Wenping Zhao

Acetylcholinesterase biosensor based on chitosan/prussian blue/multiwall carbon nanotubes/hollow gold nanospheres nanocomposite film by one-stepelectrodeposition

In this paper, chitosan-prussian blue-multiwall carbon nanotubes-hollow gold nanospheres (Chit-PB-MWNTs-HGNs) film was fabricated onto the gold electrode surface by one-step electrodeposition method; and then acetylcholinesterase (AChE) and Nafion were modified onto the film to prepare an AChE biosensor. Incorporating MWNTs and HGNs into Chit-PB hybrid film promoted electron transfer reaction, enhanced the electrochemical response and improved the microarchitecture of the electrode surface. The morphologies and electrochemistry properties of the composite were investigated by using scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy, respectively. Parameters affecting the biosensor response such as pH, enzyme loading and inhibition time were optimized. Based on the inhibition of pesticides on the AChE activity, using malathion, chlorpyrifos, monocrotophos and carbofuran as model compounds, this biosensor showed a wide range, low detection limit, good reproducibility and high stability. Moreover, AChE/Chit-PB-MWNTs-HGNs/Au biosensor can also be used for direct analysis of practical samples, which would be a new promising tool for pesticide analysis.

A Label-Free Electrochemical Immunosensor for Carbofuran Detection Based on a Sol-Gel Entrapped Antibody

In this study, an anti-carbofuran monoclonal antibody (Ab) was immobilized on the surface of a glassy carbon electrode (GCE) using silica sol-gel (SiSG) technology. Thus, a sensitive, label-free electrochemical immunosensor for the direct determination of carbofuran was developed. The electrochemical performance of immunoreaction of antigen with the anti-carbofuran monoclonal antibody was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), in which phosphate buffer solution containing [Fe(CN)6]3−/4− was used as the base solution for test. Because the complex formed by the immunoreaction hindered the diffusion of [Fe(CN)6]3−/4− on the electrode surface, the redox peak current of the immunosensor in the CV obviously decreased with the increase of the carbofuran concentration. The pH of working solution, the concentration of Ab and the incubation time of carbofuran were studied to ensure the sensitivity and conductivity of the immunosensor. Under the optimal conditions, the linear range of the proposed immunosensor for the determination of carbofuran was from 1 ng/mL to 100 μg/mL and from 50 μg/mL to 200 μg/mL with a detection limit of 0.33 ng/mL (S/N = 3). The proposed immunosensor exhibited good high sensitivity and stability, and it was thus suitable for trace detection of carbofuran pesticide residues.

Ratiometric electrochemical aptasensor based on ferrocene and carbon nanofibers for highly specific detection of tetracycline residues

A sensitive and efficient ratiometric electrochemical aptasensor was designed for tetracycline (TET) detection in milk. The ratiometric electrochemical aptasensor was constructed by integrating two aptasensors termed as aptasensor 1 and aptasensor 2. The aptasensor 1 was fabricated that based on ferrocene (Fc) and gold nanoparticles (AuNPs) nanocomposite. Meanwhile, the aptasensor 2 was prepared that based on carbon nanofibers (CNFs) and AuNPs nanocomposite. TET-aptamer was immobilized effectively onto screen-printed carbon electrodes (SPCEs) surface through forming Au-S bond between AuNPs and thiol of aptamer at 5′ end to construct the aptasensor 1 and aptasensor 2. And their detection results were calculated by ratio. Thus, the proposed ratiometric aptasensor solved the problem of low accuracy and large differences between batches. Under the optimized conditions, the TET was detected by differential pulse voltammetry (DPV). Taken advantage of ratio calculation, the as-prepared ratiometric aptasensor could detect TET quantitatively in the range of 10−8–10−3gL−1, with a detection limit of 3.3 × 10−7gL−1. Moreover, its applicability to TET-contaminated real samples (milk) showed an excellent agreement with the values determined by ultrahigh-performance liquid chromatography-tandem mass spectrometry (UPLC-ESI-MS/MS). With high sensitivity, accuracy and reliability, the developed ratiometric aptasensor held a great potential in TET detection for food safety.

A Comparative Study of Modified Materials of Acetylcholinesterase Biosensor

In this study, multi-walled carbon nanotubes (MWCNTs), gold nanoparticles (GNPs) and Prussian Blue (PB) were used for modifying glassy carbon working electrode (GCE) to construct acetylcholinesterase (AChE) biosensor respectively. Chitosan membrane was used for immobilizing AChE through glutaraldehyde cross-linking attachment to recognize pesticides selectively. Before the detection, the enzyme membrane was quickly fixed on the surfaces of modified electrode with O-ring to prepare an ampero-metric acetylcholinesterase biosensor for organophosphate pesticides. The fabrication procedures were characterized by cyclic voltammetry and amperometric i-t curve. The electrochemical behaviours of three modified sensors were compared, and the results showed that AChE-PB/GCE possessed higher oxidation peak current at a lower potential. Based on the inhibition of organophosphorus pesticides to the enzymatic activity of AChE, using dichlorvos as model compound, the sensitivity of three modified biosensors were compared, the results showed that the detection limit of AChE-PB/ GCE was lowest.

A dual-signal amplification strategy for kanamycin based on ordered mesoporous carbon-chitosan/gold nanoparticles-streptavidin and ferrocene labelled DNA

An ultrasensitive electrochemical aptasensor for kanamycin (KAN) detection was constructed with a dual-signal amplification strategy. The aptasensor achieved greatly amplified sensitivity due to the excellent electrical conductivity of the ordered mesoporous carbon-chitosan (OMC-CS)/gold nanoparticles-streptavidin (AuNPs-SA) and DNA2 labelled with ferrocene (Fc-DNA2). The AuNPs-SA was used to immobilize the DNA strand (biotin labelled) with the biotin-streptavidin system. The DNA2 strand containing the KAN aptamer was labelled with ferrocene to increase the current signal on the electrode surface when bound to KAN. Some factors that affect the performance of the aptasensor were optimized, and the proposed aptasensor provided a wide linear range from 1 × 10-10 M to 4 × 10-6 M, with a detection limit as low as 35.69 pM for KAN under the optimized conditions. This aptasensor had satisfactory electrochemical performance with good stability, sensitivity and reproducibility. Additionally, it also displayed a good specificity for KAN without interference from competitive analogues. Furthermore, the constructed aptasensor was successfully used to detect KAN in a real milk sample. The proposed method for KAN detection has great potential for the detection of other antibiotics.

Polyaniline modified electrodes acetylcholinesterase biosensor

Aniline was electropolymerized by cyclic voltammetry onto the surface of glassy carbon electrode (GCE) to fabricate the polyaniline (PANI) modified electrode, the modified electrode showed an excellent electrocatalytical effect on the oxidation of thiocholine (TCh). The PANI films were formed on the glassy carbon electrode (GCE) by cyclic voltammety between −0.2 and 0.9 V vs. saturated calomelelectrode (SCE), and acetylcholinesterase (AChE) was immobilized in chitosan membrane with a filter pore size of 0.45µm to prepare enzyme membrane. The enzyme membrane was then fixed on the surface of PANI/GCE with O-ring to prepare an amperometric AChE-PANI/GCE sensor for the detection of dichlorvos pesticides. The characteristics of the electrodeposition layer were observed to be dependent on the deposition time, PH, and aniline concentration. Under the optimal experimental conditions, the dichlorvos inhibition on AChE-PANI/ GCE was proportional to its concentration from 5 to 100µg/l, with the correlation coefficients of 0.9945. And the results showed high stability, good selectivity and reproducibility for determination of dichlorvos.