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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 ZnSiO 3 nanospheres to serve as hybrid ionophore, the blue color of which faded after successive addition of Ni 2+ due to competition and displacement of Zn 2+ 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 TiO 2 and silylating reagent to fabricate paper-based sensors for naked-eye detection of Ni 2+ . 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 μΜ. Besides, the assay enable naked-eye differentiation of nickel ions down to 0.1 μΜ. 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. [ABSTRACT FROM AUTHOR]

High-performance measurement and removal of copper ions is highly desirable in both clinical and environmental applications. Herein, an efficient, reliable and recyclable functional material was prepared to adsorb and determine Cu 2+ using N -[3-(trimethoxysilyl) propyl] ethylenediamine modified mesoporous hollow shells (HMS-NHs). By stepwise coating with mesoporous silica at highly mono-dispersed PS spheres, removal of template materials, and modification with functional diamine groups, higher absorption capacity of about 138.58 mg/g was obtained. After optimization of PS template size, thickness of SiO 2 layers, pore size of the shell, and etc, as-prepared HMS-NHs gave clear colorimetric response after color development using cupron solution. Selectively measure Cu 2+ in a wide concentration ranges from 0.025 to 49 μΜ was observed with a detection limit around 0.025 μΜ (3δ). More importantly, the functional absorbent can be regenerated by treatment with hydrochloric acid and maintains high efficiency upon repeated use for at least 10 times. Extensive investigation demonstrated that the HMS-NHs can serve as not only high-performance absorption materials but also sensitive sensor for Cu 2+ , thus offering a good alternative for potential removal and detection of copper ions in real applications. [ABSTRACT FROM AUTHOR]

A simple, cheap and effective functional paper has been fabricated to absorb and detect Cu 2+ with good sensitivity and selectivity. Using commercial cellulose filter papers as substrate, Magneli phase structure of Ti 6 O 11 was coated at the surface to serve as intermediate linker to modify N-[3-(Trimethoxysilyl) propyl] ethylenediamine for Cu 2+ binding. Under optimized conditions, i.e. at 50 °C with electromagnetic stirring, the functional paper can adsorb Cu 2+ with high performance and give clear color response using cupron as chromogenic agent. The concentration-dependent colorimetric response (Δ B value) matches well with the exponential linear curve under dynamic adsorption conditions, where the linear range was from 33.6 nM to 39.8 μM and the detection limit was measured to be about 33.6 nM. Measurement of a group of possible interfering ions and spiked real water samples demonstrated the good selectivity of the proposed paper. Furthermore, the performance can be further improved using microwave irradiation, where a lower detection limit of 16.8 nM was achieved within a wider linear range from 16.2 nM to 0.98 mM. The reaction time can be shortened to 20 min to reach final equilibrium and the saturated adsorption amount of Cu 2+ for a single piece of paper (diameter = 1.0 cm) was as high as 4.5169 μg/cm 2 . The proposed functional papers would offer an effective alternative for potential adsorption and determination of copper ions in real applications. [ABSTRACT FROM AUTHOR]

A sensor made of Fe 3 O 4 @TiO 2 @NG@Au@ETBD was developed to specifically detect Pb 2+ in a significantly toxic aqueous environment. Nitrogen–doped graphene (NG) was utilized as the substrate material of the sensor by a self–assembly method. The synergistic effect of the Fe 3 O 4 @TiO 2 as well as the expanded activated surface and good electrical conductivity of the gold nanoparticles enhanced the detection of Pb 2+ . 2, 2′–((1E)–((4–((2–mercaptoethyl) thio) −1, 2–phenylene) bis (azanylylidene)) bis (methanylylidene)) diphenol (ETBD) was employed as the capture probe for the label–free detection. The electrical characteristics of the Fe 3 O 4 @TiO 2 @NG@Au@ETBD sensor were monitored to measure and investigate the performance of the sensor. Compared with conventional detection technologies and electrodes, this sensor enabled a wide linear range from 4 × 10 −13 mol/L to 2 × 10 −8 mol/L. Lower limits of detection and quantification for Pb 2+ , 7.5 × 10 −13 and 2.5 × 10 −12 mol/L, respectively, were achieved. Furthermore, the Fe 3 O 4 @TiO 2 @NG@Au@ETBD sensor could distinguish Pb 2+ from other metal ions despite the interfering metal ions with concentrations 10 3 –fold higher than that of Pb 2+ . The proposed sensor could potentially be used in heavy–metal detection. [ABSTRACT FROM AUTHOR]

Direct detection of Fe 3+ ions is of significant importance in view of both clinical and environmental applications. In the present study, we presented the construction of a paper-based colorimetric sensor by alternative modification of commercial cellulose paper with TiO 2 membrane as intermediate layer, hydrophobic/hydrophilic coating to obtain uniform diffusion, and decoration of –NH 2 and –SH groups for gold nanoparticles (AuNPs) immobilization. After optimization of fabrication and detection conditions, the colorimetric sensor showed a linear concentration-dependent colorimetric response (ΔG) in the presence of Fe 3+ concentrations ranging from 1.0 to 37 μM (R 2 > 0.98). The detection limit was calculated to be 0.85 μM (3δ) with good selectivity. Besides, the sensor also showed high resistance to AuNPs leaking in aqueous solutions, and demonstrated consistent measurement of Fe 3+ in serum samples. Those results suggested that as-prepared sensor strip is potential useful for Fe 3+ ion determination in clinical and environmental samples. [ABSTRACT FROM AUTHOR]