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.

Construction of covalent organic framework nanozymes with photo-enhanced hydrolase activities for colorimetric sensing of organophosphorus nerve agents.

Construction of covalent organic frameworks (COFs)-based nanozymes is of great importance for the extensive applications in catalysis and sensing fields. In this work, a two-dimensional COF (DAFB-DCTP COF) was fabricated via Knoevenagel condensation reaction. The integration of catalytically active sites of pyridine groups into the donor-acceptor (D-A) conjugated skeleton endows DAFB-DCTP COF with both hydrolytic and photosensitive properties. The DAFB-DCTP COF can be utilized as an artificial enzyme with selective and photo-enhanced catalytic efficiency, facilitating its application in photocatalytic degradation of hydrolase substrates (p-nitrophenyl acetate, pNPA) by nucleophilic reaction and further realizing colorimetric detection of the nanozyme inhibitor of organophosphorus nerve agent (diethyl cyanophosphonate, DCNP). The distinct color changes could be distinguished by naked eyes even at a low DCNP concentration, and the versatile smartphone analysis featured with reliability and simplicity. For the first time, the COFs' intrinsic hydrolase activity depending on their structural characteristics was investigated in synergy with the photosensitive performance originating from their photoelectric features. The present contribution provides a promising direction towards construction of colorimetric sensing platform based on the regulation of COFs' non-oxidoreductase activity under visible light irradiation.

Simultaneous detection and separation of uranium based on a fluorescent amidoxime-functionalized covalent organic polymer.

To ensure the long-term sustainable development of nuclear energy as well as the prevention and control of uranium pollution, new materials that can simultaneously detect and separate uranium are still urgently needed. Herein, a new fluorescent covalent organic polymer (COP), namely HT-COP-AO, was synthesized andemployed as both the fluorescent probe and absorbent for simultaneous uranium detection and separationconsidering its excellent fluorescence property and strong uranium coordination ability. The results showed that the fluorescence of HT-COP-AO was quickly quenched by uranium within 2 min, and the limit of detection was 0.23 µM (3σ/K). Further studies implied that uranium was coordinated with the amidoxime groups of HT-COP-AO through U-N and O = U = O bonds, which resulted in electron transfer from uranium to HT-COP-AO and quenching the fluorescence of HT-COP-AO consequently. Meanwhile, HT-COP-AO exhibited excellent absorption ability towards uranium, and the maximum absorption capacity (qmax = 401.3 mg/g) was higher than most reported amidoxime modified materials. The HT-COP-AO also showed high selectivity for both uranium detection and separation which makes it a great promising for uranium monitoring in real water samples.