A molecular imprinting-based turn-on Ratiometric fluorescence sensor for highly selective and sensitive detection of 2,4-dichlorophenoxyacetic acid (2,4-D)

A novel molecular imprinting-based turn-on ratiometric fluorescence sensor was constructed via a facile sol-gel polymerization for detection of 2,4-dichlorophenoxyacetic acid (2,4-D) on the basis of photo induced electron transfer (PET) by using nitrobenzoxadiazole (NBD) as detection signal source and quantum dots (QDs) as reference signal source. With the presence and increase of 2,4-D, the amine groups on the surface of QDs@SiO2 could bind with 2,4-D and thereby the NBD fluorescence intensities could be significantly enhanced since the PET process was inhibited, while the QDs maintained constant intensities. Accordingly, the ratio of the dual-emission intensities of green NBD and red QDs could be utilized for turn-on fluorescent detection of 2,4-D, along with continuous color changes from orange-red to green readily observed by the naked eye. The as-prepared fluorescence sensor obtained high sensitivity with a low detection limit of 0.14 mu M within 5 min, and distinguished recognition selectivity for 2,4-D over its analogs. Moreover, the sensor was successfully applied to determine 2,4-D in real water samples, and high recoveries at three spiking levels of 2,4-D ranged from 95.0% to 110.1% with precisions below 4.5%. The simple, rapid and reliable visual sensing strategy would not only provide potential applications for high selective ultratrace analysis of complicated matrices, but also greatly enrich the research connotations of molecularly imprinted sensors. (C) 2016 Elsevier B.V. All rights reserved

Paper-based microfluidic sampling and separation of analytes for potentiometric ion sensing

This work demonstrates a paper-based microfluidic sampling and separation platform that allows potentiometric sensing of chloride ions in presence of strongly interfering salicylate ions using a solid-contact ion-selective electrode as a detector. The device was composed of two pieces of paper with different shapes and pore sizes. A "T" shaped filter paper with a pore size of 12-25 was used as the detection zone. A filter paper with a pore size of 2.0 mu m was modified with a complexing agent (Fe3+ and served as the separation zone. The two pieces of the paper were joined together just like a jigsaw. A solid-contact Cl--selective electrode and a reference electrode were gently pressed onto the detection zone to create a direct contact between the electrodes and the solution absorbed in the paper. Utilizing the possibility to form stable complexes between Fe3+ and salicylate, the proposed platform enables the separation of salicylate and detection of chloride. This system offers a convenient platform for both sampling and separation of ions, in which sample pretreatment procedures can be simplified or avoided.&nbsp

One-Step Electrochemical Synthesis of Cobalt-Doped Fe2O2CO3-Reduced Graphene Oxide Nanocomposites and Their Application for H2O2 Electro-Catalytic Reduction

In this work, cobalt-doped Fe2O2CO3-reduced graphene oxide (Co@ Fe2O2CO3-rGO) nanocomposites were synthesized by using one-step electrodeposition. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical methods were used to characterize the nanocomposites. The results showed that the Co@ Fe2O2CO3 nanoparticles with average 20-40 nm were anchored on the rGO film tightly and the resulting nanocomposites showed excellent electro-catalytic effect toward the reduction of hydrogen peroxide. The determination of hydrogen peroxide was successfully achieved in the high salinity solution (0.5 mol L-1 NaCl) and the calibration curve was observed in the range of 1.5-956 mu mol L-1 with the limit of quantitation of 1.5 mu mol L-1 and the limit of detection of 0.4 mu mol L-1. (C) The Author(s) 2017. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved