Over the past few decades, researchers have established artificial enzymes as highly stable and low-cost alternatives to natural enzymes in a wide range of applications. A variety of materials including cyclodextrins, metal complexes, porphyrins, polymers, dendrimers and biomolecules have been extensively explored to mimic the structures and functions of naturally occurring enzymes. Recently, some nanomaterials have been found to exhibit unexpected enzyme-like activities, and great advances have been made in this area due to the tremendous progress in nano-research and the unique characteristics of nanomaterials. To highlight the progress in the field of nanomaterial-based artificial enzymes (nanozymes), this review discusses various nanomaterials that have been explored to mimic different kinds of enzymes. We cover their kinetics, mechanisms and applications in numerous fields, from biosensing and immunoassays, to stem cell growth and pollutant removal. We also summarize several approaches to tune the activities of nanozymes. Finally, we make comparisons between nanozymes and other catalytic materials (other artificial enzymes, natural enzymes, organic catalysts and nanomaterial-based catalysts) and address the current challenges and future directions (302 references).

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes

Metal–organic frameworks (MOFs) or porous coordination polymers (PCPs) are open, crystalline supramolecular coordination architectures with porous facets. These chemically tailorable framework materials are the subject of intense and expansive research, and are particularly relevant in the fields of sensory materials and device engineering. As the subfield of MOF-based sensing has developed, many diverse chemical functionalities have been carefully and rationally implanted into the coordination nanospace of MOF materials. MOFs with widely varied fluorometric sensing properties have been developed using the design principles of crystal engineering and structure–property correlations, resulting in a large and rapidly growing body of literature. This work has led to advancements in a number of crucial sensing domains, including biomolecules, environmental toxins, explosives, ionic species, and many others. Furthermore, new classes of MOF sensory materials utilizing advanced signal transduction by devices based on MOF photonic crystals and thin films have been developed. This comprehensive review summarizes the topical developments in the field of luminescent MOF and MOF-based photonic crystals/thin film sensory materials.

Metal-organic frameworks: functional luminescent and photonic materials for sensing applications.

Proton conducting materials have garnered immense attention for their role as electrolytes in fuel cells. Metal Organic Frameworks (MOFs) and coordination polymers have recently been investigated as possible candidates for proton-conducting applications. Their crystallinity, chemically functionalizable pores and options for systematic structural variation are some of the factors that allow for the targeted design of better proton conductors operating over a wide variety of temperatures and/or humidity conditions. This review will examine selected examples from this nascent field, and will focus on the design and synthesis of proton conducting MOFs, their properties and conditions under which they operate.

MOFs as proton conductors – challenges and opportunities

Luminescent sensors based on metal-organic frameworks

A facile surfactant-assisted bottom-up synthetic method to prepare a series of freestanding ultrathin 2D M-TCPP (M = Zn, Cu, Cd or Co, TCPP = tetrakis(4-carboxyphenyl)porphyrin) nanosheets with a thickness of sub-10 nm is developed. As a proof-of-concept application, some of them are successfully used as new platforms for DNA detection. The Cu-TCPP nanosheet-based sensor shows excellent fluorescent sensing performance and is used for the simultaneous detection of multiple DNA targets.

Ultrathin 2D Metal–Organic Framework Nanosheets

Water-stable metal–organic frameworks with intrinsic peroxidase-like catalytic activity as a colorimetric biosensing platform

An amine-functionalized metal-organic framework as a sensing platform for DNA detection.

A series of metal–organic frameworks (MOFs) based on a phosphonate monoester ligand, with structures featuring 1D chains, 2D layers or double layers, and 3D networks, have been successfully obtained in the presence of auxiliary N-donor ligands. The phosphonate monoester, behaving as a carboxylate linker, bridges metal ions, while the auxiliary N-donor ligands play a crucial role in both the structural diversity and the dimensionality variation of the resultant MOFs. Remarkably, the hydrophobic ethyl groups present in the phosphonate monoester linker offer protection/shielding for the hydrolytically vulnerable M–O bonds, resulting in the MOFs being highly moisture stable, as expected. The porous MOFs with 3D networks exhibited CO2 adsorption and strong fluorescence emission.

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Metal–organic frameworks with improved moisture stability based on a phosphonate monoester: effect of auxiliary N-donor ligands on framework dimensionality

Zi-Yi Du

Papers

Water-stable metal–organic frameworks with intrinsic peroxidase-like catalytic activity as a colorimetric biosensing platform

An amine-functionalized metal-organic framework as a sensing platform for DNA detection.

Metal–organic frameworks with improved moisture stability based on a phosphonate monoester: effect of auxiliary N-donor ligands on framework dimensionality