Detection of Oxytetracycline Using an Electrochemical Label-Free Aptamer-Based Biosensor.

One of the most effective ways to detect and measure antibiotics is to detect their biomarkers. The best biomarker for the control and detection of oxytetracycline (OTC) is the OTC-specific aptamer. In this study, a novel, rapid, and label-free aptamer-based electrochemical biosensor (electrochemical aptasensor) was designed for OTC determination based on a newly synthesized nanocomposite including multi-walled carbon nanotubes (MWCNTs), gold nanoparticles (AuNPs), reduced graphene oxide (rGO), and chitosan (CS), as well as nanosheets to modify a glassy carbon electrode, which extremely enhanced electrical conductivity and increased the electrode surface to bind well with the amine-terminated OTC-specific aptamer through self-assembly. The (MWCNTs-AuNPs/CS-AuNPs/rGO-AuNPs) nanocomposite modified electrode was synthesized using a layer- by-layer modification method which had the highest efficiency for better aptamer stabilization. Differential pulse voltammetry (DPV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) techniques were used to investigate and evaluate the electrochemical properties and importance of the synthesized nanocomposite in different steps. The designed aptasensor was very sensitive for measuring the OTC content of milk samples, and the results were compared with those of our previously published paper. Based on the calibration curve, the detection limit was 30.0 pM, and the linear range was 1.00-540 nM for OTC. The repeatability and reproducibility of the aptasensor were obtained for 10.0 nM of OTC with a relative standard deviation (RSD%) of 2.39% and 4.01%, respectively, which were not affected by the coexistence of similar derivatives. The measurement in real samples with the recovery range of 93.5% to 98.76% shows that this aptasensor with a low detection limit and wide linear range can be a good tool for detecting OTC.

An electrochemical DNA biosensor based on Oracet Blue as a label for detection of Helicobacter pylori.

An innovative method of a DNA electrochemical biosensor based on Oracet Blue (OB) as an electroactive label and gold electrode (AuE) for detection of Helicobacter pylori, was offered. A single-stranded DNA probe with a thiol modification was covalently immobilized on the surface of the AuE by forming an Au-S bond. Differential pulse voltammetry (DPV) was used to monitor DNA hybridization by measuring the electrochemical signals of reduction of the OB binding to double-stranded DNA (ds-DNA). Our results showed that OB-based DNA biosensor has a decent potential for detection of single-base mismatch in target DNA. Selectivity of the proposed DNA biosensor was further confirmed in the presence of non-complementary and complementary DNA strands. Under optimum conditions, the electrochemical signal had a linear relationship with the concentration of the target DNA ranging from 0.3nmolL(-1) to 240.0nmolL(-1), and the detection limit was 0.17nmolL(-1), whit a promising reproducibility and repeatability.

A sensitive DNA biosensor fabricated from gold nanoparticles and graphene oxide on a glassy carbon electrode.

A sensitive electrochemical DNA biosensor was developed for Helicobacter pylori (H. pylori) detection using differential pulse voltammetry. Single-stranded DNA probe was immobilized on a graphene oxide/gold nanoparticles modified glassy carbon electrode (GO/AuNPs/GCE). A hybridization reaction was conducted with the target DNA and the immobilized DNA on the electrode surface. Oracet blue (OB) was selected for the first time as a redox indicator for amplifying the electrochemical signal of DNA. Enhanced sensitivity was achieved through combining the excellent electric conductivity of GO/AuNPs and the electroactivity of the OB. The DNA biosensor displayed excellent performance to demonstrate the differences between the voltammetric signals of the OB obtained from different hybridization samples (non-complementary, mismatch and complementary DNAs). The proposed biosensor has a linear range of 60.0-600.0 pM and a detection limit of 27.0 pM for detection of H. pylori. In addition, the biosensor have responded very well in the simulated real sample evaluations, signifying its potential to be used in future clinical detection of the H. pylori bacteria.