Yemin Guo

An acetylcholinesterase biosensor based on graphene-gold nanocomposite and calcined layered double hydroxide.

In this study, a novel acetylcholinesterase-based biosensor was fabricated. Acetylcholinesterase (AChE) was immobilized onto a glassy carbon electrode (GCE) with the aid of Cu-Mg-Al calcined layered double hydroxide (CLDH). CLDH can provide a bigger effective surface area for AChE loading, which could improve the precision and stability of AChE biosensor. However, the poor electroconductibility of CLDHs could lead to the low sensitivity of AChE biosensor. In order to effectively compensate the disadvantages of CLDHs, graphene-gold nanocomposites were used for improving the electron transfer rate. Thus, the graphene-gold nanocomposite (GN-AuNPs) was firstly modified onto the GCE, and then the prepared CLDH-AChE composite was immobilized onto the modified GCE to construct a sensitive AChE biosensor for pesticides detection. Relevant parameters were studied in detail and optimized, including the pH of the acetylthiocholine chloride (ATCl) solution, the amount of AChE immobilized on the biosensor and the inhibition time governing the analytical performance of the biosensor. The biosensor detected chlorpyrifos at concentrations ranging from 0.05 to 150μg/L. The detection limit for chlorpyrifos was 0.05μg/L.

Electrochemical Aptasensor Based on Prussian Blue-Chitosan-Glutaraldehyde for the Sensitive Determination of Tetracycline

In this paper, a novel and sensitive electrochemical aptasensor for detecting tetracycline (TET) with prussian blue (PB) as the label-free signal was fabricated. A PB-chitosan-glutaraldehyde (PB-CS-GA) system acting as the signal indicator was developed to improve the sensitivity of the electrochemical aptasensor. Firstly, the PB-CS-GA was fixed onto the glass carbon electrode surface. Then, colloidal gold nanoparticles (AuNPs) were droped onto the electrode to immobilize the anti-TET aptamer for preparation of the aptasensor. The stepwise assembly process of the aptasensor was characterized by cyclic voltammetry (C-V) and scanning electron microscope (SEM). The target TET captured onto the electrode induced the current response of the electrode due to the non-conducting biomoleculars. Under the optimum operating conditions, the response of differential pulse voltammetry (DPV) was used for detecting the concentration of TET. The proposed aptasensor showed a high sensitivity and a wide linear range of 10−9 ∼ 10−5 M and 10−5 ∼ 10−2 M with the correlation coefficients of 0.994 and 0.992, respectively. The detection limit was 3.2×10−10 M (RSD 4.12%). Due to its rapidity, sensitivity and low cost, the proposed aptasensor could be used as a pre-scanning method in TET determination for the analysis of livestock products.

Acetylcholinesterase biosensor based on the mesoporous carbon/ferroferric oxide modified electrode for detecting organophosphorus pesticides

In this paper a biosensor modified by ordered mesoporous carbon–chitosan (OMC–CS)/ferroferric oxide–chitosan (Fe3O4–CS) was developed on the surface of screen-printed carbon electrodes (SPCEs). The acetylcholinesterase (AChE) was modified onto the film to prepare an AChE biosensor. Chitosan was used as a dispersant to disperse OMC and Fe3O4. The OMC and Fe3O4 were used to enhance the electrochemical response. Before the detection of organophosphorus (OP) pesticides, the electrochemical behaviour of AChE/OMC–CS/Fe3O4–CS/SPCE was studied with cyclic voltammetry, and the results showed that the chitosan can disperse OMC and Fe3O4 evenly and fix them on the electrode surface firmly. OMC and Fe3O4 have a significant synergistic effect towards electron transfer. The parameters affecting performance, such as the pH of the test solution, the amount of AChE and the time of inhibition have been optimized. Under optimum conditions, using methamidophos and chlorpyrifos as model compounds, this biosensor showed a wide range, low detection limit, good reproducibility and high stability. Moreover, the AChE/OMC–CS/Fe3O4–CS/SPCE biosensor can be used for the detection of real samples, and is suitable for field testing of OP pesticide residues.

An ultrasensitive aptasensor for chlorpyrifos based on ordered mesoporous carbon/ferrocene hybrid multiwalled carbon nanotubes

In this study, we designed a novel and ultrasensitive aptamer sensor for the quantitative detection of chlorpyrifos. To improve the sensitivity of the aptasensor, mesoporous carbon (OMC) functionalized by chitosan (OMC-CS) and ferrocene hybrid chitosan (CS) dispersed multiwalled carbon nanotubes (Fc@MWCNTs-CS) were modified on the electrode surface. OMC-CS has a high specific surface area, high porosity and ideal dispersibility which was used to efficiently capture larger amounts of material. Fc@MWCNTs-CS can efficiently capture more aptamer and increase electron transfer between the work electrode surface and potassium ferricyanide due to the good biocompatibility and electrical conductivity. The fabrication of the aptasensor was characterized using cyclic voltammetry, scanning electron microscopy and energy dispersive spectrometry. Under optimal conditions the designed aptasensor exhibited a wide linear range from 1 to 105 ng mL−1 with a low detection limit of 0.33 ng mL−1 (S/N = 3) for chlorpyrifos. The proposed chlorpyrifos aptasensor exhibited high selectivity, reproducibility and stability performance, which may open a new door for the ultrasensitive detection of chlorpyrifos residues in vegetables and fruits.

Acetylcholinesterase biosensor for carbaryl detection based on interdigitated array microelectrodes

In this study, an acetylcholinesterase (AChE) biosensor with superior accuracy and sensitivity was successfully developed based on interdigitated array microelectrodes (IAMs). IAMs have a series of parallel microband electrodes with alternating microbands connected together. Chitosan was used as the enzyme immobilization material, and AChE was used as the model enzyme for carbaryl detection to fabricate AChE biosensor. Electrochemical impedance spectroscopy was used in conjunction with the fabricated biosensor to detect pesticide residues. Based on the inhibition of pesticides on the AChE activity, using carbaryl as model compounds, the biosensor exhibited a wide range, low detection limit, and high stability. Moreover, the biosensor can also be used as a new promising tool for pesticide residue analysis.

Aptasensors modified by antimony tin oxide nanoparticle-chitosan based on interdigitated array microelectrodes for tetracycline detection

Aptasensors modified by antimony tin oxide nanoparticle-chitosan (nano ATO-CS) based on interdigitated array microelectrodes (IDAMs) were developed for the detection of tetracycline. The nano ATO-CS film was fabricated onto the microelectrode surface, and then tetracycline aptamers were modified onto the film to prepare an aptasensor. The results showed that chitosan can disperse nano ATOs evenly and make them fixed on the microelectrode surface firmly. Nano-ATOs being incorporated into chitosan film can effectively promote the electron transfer reaction and enhance the electrochemical response. The electrochemical properties of the fabricated processes were characterized by electrochemical impedance spectroscopy (EIS). Parameters affecting the aptasensor response, such as pH of the base solution, the concentration of the aptamer and incubation time, were optimized. Under optimum conditions, different concentrations of tetracyclines were detected with the aptasensor. Based on the contributions of nano ATO-CS solutions, the proposed aptasensor displayed high sensitivity, high specificity, and a low detection limit (3.0 × 10−9 g mL−1). It could be successfully applied to the detection of tetracyclines in real milk spiked samples.

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 Miniaturized Portable Instrument for Rapid Determination Pesticides Residues in Vegetables and Fruits

In this paper, we developed a portable pesticides residues detection instrument by integrating an amperometric acetylcholinesterase (AChE) biosensor and a signal detecting circuit. The AChE biosensor was modified with tin oxide (SnO2) nanoparticles, chitosan, and multiwalled carbon nanotubes nanocomposite. Because the signal generated from the acetylcholinesterase biosensor is very weak, an analog signal detect circuit is elaborately designed to reduce lots of the noises and system drifts. This instrument could realize rapid detection of pesticides residues in fruits and vegetables on-site with automatic data processing, display, and data storage. The detection limit was 100 ng/L. The measurement time from sample treatment to detection was 15 min. Compared with traditional analytical methods, this proposed pesticides residues detection instrument possessed a good precision and high stability. This will be a new promising rapid detection instrument for pesticides residues in agricultural products.

An aptasensor with dsDNA for rapid and highly sensitive detection of kanamycin in milk

Herein, we developed an aptasensor using double-stranded DNA (dsDNA) modified with cadmium sulfide (CdS) nanoparticles and gold nanoparticles (AuNPs) on a gold electrode (GE) for kanamycin detection. The CdS nanoparticles were employed to strongly adsorb on the surface of GE via Au–S interactions. AuNPs, as the mediators, improved electron relay during the entire electron transfer process and the aptasensor response speed. Herein, we used dsDNA instead of single-stranded DNA (ssDNA) as the capture probe to prepare an aptasensor with improved stability. The proposed aptasensor exhibited a wider linearity to kanamycin in the range of 10.0–450.0 nM with a low detection limit of 2.85 nM. The aptasensor with ssDNA showed a low limit of detection of 9.76 nM. Moreover, it displayed high specificity for kanamycin and was free from interference in common milk adulterants. The proposed aptasensor had good reproducibility, stability, repeatability, and cost-effective regeneration. The aptasensor could selectively identify targets even in complex matrices, such as skimmed milk, and could be used for the detection of kanamycin in milk.

Acetylcholinesterase biosensor modified with ATO/OMC for detecting organophosphorus pesticides

This work demonstrates the sensitive amperometric determination of organophosphorus pesticides (OPs) on screen-printed electrodes (SPEs) modified with antimony tin oxide-chitosan (ATO-CS) and ordered mesoporous carbon-chitosan (OMC-CS) composite nanomaterials. ATO could effectively promote electron transfer and enhance the electrochemical reaction. OMC had a larger specific surface area, so it could effectively fix more AChE and improve the sensitivity of the sensor. Thus, ATO-CS and OMC-CS were modified onto the SPE layer-by-layer, which could improve the electrochemical response, increase the fixed amount of the enzyme on the electrode, and, accordingly, the sensitivity of the biosensor was obviously improved. The electrochemical behavior of the AChE biosensor was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. Under optimum conditions, with chlorpyrifos and methamidophos as the model compounds, the inhibition of AChE activity based on OPs was detected. The proposed acetylcholinesterase biosensor displayed an excellent analytical performance with great reproducibility. The detection limits for chlorpyrifos and methamidophos were 0.01 μg L−1 and 1 μg L−1, respectively. In addition, the as-prepared acetylcholinesterase biosensor was successfully utilized for the determination of OPs in actual samples.