Advances in the application of logic gates in nanozymes

Nanozymes are a class of nanomaterials with biocatalytic function and enzyme-like activity, whose advantages include high stability, low cost, and mass production. They can catalyze the substrates of natural enzymes based on specific nanostructures and serve as substitutes for natural enzymes. Their applied research involves a wide range of fields such as biomedicine, environmental governance, agriculture, and food. Molecular logic gates are a new cross-disciplinary discipline, which can simulate the function of silicon circuits on a molecular scale, perform single or multiple input logic operations, and generate logic outputs. A molecular logic gate is a binary operation that converts an input signal into an output signal according to the rules of Boolean logic, generating two signals, a high level, and a low level. The high and low levels represent the "true" and "false" values of the logic gates, and their outputs correspond to "l" and "0" of the molecular logic gates, respectively. The combination of nanozymes and logic gates is a novel and attractive research direction, and the cross-application of the two brings new opportunities and ideas for various fields, such as the construction of efficient biocomputers, intelligent drug delivery systems, and the precise diagnosis of diseases. This review describes the application of logic gates based on nanozymes, which is expected to provide a certain theoretical foundation for researchers' subsequent studies.

Size-matching compositing nanoprobe of AIE-type gold nanocluster supramolecular nanogels wrapped by hypergravity-tailored MnO2 nanosheets for cellular glutathione detection

Compositing has been the main approach for material creation via wisely combining material components with different properties. MnO2 nanosheets (MNSs) with thin 2 D morphology are usually applied to composite molecules or nanomaterials for biosensing and bioimaging applications. However, such composition is actually structurally unmatched, albeit performance matching. Here, a series of benefits merely on the basis of structural match have been unearthed via tailoring MNSs with four sizes by synthesis under controllable hypergravity field. The classical fluorophore-quencher couple was utilized as the subject model, where the soft supramolecular nanogels based on aggregation-induced emission (AIE)-active gold nanoclusters were wrapped by MNSs of strong absorption. By comparative study of one-on-one wrapping and one-to-many encapsulation with geometrical selection of different MNSs, we found that the one-on-one wrapping model protected weakly-bonded nanogels from combination-induced distortion and strengthened nanogel networks via endowing exoskeleton. Besides, wrapping pattern and size-match significantly enhanced the quenching efficiency of MNSs towards the emissive nanogels. More importantly, the well-wrapped nanocomposites had considerable enhanced biological compatibility with much lower cytotoxicity and higher transfection capacity than the untailored MNSs composite and could serve as cellular glutathione detection.

Enhancement of the peroxidase-like activity of hollow spherical FexNi1-xS2/SC nanozymes

Artificial nanozymes have been receiving considerable interest for their outstanding performance and wide application. However, their low activity results in a high concentration of substrates, costs, and environmental pollution. To enhance nanozymic activity, a composite, FexNi1-xS2/hollow carbon spheres (FexNi1-xS2/SC), was facilely synthesized by a solvothermal method. The response surface methodology (RSM) was used to optimize the Ni content in FexNi1-xS2/SC and the experimental conditions, where Fe0.75Ni0.25S2/SC exhibited the highest activity. The Km (Michaelis-Menten's constant) values of Fe0.75Ni0.25S2/SC are 0.025 and 0.021 mM with H2O2 and oxidized 3,3',5,5'-tetramethylbenzidine (TMB) as the substrates, respectively, which are 148 times and 20.5 times lower than those with HRP, 1.88 and 7.19 times lower than those of FeS2/SC, and 1.88 and 10.52 times lower than those of Fe0.8Ni0.2S2, meaning a strong affinity of Fe0.75Ni0.25S2/SC for the substrate. The catalytic efficiency (Kcat/Km) of Fe0.75Ni0.25S2/SC was 5.4 (H2O2) and 27.4 times (TMB), and 9.7 (H2O2) and 66.2 times (TMB) higher than those of FeS2/SC and Fe0.8Ni0.2S2, respectively. The effects of the synergistic interaction between Fe and Ni, the S-C bond formation, and the hollow carbon spheres on the activity were studied. A nanozymic mechanism was proposed. Fe0.75Ni0.25S2/SC could be used to detect cysteine (Cys) at room temperature in 1 min with a detection limit (LOD) of 0.049 μM.

Synthesis of Ti3C2T x /MnO2 composites for synergistic catalytic/photothermal-based bacterial inhibition

Human inflammation caused by bacterial infection threatens global public health. The abuse of antibiotics often leads to the development of drug resistance in bacteria. To address this issue, nanozymes with peroxidase-like (POD-like) activity have often been reported for bacteriostasis with the assistance of catalytic substrate hydrogen peroxide (H2O2). However, it is difficult to achieve efficient bactericidal outcomes only through exertion of the POD-like activity of nanozymes. Here, MnO2 loaded Ti3C2T x (Ti3C2T x /MnO2) was prepared by a two-step reaction method, in which MnO2 showed high oxidase-like (OXD-like) activity to elevate the levels of reactive oxygen species (ROS) without H2O2 and Ti3C2T x exhibited high photothermal conversion efficiency to induce hyperthermia. Thus, the obtained Ti3C2T x /MnO2 realized synergistic catalytic/photothermal-based bacterial inhibition, including for Gram-negative bacteria (Escherichia coli), Gram-positive bacteria (Staphylococcus aureus), and methicillin-resistant Staphylococcus aureus. Importantly, Ti3C2T x /MnO2 with near-infrared light irradiation successfully promoted Staphylococcus aureus-infected wound healing in mouse models, representing an alternative treatment to fight against bacterial infection.

Plasmon-Enhanced Bimodal Nanosensors: An Enzyme-Free Signal Amplification Strategy for Ultrasensitive Detection of Pathogens

Increasing foodborne illnesses have led to global health and economic burdens. E. coli O157:H7 is one of the most common disease-provoking pathogens and known to be lethal Shiga toxin-producing E. coli (STEC) strains. With a low infection dose in addition to person-to-person transmission, STEC infections are easily spread. As a result, specific and rapid testing methods to identify foodborne pathogens are urgently needed. Nanozymes have emerged as enzyme-mimetic nanoparticles, demonstrating intrinsic catalytic activity that could allow for rapid, specific, and accurate pathogen identification in the agrifood industry. In this study, we developed a sensitive nanoplatform based on the traditional ELISA assay with the synergistic properties of gold and iron oxide nanozymes, replacing the conventional enzyme horseradish peroxidase (HRP). We designed an easily interchangeable sandwich ELISA composed of a novel, multifunctional magneto-plasmonic nanosensor (MPnS) with target antibodies (MPnS-Ab). Our experiments demonstrate a 100-fold increase in catalytic activity in comparison to HRP with observable color changes within 15 min. Results further indicate that the MPnS-Ab is highly specific for E. coli O157:H7. Additionally, effective translatability of catalytic activity of the MPnS technology in the lateral flow assay (LFA) platform is also demonstrated for E. coli O157:H7 detection. As nanozymes display more stability, tunable activity, and multi-functionality than natural enzymes, our platform could provide customizable, low-cost assay that combines high specificity with rapid detection for a variety of pathogens in a point-of-care setup.

2D/3D-Shaped Fe0.8Ni0.2S2/ZIF-67 as a Nanozyme for Rapid Measurement of H2O2 and Ascorbic Acid with a Low Limit of Detection

Metal-organic frameworks (MOFs) can be used as ideal artificial nanozymes for an open structure to transfer substances and products. The nanozymic mechanism of MOFs needs further investigation for wide application. In this manuscript, no peroxidase-like activity was found for ZIF-67 (a kind of MOF), however, it enhanced the peroxidase-like activity of the Fe_0.8Ni_0.2S₂/ZIF-67 composite, in which Fe_0.8Ni_0.2S₂ was the active composition. The catalytic constant (K_cat) is higher at 1.98 (for TMB) and 2.08 (for H₂O₂) times and the catalytic efficiency (K_cat/K_m) is higher at 3.13 (for TMB) and 2.67 (for H₂O₂) times, than those of Fe_0.8Ni_0.2S₂. The K_m value decreased about 85 times (for H₂O₂) for Fe_0.8Ni_0.2S₂/ZIF-67 than that of horseradish peroxidase (natural enzyme). The mechanism was proposed. The limit of detection of H₂O₂ for Fe_0.8Ni_0.2S₂/ZIF-67 is 0.039 μM, which is lower by about 18.2 times than that of Fe_0.8Ni_0.2S₂. Simultaneously, Fe_0.8Ni_0.2S₂/ZIF-67 was used to rapidly detect ascorbic acid for only 1.0 min in food monitoring. This study may be important to design a new kind of nanozyme.

Manganese dioxide nanosheet-containing reactors as antioxidant support for neuroblastoma cells

Supporting mammalian cells against reactive oxygen species such as hydrogen peroxide (H₂O₂) is essential. Bottom-up synthetic biology aims to integrate designed artificial units with mammalian cells. Here, we used manganese dioxide nanosheets (MnO₂-NSs) as catalytically active entities that have superoxide dismutase-like and catalase-like activities. The integration of these MnO₂-NSs into 7 μm reactors was able to assist SH-SY5Y neuroblastoma cells when stressed with H₂O₂. Complementary, Janus-shaped 800 nm reactors with one hemisphere coated with MnO₂-NSs showed directed locomotion in cell media with top speeds up to 50 μm s^-1 when exposed to 300 mM H₂O₂ as a fuel, while reactors homogeneously coated with MnO₂-NSs were not able to outperform Brownian motion. These Janus-shaped reactors were able to remove H₂O₂ from the media, protecting cells cultured in the proximity. This effort advanced the use of bottom-up synthetic biology concepts in neuroscience.

Visual colorimetric detection of triacetone triperoxide based on a Fe(II)-promoted thermal decomposition process

Triacetone triperoxide (TATP) explosives, a popular choice for terrorists, have been used in many violent terrorist attacks all over the world. However, simple, rapid, and on-site detection methods of TATP are still lacking. Herein, we present a visual colorimetric method for on-site and rapid detection of TATP based on a Fe(II)-promoted thermal decomposition process of TATP. We discovered that TATP can be decomposed into H₂O₂ under heating conditions, and it reacts with Fe²⁺ to produce hydroxyl radicals (˙OH) and Fe³⁺via the Fenton reaction. The resulting ˙OH and Fe³⁺ further oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) to a yellow oxidized product (oxTMB). These reaction processes remarkably promote the chemical equilibrium shift and decrease the activation energy. Using the TATP-Fe²⁺-TMB ternary chromogenic system, the present colorimetric assay for TATP shows a dynamic range of 0.5-30 μM with a low detection limit of 0.12 μM. Additionally, common substances (e.g., inorganic salts, small organic substances, and polymers) do not interfere with TATP detection. This assay can be used for analyzing TATP in real water and camouflage samples. Furthermore, a test-paper-based method was also successfully developed for visual, rapid and on-site detection of TATP.

Artesunate-loaded poly (lactic-co-glycolic acid)/polydopamine-manganese oxides nanoparticles as an oxidase mimic for tumor chemo-catalytic therapy

Conventional tumor chemotherapy is limited by its low therapeutic efficacy and side effects, which severely hold back its further application as a first-line agent in clinic. To improve the cure efficacy of cancer, nanozyme with enzyme-like activity has now been extensively investigated as a new strategy for tumor treatment. Herein, an anti-tumor platform based on manganese oxides (MnOx) modified poly (lactic-co-glycolic acid) (PLGA)@polydopamine (PDA) nanoparticles (PP-MnOx NPs) as an oxidase mimic was developed. PP-MnOx NPs could not only produce abundant reactive oxygen species to inhibit tumor growth taking advantage of their oxidase-like activity, but also encapsulate and release antitumor drug (artesunate) to function as chemotherapy, achieving remarkable synergistic chemo-catalytic therapeutic effects. As an oxidase mimics, PP-MnOx NPs induced the decrease of mitochondrial membrane potential, down-regulation of Bcl-2, as well as activation of Bax and Caspase-3, demonstrating that the apoptosis triggered by PP-MnOx NPs was mediated via mitochondrial pathways. Importantly, the artesunate in PP-MnOx NPs further promoted this apoptosis. In addition, Mn ions released from PP-MnOx NPs facilitated the tumor-microenvironment-specific T1-weighted magnetic resonance imaging. Taken together, this study well clarifies the antitumor mechanism of artesunate-loaded PP-MnOx NPs and offer a synergistic chemo-catalytic strategy for tumor theranostics.

Recent advances in the construction of nanozyme-based logic gates

Nanozymes, nanomaterials with enzyme-like activity, have been considered as promising alternatives of natural enzymes. Molecular logic gates, which can simulate the function of the basic unit of an electronic computer, perform Boolean logic operation in response to chemical, biological, or optical signals. Recently, the combination of nanozymes and logic gates enabled bioinformation processing in a logically controllable way. In the review, recent progress in the construction of nanozyme-based logic gates integrated with their utility in sensing is introduced. Furthermore, the issues and challenges in the construction processes are discussed. It is expected the review will facilitate a comprehensive understanding of nanozyme-based logic systems.

The interaction mechanism between alkaloids and pepsin based on lum-AuNPs in the chemiluminescence analysis

Herein, novel luminol functional gold nanoparticles (lum-AuNPs) were quickly prepared in an alkaline luminol solution with HAuCl₄, which had the unique characteristics of uniform size and excellent luminescence properties. A self-made flow injection-chemiluminescence (FI-CL) system was established to study the interaction between pepsin (Pep) and five alkaloids (anisodamine, berberine, reserpine, jatrorrhizine and matrine) using lum-AuNPs as the CL probe. Based on the abovementioned home-made CL system, the possible interaction mechanisms of Pep with five alkaloids have been comprehensively discussed by molecular docking simulation, chemical thermodynamics and kinetic studies. The results indicated that there were obvious CL enhancement and inhibition effects on the lum-AuNPs CL system for the Pep and the complex of Pep/alkaloids, respectively. The possible mechanism for the interaction of Pep–five alkaloids was mainly mediated by the hydrophobic force. The binding constant K and binding site n for the Pep–alkaloid interaction are consistent with the list of Ber > Res > Ani, Jat > Mat, which is relative to the potential of groups of alkaloids interacting with the active site of Pep.

A flow injection-chemiluminescence system was established to study the interaction between pepsin and five alkaloids, combined with lum-AuNPs.

Nanomaterials Exhibiting Enzyme-Like Properties (Nanozymes): Current Advances and Future Perspectives

Biological enzymes are macromolecular catalysts that catalyze the biochemical reactions of the natural systems. Although each enzyme performs a particular function, however, holds several drawbacks, which limits its utilization in broad-spectrum applications. Natural enzymes require strict physiological conditions for performing catalytic functions. Their limited stability in harsh environmental conditions, the high cost of synthesis, isolation, and purification are some of the significant drawbacks. Therefore, as an alternative to natural enzymes, recently several strategies have been developed including the synthesis of molecules, complexes, and nanoparticles mimicking their intrinsic catalytic properties. Nanoparticles exhibiting the properties of an enzyme are termed as “nanozymes.” Nanozymes offer several advantages over natural enzymes, therefore, a rapid expansion of the development of artificial biocatalysts. These advantages include simple methods of synthesis, low cost, high stability, robust catalytic performance, and smooth surface modification of nanomaterials. In this context, nanozymes are tremendously being explored to establish a wide range of applications in biosensing, immunoassays, disease diagnosis and therapy, theranostics, cell/tissue growth, protection from oxidative stress, and removal of pollutants. Considering the importance of nanozymes, this article has been designed to comprehensively discuss the different enzyme-like properties, such as peroxidase, catalase, superoxide dismutase, and oxidase, exhibited by various nanoparticles.