Pore Environment Control and Enhanced Performance of Enzymes Infiltrated in Covalent Organic Frameworks

Ultrathin two-dimensional covalent organic framework nanoprobe for interference-resistant two-photon fluorescence bioimaging

A two-photon fluorescent covalent organic framework nanopore is designed for the first time for H₂S interference-resistant bioimaging.

The complex environment of living organisms significantly challenges the selectivity of classic small-molecule fluorescent probes for bioimaging. Due to their predesigned topological structure and engineered internal pore surface, covalent organic frameworks (COFs) have the ability to filter out coexisting interference components and help to achieve accurate biosensing. Herein, we propose an effective interference-resistant strategy by creating a COF-based hybrid probe that combines the respective advantages of COFs and small-molecule probes. As a proof of concept, a two-photon fluorescent COF nanoprobe, namely TpASH-NPHS, is developed for targeting hydrogen sulfide (H₂S) as a model analyte. TpASH-NPHS exhibits limited cytotoxicity, excellent photostability and long-term bioimaging capability. More importantly, compared with the small-molecule probe, TpASH-NPHS achieves accurate detection without the interference from intracellular enzymes. This allows us to monitor the levels of endogenous H₂S in a mouse model of cirrhosis.

Surface Pore Engineering of Covalent Organic Frameworks for Ammonia Capture through Synergistic Multivariate and Open Metal Site Approaches

Ammonia (NH₃) is a commonly used industrial gas, but its corrosiveness and toxicity are hazardous to human health. Although many adsorbents have been investigated for NH₃ sorption, limited ammonia uptake remains an urgent issue yet to be solved. In this article, a series of multivariate covalent organic frameworks (COFs) are explored which are densely functionalized with various active groups, such as -N-H, -C=O, and carboxyl group. Then, a metal ion (Ca²⁺, Mn²⁺, and Sr²⁺) is integrated into the carboxylated structure achieving the first case of an open metal site in COF architecture. X-ray photoelectron spectroscopy reveals conclusive evidence for the multiple binding interactions with ammonia in the modified COF materials. Infrared spectroscopy indicates a general trend of binding capability from weak to strong along with -N-H, -C=O, carboxyl group, and metal ion. Through the synergistic multivariate and open metal site, the COF materials show excellent adsorption capacities (14.3 and 19.8 mmol g^-1 at 298 and 283 K, respectively) and isosteric heat (Q_st) of 91.2 kJ mol^-1 for ammonia molecules. This novel approach enables the development of tailor-made porous materials with tunable pore-engineered surface for ammonia uptake.

Ion Conduction in Polyelectrolyte Covalent Organic Frameworks

Covalent organic frameworks (COFs) with ordered one-dimensional channels could offer a predesigned pathway for ion motion. However, implanting salts into bare channels of COFs gives rise to a limited ion conductivity. Here, we report the first example of polyelectrolyte COFs by integrating flexible oligo(ethylene oxide) chains onto the pore walls. Upon complexation with lithium ions, the oligo(ethylene oxide) chains form a polyelectrolyte interface in the nanochannels and offer a pathway for lithium ion transport. As a result, the ion conductivity was enhanced by more than 3 orders of magnitude compared to that of ions across the bare nanochannels. The polyelectrolyte COFs promoted ion motion via a vehicle mechanism and exhibited enhanced cycle and thermal stabilities. These results suggest that the strategy for engineering a polyelectrolyte interface in the 1D nanochannels of COFs could open a new way to solid-state ion conductors.

Enzyme-immobilized metal–organic framework nanosheets as tandem catalysts for the generation of nitric oxide

An enzyme-immobilized metal–organic framework nanosystem was developed as a tandem catalyst for in situ generation of nitric oxide in serum samples.

Photonic functional metal–organic frameworks

The recent progress in photonic MOFs for luminescence sensing, white-light emission, photocatalysis, nonlinear optics, lasing devices, and biomedicine is summarized.

Uracil grafted imine-based covalent organic framework for nucleobase recognition

An imine-based covalent organic framework (COF) decorated in its cavities with uracil groups has shown selective recognition towards adenine in water.