Colorimetric detection of hydrogen peroxide and cholesterol using Fe3O4-brominated graphene nanocomposite

Cauliflower-like CuO-ZnO modified glassy carbon electrode as an electrochemical platform for the detection of hydrogen peroxide in adulterated milk

The detection of hydrogen peroxide (H₂O₂) is a crucial process in various industries, including food safety. In this study, a cauliflower-like CuO-ZnO composite with p-n junction was successfully synthesized using a straightforward one-pot hydrothermal method. The resulting material demonstrates outstanding electrocatalytic performance for H₂O₂ detection, outperforming the individual components. The electrochemical sensor constructed from the cauliflower-like CuO-ZnO composite exhibits a well-defined linear response in the concentration range 0.0005 to 0.105 mmol·L⁻1 for H₂O₂. The sensor's limit of detection (LOD) is 0.21 µmol·L⁻1 at a signal-to-noise ratio (S/N) of 3, with a sensitivity of 1582.7 µA·(mmol·L⁻1)⁻1·cm⁻2. Furthermore, the sensor has been successfully applied to detect trace amounts of H₂O₂ in milk samples, showcasing its potential for sensitive electrochemical sensing applications.

Green production of functionalized few-layer borophene decorated with cerium-doped iron oxide nanoparticles for repeatable hydrogen peroxide detection

Functionalized few-layer borophene (FFB) was prepared using gallnut extract and coffee waste extract as natural exfoliating and stabilizing agents in an environmentally friendly ultrasonic and high shear exfoliation. Here, a facile precipitation method was employed to grow iron oxide nanoparticles doped with cerium (Ce-FeONPs) onto the surface of FFB. This intriguing combination of materials yielded Ce-FeONPs nanoparticles that exhibited exceptional peroxidase-like activity, efficiently catalyzing the conversion of 3,3',5,5'-tetramethylbenzidine (TMB) to a blue oxidized TMB (oxTMB) in the presence of hydrogen peroxide (H2O2). Additionally, the introduction of FFB contributes a reducibility effect to the catalytic oxidation of TMB, facilitating the restoration of the oxTMB to TMB. Thus, FFB-Ce-FeONPs showcase intriguing properties encompassing both oxidative and reductive characteristics, suggesting their potential as a reagent for repeated detection of H2O2. Moreover, a colorimetric sensing system enabled the liner detection of H2O2 spanning a concentration range from 0.08 to 1 mM, with a detection limit of 0.03 mM. Noteworthily, FFB-Ce-FeONPs demonstrated sustained efficacy over ten successive recycling cycles, as indicated by consistent slopes and observable color changes. In summary, this work reports the first application of nanoenzymes in repetitive H2O2 detection. Even after ten multiple cycles, the detection limit remains virtually unaltered, underscoring the robustness and enduring effectiveness of the engineered nanomaterial. The proposed simultaneous oxidation and reduction strategies for detecting H2O2 showed a commendable capability in ten cycles of H2O2 detection, thus providing a promising approach in the field of H2O2 detection.

Colorimetric sensing of hydrogen peroxide using capped Morus nigra-sawdust deposited zinc oxide nanoparticles via Trigonella foenum extract

Hydrogen peroxide (H2O2) is one of the main byproducts of most enzymatic reactions, and its detection is very important in disease conditions. Due to its essential role in healthcare, the food industry, and environmental research, accurate H2O2 determination is a prerequisite. In the present work, Morus nigra sawdust deposited zinc oxide (ZnO) nanoparticles (NPs) were synthesized by the use of Trigonella foenum extract via a hydrothermal process. The synthesized platform was characterized by various techniques, including UV-Vis, FTIR, XRD, SEM, EDX, etc. FTIR confirmed the presence of a Zn‒O characteristic peak, and XRD showed the hexagonal phase of ZnO NPs with a 35 nm particle size. The EDX analysis confirmed the presence of Zn and O. SEM images showed that the as-prepared nanoparticles are distributed uniformly on the surface of sawdust. The proposed platform (acetic acid-capped ZnO NPs deposited sawdust) functions as a mimic enzyme for the detection of H2O2 in the presence of 3,3',5,5'-tetramethylbenzidine (TMB) colorimetrically. To get the best results, many key parameters, such as the amount of sawdust-deposited nanoparticles, TMB concentration, pH, and incubation time were optimized. With a linear range of 0.001-0.360 μM and an R2 value of 0.999, the proposed biosensor's 0.81 nM limit of quantification (LOQ) and 0.24 nM limit of detection (LOD) were predicted, respectively. The best response for the proposed biosensor was observed at pH 7, room temperature, and 5 min of incubation time. The acetic acid-capped sawdust deposited ZnO NPs biosensor was also used to detect H2O2 in blood serum samples of diabetic patients and suggest a suitable candidate for in vitro diagnostics and commercial purposes.

Bimetallic Cu-Zn Zeolitic Imidazolate Frameworks as Peroxidase Mimics for the Detection of Hydrogen Peroxide: Electrochemical and Spectrophotometric Evaluation

A copper incorporated zeolitic imidazolate framework-8 (ZIF-8) has been synthesized and demonstrated to be a potential material for a peroxidase mimic. The resultant bimetallic Cu-Zn incorporated MOF is used for the dual mode sensing of hydrogen peroxide by following electrochemical as well as spectrophotometric methods. Using 3,3',5,5'-tetramethylbenzidine (TMB) as a chromogenic substrate, spectrophotometric studies are carried out, and the steady state kinetic parameters are determined for two different concentrations of Cu incorporated ZIF-8 (viz Cu@ZIF-8-1 and Cu@ZIF-8-2). It is found that both Cu@ZIF-8-1 and Cu@ZIF-8-2 exhibit more affinity toward the TMB substrate than the horseradish peroxidase (HRP) enzyme as indicated by the low Km values obtained for the substrate. Also, as the concentration of incorporated Cu increases, Vmax values are also found to be enhanced. Electrochemically, the Cu@ZIF-8 modified glassy carbon electrode (GCE) showed a good response for peroxide detection in the concentration range from 0.5 mM to 5 mM at a working potential of -0.25 V in PBS (pH 7.0) with a limit of detection (LOD) value of 0.46 mM and a sensitivity of 20.25 μA/mM. Further, the chromogenic substrate TMB is successfully immobilized on the electrode surface and subsequently used for the peroxide detection along with Cu@ZIF-8. Here, TMB acts as a mediator and shifted the working potential to 0.1 V in acetate buffer (pH 5.0) in the concentration range from 0.5 mM to 5 mM with an LOD value of 0.499 mM and a sensitivity of 0.097 μA/mM. Interestingly, the same electrode in PBS of pH 7.0 showed a response to peroxide at a working potential of -0.1 V in the concentration range from 0.5 mM to 5 mM with an LOD value of 0.143 mM and a sensitivity of 0.33 μA/mM. Moreover, the applicability of this material for peroxide sensing is evaluated using milk samples, and the proposed material is able to recover the peroxide present in milk. Thus, the bimetallic Cu-Zn MOF can be utilized for the dual mode sensing of peroxide and can be extended for various real time applications.

Biocompatible Palladium Nanoparticles Prepared Using Vancomycin for Colorimetric Detection of Hydroquinone

Hydroquinone poses a major threat to human health and is refractory to degradation, so it is important to establish a convenient detection method. In this paper, we present a novel colorimetric method for the detection of hydroquinone based on a peroxidase-like Pd nanozyme. The vancomycin-stabilized palladium nanoparticles (Van-Pd_n NPs, n = 0.5, 1, 2) were prepared using vancomycin as a biological template. The successful synthesis of Van-Pd_n NPs (n = 0.5, 1, 2) was demonstrated by UV-vis spectrophotometry, transmission electron microscopy, and X-ray diffraction. The sizes of Pd nanoparticles inside Van-Pd_0.5 NPs, Van-Pd₁ NPs, and Van-Pd₂ NPs were 2.6 ± 0.5 nm, 2.9 ± 0.6 nm, and 4.3 ± 0.5 nm, respectively. Furthermore, Van-Pd₂ NPs exhibited excellent biocompatibility based on the MTT assay. More importantly, Van-Pd₂ NPs had good peroxidase-like activity. A reliable hydroquinone detection method was established based on the peroxidase-like activity of Van-Pd₂ NPs, and the detection limit was as low as 0.323 μM. Therefore, vancomycin improved the peroxidase-like activity and biocompatibility of Van-Pd₂ NPs. Van-Pd₂ NPs have good application prospects in the colorimetric detection of hydroquinone.

NIR-induced improvement of catalytic activity and antibacterial performance over AuAg nanorods in Rambutan-like Fe3O4@AgAu@PDA magnetic nanospheres

Pathogenic bacteria and difficult-to-degrade pollutants in water have been serious problems that always plague people. Therefore, finding a "one stone-two birds" method that can quickly catalyze the degradation of pollutants and show effective antibacterial behavior become an urgent requirement. This work reports a facile one-step strategy for fabricating a Rambutan-like Fe₃O₄@AgAu@PDA (Fe₃O₄@AgAu@Polydopamine) core/shell nanosphere with both catalytic and antibacterial activities which can be critically improved by externally applying an NIR laser irradiation (NIR, 808 nm) and a rotating magnetic field. Typically, the Rambutan-like Fe₃O₄@AgAu@PDA nanosphere have a rather rough surface due to the AuAg bimetallic nanorods sandwiched between the Fe₃O₄ core and the PDA shell. Owing to the penetrated PDA shell, AgAu nanorods show high and magnetically recyclable photothermal-enhanced catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol and they can also be applied to initiate TMB oxidation under the help of NIR heating condition. Moreover, Fe₃O₄@AgAu@PDA shows a moderate antibacterial activity due to the weak release of Ag⁺. Under applying a rotating external magnetic field, the rough-surface Fe₃O₄@AgAu@PDA nanospheres produce a controllable magnetolytic force on the bacterial due to their good affinity. As a result, the Fe₃O₄@AgAu@PDA nanospheres show a "magnetolytic-photothermal-Ag⁺" synergistic antibacterial behavior against E. coli and S. aureus.

Multicolor colorimetric visual detection of Staphylococcus aureus based on Fe3O4-Ag-MnO2 composites nano-oxidative mimetic enzyme

Novel Fe₃O₄-Ag-MnO₂ composites were successfully synthesized. It was noteworthy that the obtained Fe₃O₄-Ag-MnO₂ composites were found to possess three types of enzyme-mimicking activities, including peroxidase-like, catalase-like and oxidase-like activities. Taking advantage of the oxidase properties of Fe₃O₄-Ag-MnO₂, the direct oxidation of TMB could be catalyzed to generate blue oxidation products without H₂O₂. The oxidase-like activity of Fe₃O₄-Ag-MnO₂ were carefully studied. Based on the Fe₃O₄-Ag-MnO₂-TMB system, a fast, sensitive and intuitive multicolor colorimetric method for Staphylococcus aureus (S. aureus) detection was established under the optimized conditions. The proposed method allows the detection of S. aureus with a detection limit of 3.7 cfu mL^-1 and a linear range of 10-10⁶ cfu mL^-1. This new colorimetric method has been successfully proved to be applicable to the detection S. aureus of food samples.

TiO2-In-MIL-101(Cr) with Visible Light-Induced Peroxidase Activity for Colorimetric Detection of Blood Glucose

In this work, metal-organic framework MIL-101(Cr) with regular morphology, stable structure, and good dispersion was prepared by the hydrothermal method. MIL-101(Cr) has two different sizes of pores, but after TiO2 nanoparticles (NPs) were in situ prepared, the two pores disappear. The result demonstrates that TiO2 NPs were located in the pores of MIL-101(Cr). TiO2-decorated MIL-101(Cr) forms an inside type II heterojunction and the band gap energy is narrowed, which can promote electron-hole separation and enhance the light absorption. Therefore, the heterojunction shows a high visible light-induced peroxidase-like activity. Kinetic studies exhibit that the K m value of TiO2-in-MIL-101(Cr) to TMB is 0.17 mM, and the affinity of TiO2-in-MIL-101(Cr) is higher than that of natural horseradish peroxidase (HRP). Then, a "turn-on" colorimetric assay based on TiO2-in-MIL-101(Cr) was constructed for the detection of blood glucose. The detection range is 1-100 μM (R 2 = 0.9950) with a limit of detection (LOD) of 1.17 μM. Compared with the clinical method, the constructed colorimetric method has accurate and reliable results for the clinical detection. The anti-interference experiment confirms that the method has high selectivity to glucose.

Biomimetic graphene-supported ultrafine platinum nanowires for colorimetric and electrochemical detection of hydrogen peroxide

The detection of hydrogen peroxide (H₂O₂) is of great significance in environmental monitoring, enzymatic reactions, and disease diagnosis. Here we present the peptide-mediated biomimetic synthesis of ultrafine platinum nanowires (PtNWs) on graphene oxide (GO) nanosheets for the formation of functional hybrids, which show high potential for the fabrication of colorimetric and electrochemical sensors for the detection of H₂O₂ with high performance. A multifunctional peptide with the sequence KIIIIKYWYAF was designed to create peptide nanofibers (PNFs) via a controllable self-assembly process, which serves as a bridge between GO nanosheets and PtNWs to form PtNWs-PNFs/GO hybrids. On this basis, a dual-mode sensor platform for both colorimetric and electrochemical sensing of H₂O₂ was fabricated successfully. The obtained results indicate that the synthesized PtNWs-PNFs/GO hybrids could catalyze the decomposition of H₂O₂ to generate ˙OH radicals with a significant current response, and the ˙OH radicals are capable of overoxidizing 3,3',5,5',-tetramethylbenzidine (TMB), producing a blue-colored species with a distinct color change for colorimetric sensing. In addition, due to its high catalytic activity, the fabricated PtNWs-PNFs/GO hybrid-based electrochemical sensor exhibits a wider linear detection range of 0.05 μM-15 mM and a low detection limit of 0.0206 μM, which can be applied to detect H₂O₂ with high selectivity and sensitivity. Our study provides a green and environmentally friendly synthetic strategy for the preparation of biomimetic materials from PtNWs, and the fabricated colorimetric/electrochemical dual-mode H₂O₂ sensor platform will have a great impact in bioanalysis, environmental monitoring, and biomedicine.