Lishi Wang

An enhanced sensitive electrochemical immunosensor based on efficient encapsulation of enzyme in silica matrix for the detection of human immunodeficiency virus p24

We report a new electrochemical immunosensor for enhanced sensitive detection of human immunodeficiency virus p24 (HIV-p24) based on graphene oxide (GO) as a nanocarrier and enzyme encapsulated in carbon nanotubes-silica as a matrix in a multienzyme amplification strategy. Greatly enhanced sensitivity was achieved by using the bioconjugates featuring horseradish peroxidase-HIV-p24 signal antibody (HRP-HIV-p24) linked to functionalized GO and thionine (TH) as well as efficient encapsulation of enzyme (HRP) in the silica matrix with retained bioactivity. After a sandwich immunoreactions, the HRP in carbon nanotubes-silica matrix and the HRP-HIV-p24-TH/GO captured onto the electrode surface produced an amplified electrocatalytic response by the reduction of enzymatically oxidized thionine in the presence of hydrogen peroxide. The increase of response current was proportional to the HIV-p24 concentration in the range of 0.5 pg/mL-8.5 ng/mL with the detection limit of 0.15 pg/mL, which was lower than that of the traditional sandwich electrochemical measurement for HIV-p24. The amplified immunoassay developed in this work shows acceptable stability and reproducibility, and the assay results for HIV-p24 spiked in human plasma also show good accuracy. This simple and low-cost immunosensor shows great promise for detection of other proteins and clinical applications.

A multi-walled carbon nanotubes based molecularly imprinted polymers electrochemical sensor for the sensitive determination of HIV-p24

To develop a rapid, simple and sensitive method for the determination of human immunodeficiency virus p24 (HIV-p24), a novel molecularly imprinted polymers (MIPs) electrochemical sensor was constructed on the surface of a multi-walled carbon nanotubes (MWCNTs) modified glassy carbon electrode (GCE) by surface polymerization using acrylamide (AAM) as functional monomer, N,N-methylenebisacrylamide (MBA) as cross-linking agent and ammonium persulphate (APS) as initiator. Each modification step was carefully examined by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and scanning electron microscope (SEM). The proposed MIPs electrochemical biosensor exhibited specific recognition to HIV-p24 and displayed a broad linear detection range from 1.0×10-4 to 2ngcm-3 with a low detection limit of 0.083pgcm-3 (S/N=3). This performance is superior to most HIV-p24 sensors based on other methods. Meanwhile, this sensor possessed of good selectivity, repeatability, reproducibility, stability and was successfully applied for the determination of HIV-p24 in real human serum samples, giving satisfactory results. The accuracy and reliability of the sensor is further confirmed by enzyme-linked immunosorbent assay (ELISA).

Co 3 O 4 supported on N, P-doped carbon as a bifunctional electrocatalyst for oxygen reduction and evolution reactions

Noble metals, such as platinum, ruthenium and iridium-group metals, are often used as oxygen reduction or evolution reaction (ORR/OER) electrocatalysts. To reduce the cost and provide an application of bifunctional catalysis, in this work, cobalt oxide supported on nitrogen and phosphorus co-doped carbon (Co 3 O 4 /NPC) was fabricated and examined as a bifunctional electrocatalyst for OER and ORR. To prepare Co 3 O 4 /NPC, NPC was pyrolyzed from melamine and phytic acid supported on carbon, followed by the solvothermal synthesis of Co 3 O 4 on NPC. Linear sweep voltammetry was used to evaluate the activity for OER and ORR. For OER, Co 3 O 4 /NPC showed an onset potential of 0.54 V (versus the saturated calomel electrode) and a current density of 21.95 mA/cm 2 at 0.80 V, which was better than both Co 3 O 4 /C and NPC. The high activity of Co 3 O 4 /NPC was attributed to a synergistic effect of the N, P co-dopants and Co 3 O 4 . For ORR, Co 3 O 4 /NPC exhibited an activity close to commercial Pt/C in terms of the diffusion limited current density (-4.49 vs -4.76 mA/cm 2 at -0.80 V), and Co 3 O 4 played the key role for the catalysis. Chronoamperometry (current versus time) was used to evaluate the stability, which showed that Co 3 O 4 /NPC maintained 46% current after the chronoamperometry test for OER and 95% current for ORR. Overall, Co 3 O 4 /NPC exhibited high activity and improved stability for both OER and ORR.

Glassy Carbon Electrode Modified with Citrate Stabilized Gold Nanoparticles for Sensitive Arsenic (III) Detection

The electrochemical detection of As(III) was investigated on the novel citrate stabilized gold nanoparticle modified glassy carbon electrode (AuNPs/GCE) in 1 M HCl by square wave anodic stripping voltammetry. AuNPs/GCE was prepared by simply casting citrate stabilized gold nanoparticles onto the well-polished glassy carbon electrode. Gold modification was evaluated by cyclic voltammetry, while transmission electron microscopy and UV-vis Spectroscopy revealed the size and distribution of gold nanoparticles. Anodic stripping voltammetry was performed with the modified electrode in As(III) solution. Electrochemical experiments proved that AuNPS/GCE exhibited good performance for As(III) analysis, the linear range were obtained between 0.05 and 1 ppb for trace level of As(III) as well as 1 to 15 ppb, with a limit of detection of 0.025 ppb. In terms of reproducibility, the precision of the aforementioned method in %RSD was calculated at 7.78% (n = 10), and the repeatability of the proposed method was calculated to be 1.59%. The application of the method to analyze As(III) in tap water was investigated.

MIPs-graphene nanoplatelets-MWCNTs modified glassy carbon electrode for the determination of cardiac troponin I

An electrochemical sensor with high selectivity in addition to sensitivity was developed for the determination of cardiac troponin I (cTnI), based on the modification of cTnI imprinted polymer film on a glassy carbon electrode (GCE). The sensor was fabricated by layer-by-layer assembled graphene nanoplatelets (GS), multiwalled carbon nanotubes (MWCNTs), chitosan (CS), glutaraldehyde (GA) composites, which can increase the electronic transfer rate and the active surface area to capture a larger number of antigenic proteins. MWCNTs/GS based imprinted polymers (MIPs/MWCNTs/GS) were synthesized by means of methacrylic acid (MAA) as the monomer, ethylene glycol dimethacrylate (EGDMA) as the cross linker α,α-azobisisobutyronitrile (AIBN) as the initiator and cTnI as the template. In comparison with conventional methods, the proposed electrochemical sensor is highly sensitive for cTnI, providing a better linear response range from 0.005 to 60xa0ngxa0cm-3 and a lower limit of detection (LOD) of 0.0008xa0ngxa0cm-3 under optimal experimental conditions. In addition, the electrochemical sensor exhibited good specificity, acceptable reproducibility and stability. Moreover, satisfactory results were obtained in real human serum samples, indicating that the developed method has the potential to find application in clinical detection of cTnI as an alternative approach.

A highly sensitive metronidazole sensor based on a Pt nanospheres/polyfurfural film modified electrode

In this contribution, we combine the advantages of both Pt nanospheres and polyfurfural film and successfully develop a novel Pt nanospheres/polyfurfural film modified glassy carbon electrode (GCE) for electrochemical sensing of a nitro group containing pentatomic cyclic compound, metronidazole. In particular, the polyfurfural film and Pt nanospheres were handily obtained by a one-step electropolymerization method and a potential step method, respectively. Benefiting from their excellent synergistic catalytical properties, the Pt nanospheres/polyfurfural film/GCE shows significantly enhanced electrocatalytic activity towards metronidazole. A series of experimental parameters including the electropolymerization cycles of furfural, the deposition time of platinum, accumulation time, accumulation potential and pH of the supporting electrolyte for metronidazole was also investigated and optimized. The proposed sensor exhibited excellent selectivity, stability and reproducibility for the determination of metronidazole, providing a wide linear detection range from 2.5 to 500 μmol dm−3 and a low detection limit of 50 nmol dm−3 (S/N = 3) under optimal experimental conditions. When the proposed sensor was applied to determine metronidazole in real human serum samples, it gave a satisfactory result.

Self-cleaned electrochemical protein imprinting biosensor basing on a thermo-responsive memory hydrogel

Herein, the self-cleaned electrochemical protein imprinting biosensor basing on a thermo-responsive memory hydrogel was constructed on a glassy carbon electrode (GCE) with a free radical polymerization method. Combining the advantages of thermo-responsive molecular imprinted polymers and electrochemistry, the resulted biosensor presents a novel self-cleaned ability for bovine serum albumin (BSA) in aqueous media. As a temperature controlled gate, the hydrogel film undergoes the adsorption and desorption of BSA basing on a reversible structure change with the external temperature stimuli. In particular, these processes have been revealed by the response of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of electroactive [Fe(CN)6]3-/4-. The results have been supported by the evidences of scanning electron microscopy (SEM) and contact angles measurements. Under the optimal conditions, a wide detection range from 0.02μmolL-1 to 10μmolL-1 with a detection limit of 0.012 μmolL-1 (S/N = 3) was obtained for BSA. This proposed BSA sensor also possesses high selectivity, excellent stability, acceptable recovery and good reproducibility in its practical applications.

High sensitivity chlorogenic acid detection based on multiple layer-by-layer self-assembly films of chitosan and multi-walled carbon nanotubes on a glassy carbon electrode

A chlorogenic acid sensor based on a chitosan (CS) and multi-walled carbon nanotubes (MWCNTs) modified glassy carbon electrode (GCE) was fabricated via a layer-by-layer (LBL) self-assembly method. The prepared electrode exhibited excellent catalytic performance for chlorogenic redox reactions compared to the bare GCE. The effects of the number assembly layers, scan rate, pH of the supporting electrolyte and accumulation time on chlorogenic acid detection were optimized. Under the optimal conditions, the proposed sensor was significantly sensitive for the detection of chlorogenic acid and showed wide linear detection ranges at low concentrations from 2 × 10−8 to 1 × 10−7 mol dm−3 and at high concentrations from 1 × 10−7 to 2.25 × 10−4 mol dm−3. The detection limit was estimated to be 1.16 × 10−8 mol dm−3 (S/N = 3). Furthermore, the chlorogenic acid sensor exhibited excellent selectivity and stability and was utilized in practical applications, in particular, for the determination of human real samples.

Improved performance of cobalt-based spinel by the simple solvothermal method as electrocatalyst for oxygen reduction reaction in alkaline solution

The performance of the cobalt-based spinel electrocatalysts (MCo2X4) is improved for oxygen reduction reaction (ORR) by simply optimizing solvothermal conditions via the orthogonal experiment L18 (2xa0×xa037). Five conditions are investigated, and the order of significant factors for ORR efficiency is metal componentxa0>xa0solvothermal temperaturexa0>xa0calcining temperaturexa0>xa0precipitantxa0>xa0solvent component. Mn, Ni, or S is considered as the factor of metal component or precipitant respectively and is introduced into the Co3O4 to find the best MCo2X4 for ORR. But, the pure Co3O4 exhibits the best performance among these cobalt-based catalysts. The optimized product, 9.6xa0wt.% Co3O4 supported on carbon (Co3O4/C), can reach 90xa0% of the 20xa0wt.% Pt/C in term of the limited diffusion current exhibiting the close efficiency of Co3O4/C to Pt/C. Methanol-poisoning tests performed by chronoamperometry show the Co3O4/C remained 95xa0% current after 6xa0h, exhibiting superior methanol resistance and long-time stability.

Coordination matrix/signal amplifier strategy for simultaneous electrochemical determination of cadmium(II), lead(II), copper(II), and mercury(II) ions based on polyfurfural film/multi-walled carbon nanotube modified electrode

In this work, we firstly propose and confirm a novel coordination matrix/signal amplifier strategy to construct a highly sensitive lead(II) electrochemical sensor. Lead(II) ions can be efficiently accumulated and deposited on the electrode surface by strong coordination bonds between the unoccupied d-orbital of lead(II) ions and conjugated π-electron backbones of polyfurfural film (coordination matrix), and then the anodic stripping current can be significantly enhanced by multi-walled carbon nanotubes (MWCNTs, signal amplifier), finally realizing the highly sensitive determination of lead(II). The polyfurfural film/MWCNT modified glassy carbon electrode (GCE) sensor provided a wide linear detection range from 0.05 to 10 μg L−1 and a low detection limit of 0.01 μg L−1 (S/N = 3) for lead(II). Compared with a classical mercury film sensor (a classical and effective method for determining heavy metal ions), our proposed sensor was more sensitive and achieved better results. Moreover, based on the coordination matrix/signal amplifier strategy, the polyfurfural film/MWCNTs/GCE sensor was further successfully utilized for the simultaneous determination of Cd2+, Pb2+, Cu2+, and Hg2+, demonstrating a wide linear detection range for Cd2+ (0.5–15 μg L−1), Pb2+ (0.1–15 μg L−1), Cu2+ (0.1–12 μg L−1), and Hg2+ (1.5–12 μg L−1) and a low detection limit for Cd2+ (0.03 μg L−1, S/N = 3), Pb2+ (0.01 μg L−1, S/N = 3), Cu2+ (0.06 μg L−1, S/N = 3), and Hg2+ (0.1 μg L−1, S/N = 3). Finally, the proposed sensor was successfully applied to simultaneously determine Cd2+, Pb2+, Cu2+, and Hg2+ in real tap water samples. This work provides a novel and effective analytical strategy for constructing novel electrochemical sensors and shows broad application prospects in heavy metal ion determination for the future.