Nanomaterial-based optical colorimetric sensors for rapid monitoring of inorganic arsenic species: a review.

Health concerns about the toxicity of arsenic compounds have therefore encouraged the development of new analytical tools for quick monitoring of arsenic in real samples with improved sensitivity, selectivity, and reliability. An overview of advanced optical colorimetric sensor techniques for real-time monitoring of inorganic arsenic species in the environment is given in this review paper. Herein, several advanced optical colorimetric sensor techniques for arsenite (As+3) and arsenate (As+5) based on doping chromogenic dyes/reagents, biomolecule-modified nanomaterials, and arsenic-binding ligand tethered nanomaterials are introduced and discussed. This review also highlights the benefits and limitations of the colorimetric sensor for arsenic species. Finally, prospects and future developments of an optical colorimetric sensor for arsenic species are also proposed. For future study in this sector, particularly for field application, authors recommend this review paper will be helpful for readers to understand the design principles and their corresponding sensing mechanisms of various arsenic optical colorimetric sensors.

Graphene-based biosensors for detecting coronavirus: a brief review.

The coronavirus (SARS-CoV-2) disease has affected the globe with 770 437 327 confirmed cases, including about 6 956 900 deaths, according to the World Health Organization (WHO) as of September 2023. Hence, it is imperative to develop diagnostic technologies, such as a rapid cost-effective SARS-CoV-2 detection method. A typical biosensor enables biomolecule detection with an appropriate transducer by generating a measurable signal from the sample. Graphene can be employed as a component for ultrasensitive and selective biosensors based on its physical, optical, and electrochemical properties. Herein, we briefly review graphene-based electrochemical, field-effect transistor (FET), and surface plasmon biosensors for detecting the SARS-CoV-2 target. In addition, details on the surface modification, immobilization, sensitivity and limit of detection (LOD) of all three sensors with regard to SARS-CoV-2 were reported. Finally, the point-of-care (POC) detection of SARS-CoV-2 using a portable smartphone and a wearable watch is a current topic of interest.

Magnetite nanoparticle decorated reduced graphene oxide for adsorptive removal of crystal violet and antifungal activities.

This work reports the synthesis and application of magnetic rGO/Fe3O4 NCs using a pod extract of Dolichos lablab L. as areducing agent. GO was synthesized by a modified Hummers method, however GO was reduced using the plant extract to produce rGO. The as-synthesized rGO/Fe3O4 NCs were characterized by UV-vis spectrophotometer, Fourier transform infrared (FT-IR) spectroscopy, FT-Raman spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy supported with energy dispersed X-ray spectroscopy (FESEM-EDX), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The synthesis of magnetic rGO/Fe3O4 NCs was confirmed from characterization results of FT-Raman, TEM and VSM. The FT-Raman results showed the D and G bands at 1306.92 cm-1 and 1591 cm-1 due to rGO and a peak at around 589 cm-1 due to Fe3O4 NPs that were anchored on rGO sheets; TEM results showed the synthesis of Fe3O4 with an average particle size of 8.86 nm anchored on the surface of rGO sheets. The VSM result confirmed the superparamagnetic properties of the rGO/Fe3O4 NCs with a saturation magnetization of 42 emu g-1. The adsorption capacity of rGO/Fe3O4 NCs towards crystal violet (CV) dye was calculated to be 62 mg g-1. The dye removal behavior fitted well with the Freundlich isotherm and the pseudo-second-order kinetic model implies possible chemisorption. Besides, rGO/Fe3O4 NCs showed antifungal activities against Trichophyton mentagrophytes and Candida albicans by agar-well diffusion method with a zone inhibition of 24 mm and 21 mm, respectively. Therefore, rGO/Fe3O4 NCs can be used as an excellent adsorbent to remove organic dye pollutants and kill pathogens.

Green synthesis of zinc oxide nanostructures and investigation of their photocatalytic and bactericidal applications.

We report a facile one-pot green synthesis of zinc oxide (ZnO) nanostructures using aqueous leaf extract of Dolichos Lablab L. as the reducing and capping agent. The optical properties, structure and morphology of the as-synthesized ZnO nanostructures have been characterized by UV-Visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) supported with energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). TEM analysis revealed that the as-synthesized ZnO nanostructures have an average particle diameter of 29 nm. XRD patterns confirmed the formation of phase-pure ZnO nanostructures with a hexagonal wurtzite structure. The synthesized ZnO nanostructures were used as a catalyst in the photodegradation of methylene blue (MB), rhodamine B (RhB) and orange II (OII) under visible and near-UV irradiation. The results showed the highest efficiency of photodegradation of ZnO nanostructures for MB (80%), RhB (95%) and OII (66%) at pH values of 11, 9 and 5, respectively, in a 210 min time interval. In addition, the antimicrobial activity of the ZnO nanostructures using the agar well diffusion method against Bacillus pumilus and Sphingomonas paucimobilis showed the highest zones of inhibition of 18 mm and 20 mm, respectively. Hence, ZnO nanostructures have the potential to be used as a photocatalyst and bactericidal component.