Fabrication of edge-curled petals-like covalent organic frameworks and their properties for extracting indole alkaloids from complex biological samples

A novel electrochemical immunosensor for sensitive detection of depression marker Apo-A4 based on bipyridine-functionalized covalent organic frameworks

A novel electrochemical immunosensor for detecting potential depression biomarker Apolipoprotein A4 (Apo-A4) was developed using a multi-signal amplification approach. Firstly, the sensor utilized a modified electrode material, NG-PEI-COF, combining bipyridine-functionalized covalent organic framework (COF) and polyethyleneimine-functionalized nitrogen-doped graphene (NG-PEI), providing high surface area and excellent electron transfer capability for the first-stage amplification in electrical signal conduction. Subsequently, gold nanoparticles (AuNPs) were further electrodeposited onto the electrode, providing good biocompatibility and abundant binding sites for immobilizing the target antigen, thus achieving the second-stage amplification in target recognition and binding. To address the lack of redox properties of the antigen, a tracer probe was formed by loading AuNPs, anti-Apo-A4, and toluidine blue (TB) successively onto COF, leading to the third-stage amplification in signal conversion. The constructed electrochemical immunosensor TB/Ab/AuNPs/COF-Apo-A4/AuNPs/NG-PEI-COF/GCE exhibited excellent detection performance against Apo-A4 with a linear range of 0.01 to 300 ng mL-1 and had a low detection limit of 2.16 pg mL-1 (S/N = 3). In addition, the biosensor had good reproducibility (RSD = 2.31%), stability, and significant anti-interference performance toward other depression biomarkers. The sensor has been successfully used for the quantitative detection of Apo-A4 in serum, providing potential applications for detecting Apo-A4 in the clinic and serving as a reference for constructing sensing methods based on COF.

Photosensitized covalent organic framework as a light-induced oxidase mimic for colorimetric detection of uric acid

As large numbers of people are suffering from gout, an accurate, rapid, and sensitive method for the detection of gout biomarker, uric acid, is important for its effective control, diagnosis, and therapy. Although colorimetric detection methods based on uricase have been considered, they still have limitations as they produce toxic H2O2 and are expensive and not stable. Here, a novel uricase-free colorimetric method was developed for the sensitive and selective detection of uric acid based on the light-induced oxidase-mimicking activity of a new photosensitized covalent organic framework (COF) (2,4,6-trimethylpyridine-3,5-dicarbonitrile-4-[2-(4-formylphenyl)ethynyl]benzaldehyde COF [DCTP-EDA COF]). DCTP-EDA COF has a strong ability to harvest visible light, and it could catalyze the oxidation of 1,4-dioxane, 3,3',5,5'-tetramethylbenzidine under visible light irradiation to produce obvious color changes. With the addition of uric acid, however, the significant inhibition of the oxidase-mimicking activity of DCTP-EDA COF remarkably faded the color, and thus uric acid could be colorimetrically detected in the range of 2.0-150 μM with a limit of detection of 0.62 μM (3σ/K). Moreover, the present colorimetric method exhibited high selectivity; uric acid level in serum samples was successfully determined, and the recoveries ranged from 96.5% to 105.64%, suggesting the high accuracy of the present colorimetric method, which demonstrates great promise in clinical analysis.

Extraction and Determination of Evodiamine from Euodia Fructus with SPE-HPLC Based on a Homemade Phenyl-Based Monolithic Cartridge

A phenyl-based monolithic adsorbent was prepared in a 50-mm-long stainless steel tube, which was initiated by the redox system, using ethylene glycol phenyl ether acrylate as the monomer and ethylene glycol dimethacrylate as the crosslinker. The effects of monomer/crosslinker ratio and the porogens on the permeability and morphology of the resulting adsorbents were investigated, and the optimal adsorbent shows relatively uniform pore structure according to the characterizations of scanning electron microscopy and nitrogen adsorption-desorption method. The column that filled with the adsorbent was used as the solid-phase extraction (SPE) cartridge, exhibiting unique selectivity for the extraction of evodiamine from Euodia fructus (the fruits of Euodia rutaecarpa (Juss.)Benth.), which attributes to the interactions of π-π and hydrogen bonding between the adsorbent and evodiamine. Combined with a C18 analytical column via high-performance liquid chromatography (HPLC) system, an online SPE-HPLC method was established for extraction, enrichment and determination of evodiamine from Euodia fructus. Method validation demonstrates that the relative standard deviation of the precision is less than 0.66%, and the spiked recovery is in the range of 93.11-98.06%. Furthermore, it is worth noting that the prepared SPE cartridge can be reused for no less than 100 times. These results show that the developed method is simple and efficient for online extraction and enrichment of evodiamine from Euodia fructus.