky Co 9 S 8 /Ni 3 S 2 heterojunction was constructed, which was employed as a RM to separate the hydrogen and oxygen production in space and time in MEP system for H 2. The MEP system for H 2 involved a two−step electrochemical−electrochemical (EC−EC) looping process. The reversible redox reaction of Co 9 S 8 /Ni 3 S 2 was paired with HER in step 1 and subsequently paired with OER in step 2. The Mott–Schottky hetero-structures enabled the redistribution of Ni central charge and accelerated the electron transfer from semiconductor Ni 3 S 2 to metallic Co 9 S 8 on the interface. This made the formation of Lewis acid at the Ni 3 S 2 in the heterojunction, which bonded with the OH− Lewis base, facilitating the electrochemical redox kinetics of Co 9 S 8 /Ni 3 S 2. Thus, the Co 9 S 8 /Ni 3 S 2 RM presented a high area capacitance (29.60 F/cm2 at 5 mA/cm2), and an excellent stability upon operation over 5000 cycles (15 days). The MEP system can continuously produce H 2 for 1502 s at 10 mA/cm2 with a Faradaic efficiency of 100%. The MEP system possessed a high energy efficiency (83%), requiring a lower cell voltage than that of a conventional water electrolysis system. The MEP system for H 2 enabled flexible utilization of renewable solar energy by photovoltaic (PV) panels, thereby facilitating solar-to-hydrogen conversion. [Display omitted] • Charge redistribution facilitates redox kinetics of Mott–Schottky Co 9 S 8 /Ni 3 S 2. • H 2 and O 2 are separated in time and space avoiding gas mixing and purification. • The MEP system shows high energy efficiency (80%) at 10 mA/cm2. • Modular PV-water electrolysis system provides a promising strategy for conversion of solar to H 2. [ABSTRACT FROM AUTHOR]

Electrochemical CO2 reduction (CO2RR) to produce high value-added chemicals or fuels is a promising technology to address the greenhouse effect and energy challenges. Formate is a desirable product of CO2RR with great economic value. Here, nitrogen-doped bismuth nanosheets (N-BiNSs) were prepared by a facile one-step method. The N-BiNSs were used as efficient electrocatalysts for CO2RR with selective formate production. The N-BiNSs exhibited a high formate Faradic efficiency (FEformate) of 95.25% at −0.95 V (vs. RHE) with a stable current density of 33.63 mA cm−2 in 0.5 M KHCO3. Moreover, the N-BiNSs for CO2RR yielded a large current density (300 mA cm−2) for formate production in a flow-cell measurement, achieving the commercial requirement. The FEformate of 90% can maintain stability for 14 h of electrolysis. Nitrogen doping could induce charge transfer from the N atom to the Bi atom, thus modulating the electronic structure of N-Bi nanosheets. DFT results demonstrated the N-BiNSs reduced the adsorption energy of the *OCHO intermediate and promoted the mass transfer of charges, thereby improving the CO2RR with high FEformate. This study provides a valuable strategy to enhance the catalytic performance of bismuth-based catalysts for CO2RR by using a nitrogen-doping strategy. [ABSTRACT FROM AUTHOR]

Abstract: A novel electrogenerated chemiluminescence (ECL) aptamer-based biosensing method for the determination of thrombin was developed on basis of a structure-switching ECL-dequenching mechanism. A thiolated ss-DNA capture probe, composing of a ss-DNA sequence to adopt two distinct structures-a DNA double strand with a complementary DNA sequence tagged with a ECL signal producer tris(2,2′-bipyridyl)ruthenium derivative and a DNA duplex with a thrombin-binding aptamer tagged with a ECL-quencher ferrocene (FcDNA), was self-assembled onto surface of a gold electrode. In the presence of thrombin, the aptamer sequence prefers to form the aptamer-thrombin complex and the switch of the binding partners occurs in conjunction with the generation of a strong ECL signal owing to the dissociation of FcDNA. The integrated ECL intensity versus the concentration of thrombin was linear in the range from 2.0×10−10 M to 2.0×10−7 M. The detection limit was 6×10−11 M. The relative standard derivation for 2.0×10−9 M was 5.7% (n =7). This work demonstrates that the sensitivity and specificity of ECL aptamer-based method for proteins can be greatly improved using quenching ECL signal producer by a chemical quencher such as ferrocene. [Copyright &y& Elsevier]

Abstract: A homogeneous electrogenerated chemiluminescence (ECL) immunoassay for human immunoglobulin G (hIgG) has been developed using a N-(aminobutyl)-N-ethylisoluminol (ABEI) as luminescence label at gold nanoparticles modified paraffin-impregnated graphite electrode (PIGE). ECL emission was electrochemically generated from the ABEI-labeled anti-hIgG antibody and markedly increased in the presence of hIgG antigen due to forming a more rigid structure of the ABEI moiety. The concentration of hIgG antigen was determined by the increase of ECL intensity at a gold nanoparticles modified PIGE. It was found that the ECL intensity of ABEI in presence of hydrogen peroxide was dramatically enhanced at gold nanoparticles modified PIGE in neutral aqueous solution and the detection limit of ABEI was 2×10−14 mol/L (S/N=3). The integral ECL intensity was linearly related to the concentration of hIgG antigen from 3.0×10−11 to 1.0×10−9 g/mL with a detection limit of 1×10−11 g/mL (S/N=3). The relative standard deviation was 3.1% at 1.0×10−10 g/mL (n =11). This work demonstrates that the enhancement of the sensitivity of ECL and ECL immunoassay at a nanoparticles modified electrode is a promising strategy. [Copyright &y& Elsevier]

Abstract: A novel electrogenerated chemiluminescence aptamer-based (ECL-AB) biosensor for the determination of a small molecule drug is designed employing cocaine-binding aptamer as molecular recognition element for cocaine as a model analyte and ruthenium complex served as an ECL label. A 5′-terminal cocaine-binding aptamer with the ECL label at 3′-terminal of the aptamer was utilized as an ECL probe. The ECL-AB biosensors were fabricated by immobilizing the ECL probe onto a gold electrode surface via thiol-Au interactions. An enhanced ECL signal is generated upon recognition of the target cocaine, attributed to a change in the conformation of the ECL probe from random coil-like configuration on the probe-modified film to three-way junction structure, in close proximity to the sensor interface. The integrated ECL intensity versus the concentration of cocaine was linear in the range from 5.0×10−9 to 3.0×10−7 M. The detection limit was 1.0×10−9 M. This work demonstrates that the combination of a highly binding aptamer to analyte with a highly sensitive ECL technique to design ECL-AB biosensor is a great promising approach for the determination of small molecule drugs. [Copyright &y& Elsevier]

[Display omitted] • Zn-doped Co 9 S 8 nanoparticles were loaded to BiVO 4 photoelectrode by spin coating. • Zn-Co 9 S 8 /BiVO 4 photoanode showed enhanced photoelectrocatalytic (PEC) activity. • Optimized Zn-Co 9 S 8 /BiVO 4 had a photocurrent density 2.5 times higher than BiVO 4. • Separation of photogenerated carriers and electrical conductivity were improved. • Holes, OH, and O 2 − were the main active species in the degradation. The Zn-Co 9 S 8 /BiVO 4 composite photoanodes were fabricated by loading Zn-doped Co 9 S 8 nanoparticles to the electrodeposited BiVO 4 photoelectrode. The composite photoanodes showed enhanced photoelectrocatalytic performance for the degradation of tetracycline. The improved separation of photogenerated carriers were evidenced by photocurrent measurement, electrochemical impedance spectroscopy, photoluminescence spectroscopy, and applied bias photon-to-current efficiency. Electron spin resonance spectroscopy and free radical scavenging experiments confirmed that OH, h + and O 2 − played dominant roles. The optimized Zn-Co 9 S 8 /BiVO 4 composite photoanode showed 2.5 times higher photocurrent density than BiVO 4 photoanode. The Zn-Co 9 S 8 /BiVO 4 photoanode presented an incident photon-to-current conversion efficiency of 56 %, higher than BiVO 4 (25 %). According to the density functional theory results, a heterojunction between Zn-Co 9 S 8 to BiVO 4 was formed, prompting the separation of photogenerated pairs. The Zn-Co 9 S 8 /BiVO 4 photoanode maintained good photoelectrocatalytic activity after five reuse cycles, confirming its good stability. [ABSTRACT FROM AUTHOR]

The diffusion of target analytes is a determining factor for the sensitivity of a given gas sensor. Surface adsorption results in a low‐concentration region near the sensor surface, producing a concentration gradient perpendicular to the surface, and drives a net flux of molecules toward solid reactive reagents on the sensor surface, that is, vertical diffusion. Here, organic semiconductor supramolecules were patterned into micromeshed arrays to integrate vertical and horizontal diffusion pathways. When used as a gas sensor, these arrays have an order of magnitude higher sensitivity than traditional film‐based sensors. The sensor sensitivity ramp down with the increase in coverage density of reactive reagents, yielding two linear regions demarcated by 0.3 coverage, which are identified by the experimental results and simulations. The universal nature of template‐assisted patterning allows adjustments in the composition, size, and shape of the constituent material, including nanofibers, nanoparticles, and molecules, and thus serves to improve the sensitivity of gas sensors for detecting various volatile organic compounds. [ABSTRACT FROM AUTHOR]

The diffusion of target analytes is a determining factor for the sensitivity of a given gas sensor. Surface adsorption results in a low‐concentration region near the sensor surface, producing a concentration gradient perpendicular to the surface, and drives a net flux of molecules toward solid reactive reagents on the sensor surface, that is, vertical diffusion. Here, organic semiconductor supramolecules were patterned into micromeshed arrays to integrate vertical and horizontal diffusion pathways. When used as a gas sensor, these arrays have an order of magnitude higher sensitivity than traditional film‐based sensors. The sensor sensitivity ramp down with the increase in coverage density of reactive reagents, yielding two linear regions demarcated by 0.3 coverage, which are identified by the experimental results and simulations. The universal nature of template‐assisted patterning allows adjustments in the composition, size, and shape of the constituent material, including nanofibers, nanoparticles, and molecules, and thus serves to improve the sensitivity of gas sensors for detecting various volatile organic compounds. [ABSTRACT FROM AUTHOR]

Herein, Cu-doped Bi 2 O 2 S catalysts with abundant oxygen vacancies (abbreviated Cu/BOS-OV) were prepared by calcining one-step hydrothermally synthesized Cu-doped Bi 2 O 2 S in a tube furnace. The photodegradation efficiency of tetracycline (TC, 15 mg L−1) over Cu/BOS-OV reached 79% under visible light owing to the introduction of impurity bands by Cu doping and oxygen vacancies, improving the separation efficiency of photogenerated carriers. However, the Cu/BOS-OV catalyst achieved an efficiency of 90.4% for 30 mg L−1 TC degradation within 30 min due to peroxymonosulfate (PMS) activation by oxygen vacancies and copper ions. The intermediates of TC degradation were analyzed by LC‒MS, and the possible decomposition process of TC was proposed. The free radical trapping and ESR experiments showed that ·O 2 −, 1O 2 , and ⋅OH/SO 4 •− participated in the degradation of TC. Furthermore, the free energy diagram of HSO 5 − dissociation and ·OH/SO 4 •− desorption processes indicated that the enhanced PMS activation efficiency toward TC degradation was contributed by the decreased adsorption energy and increased O–O bond length of HSO 5 − on Cu/BOS-OV. This study provides good application prospects for removing organic contaminants based on photocatalysis and PMS activation technology. [Display omitted] • Both Cu2+ doping and oxygen vacancies could activate PMS and produce SO 4.•− • The oxygen vacancies could introduce abundant active sites. • O 2 −, 1O 2 , and OH/SO 4.•− were the main active species in the TC degradation • The adsorption energy of HSO 5 − on Cu/BOS-OV were reduced. • The O–O bond length of HSO 5 − on Cu/BOS-OV increased. [ABSTRACT FROM AUTHOR]