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In this paper, we prepared fluorescence-tunable water-soluble CdS quantum dots (QDs) with hexametaphosphate as stabilizers by a simple route. The prepared CdS QDs were utilized to detect calcium ion (Ca 2+ ) based on an obvious fluorescence enhancement of CdS QDs induced by Ca 2+ . The results demonstrated there was an excellent linear relationship between the fluorescence intensity of hexametaphosphate-capped CdS QDs and Ca 2+ concentration in the range from 10 μmol/L to 400 μ mol/L and the detection limit for Ca 2+ was 4 μmol/L. Furthermore, fluoride ions (F − ) can react with Ca 2+ to generate the insoluble calcium fluoride that would inhibit the Ca 2+ -induced fluorescence enhancement of CdS QDs. Therefore, the designed Ca 2+ -induced fluorescence enhancement system was also able to effectively detect fluoride. [ABSTRACT FROM AUTHOR]

In this paper, a simple and sensitive sensing strategy for the determination of Pb 2+ ions was designed, in which anticancer drug AGRO100, a guanine (G)-quadruplex DNA aptamer, was selected as the probe to detect Pb 2+ ions and graphene oxide (GO) was adopted as the fluorescence quencher. A dye-labeled AGRO100 aptamer in a flexible single stranded state could be adsorbed on the surface of GO, and the fluorescence was quenched via Förster resonance energy transfer (FRET) from fluorescence dyes to GO. AGRO100 can interact with Pb 2+ ions to form an intermolecular G-quadruplex/Pb 2+ complex, which has a weaker binding affinity with GO. By this way, the dyes were kept away from the GO sheet and the fluorescence was restored. Thus the AGRO100 aptamer could be used as a fluorescence probe for the determination of Pb 2+ ions. Under the optimized conditions, there was a good linear relationship between the fluorescence intensity of the dyes and the concentration of Pb 2+ ions in the range from 0.75 to 6.0 nmol/L with a detection limit of 0.40 nmol/L. [ABSTRACT FROM AUTHOR]

Highlights: [•] The water-soluble CuInS2 QDs was functionalized with dopamine molecules. [•] The fluorescence of the dopamine functionalized CuInS2 QDs was sensitive to pH value changes. [•] Urea would release OH− to change the pH value with urase as the catalyst. [•] The dopamine functionalized CuInS2 QDs could be utilized as a fluorescence probe for urea. [ABSTRACT FROM AUTHOR]

Benefiting from the enhanced electrostatic adsorption derived from surface oxygen vacancy, the reported MEMS based hollow-porous Co-In 2 O 3 gas sensor exhibits excellent selectivity and response, and toluene detection limits as low as 100 ppb at the lowest temperature so far. [Display omitted] • The hollow-porous Co-doped In 2 O 3 microspheres with abundant electrostatic adsorption sites were synthesized by ultrasonic spray pyrolysis. • The MEMS toluene sensor reported in this work with the characteristic of low power consumption. • The Co-In 2 O 3 gas sensor exhibits high sensitivity and superior selectivity to ppb level of toluene at relatively lower temperature. • Demonstrating the impact of electrostatic adsorption on charge carrier transport and toluene sensing performance by DFT calculation. Semiconductor metal oxide (SMO) gas sensor has been widely researched in artificial olfactory for monitoring gases and odor. However, realizing the characteristics of low detection limit, immunity from interference capacity and low operating temperature still remains challenge. Herein, the synthesis of hollow-porous cobalt-doped In 2 O 3 sensing material with abundant surface oxygen vacancy (SOV) via one-pot and in-situ doping approach is reported. With their rich active sites, the Co-In 2 O 3 exhibits unexpected and high electrostatic adsorption of toluene at 175 °C, which obviously inducing the charge carrier transport. Accordingly, the final Microelectro Mechanical Systems (MEMS) based Co-In 2 O 3 gas sensor exhibits excellent selectivity and response, and toluene detection limits as low as 100 ppb at the lowest temperature so far. Density functional theory (DFT) calculations elucidated that the enhanced electrostatic adsorption is ascribed to the toluene preferentially bound to O 3c atom site (bridging oxygen atom near SOV) on Co-In_b-D 4 (110) surface, which will induce charge carrier accumulation layer and cause temperature-dependent abnormal pseudo p-type response. This work points out that the electrostatic adsorption derived from SOV could obviously modulate SMO sensing properties, and further supplements the defect engineering. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The dual-emission carbon dots were directly prepared by carbonizing glutathione in the water/formamide mixture. • The carbon dots exhibited dual emission peaks at 470 nm and 655 nm with excitation of 400 nm. • Fe3+ can be detected based on the fluorescence quenching at 655 nm of DCDs in acidic environments. • Zn2+ can be detected based on the fluorescence quenching at 470 nm of DCDs in alkaline environments. Abstract Herein, we developed a facile route for the preparation of dual-emission carbon dots (DCDs) by carbonizing glutathione in the water/formamide mixture. The synthesized DCDs displayed dual emission band respectively at 470 nm and 655 nm under the single-wavelength excitation at 400 nm, which can be used for the detection iron ions (Fe3+) and zinc ions (Zn2+) in different pH environments. An obvious fluorescence quenching around 655 nm was detected with the addition of Fe3+ in acidic environments, and a linear range of 2.5–30 μmol·L−1 and a detection limit of 0.8 μmol L−1 for Fe3+ were achieved. Moreover, another fluorescence quenching at 470 nm was also observed with the addition of Zn2+ in alkaline environments, and a linear range of 2.5–50 μmol L−1 and a detection limit of 1.2 μmol L−1 for Zn2+ were achieved. The prepared DCDs was used as a ratiometric fluorescent probe for determination of Fe3+ and Zn2+ ions in serum samples. [ABSTRACT FROM AUTHOR]

A fluorescent suspension array combining digital encoding and molecular imprinting technologies was applied for multiplexed detection of phenols in aqueous medium. In this assay, nanomaterials such as silver (Ag), cuprous oxide (Cu 2 O), magnesium oxide (MgO), and zinc oxide (ZnO) were assembled on microbeads as digital encoding signal sources, then, (Digital encoding signal sources were produced by assembling silver (Ag), cuprous oxide Cu2O), magnesium oxide (MgO), and zinc oxide (ZnO) on microbeads. Molecular imprinted nanoparticles based on CdSe/ZnS quantum dots with various emission wavelengths (525, 565 and 585 nm) were grafted on the encoded beads through electrostatic adsorption and were used as the sensing units. The decoding spectra of the suspension array were stimulated and collected by a home-built laser induced breakdown spectroscopy system. The resulted spectra were transformed into digital sequences for encoding. As demonstrated in the gradient detections to various phenol solutions in concentration range of 0.98–62.5 μg/mL, the functionality of the suspension array was proven in the control experiments between the parent sensor beads and the molecular imprinting silica nanoparticles assembled sensor beads. Furthermore, the selectivity of suspension array was verified by the mixed adsorption experiments conducted in multicomponent analytes. [ABSTRACT FROM AUTHOR]