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

Recent developments in paper-based microfluidic devices.

Metal nanoclusters: New fluorescent probes for sensors and bioimaging

Metal ions are essential to many chemical, biological, and environmental processes. In the past two decades, many DNA-based metal sensors have emerged. While the main biological role of DNA is to store genetic information, its chemical structure is ideal for metal binding via both the phosphate backbone and nucleobases. DNA is highly stable, cost-effective, easy to modify, and amenable to combinatorial selection. Two main classes of functional DNA were developed for metal sensing: aptamers and DNAzymes. While a few metal binding aptamers are known, it is generally quite difficult to isolate such aptamers. On the other hand, DNAzymes are powerful tools for metal sensing since they are selected based on catalytic activity, thus bypassing the need for metal immobilization. In the last five years, a new surge of development has been made on isolating new metal-sensing DNA sequences. To date, many important metals can be selectively detected by DNA often down to the low parts-per-billion level. Herein, each me...

Metal Sensing by DNA

Metal nanoclusters, composed of several to a few hundred metal atoms, have received worldwide attention due to their extraordinary physical and chemical characteristics. Recently, great efforts have been devoted to the exploration of the potential diagnostic and therapeutic applications of metal nanoclusters. Here we focus on the recent advances and new horizons in this area, and introduce the rising progress on the use of metal nanoclusters for biological analysis, biological imaging, therapeutic applications, DNA assembly and logic gate construction, enzyme mimic catalysis, as well as thermometers and pH meters. Furthermore, the future challenges in the construction of biofunctional metal nanoclusters for diagnostic and therapeutic applications are also discussed. We expect that the rapidly growing interest in metal nanocluster-based theranostic applications will certainly not only fuel the excitement and stimulate research in this highly active field, but also inspire broader concerns across various disciplines.

Metal nanoclusters: novel probes for diagnostic and therapeutic applications

Double-strand DNA (dsDNA) can act as an efficient template for the formation of copper nanoparticles (Cu NPs) at low concentration of CuSO4, and the formed Cu NPs have excellent fluorescence, whereas a single-strand DNA (ssDNA) template does not support Cu NPs’ formation. This property of dsDNA-Cu NPs makes it suitable for DNA sensing. However, exploration of dsDNA-Cu NPs applied in biological analysis is still at an early stage. In this regard, we report herein for the first time a sensitive, cost-effective, and simple aptamer sensor (aptasensor) using dsDNA-Cu NPs as fluorescent probe. The design consists of a dsDNA with reporter DNA (here, aptamer) as template for the formation of Cu NPs, and the formed dsDNA-Cu NPs show high fluorescence. Using adenosine triphosphate (ATP) as a model analyte, the introduction of ATP triggers the structure switching of reporter DNA to form aptamer-ATP complex, causing the destruction of the double helix and thus no formation of the Cu NPs, resulting in low fluorescence...

Double-Strand DNA-Templated Formation of Copper Nanoparticles as Fluorescent Probe for Label-Free Aptamer Sensor

Fluorescent silver nanoclusters in hybridized DNA duplexes for the turn-on detection of Hg2+ ions

DNA-Ag nanoclusters as fluorescence probe for turn-on aptamer sensor of small molecules.

Dynamic DNA assembly, operated in an autonomous and reconfigurable manner by controlling the kinetics of strand displacement reactions (SDR), is an ideal approach to amplify the fluorescent signals for molecular diagnostic and imaging. Herein, we for the first time have demonstrated an enhancement of fluorescence intensity of DNA/Ag nanocluster-based beacons by the modulation of SDR. This is a new DNA/Ag NCs fluorescence light-up system through the use of the enhancer of G-rich overhang. Such a sensing system can be used to develop a DNA/Ag nanocluster-based beacon for the fluorescent detection of nucleic acid and thrombin with high selectivity and sensitivity, in which the detection sensitivity could be further enhanced through additional Exo III based amplification.

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A new approach to light up DNA/Ag nanocluster-based beacons for bioanalysis

The appearance of the aptamer provides good recognition elements for small molecules, especially for drugs. In this work, by combining the advantages of magnetic nanoparticles (MNPs) with colorimetric drug detection using hemin-G-quadruplex complex as the sensing element, we report a simple and sensitive DNAzyme-based colorimetric sensor for cocaine detection in a 3,3,5,5-tetramethylbenzidine sulfate (TMB)–H2O2 reaction system. The whole experimental processes are simplified. Cocaine aptamer fragments, SH–C2, are covalently labeled onto the amine-functionalized MNPs. When the target cocaine and another cocaine aptamer fragments (C1) grafted with G-riched strand AG4 (i.e. C1–AG4) are present simultaneously, the C2 layer on MNPs hybridizes partly with C1–AG4 to bind the cocaine. The C1–AG4 can be combinded with hemin to form DNAzyme which can effectively catalyze the H2O2-mediated oxidation of TMB, giving rise to a change in solution color. Importantly, using MNPs as the separation and amplification elements could effectively reduce the background signal and the interference from the real samples. A linear response from 0.1 μM to 20 μM is obtained for cocaine and a detection limit of 50 nM is achieved, which provides high sensitivity and selectivity to detect cocaine.

Zhixue Zhou

Papers

Double-Strand DNA-Templated Formation of Copper Nanoparticles as Fluorescent Probe for Label-Free Aptamer Sensor

Fluorescent silver nanoclusters in hybridized DNA duplexes for the turn-on detection of Hg2+ ions

DNA-Ag nanoclusters as fluorescence probe for turn-on aptamer sensor of small molecules.

A new approach to light up DNA/Ag nanocluster-based beacons for bioanalysis

G-Quadruplex-based DNAzyme for colorimetric detection of cocaine: Using magnetic nanoparticles as the separation and amplification element