Intrinsic peroxidase-like activity of rhodium nanoparticles, and their application to the colorimetric determination of hydrogen peroxide and glucose

Enhanced peroxidase-like activity of platinum nanoparticles decorated on nickel- and nitrogen-doped graphene nanotubes: colorimetric detection of glucose

A nanostructured catalyst is introduced that demonstrates peroxidase mimicking activity. It consists of nickel- and nitrogen-doped graphene nanotubes loaded with platinum nanoparticles. Pt-decorated Ni-doped nitrogen-rich graphitic nanotube (Pt/Ni@NGT) was synthesized using a two-step procedure in which the precursors were first refluxed to form a supramolecular assembly followed by a pyrolysis and leaching step to form nanotubes. Afterwards, Pt was decorated on the outer surface of nanotube by an ultrasound assisted method. Pt/Ni@NGT was characterized by XPS, TEM, SEM, and HAADF-STEM. The as-prepared Pt/Ni@NGT nanostructure was used for the detection of glucose via catalyzing the oxidation of a substrate, 3,3',5,5'-tetramethylbenzidine (TMB), to form a blue product (ox-TMB), thereby enabling colorimetric assay for enzymatically generated H₂O₂. The nanostructure exhibited excellent biocompatibility and led to highly efficient immobilization and retention of GOx. The method has a linear response in the 43 pM to 220 μM glucose concentration range, a detection limit as low as 1 pM and a limit of quantification of 3.4pM, along with good reproducibility(< 3%). A paper based visual microfluidic assay was also worked out that has an analytical range that extends from 0.1-50 mM. It is simple and rapid enough to be useful as a glucose home test.. The method was successfully applied to the determination of glucose in tear and saliva samples. Graphical abstract Graphene nanotubes doped with nitrogen and nickel (Ni@NGT) have been synthesized as the support to construct the unique Pt/Ni@NGT for providing artificial peroxidase activity for the GOx-based detection of glucose, which was further used for the construction of a glucose paper assay.

Colorimetric detection of hydrogen peroxide and glucose by exploiting the peroxidase-like activity of papain

Papain, a natural plant protease that exists in the latex of Carica papaya, catalyzes the hydrolysis of peptide, ester and amide bonds. In this work, we found that papain displayed peroxidase-like activity and catalyzed the oxidation of 3,3',5',5'-tetramethylbenzidine (TMB) in the presence of H2O2. This results in the formation of a blue colored product with an absorption maximum at 652 nm. The effects of experimental parameters including pH and reaction temperature on catalytic activity of papain were investigated. The increase of absorbance induced by the catalytic effect of papain offers accurate detection of H2O2 in the range of 5.00-90.0 μM, along with a detection limit of 2.10 μM. A facile colorimetric method for glucose detection was also proposed by combining the glucose oxidase (GOx)-catalyzed glucose oxidation and papain-catalyzed TMB oxidation, which exhibited a linear response in the range of 0.05-0.50 mM with a detection limit of 0.025 mM. The method proposed here displayed excellent selectivity, indicating that common coexisting substances (urea, uric acid, ascorbic acid, maltose, lactose and fructose) in urine did not interfere with detection of glucose. More importantly, the suggested method was successfully used to precisely detect the glucose concentration in human urine samples with recoveries over 96.0%.

Ferroxidase-like and antibacterial activity of PtCu alloy nanoparticles

Many metal nanoparticles are reported to have intrinsic enzyme-like activities and offer great potential in chemical and biomedical applications. In this study, PtCu alloy nanoparticles (NPs), synthesized through hydrothermal treatment of Cu²⁺ and Pt²⁺ in an aqueous solution, were evaluated for ferroxidase-like and antibacterial activity. Electron spin resonance (ESR) spectroscopy and colorimetric methods were used to demonstrate that PtCu NPs exhibited strong ferroxidase-like activity in a weakly acidic environment and that this activity was not affected by the presence of most other ions, except silver. Based on the color reaction of salicylic acid in the presence of Fe³⁺, we tested the ferroxidase-like activity of PtCu NPs to specifically detect Fe²⁺ in a solution of an oral iron supplement and compared these results with data acquired from atomic absorption spectroscopy and the phenanthroline colorimetric method. The results showed that the newly developed PtCu NPs detection method was equivalent to or better than the other two methods used for Fe²⁺ detection. The antibacterial experiments showed that PtCu NPs have strong antibacterial activity against Staphylococcus aureus and Escherichia coli. Herein, we demonstrate that the peroxidase-like activity of PtCu NPs can catalyze H₂O₂ and generate hydroxyl radicals, which may elucidate the antibacterial activity of the PtCu NPs against S. aureus and E. coli. These results showed that PtCu NPs exhibited both ferroxidase- and peroxidase-like activity and that they may serve as convenient and efficient NPs for the detection of Fe²⁺ and for antibacterial applications.

Titanium dioxide nanoparticles-based colorimetric sensors for determination of hydrogen peroxide and triacetone triperoxide (TATP)

Due to its relatively simple preparation and readily available precursors, determination of triacetone triperoxide (TATP) by portable devices has become important. In this work, two different titanium dioxide nanoparticles (TiO₂NPs)-based colorimetric sensors based on complex formation on the solid surface were developed for determination of H₂O₂ and TATP. The first sensor, (3-aminopropyl)triethoxysilane (APTES) modified-TiO₂NPs-based paper sensor (APTES@TiO₂NPs), exploits peroxo-titanate binary complex formation between APTES@TiO₂NPs and H₂O₂ on chromatographic paper. The second sensor, 4-(2-pyridylazo)-resorcinol-modified-TiO₂NPs-based solid sensor (PAR@TiO₂NPs), relies on the formation of a ternary complex between Ti(IV), PAR and H₂O₂. The developed sensors were also applied to TATP determination after acidic hydrolysis of samples to H₂O₂. The limits of detection (LODs) of APTES@TiO₂NPs-based paper sensor were 3.14 × 10^-4 and 5.13 × 10^-4 mol L^-1 for H₂O₂ and TATP, respectively, whereas the LODs of PAR@TiO₂NPs solid sensor were 6.06 × 10^-7 and 3.54 × 10^-7 mol L^-1 for H₂O₂ and TATP, respectively. Possible interferences of common soil ions, passenger belongings used as camouflage materials during public transport (e.g., detergent, sweetener, acetylsalicylic acid and paracetamol-caffeine based analgesic drugs) and of other explosives were examined. The developed methods were statistically validated using t- and F- tests against the titanyl sulfate (TiOSO₄) colorimetric literature method.

Peroxidase-Like Activity of Smart Nanomaterials and Their Advanced Application in Colorimetric Glucose Biosensors

Diabetes is a dominating health issue with 425 million people suffering from the disease worldwide and 4 million deaths each year. To avoid further complications, the diabetic patient blood glucose level should be strictly monitored despite there being no cure for diabetes. Colorimetric biosensing has attracted significant attention because of its low cost, simplicity, and practicality. Recently, some nanomaterials have been found that possess unexpected peroxidase-like activity, and great advances have been made in fabricating colorimetric glucose biosensors based on the peroxidase-like activity of these nanomaterials using glucose oxidase. Compared with natural horseradish peroxidase, the nanomaterials exhibit flexibility in structure design and composition, and have easy separation and storage, high stability, simple preparation, and tunable catalytic activity. To highlight the significant progress in the field of nanomaterial-based peroxidase-like activity, this work discusses the various smart nanomaterials that mimic horseradish peroxidase and its mechanism and development history, and the applications in colorimetric glucose biosensors. Different approaches for tunable peroxidase-like activity of nanomaterials are summarized, such as size, morphology, and shape; surface modification and coating; and metal doping and alloy. Finally, the conclusion and challenges facing peroxidase-like activity of nanomaterials and future directions are discussed.

Additive-based stability assessment of biologically designed CuO and GSH-CuO nanospheres and their applicability as Nano-biosensors

Uncapped and Glutathione capped Cupric oxide nanospheres were synthesized by the interaction of Berberis lycium (Bl) root extract with corresponding salt solution. CuO nanospheres were best optimized by mixing 2% Bl extract solution with 1 mM CuSO₄·5H₂O (pH 11, 90 °C) Reduced glutathione (0.25 mM) in solution form was added in respective emulsion after 24 h. Synthesis of nanospheres was ensured by distinct surface plasmonic resonance peaks shown by CuO (370-420 nm). Addition of glutathione resulted in sharp blue shift and lowered absorbance values in UV spectra suggesting the decrease in nanoparticles' size and concentration. Average particle sizes as deduced with XRD were found to be 18.52 and 16.57 nm for CuO and GSH-CuO nanospheres respectively. Additive based stability assessment of synthesized nanospheres revealed CuO and GSH-CuO nanospheres to be highly stable in the presence of Catechin hydrate among various tested chemical compounds while ascorbic acid appeared as a strong destabilizing agent. TMB was oxidized by H₂O₂ in the presence of synthesized enzymes likewise horseradish peroxidase; though exhibited moderate results. Glutathione stabilized cupric oxide nanospheres exhibited the potential to be modulated further into efficient nanozymes as these showed better affinity towards chromogenic substrate TMB (K_m value 0.32 mM) and better catalytic efficiency (0.075 mM^-1 s^-1) compared to uncapped CuO nanomimetics (1.6 mM, 0.033 mM^-1 s^-1). All of the tested additives served as inhibitors to the peroxidase mimicking potential of CuO and GSH-CuO nanozymes.

Intrinsic catalytic activity of rhodium nanoparticles with respect to reactive oxygen species scavenging: implication for diminishing cytotoxicity

Noble metal nanoparticles (NPs) and their hybrids have demonstrated a strong potential to mimic the catalytic activity of natural enzymes and diminish oxidative stress. There is a large space to explore the intrinsic catalytic activity of Rh NPs with respect to reactive oxygen species (ROS) scavenging. We found that Rh NPs can quench H₂O₂, ^•OH, O₂^•-, ¹O₂ and inhibit lipid peroxidation under physiological conditions. In vitro cell experiments proved that Rh NPs have great biocompatibility and protect cells from oxidative damage caused by H₂O₂. This study can provide important insights that could inform future biological applications.

Atomic layer deposition-assisted growth of CuAl LDH on carbon fiber as a peroxidase mimic for colorimetric determination of H2O2 and glucose

An atomic-layer-deposited Al₂O₃-induced LDH growth strategy was proposed to prepare carbon fiber-supported ultrathin CuAl LDH nanosheets (CF@CuAl-LDH). The CF@CuAl-LDH exhibited superior peroxidase-like catalytic activity.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Regulating peroxidase-like activity of Pd nanocubes through surface inactivation and its application for sulfide detection

The peroxidase-like activity of Pd nanocubes is regulated by the formation of surface PdS layers, which has been applied for sulfide assay in environmental water samples.

Functional nanomaterials with unique enzyme-like characteristics for sensing applications

We highlight the recent developments in functional nanomaterials with unique enzyme-like characteristics for sensing applications.

Pd nanoparticle-decorated graphitic C3N4 nanosheets with bifunctional peroxidase mimicking and ON–OFF fluorescence enable naked-eye and fluorescent dual-readout sensing of glucose

Pd nanoparticle-decorated graphitic C₃N₄ nanosheets with peroxidase mimicking and ON–OFF fluorescence for the naked-eye and fluorescent dual-readout detection of glucose.

Mustard seeds derived fluorescent carbon quantum dots and their peroxidase-like activity for colorimetric detection of H2O2 and ascorbic acid in a real sample

Herein, we were synthesized fluorescent carbon quantum dots via facile one-step hydrothermal treatment of mustard seeds (M-CQDs). It showed excellent optical property with fluorescent quantum yield 4.6%. The as-prepared M-CQDs exhibited peroxidase-like mimetic activity and catalyzed the oxidation of chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂ to produce a blue color reaction mixture with the prominent peak at 652 nm. Furthermore, the peroxidase-like catalytic performance of M-CQDs followed the steady-state kinetics behavior and exhibited similar catalytic activity as that of natural enzyme Horseradish peroxidase (HRP). In addition to this, the double reciprocal plot showed a parallel line which suggested the occurrence of Ping-Pong type of mechanism. The H₂O₂ dependent oxidation of TMB was helpful for the colorimetric detection of H₂O₂ in the linear range of 0.02-0.20 mM with the limit of detection (LOD) of 0.015 mM. Interestingly, the oxidized TMB (ox-TMB) was further reduced to native TMB by the reducing agent ascorbic acid. Hence M-CQDs showed its potential towards the selective and sensitive detection of ascorbic acid in the linear range of 10-70 μM having a correlation coefficient of 0.998 with LOD of 3.26 μM. The practical feasibility of the proposed detection method of AA was also investigated in common fresh fruits.

Enhanced glucose detection using dendrimer encapsulated gold nanoparticles benefiting from their zwitterionic surface

The application of ultrasmall gold nanoparticles as enzyme mimics has been drawing great attention. Herein, we developed zwitterionic dendrimer encapsulated gold nanoparticles (Au-G5MC NPs) for highly sensitive and simple colorimetric detection of glucose. Au-G5MC NPs showed peroxidase-like property, which could efficiently catalyze oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂, producing a blue color product (oxTMB). This peroxidase-like reaction follows a typical Michaelis-Menten kinetics. The K_m towards TMB exhibited a lower value (0.194 mM) than that of horseradish peroxidase (HRP, 0.434 mM). Furthermore, the peroxidase-like properties of Au-G5MC NPs enable colorimetric detection of the concentration of glucose with high selectivity. The linear concentration range of this method was from 14 μM to 166 μM with the detection limit down to 3.8 μM. More importantly, the detection was not interfered by proteins due to the single zwitterionic layer on the Au-G5MC NPs surface. These excellent properties are attributed to the ultrasmall size of gold nanoparticles and high stability of Au-G5MC NPs in complex medium. This catalytic system might have great potential applications for glucose detection in medical diagnostics and biochemistry in the future.

Human serum albumin templated MnO2 nanosheets are oxidase mimics for colorimetric determination of hydrogen peroxide and for enzymatic determination of glucose

This paper reports on a colorimetric assay for H₂O₂ and glucose. It is based on the use of human serum albumin-templated MnO₂ nanosheets that possess oxidase-like activity. They are capable of oxidizing 3,3',5,5'-tetramethylbenzidine (TMB) with oxygen to give a blue product (oxTMB) with an absorbance maximum at 652 nm. When H₂O₂ is introduced, the MnO₂ nanosheets are reduced to Mn(II) ions, and this inhibits the formation of oxTMB. Based on these findings, a colorimetric assay was established for H₂O₂ that has a 0.56 μM detection limit. If glucose is oxidized by glucose oxidase under formation of H₂O₂, the nanosheets can be used to quantify H₂O₂ and thereby to sense glucose. Response is linear in the 0.5 μM to 50 μM glucose concentration range, and the detection limit is 0.32 μM. The method was applied to the determination of glucose in spiked serum samples and gave satisficatory results. Graphical abstract Human serum albumin (HSA) is used as a template for the synthesis of MnO₂ nanosheet. These possess oxidase mimicking activity. H₂O₂ can reduce the nanosheets. The effect is exploited in colorimetric assays for H₂O₂ and glucose using tetramethylbenzidine (TMB) as a chromogenic substrate.

Colorimetric aptasensor for Campylobacter jejuni cells by exploiting the peroxidase like activity of Au@Pd nanoparticles

The authors describe a method for colorimetric determination of Campylobacter jejuni (C. jejuni) in milk samples. It is based on the interaction of a specific DNA aptamer with surface protein in the cell membranes of C. jejuni. Specific binding of the aptamer with the cell membrane leads to an uptake of aptamer from solution. As a result, the concentration of aptamer floating in the solution is reduced. In the presence of large quantities of aptamer, the surface of added Au@Pd nanoparticles (NPs) is covered with aptamer via electrostatic interactions. Hence, they cannot act as a peroxidase mimic and oxidize the substrate 3,3^',5,5^'-tetramethylbenzidine (TMB) to give a blue product. However, when the aptamer is bound by the target cells, the surface of the NPs is not blocked by aptamer and the NPs exert a strong peroxidase -like activity. Under defined experimental conditions, the intensity of the blue color increases with the concentration of C. jejuni, and as little as 100 CFU·mL^-1 can bedetected in milk. Graphical abstract A colorimetric aptasensor for assay Campylobacter jejuni whole cell in food samples was investigated. This assay was designed based on interaction of specific DNA aptamer with surface protein in c. jejuni cell membrane without any modification of aptamer.