A ratiometric electrochemical biosensor via alkaline phosphatase mediated dissolution of nano-MnO2 and Ru(III) redox recycling for the determination of dimethoate.

A sensitive and ratiometric electrochemical biosensor was developed for the determination of dimethoate via alkaline phosphatase (ALP) mediated dissolution of nano-MnO2 and [Ru(NH3)6]3+(Ru(III)) redox recycling. The electroactive probe Ru(III) was adsorbed on the nano-MnO2 with the high specific surface area through electrostatic interaction to form the MnO2-Ru(III) nanocomposite, which was then fixed on the surface of the glassy carbon electrode. When the dimethoate inhibited the catalytic activity of ALP in a homogeneous system, the hydrolysate L-ascorbic acid (AA) produced by ALP hydrolysis of L-ascorbic acid-trisodium 2-phosphate (AAP) decreased. The solution was then incubated with a glassy carbon electrode modified by MnO2-Ru(III). At this time, only a small amount of MnO2-Ru(III) was decomposed and Ru(III) was rapidly electroreduced to Ru(II) on the surface of the electrode. The in-situ produced Ru(II) was chemically oxidized back to Ru(III) by Fe(III). The redox recycling of Ru(III) was completed and the Ru(III) reduction current signal was amplified. The process consumed part of Fe(III) to reduce the reduction current signal of Fe(III), and the ratio of the two reduction currents (IRu(III)/IFe(III)) increased significantly. The IRu(III)/IFe(III) value increased with the increase of dimethoate concentration in the linear range of 0.01-300 ng mL-1, and the detection limit was 6.3 pg mL-1. It has been successfully applied to the determination of dimethoate in oilseed rape and lettuce with a satisfactory result.

Investigation of Graphene Derivatives on Electrical Properties of Alkali Activated Slag Composites.

Reduced graphene oxide (rGO) has been widely used to modify the mechanical performance of alkali activated slag composites (AASC); however, the mechanism is still unclear and the electrical properties of rGO reinforced AASC are unknown. Here, the rheological, mechanical, and electrical properties of the AASC containing rGO nanosheets (0, 0.1, 0.2, and 0.3% wt.) are investigated. Results showed that rGO nanosheets addition can significantly improve the yield stress, plastic viscosity, thixotropy, and compressive strength of the AASC. The addition of 0.3% wt. rGO nanosheets increased the stress, viscosity, thixotropy, and strength by 186.77 times, 3.68 times, 15.15 times, and 21.02%, respectively. As for electrical properties, the impedance of the AASC increased when the rGO content was less than 0.2% wt. but decreased with the increasing dosage. In contrast, the dielectric constant and electrical conductivity of the AASC containing rGO nanosheets decreased and then increased, which can be attributed to the abundant interlayer water and the increasing structural defects as the storage sites for charge carriers, respectively. In addition, the effect of graphene oxide (GO) on the AASC is also studied and the results indicated that the agglomeration of GO nanosheets largely inhibited the application of it in the AASC, even with a small dosage.

A self-correcting fluorescent assay of tyrosinase based on Fe-MIL-88B-NH2 nanozyme.

A self-correcting fluorescent assay of tyrosinase (TYR) was developed by utilization of Fe-MIL-88B-NH2 as a peroxidase-like nanozyme and a capture probe. Fe-MIL-88B-NH2 nanozyme was selected as an electron donor, and the oxidization product (dopamine-o-quinone) acts as an energy acceptor. First, TYR catalyzes the oxidation of tyramine hydrochloride to dopamine and then to dopamine-o-quinone. Second, Fe-MIL-88B-NH2 with intrinsic peroxidase-like activity decomposes H2O2 to produce ·OH radicals, which further accelerate the oxidation of dopamine to dopamine-o-quinone. Excessive H2O2 and ·OH radicals reduce the interferences from ascorbic acid at the same time providing a self-correcting ability. Dopamine-o-quinone reacts with -NH2 groups on the ligand of Fe-MIL-88B-NH2 through Michael reaction which results in fluorescence quenching. Under 365-nm excitation, the fluorescence emission intensity at 452 nm gradually decreased with increasing TYR concentration varying from 0 to 10 U mL-1. The linear range is from 1 to 5 U mL-1 and the detection limit is 0.05679 U mL-1. This self-correcting fluorescent assay of tyrosinase exhibits good sensitivity and selectivity which is also successfully applied for tyrosinase inhibitor detection. Schematic representation of fluorescent assay for tyrosinase determination based on Fe-MIL-88B-NH2 nanozyme. A self-correcting fluorescent assay for tyrosinase was developed based on the Fe-MIL-88B-NH2 nanozyme.

Carbonation and Chloride Ions' Penetration of Alkali-Activated Materials: A Review.

Alkali-activated materials (AAMs) are widely recognized as potential alternatives to ordinary Portland cement (OPC) due to their lower carbon footprint. However, like OPC, AAMs can also generate some durable problems when exposed to aggressive environments and the mechanisms and possible improvements are still not fully clear in existing investigations. Furthermore, the corrosion mechanisms of AAMs are different from OPC due to the discrepant reaction products and pore structures. Thus, this study's aim is to review the chemical reaction mechanisms, factors, and mitigation methods when AAMs are attacked by carbonation and chloride ions, along with a summative discussion regarding instructive insights to durable problems of AAMs.

Accelerating the peroxidase-like activity of MoSe2 nanosheets at physiological pH by dextran modification.

Surface modification of MoSe2via dextran during ultrasound exfoliation is demonstrated to be an efficient and easy strategy to accelerate the peroxidase-like catalytic activity of MoSe2 nanosheets at neutral pH. The enhancement of catalytic activity is owing to the rich negative charges of dextran on the dextran-modified MoSe2 nanosheets.

A competitive immunoassay for electrochemical impedimetric determination of chlorpyrifos using a nanogold-modified glassy carbon electrode based on enzymatic biocatalytic precipitation.

A direct competitive impedimetric immunoassay for chlorpyrifos (CPF) was developed that is based on the specific affinity of immunoassay and the enzymatic biocatalytic precipitation amplification strategy. The CPF antibody (anti-CPF) was anchored onto an electro-deposited nanogold modified glassy carbon electrode surface by adsorption of the Au-NH2 bond and Au-SH bond. This improved the electrode reactivity and the loading amount of anti-CPF. Abundant horseradish peroxidase (HRP) and bovine serum albumin-CPF (BSA-CPF) were anchored onto spherical gold nanoparticles (AuNPs, 16 ± 2 nm) to form HRP-AuNP-BSA-CPF (analyte competitor). CPF determination was achieved when the competitive immunoassay occurred between CPF and analyte competitor with anti-CPF. In the presence of H2O2 and 4-chloro-1-naphthol, an enzyme-mediated biocatalytic precipitation process was triggered and produced an insoluble 4-chloro-1(4H)-naphthalenone. This insoluble substance increased the Faradaic impedance of the base electrode. The impedimetric signal was determined at the formal potential of 220 mV and alternating voltage of 10 mV. This signal decreased with increasing concentration of CPF over a linear range of 1.0 × 10-3 ng mL-1~10 ng mL-1 with a detection limit of 0.070 pg mL-1. The immunoassay has been tested for determination of chlorpyrifos in complex matrices such as artificially spiked vegetables with recoveries in the range 85 to 110%. The relative standard deviations were less than 7.5%. Graphical abstractSchematic representation of electrochemical impedimetric immunoassay for chlorpyrifos determination before enzymatic biocatalytic precipitation (BCP, red line) process and after BCP process (blue line).