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An electrochemical sensor based on a new nanocomposite of graphene/Fe3O4 has been fabricated for simultaneous determination of melatonin and dopamine.

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The fast detection of trace amounts of hazardous contaminations can prevent serious damage to the environment. Paper-based sensors offer a new perspective on the world of analytical methods, overcoming previous limitations by fabricating a simple device with valuable benefits such as flexibility, biocompatibility, disposability, biodegradability, easy operation, large surface-to-volume ratio, and cost-effectiveness. Depending on the performance type, the device can be used to analyze the analyte in the liquid or vapor phase. For liquid samples, various structures (including a dipstick, as well as microfluidic and lateral flow) have been constructed. Paper-based 3D sensors are prepared by gluing and folding different layers of a piece of paper, being more user-friendly, due to the combination of several preparation methods, the integration of different sensor elements, and the connection between two methods of detection in a small set. Paper sensors can be used in chromatographic, electrochemical, and colorimetric processes, depending on the type of transducer. Additionally, in recent years, the applicability of these sensors has been investigated in various applications, such as food and water quality, environmental monitoring, disease diagnosis, and medical sciences. Here, we review the development (from 2010 to 2021) of paper methods in the field of the detection and determination of toxic substances.

A novel electrochemical sensor based on the reduced graphene oxide-Cu/CuO-Ag nanocomposite modified glassy carbon electrode (rGO/Cu/CuO-Ag/GCE) has been applied for the simultaneous analysis of carbaryl and fenamiphos as two important pesticides. The electrochemical behavior of carbaryl and fenamiphos at rGO/Cu/ CuO-Ag/GCE was studied by cyclic voltammetry and differential pulse voltammetry. The modified electrode exhibited two separated oxidation signals for the simultaneous determination of both carbaryl and fenamiphos with excellent sensitivity. The characteristics of the modified electrode were studied with transmission electron microscopy, X-ray diffraction and Fourier transform-infrared spectroscopy techniques. Under optimized conditions, the rGO/Cu/CuO-Ag/GCE detected carbaryl and fenamiphos with the wide linear ranges of 0.05-20 and 0.01-30 μM, and the detection limits were 0.005 and 0.003 μM, respectively. This developed electrochemical platform applied as a simple and cost-effective sensor for the detection of low levels of carbaryl and fenamiphos in fruit and vegetable samples successfully.

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