Multi-functional Fe-metallohydrogel with peroxidase/oxidase activities for dye degradation and nitrite detection.

Enzyme-mimicking (nanozyme)-based biosensors are attractive owing to their unique catalytic efficiency, multifunctionality, and tunable activity, but examples of oxidase-like nanozymes are quite rare. Herein, we demonstrated that histidine-capped gold nanoclusters (His@AuNCs) possessed intrinsic oxidase-like activity, which could directly oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to blue colored ox-TMB without H2O2. The assembly of reduced graphene oxide (RGO) with His@AuNCs could further improve its oxidase-like activity and the His@AuNCs/RGO nanocomposites had a lower Michaelis constant (Km) and higher catalytic constant (Kcat) for TMB oxidation. Furthermore, compared to other nanomaterials, the as-prepared His@AuNCs/RGO also exhibited enhanced electrocatalytic activity toward TMB. Interestingly, nitrite inhibited the catalytic (chromogenic) and electrocatalytic processes of His@AuNCs/RGO in the oxidation of TMB. The oxidase-like and electrocatalytic activity of His@AuNCs/RGO was evaluated with nitrite and TMB as substrates, and the results indicated that TMB and nitrite might share the same catalytic active sites. On the basis of these findings, a colorimetric and electrochemical sensor was developed with the His@AuNCs/RGO composite as an oxidase mimic for determination of nitrite with linear ranges of 10-500μM and 2.5-5700μM, respectively. The developed method was successfully applied to the detection of nitrites in real samples. The present work suggests that the oxidase-like nanozyme is not only suitable for colorimetric assay but also for development of electrochemical sensors in bioanalysis. Graphical abstract The colorimetric and electrochemical detection of nitrite using His@AuNCs/RGO.

Introduction of Lewis acid sites to endow cobalt phosphide with peroxidase-like and oxidase-like activities and application in colorimetric sensing analysis

Here, a sensitive and selective strategy for the detection of nitrite via colorimetry and test strips was developed based on Fe-single-atom catalysts (Fe SACs) through the oxidation–reduction and diazotization reactions. Fe SACs possess excellent oxidase-like (OXD) catalytic activity, which can catalyze the oxidation of the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) into blue TMBox with the appearance of an obvious absorbance peak at 652 nm in the presence of oxygen. With the addition of nitrite (NO2–), the oxidation–reduction and diazotization reactions between TMB/TMBox and nitrite can induce the color of the solution to change from blue to green and finally to yellow, with the increase of the peak at 445 nm. Based on this strategy, a dual-signal-ratio colorimetric detection method for nitrite was proposed. Within the concentration range of 1–120 μM, the ratio of A652/A445 has a favorable linear relationship with the logarithm concentration of NO2–, with a detection limit of 0.238 μM. By combining smartphones with the colorimetric method, a more intuitive, visual, and convenient test strip detection platform was developed, which can be utilized for the detection of nitrite within 2–200 μM. The analysis strategy based on the Fe-single-atom nanozyme catalysis integrated with the specific redox/diazotization reaction not only provides a dual-signal ratio sensing with good sensitivity but holds the advantage of good selectivity for the utilization of the specific chemical reaction, which has broad application prospects in food safety supervision and food screening.

Cadmium cobaltite (CdCo2O4) nanosheets were ultra-fast synthesized based on a new basic deep eutectic solvent (DES) which served simultaneouslyas reactant, solvents, and template. Interestingly, the nanosheets were found to exhibit triple-enzyme mimetic activities including oxidase-like activity, peroxidase-like activity, and catalase-like activity. Their catalytic activity followed the typical Michaelis-Menten kinetics, and high affinity for H2O2 and TMB was observed. Based on the superior peroxidase-like catalytic activity of CdCo2O4 nanosheets, a highly sensitive and selective colorimetric strategy for the determination of glucose was established. Under optimized conditions, the absorbance at 652nm increases linearly in the 0.5 to 100μM concentration range, and the limit of detection is 0.13μM (S/N= 3). Finally, the method was successfully used for determination of glucose in serum samples. Graphical abstract The CdCo2O4 nanosheets were ultra-fast synthesized with a basic deep eutectic solvent, and this nanomaterial exhibited triple-enzyme mimetic activities: oxidase-like activity, peroxidase-like activity, and catalase-like activity. Based on the peroxidase-like activity, a highly sensitive and selective glucose colorimetric sensor was established.

Adenosine triphosphate (ATP) is produced mainly in the mitochondrion, and its primary task is to function as a ubiquitous energy currency to meet the cellular metabolic demands in biological system...

A peroxidase-like nanoenzyme based on strontium(II)-ion-exchanged Prussian blue analogue derivative SrCoO3/Co3O4 nanospheres and carbon quantum dots for the colorimetric detection of tigecycline in river water

Colorimetric nanozyme sensor based on chain-like PtNi nanoparticles for nitrite ion detection in food samples.

Appropriate addition of phosphate salt in food can improve the food quality and taste. However, extensive intake of phosphate salt may lead to some human diseases such as hyperphosphatemia and renal insufficiency. Thus, it is essential to establish a cost-effective, convenient, sensitive, and selective method for monitoring phosphate ion (Pi) to ensure food quality control. In this work, a Co-based metal-organic frameworks (Co-MOF) nanomaterial with dual functions (peroxidase-like activity and specific recognition) was designed for acting as a catalytic chromogenic platform for sensitive detection of Pi. The Co2+ nodes not only provide high enzyme-like activity to catalyze the 3,3′,5,5′--tetramethylbenzidine (TMB) substrate to blue oxTMB (652 nm) but also act as selective sites for Pi recognition. The use of cationic organic ligands (2-methylimidazole) and cationic metal ions (Co2+) endows the Co-MOF with a strong positive surface charge, which is beneficial to the capture of negative-charged Pi and the dramatically suppressed TMB oxidation. When Pi exists, it specifically adsorbs onto the Co-MOF through the Co-O-P bond and the strong electrostatic interaction, leading to the change of surface charge on Co-MOF. The peroxidase-like catalytic activity of Co-MOF is thus restrained, causing a different catalytic effect on TMB oxidation from that without Pi. Based on this principle, a colorimetric assay was established for rapid and sensitive detection of Pi. A good linear relationship was obtained between Pi concentration and the absorbance at 652 nm, with a linear range of 0.009–0.144 mg/L and a detection limit of 5.4 μg/L. The proposed assay was applied to the determination of Pi in actual food samples with recoveries of 92.2–108% and relative standard deviations (RSDs) of 2.7–7.3%, illustrating the promising practicality for actual samples analysis.

Two-dimensional metal-organic framework nanosheets are attractive as peroxidase mimicking nanocatalysts due to their rich chemical functional groups, large surface area, high porosity, and accessible active sites. In this study, we synthesized FeCu bifunctional 2D MOF nanosheets using a solvothermal method. Fe and Cu ions were added as metal precursors, while organic amine and acid served as the organic ligands to construct the FeCu-MOF nanosheets. These nanosheets demonstrated robust peroxidase-like catalytic activities and were employed to develop a visual detection system for multiple targets, such as glucose and kanamycin. In the detection mechanism, glucose was oxidized into gluconic acid by glucose oxidase (GOx), leading to the generation of H2O2. When H2O2 is present, the FeCu-MOF NSs demonstrate high intrinsic peroxidase-like activity, which might catalytically oxidize 3,3',5,5'-tetramethylbenzidine (TMB) into a blue-coloured oxTMB product with a strong UV absorption at 654 nm. Subsequently, kanamycin was added to the above sensing system. The kanamycin strongly interacted with the FeCu-MOF NSs through H-bonding and blocked electron transfer, resulting in a colour change of the solution from blue to colourless with a weak UV absorption at 654 nm. Under the optimal conditions, the proposed colorimetric sensor exhibits an excellent linear response to glucose and kanamycin over the 0.25-5 μM and 0.02-0.1 μM ranges, respectively. The proposed colorimetric assay detection limits for glucose and kanamycin were found to be as low as 0.1 μM and 8 nM, respectively, and such a sensor shows excellent selectivity and sensitivity against different potential interferents. Thus, our proposed colorimetric assay was satisfactory when applied to glucose and kanamycin detection in agricultural and livestock husbandry samples.

Bifunctional colorimetric biosensors via regulation of the dual nanoenzyme activity of carbonized FeCo-ZIF

Manganese oxide functionalized silk fibers for enzyme mimic application

The intrinsic peroxidase-like activity of hollow Prussian Blue nanoparticle-loaded with gold nanoparticles (Au@HMPB NPs) were applied to oxidize the substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2 to give a blue-green coloration. The morphology of the Au@HMPB NPs and its peroxidase-mimicking activity was characterized in detail. The catalytic activity follows Michaelis-Menten kinetics and is higher than that of HMPB NPs not loaded with gold nanoparticles. The NPs were employed to detect L-lactic acid colorimetrically (at 450nm) via detection of H2O2 that is generated during enzymatic oxidation by L-lactate oxidase (LOx). The limit of detection is 4.2μM. The assay was successfully applied to the quantitation of L-lactic acid in spiker human serum samples. Graphical abstract Gold nanoparticle-loaded hollow Prussian Blue nanoparticles (Au@HMPB NPs) with peroxidase-like catalytic activity can oxidize the substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. The nanoparticles were applied for the detection of L-lactic acid through detection of H2O2 that is generated by L-lactate oxidase (LOx) catalyzed oxidation of L-lactic acid.

In recent years, the exploration of the nanozyme, an artificial enzyme with the structure and function of natural enzymes, has become a hot topic in this field. Although significant progress has been made, it is still a huge challenge to design nanozymes with multiple enzyme-like catalytic activities. In this work, we have successfully fabricated a colorimetric sensing platform to mimic peroxidase-like and oxidase-like activities by the CoS1.035 nanoparticles decorated N-doped carbon framework porous dodecahedrons (abbreviated to CoS1.035/N-C PDHs). And the catalytic mechanism of CoS1.035/N-C PDHs toward the peroxidase-like and oxidase-like activities is systematically explored. The results display that CoS1.035/N-C PDHs can catalyze the oxidation of the colorless substrate 3,3,′5,5′-tetramethylbenzidine (TMB) into blue oxidized TMB (ox-TMB) by disintegrating H2O2 or the physically/chemically absorbed O2 into different ROS species (·OH or O2·–) in the presence or absence of H2O2. Therefore, on the basis of the dual-enzyme mimic activities of CoS1.035/N-C PDHs, the bifunctional colorimetric sensing platform is established for H2O2 detection with a wide linear range of 0.5–120 μM and glutathione detection with a linear range of 1–60 μM, respectively. This work provides an efficient platform for dual-enzyme mimics, expanding the application prospect of Co-based chalcogenides as enzyme mimics in biosensing, medical diagnosis, and environment monitoring.

Rice-shaped protein–copper oxide hybrid (RSPCO) was prepared by one-pot method in the presence of amphiphilic proteins. The enzyme-mimicking activity of RSPCO depends much on the substrate structure. RSPCO shows superior peroxidase-like activity with 3,3′,5,5′-tetramethylbenzidine (TMB) as a substrate. RSPCO exhibits both peroxidase- and oxidase-like activities with 1,2-diaminobenzene (OPD) as the substrate. RSPCO does not exhibit peroxidase-/oxidase-like activity when using 2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonic acid)diammonium salt (ABTS) as the substrate. Furthermore, pyrogallol (PA)-induced activity switching effect is dependent on the type of enzyme-like activity of nanozyme and the substrate structure. The different effect of PA on the enzyme-like activity of RSPCO attributes mainly to the different affinity of substrates toward RSPCO. PA can significantly inhibit the peroxidase-like activity of RSPCO with TMB used as the substrate. Due to the efficient inhibiting effect, an excellent PA colorimetric sensor with low limit of detection being 15 nM (signal-to-noise ratio of 3) was developed based on RSPCO. With the features of simplification and low cost, protein–copper oxide hybrid nanozymes has the potential application in medial, environmental, and food areas. The present work provides new information about activity–structure relationship of copper oxide nanozyme, which is important for the applications of nanozymes in practice.

Nanoarchitectured biomass-waste derived activated charcoal nanozymes and its application in visual analysis of nitrite in pickled food.