
An artificial enzyme is a synthetic organic molecule or ion that recreates one or more functions of an enzyme. It seeks to deliver catalysis at rates and selectivity observed in naturally occurring enzymes.
History
Enzyme catalysis of chemical reactions occur with high selectivity and rate. The substrate is activated in a small part of the enzyme's macromolecule called the active site. There, the binding of a substrate close to functional groups in the enzyme causes catalysis by so-called proximity effects. It is possible to create similar catalysts from small molecules by combining substrate-binding with catalytic functional groups. Classically, artificial enzymes bind substrates using receptors such as cyclodextrin, crown ethers, and calixarene.
Artificial enzymes based on amino acids or peptides have expanded the field of artificial enzymes or enzyme mimics. For instance, scaffolded histidine residues mimic certain metalloproteins and enzymes such as hemocyanin, tyrosinase, and catechol oxidase.
Artificial enzymes have been designed from scratch via a computational strategy using Rosetta. A December 2014 publication reported active enzymes made from molecules that do not occur in nature. In 2016, a book chapter entitled "Artificial Enzymes: The Next Wave" was published.
Nanozymes
Nanozymes are nanomaterials with enzyme-like characteristics. They have been explored for applications such as biosensing, bioimaging, tumor diagnosis and therapy, and anti-biofouling.
1990s
In 1996 and 1997, Dugan et al. discovered superoxide dismutase (SOD)-mimicking activities of fullerene derivatives.
2000s
The term "nanozyme" was coined in 2004 by Flavio Manea, Florence Bodar Houillon, Lucia Pasquato, and Paolo Scrimin. A 2005 review article
attributed this term to "analogy with the activity of catalytic
polymers (synzymes)", based on the "outstanding catalytic efficiency of
some of the functional nanoparticles synthesized". In 2006, nanoceria
(CeO2 nanoparticles) was reported to prevent retinal degeneration induced by intracellular peroxides (toxic reactive oxygen intermediates) in rat. This was seen as indicating a possible route to a treatment for certain causes of blindness. In 2007 intrinsic peroxidase-like activity of ferromagnetic nanoparticles was reported by Yan Xiyun
and coworkers as suggesting a wide range of applications in, for
example, medicine and environmental chemistry, and the authors designed
an immunoassay based on this property.
Hui Wei and Erkang Wang then (2008) used this property of easily
prepared magnetic nanoparticles to demonstrate analytical applications
to bioactive molecules, describing a colorimetric assay for hydrogen peroxide (H
2O
2) and a sensitive and selective platform for glucose detection.
2010s
As of 2016, many review articles have appeared.
A book-length treatment appeared in 2015, described as providing "a
broad portrait of nanozymes in the context of artificial enzyme
research", and a 2016 Chinese book on enzyme engineering included a chapter on nanozymes.
Colorimetric applications of peroxidase mimesis in different
preparations were reported in 2010 and 2011, detecting, respectively,
glucose (via carboxyl-modified graphene oxide) and single-nucleotide polymorphisms (in a label-free method relying on hemin−graphene hybrid nanosheets),
with advantages in both cost and convenience. A use of colour to
visualise tumour tissues was reported in 2012, using the peroxidase
mimesis of magnetic nanoparticles coated with a protein that recognises
cancer cells and binds to them.
Also in 2012, nanowires of vanadium pentoxide (vanadia, V2O5) were shown to suppress marine biofouling by mimicry of vanadium haloperoxidase, with anticipated ecological benefits. A study at a different centre two years later reported V2O5 showing mimicry of glutathione peroxidase in vitro in mammalian cells, suggesting future therapeutic application. The same year, a carboxylated fullerene dubbed C3 was reported to be neuroprotective in a primate model of Parkinson's disease.
In 2015, a supramolecular nanodevice was proposed for bioorthogonal
regulation of a transitional metal nanozyme, based on encapsulating the
nanozyme in a monolayer of hydrophilic gold nanoparticles, alternately
isolating it from the cytoplasm or allowing access according to a
gatekeeping receptor molecule controlled by competing guest
species; the device, aimed at imaging and therapeutic applications, is
of biomimetic size and was successful within the living cell,
controlling pro-fluorophore and prodrug activation. An easy means of producing Cu(OH)
2 supercages was reported, along with a demonstration of their intrinsic peroxidase mimicry. A scaffolded "INAzyme" ("integrated nanozyme") arrangement was described, locating hemin (a peroxidase mimic) with glucose oxidase
(GOx) in sub-micron proximity, providing a fast and efficient enzyme
cascade reported as monitoring cerebral brain-cell glucose dynamically in vivo.
A method of ionising hydrophobe-stabilised colloid nanoparticles was
described, with confirmation of their enzyme mimicry in aqueous
dispersion. De novo designed metallopeptides with self-assembling properties carry out the oxidation reaction of dimethoxyphenol.
Field trials in West Africa were announced of a magnetic nanoparticle–amplified rapid low-cost strip test for Ebola virus. H
2O
2
was reported as displacing label DNA, adsorbed to nanoceria, into
solution, where it fluoresces, providing a highly sensitive glucose
test. Oxidase-like nanoceria was used for developing self-regulated bioassays. Multi-enzyme mimicking Prussian blue was developed for therapeutics. A review on metal organic framework (MOF)-based enzyme mimics was published. Histidine was used to modulate iron oxide nanoparticles' peroxidase-mimicking activities. Gold nanoparticles' peroxidase-mimicking activities were modulated via a supramolecular strategy for cascade reactions. A molecular imprinting strategy was developed to improve the selectivity of Fe3O4 nanozymes with peroxidase-like activity. A new strategy was developed to enhance the peroxidase-mimicking activity of gold nanoparticles by using hot electrons.
Researchers designed gold nanoparticle–based integrative nanozymes with
both surface-enhanced Raman scattering and peroxidase-mimicking
activities for measuring glucose and lactate in living tissues. Cytochrome c oxidase mimicking activity of Cu2O nanoparticles was modulated by receiving electrons from cytochrome c. Fe3O4 nanoparticles were combined with glucose oxidase for tumor therapeutics. Manganese dioxide nanozymes were used as cytoprotective shells. An Mn3O4 nanozyme for Parkinson's disease (cellular model) was reported. Heparin elimination in live rats was monitored with two-dimensional MOF-based peroxidase mimics and AG73 peptide.
Glucose oxidase and iron oxide nanozymes were encapsulated within
multi-compartmental hydrogels for incompatible tandem reactions. A cascade nanozyme biosensor was developed for detection of viable Enterobacter sakazakii. An integrated nanozyme of GOx@ZIF-8(NiPd) was developed for tandem catalysis. Charge-switchable nanozymes were developed. Site-selective RNA splicing nanozyme was developed. A nanozymes special issue in Progress in Biochemistry and Biophysics was published. Mn3O4 nanozymes with the ability to scavenge reactive oxygen species were developed and showed in vivo anti-inflammatory activity. A proposal entitled "A Step into the Future – Applications of Nanoparticle Enzyme Mimics" was presented. Facet-dependent oxidase and peroxidase-like activities of palladium nanoparticles were reported. Au@Pt multibranched nanostructures as bifunctional nanozymes were developed. Ferritin-coated carbon nanozymes were developed for tumor catalytic therapy. CuO nanozymes were developed to kill bacteria in a light-controlled manner. Enzymatic activity of oxygenated CNT was studied. Nanozymes were used to catalyze the oxidation of L-tyrosine and L-phenylalanine to dopachrome. Nanozymes were presented as an emerging alternative to natural enzyme for biosensing and immunoassays. A standardized assay was proposed for peroxidase-like nanozymes. Semiconductor quantum dots were utilized as nucleases for site-selective photoinduced cleavage of DNA. Two-dimensional MOF nanozyme-based sensor arrays were constructed for detecting phosphates and probing their enzymatic hydrolysis. Nitrogen-doped carbon nanomaterials as specific peroxidase mimics were reported. Nanozyme sensor arrays were developed to detect analytes from small molecules to proteins and cells. A copper oxide nanozyme for Parkinson's disease was reported. Exosome-like nanozyme vesicles for tumor imaging were developed. A comprehensive review on nanozymes was published by Chemical Society Reviews. A progress report on nanozymes was published. eg occupancy as an effective descriptor was developed for the catalytic activity of perovskite oxide–based peroxidase mimics. A Chemical Reviews paper on nanozymes was published. A single-atom strategy was used to develop nanozymes. A nanozyme for metal-free bioinspired cascade photocatalysis was reported. Chemical Society Reviews published a tutorial review on nanozymes. Cascade nanozyme reactions to fix CO2 were reported. Peroxidase-like gold nanoclusters were used to monitor renal clearance. A copper–carbon hybrid nanozyme was developed for antibacterial therapy. A ferritin nanozyme was developed to treat cerebral malaria. Accounts of Chemical Research reviewed nanozymes. A new strategy called strain effect was developed to modulate metal nanozyme activity. Prussian blue nanozymes were used to detect hydrogen sulfide in the brains of living rats. Photolyase-like CeO2 was reported. An editorial on nanozymes titled "Can Nanozymes Have an Impact on Sensing?" was published.