Detection of trace nickel ions with a colorimetric sensor based on indicator displacement mechanism

A facile and reliable colorimetric sensor in both solution and paper-based membrane was presented for the determination of nickel ions. Commercial organometallic reagent zincon had been incorporated within hollow ZnSiO3 nanospheres to serve as hybrid ionophore, the blue color of which faded after successive addition of Ni2+ due to competition and displacement of Zn2+ in the ionophore. The selectivity was very good and can be further improved using Na-2-EDTA as a masking agents which eventually becomes a co-ionophore. The detection solutions were further used to coat cellulose membrane modified with TiO2 and silylating reagent to fabricate paper-based sensors for naked-eye detection of Ni2+. With optimum conditions selected, the assays in solution obtained a detection limit of 35.6 nM with linear range from 32 nM to 9.2 mM, while for the paper-based assays, the detection limit goes to 83 nM with linear range between 78 nM and 76 mu M. Besides, the assay enable naked-eye differentiation of nickel ions down to 0.1 mu M. Testing the present paper sensor on real river turbulent water shows a maximum 5% relative error, demonstrating the feasibility of present assays for real applications. (C) 2016 Elsevier B.V. All rights reserved.