Gangbing Zhu

Highly sensitive and simultaneous electrochemical determination of 2-aminophenol and 4-aminophenol based on poly(l-arginine)-β-cyclodextrin/carbon nanotubes@graphene nanoribbons modified electrode

Owing to the similar characteristics and physiochemical property of 2-aminophenol (2-AP) and 4-aminophenol (4-AP), the highly sensitive simultaneous electrochemical determination of 2- and 4-AP is a great challenge. In this paper, by electropolymerizing β-cyclodextrin (β-CD) and l-arginine (l-Arg) on the surface of carbon nanotubes@graphene nanoribbons (CNTs@GNRs) core-shell heterostructure, a P-β-CD-l-Arg/CNTs@GNRs nanohybrid modified electrode was prepared successfully, and it could exhibit the synergetic effects of β-CD (high host-guest recognition and enrichment ability), l-Arg (excellent electrocatalytic activity) and CNTs@GNRs (prominent electrochemical properties and large surface area), the P-β-CD-l-Arg/CNTs@GNRs modified electrode was used in the electrochemical determination of 2- and 4-AP, the results demonstrated that the highly sensitive and simultaneous determination of 2- and 4-AP is successfully achieved and the modified electrode has a linear response range of 25.0-1300.0 nM for both 2- and 4-AP, and the detection limits of 2- and 4-AP obtained in this work are 6.2 and 3.5 nM, respectively.

Multiwalled carbon nanotube@reduced graphene oxide nanoribbon heterostructure: synthesis, intrinsic peroxidase-like catalytic activity, and its application in colorimetric biosensing

In this study, multiwalled carbon nanotube@reduced graphene oxide nanoribbon (MWCNT@rGONR) core-shell heterostructures have been synthesized by the facile unzipping of MWCNTs and subsequent chemical reduction with hydrazine. MWCNTs with diameter <10 nm were selected as the starting material to maintain narrow ribbons <30 nm wide with a few-layer structure. The most important discovery is that the resulting MWCNT@rGONR heterostructures possess intrinsic peroxidase-like activity, 15.9 times higher than that of MWCNTs and 8.4 times higher than that of their unreduced form. The nature of the peroxidase-like activity of the MWCNT@rGONR heterostructures can be attributed to the acceleration of their electron-transfer process and the consequent facilitation of ˙OH radical generation. Kinetic analysis demonstrates that the catalytic behavior is in accordance with typical Michaelis-Menten kinetics and the obtained kinetic parameters indicate that the MWCNT@rGONR heterostructures display a higher affinity for both H2O2 and 3,3,5,5-tetramethylbenzidine than that of horseradish peroxidase. On this basis, we have employed the MWCNT@rGONR heterostructures as novel biosensing platforms to develop a simple, sensitive, and selective colorimetric biosensor for free cholesterol determination. This work will facilitate the formation of MWCNT@rGONR heterostructures with narrow ribbons and the utilization of their intrinsic peroxidase-like activity in biotechnology and medical diagnostics.

Graphene quantum dots enhanced electrochemiluminescence of cadmium sulfide nanocrystals for ultrasensitive determination of pentachlorophenol

An ultrasensitive electrochemiluminescence (ECL) sensor based on the ECL amplifying behavior of the graphene quantum dots-CdS nanocrystals (GQDs-CdS NCs) was constructed for the detection of pentachlorophenol (PCP). Because of the presence of doped GQDs, the resulting GQDs-CdS NCs exhibited 5-fold enhanced ECL intensity than pure CdS NCs with the ECL onset potential positively shifted by 80 mV. Furthermore, based on the effective inhibition of the ECL response of GQDs-CdS NCs film by PCP, a simple method for ultrasensitive determination of PCP was devised, which showed a wide linear range of 0.01-500 ng mL(-1) and a low detection limit of 3 pg mL(-1) (S/N = 3) with good stability, reproducibility and applicability for PCP detection in real water samples. Thus, it can be expected that GQDs-based composites with excellent performance may play a more important role in pesticide determination.

Nitrogen-doped hollow carbon spheres wrapped with graphene nanostructure for highly sensitive electrochemical sensing of parachlorophenol.

Owing to awfully harmful to the environment and human health, the qualitative and quantitative determination of parachlorophenol (PCP) is of great significance. In this paper, by using silica@polydopamine as template, nitrogen-doped hollow carbon spheres wrapped with reduced graphene oxide (NHCNS@RG) nanostructure was prepared successfully via a self-assembly approach due to the electrostatic interaction, and the obtained NHCNS@RG could exhibit the unique properties of NHCNS and RG: the NHCNS could impede the aggregation tendency of RG and possess high electrocatalytic activity; the RG enlarges the contacting area and offers many area-normalized edge-plane structures and active sites. Scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray diffraction and electrochemical method were used to characterize the morphology and structure of NHCNS@RG. Then, the NHCNS@RG hybrids were applied for the electrochemical sensing of PCP, under the optimized conditions, the detection limit of PCP obtained in this work is 0.01μM and the linear range is 0.03-38.00μM.

Sensitive electrochemical determination of rhodamine B based on cyclodextrin-functionalized nanogold/hollow carbon nanospheres

Due to being harmful to the human health, the qualitative and quantitative determination of rhodamine B (RhB) is of great significance. In this paper, per-6-thio-β-cyclodextrin functionalized nanogold/hollow carbon nanospheres (β-CD-AuNPs/HCNS) nanohybrids were prepared and then applied successfully for the highly sensitive electrochemical detection of RhB. Due to the synergetic effects from the HCNS (excellent electrochemical properties and large surface area), β-CD (high host–guest recognition and water-solubility) and AuNPs (excellent electrocatalytic activity), the oxidation peak currents of RhB on the β-CD-AuNPs/HCNS modified glassy carbon electrode (GCE) are much higher than those on the AuNPs/HCNS/GCE and bare GCE. The β-CD-AuNPs/HCNS/GCE has a linear response range of 4.79–958.00 μg L−1 with a detection limit of 0.96 μg L−1 for RhB.

Rapid screening of flonicamid residues in environmental and agricultural samples by a sensitive enzyme immunoassay

A fast and sensitive polyclonal antibody-based enzyme-linked immunosorbent assay (ELISA) was developed for the analysis of flonicamid in environmental and agricultural samples. Two haptens of flonicamid differing in spacer arm length were synthesized and conjugated to proteins to be used as immunogens for the production of polyclonal antibodies. To obtain most sensitive combination of antibody/coating antigen, two antibodies were separately screened by homologous and heterologous assays. After optimization, the flonicamid ELISA showed that the 50% inhibitory concentration (IC50 value) was 3.86mgL(-1), and the limit of detection (IC20 value) was 0.032mgL(-1). There was no cross-reactivity to similar tested compounds. The recoveries obtained after the addition of standard flonicamid to the samples, including water, soil, carrot, apple and tomato, ranged from 79.3% to 116.4%. Moreover, the results of the ELISA for the spiked samples were largely consistent with the gas chromatography (R(2)=0.9891). The data showed that the proposed ELISA is an alternative tool for rapid, sensitive and accurate monitoring of flonicamid in environmental and agricultural samples.

Highly efficient detection of paclobutrazol in environmental water and soil samples by time-resolved fluoroimmunoassay

A fast and ultrasensitive indirect competitive time-resolved fluoroimmunoassay (TRFIA) was developed for the analysis of paclobutrazol in environmental water and soil samples. Paclobutrazol hapten was synthesized and conjugated to bovine serum albumin (BSA) for producing polyclonal antibodies. Under optimal conditions, the 50% inhibitory concentration (IC50 value) and limit of detection (LOD, IC20 value) were 1.09μgL(-1) and 0.067μgL(-1), respectively. The LOD of TRFIA was improved 30-fold compared to the already reported ELISA. There was almost no cross-reactivity of the antibody with the other structural analogues of triazole compounds, indicating that the antibody had high specificity. The average recoveries from spiked samples were in the range from 80.2% to 104.7% with a relative standard deviation of 1.0-9.5%. The TRFIA results for the real samples were in good agreement with that obtained by high-performance liquid chromatography analyses. The results indicate that the established TRFIA has potential application for screening paclobutrazol in environmental samples.

3,4,9,10-Perylene Tetracarboxylic Acid Noncovalently Modified Multiwalled Carbon Nanotubes: Synthesis, Characterization, and Application for Electrochemical Determination of 2-Aminonaphthalene

Carbon nanotubes have been intensively studied for their diverse applications but are insoluble in water. In this paper, 3,4,9,10-perylene tetracarboxylic acid noncovalently modified multiwalled carbon nanotubes were prepared by a facile approach and applied successfully for electrochemical determination of 2-aminonaphthalene. Infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and electrochemical methods were used to characterize the hybridized nanotubes. The results reveal that the hybrids exhibit high dispersibility in water, and a glassy carbon electrode modified by the hybrids displayed a higher electrochemical response toward 2-aminonaphthalene than bare glassy carbon and multiwalled carbon nanotube–glassy carbon electrodes with a linear dynamic range of 15.0–500.0 nM and a detection limit of 4.5 nM. The modified hybrid electrode was successfully applied for the determination of 2-aminonaphthalene in water.

An ultrasensitive competitive immunosensor using silica nanoparticles as an enzyme carrier for simultaneous impedimetric detection of tetrabromobisphenol A bis(2-hydroxyethyl) ether and tetrabromobisphenol A mono(hydroxyethyl) ether

Based on our produced polyclonal antibody capable of recognizing tetrabromobisphenol A bis(2-hydroxyethyl) ether (TBBPA-DHEE) and tetrabromobisphenol A mono(hydroxyethyl) ether (TBBPA-MHEE) (cross-reactivity, 100% for TBBPA DHEE; 98.7% for TBBPA MHEE), an important derivative and byproduct of tetrabromobisphenol A (TBBPA), respectively, a novel ultrasensitive competitive immunosensor was established using an electrochemical impedimetric strategy for the simultaneous detection of both chemicals. A significantly amplified electrochemical impedance spectroscopy (EIS) for quantitative target analysis was obtained through (i) the biocatalytic precipitation of 4-chloro-1-naphthol (CN) on the electrode surface triggered by horseradish peroxidase (HRP) and (ii) increased amounts of the enzyme with HRP-loaded silica nanoparticles carrying poly-brushes (SiO2@PAA) as labels, achieving a remarkable improvement in catalytic performance. Under the optimized conditions, the immunosensor showed satisfactory accuracy (recovery, 84.6-118%) and a good linear range (0.21- 111.31ng/mL) with a limit of detection (LOD) of 0.08ng/mL (S/N = 3) for TBBPA DHEE and TBBPA MHEE. In addition, the proposed approach was used to analyse real environmental water samples, and our results indicated that this immunosensor had great potential for the determination of the trace pollutants in aquatic environments.

A novel ratiometric fluorescent probe for the detection of uric acid in human blood based on H2O2-mediated fluorescence quenching of gold/silver nanoclusters

In this work, a ratiometric fluorescent probe (RF-probe) for highly sensitive and selective detection of uric acid was reported for the first time toward H2O2 based on inner filter effect (IFE) between bimetallic gold/silver nanoclusters (Au/Ag NCs) and 2,3-diaminophenazine (DAP). For this RF-probe, uric acid was degraded to allantoin and H2O2. Upon the addition of HRP, o-phenylenediamine (OPD) could be catalytically oxidized to DAP in the presence of H2O2, then the fluorescence intensity corresponding to DAP at 580 nm increased dramatically with a fluorescence quenching of BSA-Au/Ag NCs at 690 nm, resulting in a RF-probe toward uric acid. This RF-probe allowed for the sensitive detection of uric acid in range of 5.0 × 10-6 M to 5.0 × 10-5 M with a detection limit (S/N = 3) as low as 5.1 × 10-6 M. At the same time, it has been successfully used for uric acid levels detection in human serum, and the results are consistent with those of the hospital. RF-probe built may provide a ratiometric fluorescence universal platform for detection of various species involving in the production of H2O2 in other biological systems.