Oxidation Of Tetramethylbenzidine Research Articles

A multifunctional nanoplatform for dual-readout visual detection and real-time inactivation of Staphylococcus aureus with nanozymes and Au nanorods

Pathogenic bacteria pose a significant burden on global public health. To ensure food safety and prevent the spread of foodborne diseases, the multifunctional technical platforms for rapid detection and inactivation of pathogens are urgently needed. Herein, a new dual-readout detection and bacterial inactivation nanoplatform was constructed based on K10P2W18Fe4(H2O)2O68@polydopamine (P2W18Fe4@PDA) nanozymes and Au nanorods (AuNRs). The target bacteria such as Staphylococcus aureus (S. aureus) was firstly specifically isolated by the Fe3O4-Apt in complex sample matrices. Then, the isolated bacteria (Fe3O4-Apt-S. aureus) were strongly bound by the P2W18Fe4@PDA nanozymes with excellent peroxidase-like activity and highly efficient photothermal conversion. Accordingly, bacteria can be sensitively detected with monochrome signal catalyzed by the nanozyme (3, 3′, 5, 5′-tetramethylbenzidine (TMB) oxidation) and multicolor signal produced by TMB2+ etching AuNRs. With the assay, as low as 29 CFU/mL S. aureus could be distinguished. Meanwhile, over 99% S. aureus in the magnetic separation can be effectively inactivated by 808 nm Near-infrared (NIR) light within 10 min. Moreover, S. aureus was detected successfully in spiked milk with a recovery rate of 98.64%–109.04% using this method, indicated that the method held significant promise for applications in food analysis and control.

FcCe-MOF-NH2-based colorimetric and fluorometric dual-mode detection of sulfide ions

Sulfide ions, commonly present as toxic anions in industrial processes, require the creation of a convenient and reliable detection platform. In this study, we developed a dual-mode colorimetric and fluorometric method to detect sulfide ions using the cerium-ferrocene bimetal-organic framework (MOF), i.e., FcCe-MOF-NH2, which was synthesized by a common solvo-thermal approach. The FcCe-MOF-NH2 promises the peroxidase-like activity and blue emission peaked at 453 nm. In the presence of H2O2, the FcCe-MOF-NH2 catalyzed 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation, yielding the blue oxidized product (oxTMB), while the fluorescence peak at 453 nm was suppressed due to the inner filter effect (IFE). The Km values of FcCe-MOF-NH2 for TMB and H2O2 were 0.099 mM and 0.179 mM, respectively, showing its good affinity with the substrates. Due to a unique redox reaction between H2O2 and S2−, the peroxidase-like activity of FcCe-MOF-NH2 was markedly suppressed, leading to fluorescence restoration. Hence, the colorimetric and fluorometric dual-mode detection of S2− was realized, exhibiting a linear range of 0.5–100 μM and 0.2–60 μM with a detection limit of 0.43 μM and 0.078 μM, respectively. The developed platform was successfully applied to the detection of S2− in actual water samples.

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.

Hexagonal Boron Nitride Quantum Dots Embedded on Layer-by-Layer Films for Peroxidase-Assisted Colorimetric Detection of β-Galactosidase Producing Pathogens.

Pathogen detection has become a major research area all over the world for water quality surveillance and microbial risk assessment. Therefore, designing simple and sensitive detection kits plays a key role in envisaging and evaluating the risk of disease outbreaks and providing quality healthcare settings. Herein, we have designed a facile and low-cost colorimetric sensing strategy for the selective and sensitive determination of β-galactosidase producing pathogens. The hexagonal boron nitride quantum dots (h-BN QDs) were established as a nanozyme that showed prominent peroxidase-like activity, which catalyzes 3,3',5,5'-tetramethylbenzidine (TMB) oxidation by H2O2. The h-BN QDs were embedded on a layer-by-layer assembled agarose biopolymer. The β-galactosidase enzyme partially degrades β-1,4 glycosidic bonds of agarose polymer, resulting in accessibility of h-BN QDs on the solid surface. This assay can be conveniently conducted and analyzed by monitoring the blue color formation due to TMB oxidation within 30 min. The nanocomposite was stable for more than 90 days and was showing TMB oxidation after incubating it with Escherichia coli (E. coli). The limit of detection was calculated to be 1.8 × 106 and 1.5 × 106 CFU/mL for E. coli and Klebsiella pneumonia (K. pneumonia), respectively. Furthermore, this novel sensing approach is an attractive platform that was successfully applied to detect E. coli in spiked water samples and other food products with good accuracy, indicating its practical applicability for the detection of pathogens in real samples.

Platinum-nickel nanoparticle-based oxidase-like nanozyme for colorimetric/photothermal dual-mode detection of organophosphorus pesticides

In this study, based on the oxidase-like (OXD) activity of platinum-nickel nanoparticles (Pt-Ni NPs) nanozyme and further in collaboration with 3,3′,5,5′-tetramethylbenzidine (TMB), a colorimetric/photothermal dual-mode probe for organophosphorus pesticides (OPs) detection was developed. TMB undergone the catalytic oxidation of Pt-Ni NPs to change from colorless to blue oxidized substance (oxTMB) and exhibited higher temperature under near-infrared irradiation. The hydrolysis product of acid phosphatase (ACP) with L-ascorbic acid 2-phosphate trisodium competed with the OXD-like activity of Pt-Ni NPs to prevent the oxidation of TMB. As the concentration of OPs grew, inhibiting the blocking effect by deactivating ACP, the generated oxTMB caused notable color and temperature changes in the reaction system. The dual-mode probe responded linearly to chlorpyrifos, with the detection limits for colorimetric and photothermal modes of 1.2 ng/mL and 1.66 ng/mL, respectively. This work proposes a simple and reliable colorimetric/photothermal platform for OPs identification, which overcomes the problem that single-mode detection probes are susceptible to external factors, and has broad application potential in the field of food safety.

MOF-based Ag NPs/Co3O4 nanozyme for colorimetric detection of thiophanate-methyl based on analyte-enhanced sensing mechanism.

Silver nanoparticles supported on metal-organic framework (ZIF-67)-derived Co3O4 nanostructures (Ag NPs/Co3O4) were synthesized via a facile in situ reduction strategy. The resulting materials exhibited pH-switchable peroxidase/catalase-like catalytic activity. Ag NP doping greatly enhanced the catalytic activity of Ag NPs/Co3O4 towards 3,3',5,5'-tetramethylbenzidine (TMB) oxidation and H2O2 decomposition which were 59 times (A652 of oxTMB) and 3 times (A240 of H2O2) higher than that of ZIF-67, respectively. Excitingly, thiophanate-methyl (TM) further enhanced the peroxidase-like activity of Ag NPs/Co3O4 nanozyme due to the formation of Ag(I) species in TM-Ag NPs/Co3O4 and generation of more radicals resulting from strong interaction between Ag NPs and TM. The TM-Ag NPs/Co3O4 nanozyme exhibited lower Km and higher Vmax values towards H2O2 when compared with Ag NPs/Co3O4 nanozyme. A simple, bioelement-free colorimetric TM detection method based on Ag NPs/Co3O4 nanozyme via analyte-enhanced sensing strategy was successfully established with high sensitivity and selectivity. Our study demonstrated that hybrid noble metal NPs/MOF-based nanozyme can be a class of promising artificial nanozyme in environmental and food safety applications.

Synergistic signal amplification of ultrathin nanowire-like PtCoFeRuMo high-entropy nanozyme and Z-scheme WO3/ZnIn2S4 heterostructure for split-typed photoelectrochemical aptasensing of myoglobin

Enzyme-initiated sensing strategy has wide applications in photoelectrochemical (PEC) analysis for its high specificity and excellent catalytic efficiency. Herein, ultrathin PtCoFeRuMo high-entropy alloy nanowires (PtCoFeRuMo HEANWs) were prepared by a simple solvothermal method, whose peroxidase-like (POD-like) catalytic property was critically investigated by tetramethylbenzidine (TMB) oxidation in the presence of H2O2. Simultaneously, Z-scheme WO3/ZnIn2S4 heterostructures (labeled WO3/ZnIn2S4) were constructed under solvothermal treatment, whose optical properties and photoactivity were rigorously studied by a set of techniques, combined by elaborating the interfacial charge transfer mechanism. On such foundation, a split-typed PEC aptasensor was established with the WO3/ZnIn2S4 substrate, whose detection signals were further magnified through catalytic oxidation of 3-amino-9-ethylcarbazole (AEC) initiated by the PtCoFeRuMo HEANWs. The resultant PEC sensor realized excellent bioanalysis of biomarker myoglobin, showing a broader linear range from 1.0 × 10−2 to 1.0 × 105 pg mL−1 and a lower limit of detection (0.96 fg mL−1, S/N = 3). This split-typed PEC biosensing strategy shows substantial promise in bioanalysis and clinical diagnosis.

Rapid aqueous preparation of carbon quantum dots and their application as nanozyme for the detection of hydrogen peroxide and uric acid

A green and rapid method was developed to synthesize a series of carbon quantum dots (Fe,N/CQDs, Fe,S/CQDs, S,N/CQDs and Fe,S,N/CQDs) through thermal decomposition using persimmon frost as a carbon source. All the synthesized CQDs have peroxidase-like activity, and the comparision of their steady-state kinetic parameters inferred that the peroxidase-like activity of Fe,S,N/CQDs is superior to those of Fe,S/CQDs and Fe,N/CQDs. Furthermore, Fe,S,N/CQDs exhibited good affinity towards 3,3′,5,5′-Tetramethylbenzidine (TMB) and H2O2 compared to natural horseradish peroxidase (HRP) and other nanozymes. In theory, uric acid (UA) can produce H2O2 with the catalysis by uricase. Fe,S,N/CQDs could catalyze the breakdown of H2O2 to produce reactive oxygen species (ROS), which can oxidize TMB (colorless) to oxTMB (blue). Based on the nanozyme-catalyzed oxidation of TMB, a simple and sensitive colorimetric sensor was developed for the quantitative analysis of H2O2 and UA. Low limit of detection (0.73 μM), wide linear range (1–80 μM) and good repeatability were obtained. The sensor was also demonstrated for the determination of UA in biological samples and satisfactory results were obtained.

Au/Ag2MoO4 nanocomposite: A dual-function catalyst for dye degradation and colorimetric detection

The authors have successfully synthesized a distinctive potato-shaped Au/Ag2MoO4 nanocomposite with exceptional photocatalytic capabilities in the degradation of methylene blue (MB) under UV irradiation even in neutral conditions. Furthermore, this material displays noteworthy peroxidase-like oxidation activity, facilitating the detection of hydrogen peroxide (H2O2) and ascorbic acid (AA) in aqueous environments. This detection method relies on the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB). The signal generated by TMB adsorption on the catalyst's surface plays a pivotal role in the oxidation of TMB in the presence of H2O2, resulting in the formation of a distinct blue-colored product. This reaction is equally influenced by the presence of AA, which, owing to its antioxidant properties, impedes the development of the color signal. This colorimetric approach exhibits high sensitivity, boasting low limits of detection (LOD) and quantification (LOQ) of 0.0252 and 0.0839 mM for H2O2, and 1.7724 and 5.7109 mg/L for AA, respectively. The method offers a broad linear range spanning from 0.029 to 26.47 mM for H2O2 and 0–40 mg/L for AA with a straightforward, cost-effective analytical procedure, and yields highly reliable results. The proposed method displays superior selectivity in detecting AA and high anti-interference capabilities. These findings underscore the photocatalytic and peroxidation-like activities of Au/Ag2MoO4 nanocomposite, positioning it as a promising candidate for various biomedical applications.

Dual amplification for PEC ultrasensitive aptasensing of biomarker HER-2 based on Z-scheme UiO-66/CdIn2S4 heterojunction and flower-like PtPdCu nanozyme

As an important prognostic indicator in breast cancer, human epithelial growth factor receptor-2 (HER-2) is of importance for assessing prognosis of breast cancer patients, whose accurate and facile analysis are imperative in clinical diagnosis and treatment. Herein, photoactive Z-scheme UiO-66/CdIn2S4 heterojunction was constructed by a hydrothermal method, whose optical property and photoactivity were critically investigated by a range of techniques, combined by elucidating the interfacial charge transfer mechanism. Meanwhile, PtPdCu nanoflowers (NFs) were fabricated by a simple aqueous wet-chemical method, whose peroxidase (POD)-mimicking catalytic activity was scrutinized by representative tetramethylbenzidine (TMB) oxidation in H2O2 system. Taken together, the UiO-66/CdIn2S4 based photoelectrochemical (PEC) aptasensor was established for quantitative analysis of HER-2, where the detection signals were further magnified through catalytic precipitation reaction towards 4-chloro-1-naphthol (4-CN) oxidation (assisted by the PtPdCu NFs nanozyme). The PEC aptasensor presented a broader linear range within 0.1 pg mL−1–0.1 μg mL−1 and a lower limit of detection of 0.07 pg mL−1. This work developed a new PEC aptasensor for ultrasensitive determination of HER-2, holding substantial promise for clinical diagnostics.

Phosphorus Modulated Peroxidase-Like Activity of Carbon Dots for Colorimetric Detection of Acid Phosphatase.

The precise regulation of nanoenzyme activity is of great significance for application to biosensing analysis. Herein, the peroxidase-like activity of carbon dots was effectively modulated by doping phosphorus, which was successfully employed for sensitive, selective detection of acid phosphatase (ACP). Phosphorus-doped carbon dots (P-CDs) with excellent peroxidase-like activity were synthesized by a one-pot hydrothermal method, and the catalytic activity could be easily modulated by controlling the additional amount of precursor phytic acid. P-CDs could effectively catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue TMB oxidation products in the presence of hydrogen peroxide. While ACP was able to catalyze the hydrolysis of L-ascorbyl-2-phosphate trisodium salt (AAP) to produce ascorbic acid (AA), which inhibited the peroxidase-like activity of P-CDs, by combining P-CDs nanoenzymes and ACP-catalyzed hydrolysis the colorimetric method was established for ACP detection. The absorbance variation showed a good linear relationship with ACP concentration in the range of 0.4-4.0 mU/mL with a limit of detection at 0.12 mU/mL. In addition, the method was successfully applied to detect ACP in human serum samples with recoveries in the range of 98.7-101.6%. The work provides an effective strategy for regulating nanoenzymes activity and a low-cost detection technique for ACP.

Enhanced peroxidase-like activity of Cu–Cu2O composite film through PtPd immobilization for colorimetric glucose detection

In this study, Cu–Cu2O/PtPd nanocomposites were synthesized and characterized for their peroxidase-like enzyme activity. X-ray diffraction and energy dispersive X-ray spectroscopy analyses confirmed the successful synthesis of the nanocomposites, which exhibited a flower-like morphology and a more uniform dispersion than Cu–Cu2O. The catalytic activity of Cu–Cu2O/PtPd was evaluated using the chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB), finding that Cu–Cu2O/PtPd outperformed Cu–Cu2O. The optimal temperature and pH for the catalytic activity of Cu–Cu2O/PtPd were determined to be 40 °C and pH 4.0, respectively. A kinetic analysis revealed that Cu–Cu2O/PtPd followed Michaelis–Menten kinetics and exhibited a higher affinity toward TMB than the horseradish peroxidase enzyme. The catalytic mechanism of Cu–Cu2O/PtPd involved the generation of hydroxyl radicals, which facilitated the oxidation of TMB. Furthermore, the Cu–Cu2O/PtPd nanocomposite was successfully applied for the colorimetric detection of glucose, demonstrating a linear range of 8–90 μM, a detection limit of 2.389 μM, and high selectivity for glucose over other sugars.

G-quadruplex DNA-based colorimetric biosensor for the ultrasensitive visual detection of strontium ions using MnO2 nanorods as oxidase mimetics.

Strontium-90 (90Sr) is a major radioactive component that has attracted great attention, but its detection remains challenging since there are no specific energy rays indicative of its presence. Herein, a biosensor that is capable of rapidly detecting Sr2+ ions is demonstrated. Simple colorimetric method for sensitive detection of Sr2+ with the help of single-stranded DNA was developed by preparing MnO2 nanorods as oxidase mimic catalysis 3,3',5,5'-tetramethylbenzidine (TMB). Under weakly acidic conditions, MnO2 exhibited a strong oxidase-mimicking activity to oxidize colorless TMB into blue oxidation products (oxTMB) with discernible absorbance signals. Nevertheless, the introduction of a guanine-rich DNA aptamer inhibited MnO2-mediated TMB oxidation and reduced oxTMB formation, resulting in blue fading and diminished absorbance. Upon the addition of strontium ions to the system, the aptamers formed a stable G-quadruplex structure with strontium ions, thereby restoring the oxidase-mimicking activity of MnO2. Under the best experimental conditions, the absorbance exhibits a linear relationship with the Sr2+ concentration within the range 0.01-200μM, with a limit of detection of 0.0028µM. When the concentration of Sr2+ from 10-8 to 10-6mol L-1, a distinct color change gradient could be observed in paper-based sensor. We successfully applied this approach to determine Sr2+ in natural water samples, obtaining recoveries ranging from 97.6 to 103% with a relative standard deviation of less than 5%. By providing technical solutions for detection, our work contributed to the effective monitoring of transportation of radioactive Sr in the environment.

Fe Single-Atom Carbon Dots Nanozyme Collaborated with Nucleic Acid Exonuclease III-Driven DNA Walker Cascade Amplification Strategy for Circulating Tumor DNA Detection.

Circulating tumor DNA (ctDNA), as a next-generation tumor marker, enables early screening and monitoring of cancer through noninvasive testing. Exploring the development of new methods for ctDNA detection is an intriguing study. In this work, a unique electrochemical biosensor for the ctDNA detector was constructed in the first utilizing Fe single-atom nanozymes-carbon dots (SA Fe-CDs) as a signaling carrier in collaboration with a DNA walker cascade amplification strategy triggered by nucleic acid exonuclease III (Exo III). The electrochemical active surface area of AuNPs/rGO modified onto a glassy carbon electrode (AuNPs/rGO/GCE) was about 1.43 times that of a bare electrode (bare GCE), with good electrical conductivity alongside a high heterogeneous electron transfer rate (5.81 × 10-3 cm s-1), that is, as well as the ability to load more molecules. Sequentially, the DNA walker cascade amplification strategy driven by Exo III effectively converted the target ctDNA into an amplified biosignal, ensuring the sensitivity and specificity of ctDNA. Ultimately, the electrochemical signal was further amplified by introducing SA Fe-CDs nanozymes, which could serve as catalysts for 3,3',5,5'-tetramethylbenzidine (TMB) oxidation with facile responding (Vmax = 0.854 × 10-6 M s-1) and robust annexation (Km = 0.0069 mM). The integration of the triple signal amplification approach achieved detection limits as low as 1.26 aM (S/N = 3) for a linearity spanning from 5 aM to 50 nM. In this regard, our proposal for a biosensor with exceptional assay properties in complicated serum environments had great potential for early and timely diagnosis of cancer.

Borophene Quantum Dots as Novel Peroxidase-Mimicking Nanozyme: A Dual-Mode Assay for the Detection of Oxytetracycline and Tetracycline Antibiotics.

The greater advantages and wide applications of zero-dimensional nanodots inspire researchers to develop new materials. Therefore, novel borophene quantum dots (QDs) were prepared by a hydrothermal liquid exfoliation technique using water medium. The borophene QDs proved to be highly stable in water medium for more than 120 days. The synthesized borophene QDs revealed intrinsic peroxidase mimetic activity using two chromogenic substrates, 3,3',5,5'-tetramethylbenzidine (TMB) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt (ABTS). The excellent intrinsic peroxidase activity toward TMB and ABTS substrates was executed using optimal reaction conditions (pH, borophene QDs' concentration, incubation time, and temperature). The formation of hydroxyl radicals in the presence of H2O2 upon TMB and ABTS oxidation played a significant role in the peroxidase reaction. The borophene QDs further proved to be successful for the colorimetric detection of antibiotics (oxytetracycline and tetracycline) using both TMB and ABTS peroxidase substrates. The limit of detection (LOD) for oxytetracycline and tetracycline was found to be 1.10 and 1.02 μM using TMB and 1.03 and 1.02 μM using ABTS chromogenic substrates, respectively. In addition, the fluorescence sensing of oxytetracycline and tetracycline over borophene QDs was also examined. The high fluorescence of borophene QDs (turn ON) was quenched (turn OFF) by oxytetracycline and tetracycline through the inner filter effect mechanism. The LOD of the fluorescence sensing of oxytetracycline and tetracycline was 1.14 and 1.08 μM, respectively. Interestingly, the borophene QDs could be used for the sensitive and selective colorimetric and fluorometric sensing of oxytetracycline and tetracycline after 120 days of storage. The synthesized borophene QDs with long-term stability and real sample analysis provide new insight as nanozymes with higher peroxidase mimetic and fluorescence performance and can be further exploited for medical diagnosis and environmental toxicants' detection.

High Peroxidase-like Activity of Single Iron Atoms Anchored on N-doped Porous Carbon for the Colorimetric Detection of Biothiols

In this report, single iron atoms anchored on nitrogen-doped porous carbon (Fe-ISAs/CN) was prepared and shown to possess high peroxidase-like activity. Fe-ISAs/CN could effi ciently catalyze the oxidation of the peroxidase substrate 3,3?,5,5?-tetramethylbenzidine (TMB) in the presence of H2O2, producing a blue color. In terms of the excellent peroxidase-like activity, single iron atoms anchored on nitrogen-doped porous carbon playing a critical role. Besides, an inhibition effect on the oxidation of TMB catalyzed by Fe-ISAs/CN was induced by biothiols in the presence of H2O2. Taking these advantages together, a simple colorimetric method for rapid and sensitive detection of biothiols was established.

Dimensionality engineering of flower-like bimetallic nanozyme with high peroxidase-activity for naked-eye and on-site detection of acrylamide in thermally processed foods

Acrylamide (AA) is a neurotoxin and carcinogen that formed during the thermal food processing. Conventional quantification techniques are difficult to realize on-site detection of AA. Herein, a flower-like bimetallic FeCu nanozyme (FeCuzyme) sensor and portable platform were developed for naked-eye and on-site detection of AA. The FeCuzyme was successfully prepared and exhibited flower-like structure with 3D catalytic centers. Fe/Cu atoms were considered as active center and ligand frameworks were used as cofactor, resulting in collaborative substrate-binding features and remarkably peroxidase-like activity. During the catalytic process, the 3,3′,5,5′-tetrame-thylbenzidine (TMB) oxidation can be quenched by glutathione (GSH), and then restored after thiolene Michael addition reaction between GSH and AA. Given the “on–off–on” effect for TMB oxidation and high POD-like activity, FeCuzyme sensor exhibited a wide linear relationship from 0.50 to 18.00 ​μM ​(R2 ​= ​0.9987) and high sensitivity (LOD ​= ​0.2360 ​μM) with high stability. The practical application of FeCuzyme sensor was successfully validated by HPLC method. Furthermore, a FeCuzyme portable platform was designed with smartphone/laptop, and which can be used for naked-eye and on-site quantitative determination of AA in real food samples. This research provides a way for rational design of a novel nanozyme-based sensing platform for AA detection.

An experimental and theoretical aided 2D MoS2 nanoflowers strategy for rapid visual sensing of Gallic acid in food and clinical matrixes

Gallic acid (GA), an important phenolic component, is gaining popularity due to its biological and industrial applications. However, its rapid expansion can be hazardous, causing cancer and gene damage, making the design of a low-cost and fast GA sensor difficult. We used a single-step hydrothermal approach to synthesize MoS2 nanoparticles for colorimetric detection of GA. The nanoparticles were analyzed using techniques like; UV–Vis spectroscopy, FT-IR spectroscopy, SEM, EDX and XRD. The optimization of key parameters such as MoS2 concentration (2.0 mg), temperature (30 °C), and pH (7) resulted in a limit of detection (LOD) of 0.125 × 10−6 M with a dynamic range of 0.5 to 36 × 10−6 M. MoS2 nanoflowers performed as nanozymes in the filter paper-based sensor, catalyzing 3, 3′, 5, 5′-tetramethylbenzidine (TMB) oxidation, while GA acted as an inhibitor to prevent further reaction progression. The detection was made feasible through capturing an image support by an ordinary smartphone and the steady-state kinetic study validated MoS2 nanoflowers' affinity for sensing H2O2. The sensor performed well in real-world samples such as diet tea, green tea, water, blood serum, and urine, with recovery rates ranging from 93.2 % to 102.1 %. Density functional theory calculations were applied to provide an insight into GA-MoS2 binding interactions and changes in electronic properties. With all of these merits, we believe MoS2 nanoparticles can provide low-cost and portable filter paper-based strips as a sensing platform for visual assessment of GA.

Ultrafine FeCuAgCeGd–based high–entropy nanozyme: Preparation, catalytic mechanism, and point–of–care detection of dopamine in human serum

Point–of–care testing (POCT) plays vital role in clinic field, especially in resource–limited areas. The nanozyme–based colorimetric platform is the potential strategy for POCT. Therefore, a high–entropy allay nanozyme (HEAzyme) was prepared via formaldehyde–assisted metal–ligand crosslinking method using multi–metal (FeCuAgCeGd) species. The obtained FeCuAgCeGd–HEAzyme showed coordination nanoparticles with ultrafine size (average size was approximately 5 nm). The peroxidase–like (POD–like) activity of FeCuAgCeGd–HEAzyme was verified through density functional theory (DFT) calculations, demonstrating the capability of FeCuAgCeGd–HEAzyme to catalyze H2O2 and generate hydroxyl radicals (•OH). These radicals can oxidize colorless 3,3′,5,5′–tetramethylbenzidine (TMB) to blue oxTMB. Dopamine (DA) scavenges •OH, resulting in an “on–off” effect for TMB oxidation. Subsequently, an FeCuAgCeGd–HEAzyme colorimetric sensor was developed for DA detection, which features a low detection limit of 0.77 µM and a linear range of 5.0–70.0 µM. The sensor demonstrated a recovery ratio in spiked serum samples ranging from 97.7 % to 104.3 % with high stability and favorable selectivity. Furthermore, an FeCuAgCeGd–HEAzyme POCT platform was designed for on–site detection of DA, achieving a reliable linear detection range (5.0–70.0 µM) and a low detection limit (5.69 µM). This platform offers a facile and efficient strategy for rapid, visual, and on–site DA detection in clinical settings with advantages of cost–effectiveness and ease of operation.

Manganese coordination polymer nanoparticles with excellent oxidase-like activity for the rapidly and selectively colorimetric detection of glutathione

Novel kinds of manganese coordination polymer nanoparticles (Mn-IMZs CPNs) were fabricated through self-assemble of imidazole with Mn2+ ions in aqueous solution. The prepared Mn-IMZs CPNs, with remarkable stability, exhibit excellent oxidase-like activity that can effectively catalyze the conversion of the dissolved O2 to O2•−, turning the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxidized TMB (ox-TMB). Based on the inhibitory effect of glutathione (GSH) on the TMB oxidation, a rapid and highly sensitive colorimetric method for the detection of GSH was developed, and the linear ranges are 1.25–50 μM and 50–112.5 μM. Besides, the discriminative detection of GSH from cysteine was achieved by using the time lag between N-ethylmaleimide on the destruction of thiol compounds. Finally, the developed method was successfully applied in the quantification of GSH in tablets and rabbit plasma with high accuracy and good recovery.