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Given that hexavalent chromium ions (Cr(VI)) are among the most biologically toxic heavy metal ions in the environment, it would be desirable to develop approaches that are easy-to-use, practical, and cost-effective for monitoring Cr(VI) content in environmental matrices. Herein, we report a colorimetric assay for Cr(VI) detection based on the oxidase-like activity of a series of nanoscale substituted transition metal vanadates (STMVs) with the general formula M3V2O8, where M represents divalent metal cations such as Ni2+, Cu2+, and Zn2+. The structural and physicochemical characterisations indicated that mesoporous Cu3V2O8 and Ni3V2O8 with roughly nano-spherical morphologies were successfully formed with monoclinic and orthorhombic phases, respectively. In addition, micro/mesoporous Zn3V2O8 had uniform hexagonal nanosheets with an orthorhombic crystalline phase. The UV-vis spectroscopy showed that Cu3V2O8 and Ni3V2O8 oxidised O-phenylenediamine (OPD) to 2,3-diaminophenazine (DAP); however, Zn3V2O8 did not exhibit the desired activity. Under the optimised reaction conditions, a simple, fast, and low-cost colorimetric sensor was designed based on the outstanding oxidase-like activity of Cu3V2O8 (Vmax = 0.25 µM s−1) to detect Cr(VI). The Cu3V2O8/OPD system operated selectively for Cr(VI) against other ions, and the lowest detectable [Cr(VI)] within the linear range of 2–32 μM was 0.24 μM, which is lower than the standard Cr(VI) levels (0.96 µM) for drinking water set by the World Health Organisation (WHO). This colorimetric technique was also applicable for assessing Cr(VI) in untreated tap water and Caspian Sea water samples. The analytical results showed that mesoporous Cu3V2O8 reliably developed a sensitive colorimetric system with thermal stability for the determination of toxic ions in water sources based on an intrinsic oxidase mimic. [ABSTRACT FROM AUTHOR]

Enzyme-mimetic reactions have led to the development of rapid and cost-effective visual sensors for colorimetric detection of essential molecules. In this study, β-Mn2V2O7 nanoparticles were synthesized using a hydrothermal method that mimics oxidase and peroxidase activities owing to the formation of 1O2 and OH• as reactive oxygen species (ROS), Mn2+/Mn3+, and V4+/V5+ surface couples in o-phenylenediamine (OPD) oxidation. The maximum velocity measured using Michaelis–Menten kinetics for the peroxidase-like activity (0.1 µM s−1) was higher than that of the oxidase mimic (0.033 µM s−1). Therefore, peroxidase-like system (β-Mn2V2O7/OPD/H2O2) was used to detect vitamin C (ascorbic acid), a well-known bioactive antioxidant. Ascorbic acid (AA) inhibited the oxidation of the OPD to 2,3-diaminophenazine by scavenging OH•, an oxidizing agent produced in a peroxidase system, and was detected based on UV–vis signal attenuation. The detection limit of AA using the colorimetric assay in the linear range of 1–10 µM was 0.47 µM (S/N = 3). Furthermore, the feasibility of the colorimetric sensor was confirmed by detecting AA in fresh juice. This study presents a dual-functional nanozyme and develops a sensitive and selective colorimetric sensor based on the peroxidase-like activity of a nanozyme to detect AA among the potential interfering components. In this study, we developed a practical visual sensor for ascorbic acid detection as a well-known antioxidant based on the catalytic oxidation of o-phenylenediamine using β-Mn2V2O7 NPs as an oxidase/peroxidase nanozyme. This sensitive colorimetric sensor was feasible for detecting ascorbic acid in orange juice. [ABSTRACT FROM AUTHOR]

The cancer immunotherapy method uses the specificity of the immune system to provide a more effective than more conventional treatments, such as chemotherapy and radiotherapy. Immunotherapy has two main strategies (passive or active) to organize the immune system. Passive strategies use advantage of tumor-hyperpermeable cells, which have enhanced permeability and retention effects. Nanoparticles due to their better accumulation within tissues and cells of the immune system are well suitable for delivery of immune therapies such as vaccines or adjuvants. In this review, we explained application of nanotechnology in immunotherapy of cancer. [ABSTRACT FROM AUTHOR]