Functionalizing porous materials with capping agents generates hybrid materials with enhanced properties, while the challenge is how to improve the selectivity and maintain the porosity of the parent framework. Herein, we developed a “Cage-on-MOF” strategy to tune the recognition and catalytic properties of MOFs without impairing their porosity. Two types of porous coordination cages (PCCs) of opposite charges containing secondary binding groups were developed to coordinatively functionalize two distinct porous MOFs, namely MOF@PCC nanocomposites. We demonstrated that the surface-capped PCCs can act as “modulators” to effectively tune the surface charge, stability, and adsorption behavior of different host MOF particles. More importantly, the MOF@PCCs can serve as selective heterogeneous catalysts for condensation reactions to achieve reversed product selectivity and excellent recyclability. This work sets the foundation for using molecular cages as porous surface-capping agents to functionalize and manipulate another porous material, without affecting the intrinsic properties of the parent framework.

Functional nanomaterials with enzyme-mimicking activities, termed as nanozymes, have found wide applications in various fields. However, the deviation between the working and optimal pHs of nanozymes has been limiting their practical applications. Here we develop a strategy to modulate the microenvironmental pHs of metal–organic framework (MOF) nanozymes by confining polyacids or polybases (serving as Brønsted acids or bases). The confinement of poly(acrylic acid) (PAA) into the channels of peroxidase-mimicking PCN-222-Fe (PCN = porous coordination network) nanozyme lowers its microenvironmental pH, enabling it to perform its best activity at pH 7.4 and to solve pH mismatch in cascade systems coupled with acid-denatured oxidases. Experimental investigations and molecular dynamics simulations reveal that PAA not only donates protons but also holds protons through the salt bridges between hydroniums and deprotonated carboxyl groups in neutral pH condition. Therefore, the confinement of poly(ethylene imine) increases the microenvironmental pH, leading to the enhanced hydrolase-mimicking activity of MOF nanozymes. This strategy is expected to pave a promising way for designing high-performance nanozymes and nanocatalysts for practical applications.

While it has been well recognized that affordable and pocket-size devices play a major role in environmental monitoring, food safety and medical diagnostics, it often takes a tremendous amount of resources to develop such devices. Devices that have been developed are often dedicated devices that can detect only one or a few targets. To overcome these limitations, we herein report a novel target-responsive smart thermometer for translating molecular detection into a temperature test. The sensor system consists of a functional DNA–phospholipase A₂ (PLA₂) enzyme conjugate, a liposome-encapsulated NIR dye, and a thermometer interfaced with a NIR-laser device. The sensing principle is based on the target-induced release of PLA₂ from the DNA–enzyme conjugate, which catalyzes the hydrolysis of liposome to release the NIR dye inside the liposome. Upon NIR-laser irradiation, the released dye can convert excitation energy into heat, producing a temperature increase in solution, which is detectable using a thermometer. Considering the low cost and facile incorporation of the system with suitable functional DNAs to recognize many targets, the system demonstrated here makes the thermometer an affordable and pocket-size meter for the detection and quantification of a wide range of targets.