A direct electrochemical sensor based on covalent organic frameworks/platinum nanoparticles for the detection of ofloxacin in water.

A direct electrochemical sensor based on covalent organic frameworks (COFs)/platinum nanoparticles (PtNPs) composite was fabricated for the detection of ofloxacin (OFX) in water. Firstly, the COF material was synthesized via the condensation reaction of 1,3,5-tris(4-aminophenyl)benzene (TAPB) with terephthalaldehyde (TPA) and integrated with PtNPs by in situ reduction. Then, TAPB-TPA-COFs/PtNPs composite was loaded onto the surface of the glassy carbon electrode (GCE) by drip coating to construct the working electrode (TAPB-TPA-COFs/PtNPs/GCE). The electrochemical performance of TAPB-TPA-COFs/PtNPs/GCE showed a significant improvement compared with that of TAPB-TPA-COFs/GCE, leading to a 3.2-fold increase in the electrochemical signal for 0.01 mM OFX. Under optimal conditions, the TAPB-TPA-COFs/PtNPs/GCE exhibited a wide linear range of 9.901 × 10-3-1.406 µM and 2.024-15.19 µM with a detection limit of 2.184 × 10-3 µM. The TAPB-TPA-COFs/PtNPs/GCE-based electrochemical sensor with excellent performance provides great potential for the rapid and trace detection of residual OFX.

Eco-friendly fabrication of multifunctional magnetic plasmonic photocatalyst for adsorption, SERS monitoring and photodegradation of residual fluoroquinolone antibiotics in water.

In this work, a kind of multifunctional magnetic plasmonic photocatalyst was prepared by a green and efficient process. Magnetic mesoporous anatase titanium dioxide (Fe3O4@mTiO2) was synthesized by microwave-assisted hydrothermal, and Ag NPs were simultaneously in-situ grown on Fe3O4@mTiO2 (Fe3O4@mTiO2@Ag), graphene oxide (GO) was then wrapped on Fe3O4@mTiO2@Ag (Fe3O4@mTiO2@Ag@GO) to increase its adsorption capacity for fluoroquinolone antibiotics (FQs). Owing to the localized surface plasmon resonance (LSPR) effect of Ag, as well as the photocatalytic capacity of TiO2, a multifunctional platform based on Fe3O4@mTiO2@Ag@GO was constructed for adsorption, surface-enhanced Raman spectroscopy (SERS) monitoring and photodegradation of FQs in water. The quantitative SERS detection of norfloxacin (NOR), ciprofloxacin (CIP), and enrofloxacin (ENR) was demonstrated with LOD of 0.1 µg mL-1, and the qualitative analysis was confirmed by density functional theory (DFT) calculation. The photocatalytic degradation rate of NOR over Fe3O4@mTiO2@Ag@GO was about 4.6 and 1.4 times faster than that of Fe3O4@mTiO2 and Fe3O4@mTiO2@Ag, indicating the synergetic effects of Ag NPs and GO, the used Fe3O4@mTiO2@Ag@GO can be easily recovered and recycled for at least 5 times. Thus, the eco-friendly magnetic plasmonic photocatalyst provided a potential solution for the removal and monitoring of residual FQs in environmental water.

An accuracy improved ratiometric SERS sensor for rhodamine 6G in chili powder using a metal-organic framework support.

Internal standard molecule 4-mercaptobenzoic acid (4-MBA) embedded Au core-Ag shell nanorods (Au-MBA@Ag NRs) were prepared by a seed-mediated growth method, then loaded on octahedral MIL-88B-NH2 to obtain a novel ratiometric SERS substrate of Au-MBA@Ag NRs/PSS/MIL-88B-NH2 (AMAPM) for detecting rhodamine 6G (R6G) in chili powder. The porous structure and excellent adsorption ability of MIL-88B-NH2, allowed for increased loading of Au-MBA@Ag NRs, thereby shortening the distance between adsorbed R6G and the "hot spot" resulting from local surface plasmon resonance (LSPR) of Au-MBA@Ag NRs. Based on the SERS characteristic peak ratio of R6G to 4-MBA, the ratiometric SERS substrate displayed improved accuracy and excellent performance for R6G detection, with a wide linear range of 5-320 nM and a low detection limit of 2.29 nM as well as fine stability, reproducibility and specificity. The proposed ratiometric SERS substrate offered a simple, fast and sensitive sensing strategy for R6G detection in chili powder, which demonstrated potential applications in food safety and the analysis of trace analytes in complex matrices.

Molecularly imprinted 3D SERS sensor with inorganic frameworks for specific and recyclable SERS sensing application.

Poor selectivity and reusability of Au/Ag nanostructures are the main challenges for surface-enhanced Raman spectroscopy (SERS) in real sample detection. Herein, a novel specific and reusable three-dimensional (3D) SERS sensor with dual functions of selective trapping and photocatalytic degradation was designed. Firstly, Au-Ag bimetallic nanoparticles decorated silicon nanowires array (SiNWs-AuAg) were prepared as 3D SERS substrate. Then, silicon-based inorganic-framework molecularly imprinted TiO2 (TiO2@SiMIP) was synthesized and immobilized on SiNWs-AuAg by using rhodamine 6G (R6G) as template molecule. Owing to the excellent SERS performance of SiNWs-AuAg and the specific affinity of TiO2@SiMIP to template molecule, the prepared SERS sensor enables sensitive and selective detection of R6G in food samples with a limit of detection (LOD) of 0.27 nM. In addition, due to the photocatalysis of TiO2 and the stability of silicon-based inorganic framework, the residual templates in TiO2@SiMIP can be completely removed by UV irradiation, and the imprinted cavity of regenerated sensors still maintained good selectivity after regeneration by UV irradiation.

Simple and sensitive nitric oxide biosensor based on the electrocatalysis of horseradish peroxidase on AuNPs@metal-organic framework composite-modified electrode.

Fe-based metal-organic framework (MIL-101(Fe)) was synthesized through a simple solvothermal synthesis and then used to prepare the AuNPs-decorated MIL-101(Fe) nanocomposite (APPPM(Fe)) by a multi-step layer-by-layer assembly process. Benefited from the porous structure of MIL-101(Fe) and the multilayer assemble process, the loading amount of AuNPs on APPPM(Fe) was enhanced and exhibited a fine biocompatible interface and high conductivity. Through the intense Au-S bond, high loading amount of horseradish peroxidase was immobilized on APPPM(Fe) and the native bioactivity of HRP was kept to realize its direct electrochemistry. From the electrochemical kinetics, the constructed biosensor displayed fast electron transfer and good electrocatalysis activity for the detection of nitric oxide (NO) with wide linear range from 0.033 to 5370 µM and a low detection limit of 0.01 µM (3 σ) as well as fine stability, reproducibility and specificity. According to results of real sample analysis, the proposed electrochemical biosensor offers fast and simple detection of NO in real serum. Therefore, the present strategy definitely provided a potential application prospect in NO clinic detection and disease therapy.