Scientists have unveiled a sweeping critical review of photonanozymes, a new class of artificial enzymes that switch their catalytic activity on and off with light. Published in Advanced Biotechnology, the review by Faria Fatima, Syed Saqib Ali Zaidi, Yang Guang, He Huang and Xiao-Man Sun argues that these light-gated nanomaterials could overcome the central weakness of conventional nanozymes: their always-on catalysis, which produces unwanted reactive oxygen species, fouls catalysts and makes recovery at industrial scale an energy-intensive headache. By making photons the master switch, photonanozymes promise catalysis that is precise, programmable and confined to exactly where and when it is wanted.
The core insight of the review is architectural. The authors deconstruct every photonanozyme into three functional domains: a light-harvesting domain that captures high-energy photons and converts them into excited carriers; an enzyme-mimetic active site that turns that photoenergy into chemical outcomes; and a nano-environment that pre-organizes substrates and prevents the wasteful recombination of electrons and holes. Together these domains reproduce enzyme-like behavior that follows Michaelis–Menten kinetics, but with a twist: the familiar parameters Km and Vmax can be tuned not only by pH, temperature and substrate concentration, but by photon flux itself.
The light-harvesting domain comes in three main flavors. Semiconductor band-gap engineering adjusts absorption through doping, alloying, defect creation and heterojunction formation; nitrogen-doped TiO2 nanosheets, for example, have their band gap narrowed from 3.2 to 2.4 electron volts while preserving the redox potential needed for peroxidase-like hydroxyl radical generation. Plasmonic antennas built from gold, silver or copper exploit localized surface plasmon resonance, in which coherent electron oscillations create electromagnetic hot spots roughly ten million times stronger than solar flux, injecting hot electrons into the catalytic site within femtoseconds. Up- and down-conversion chromophores act as optical frequency transformers, converting deep-penetrating near-infrared photons into the ultraviolet or visible light needed to drive catalysis inside tissue.
Each strategy carries a fundamental trade-off that the review does not shy away from. Semiconductor heterojunctions achieve the highest apparent quantum yields, up to 35.6 percent, but suffer rapid electron–hole recombination. Plasmonic systems offer tunable absorption across the visible and near-infrared yet record quantum efficiencies as low as 0.38 percent, with hot-carrier utilization often below one percent of absorbed energy. Upconversion materials unlock wavelengths previously inaccessible for deep-tissue therapy but are inherently inefficient. The authors conclude that no single domain wins outright; the optimal choice depends on balancing quantum yield, catalytic turnover and stability for each application.
At the active site, the review identifies several biomimetic hallmarks. Electronic states trap and shuttle photogenerated charge carriers through mid-gap defects, split d-orbitals of single atoms, or delocalized pi-star bands. Hydrophobic gating, achieved with fluorine or alkyl-silane dopants, excludes water from the active site and lowers activation energy; a single-iron-atom carbon nitride nanozyme with fluoroalkyl silane gates cut activation energy by 0.3 electron volts. Substrate-induced dynamic restructuring lets the active site reconfigure in real time, exemplified by short-lived peroxo bridges that transfer oxygen atoms during photo-oxidation. Photonic gating acts like an allosteric effector: azobenzene flips from trans to cis under 365-nanometer ultraviolet light to switch peroxidase activity on, while diarylethene opens its ring under green light to catalyze carbon dioxide reduction, all within sub-millisecond response times.
The nano-environment completes the design. Mesopores, surface cavities and molecularly imprinted pockets geometrically confine and pre-organize substrates, mimicking the induced-fit model of natural enzymes. Polarity matters too: according to Marcus theory, shifting from a polar aqueous environment to a hydrophobic one can accelerate electron transfer up to tenfold, and fluorinated TiO2 nanosheets with a reorganization energy of 0.34 electron volts show threefold faster peroxidase-like activity than their hydrophilic counterparts. Defect-mediated charge separation, tuned by defect density, lattice polarity and mechanical strain, together with Z-scheme heterojunctions that route electrons along staggered band alignments, keeps electrons and holes apart long enough to do useful chemistry.
What can these machines actually do? The review catalogs a remarkable enzymatic repertoire. Under light, photonanozymes mimic peroxidase, oxidase, catalase, superoxide dismutase, nitroreductase, DNA-cleaving nuclease and fatty-acid photodecarboxylase. TiO2 nanorods display catalase-like activity in the dark but switch to peroxidase-like activity under visible illumination. Glutathione-modified gold nanoclusters reduce nitroaromatics stepwise to anilines under visible light, opening a route to light-controlled prodrug activation. Iron-doped TiO2 nanozymes decarboxylate palmitic acid into pentadecane, a diesel-range hydrocarbon, pointing toward solar-driven biofuel synthesis.
The application landscape is correspondingly broad. In environmental remediation, CeO2/ZnO nanoflowers with Z-type heterojunctions degrade antibiotics and dyes under visible light, while persulfate-activated systems generate sulfate radicals for complete pollutant mineralization. In diagnostics, light-enhanced peroxidase activity amplifies colorimetric glucose and metabolite assays, and CeO2–MoS2 nanozymes paired with lactate oxidase transmit sweat-lactate readings wirelessly to a smartphone. In oncology, photonanozymes power photodynamic therapy, photothermal-chemodynamic combinations and catalytic immunotherapy that relieves tumor hypoxia and recruits immune cells. They also heal infected wounds by modulating reactive oxygen species, inhibit biofilms, fix nitrogen and sequester heavy metals.
The review is refreshingly candid about the obstacles. Non-specific reactive oxygen species can damage healthy tissue; inorganic nanozymes accumulate in the liver and spleen with slow biodegradation; tumor levels of endogenous hydrogen peroxide are too low for efficient chemodynamic therapy; metal leaching, batch-to-batch irreproducibility and the gap between microscale laboratory synthesis and industrial manufacturing all loom large. Interfacial defects between the three domains obstruct charge transfer, and the trade-off between light absorption and recombination remains unresolved. The authors call for operando characterization techniques such as time-resolved X-ray absorption, machine-learning models trained on defect-engineered catalyst libraries, biodegradable constructs with regulated degradation kinetics, and standardized synthesis protocols.
Their forward-looking roadmap is phased and concrete: systematic operando studies to establish mechanistic foundations, followed by artificial-intelligence-driven discovery cycles to identify biodegradable, near-infrared-responsive candidates, and finally pilot-scale validation in membrane reactors and immobilized photoreactor coatings. If that pathway holds, photonanozymes could graduate from laboratory proof-of-concept to programmable, self-healing nanomaterials that treat tumors with a flash of light, scrub pollutants from water and brew fuels from fatty acids, all under the control of a switch as simple and universal as a photon.
Subject of Research: Light-activated nanozymes with enzyme-like catalytic activity and their design, mechanisms and applications
Article Title: Light as a master switch: a critical review of photonanozymes from design to applications
Article References: Fatima, F., Zaidi, S. S. A., Guang, Y., Huang, H., & Sun, X.-M. (2026). Light as a master switch: a critical review of photonanozymes from design to applications. Advanced Biotechnology, 4(4), Article 40. https://doi.org/10.1007/s44307-026-00138-3
Image Credits: AI Generated
DOI: 10.1007/s44307-026-00138-3
Keywords: photonanozymes, nanozymes, photocatalysis, enzyme mimetics, light-activated catalysis, reactive oxygen species, photodynamic therapy, biosensing, environmental remediation, defect engineering, single-atom catalysts, biofuel synthesis
