Visual test paper based on Au/δ-MnO_(2) hollow nanosphere oxidase-like activity regulation using hexavalent chromium as a smart switch

Paper-based sensing platform is a point of need analytical toolkit for safety testing.However,the sensitivity,specificity,and simplicity are still challenging.Herein,we report a novel strategy(Au/δ-MnO_(2) hollow nanosphere and 3,3′,5,5′-tetramethylbenzidine(TMB)induced test strips for signal-on detection)that can be utilized for hexavalent chromium(Cr^(6+))detection.Interestingly,Cr^(6+)(CrO_(4)^(2−)) as a smart switch can remarkably enhance the oxidase-like activity of Au/δ-MnO_(2) hollow nanosphere.The presence of Cr^(6+) can regulate the surface electronic redistribution of Au/δ-MnO_(2) and adjust the geometric configuration,which leads to the improvement in oxidase-like activity of Au/δ-MnO_(2).As a proof-of-concept application,a visual paper-based sensing platform of Cr^(6+) along with quantitative analysis by the test strips was successfully constructed.This paper-based sensing platform exhibits a linear range with excellent selectivity for other interfering substances and lower limit of detection of 0.09μmol·L^(−1),providing a promising toolkit at-home Cr^(6+) measurement and environmental monitoring.

Functionalized periodic Au@MOFs nanoparticle arrays as biosensors for dual-channel detection through the complementary effect of SPR and diffraction peaks

A facile and low-cost method to prepare periodic Au@metal-organic framework （MOF） （MIL-100（Fe）） nanoparticle arrays was developed. The arrays were fabricated in situ using monolayer colloidal crystals as templates, followed by Au deposition on substrates, and annealing. MIL-100（Fe） coatings were applied on the nanospheres using a simple solvent thermal process. The prepared periodic Au@MIL-100（Fe） nanoparticle （NP） arrays were characterized by two peaks in the visible spectra. The first peak represented the surface plasmon resonance （SPR） of the Au nanospheres, and the other peak, or the diffraction peak originated from the periodic structure in the NP array. After modification with 3-aminophenylboronic acid hemisulfate （PBA）, the Au@MIL-100（Fe） NP arrays exhibited sensitive responses to different glucose concentrations with good selectivity. These responses could be due to the strong interaction between PBA and glucose molecules. The diffraction peak was sensitive at low glucose concentrations （less than 12 mM）, whereas the SPR peak rapidly responded at high concentrations. The peaks thus demonstrated satisfactory complementary sensitivity for glucose detection in different concentration regions. These results can be used to develop a dual-channel biosensor. We also created a standard diagram, which can be used to efficiently monitor blood glucose levels. The proposed strategy can be extended to develop different dual-channel sensors using Au@MIL-100（Fe） NP arrays agents. functionalized with different recognition

Layered sphere-shaped TiO_2 capped with gold nanoparticles on structural defects and their catalysis of formaldehyde oxidation

We describe here a one-step method for the synthesis of Au/TiO2 nanosphere materials,which were formed by layered deposition of multiple anatase TiO2 nanosheets.The Au nanoparticles were stabilized by structural defects in each TiO2 nanosheet,including crystal steps and edges,thereby fixing the Au-TiO2 perimeter interface.Reactant transfer occurred along the gaps between these TiO2 nanosheet layers and in contact with catalytically active sites at the Au-TiO2 interface.The doped Au induced the formation of oxygen vacancies in the Au-TiO2 interface.Such vacancies are essential for generating active oxygen species（-＊O^-） on the TiO2 surface and Ti^3＋ ions in bulk TiO2.These ions can then form Ti^3＋-O^--Ti^4＋species,which are known to enhance the catalytic activity of formaldehyde（HCHO） oxidation.These studies on structural and oxygen vacancy defects in Au/TiO2 samples provide a theoretical foundation for the catalytic mechanism of HCHO oxidation on oxide-supported Au materials.