Tetramethylbenzidine Research Articles

Fluorine-fluorine interaction-driven colorimetric sensor for PFOA-sensitive detection using F-functionalized Ce-UiO-66-NH2 MOF with oxidase-like activity.

Anovel colorimetric sensor was designedfor sensitive perfluorooctanoicacid (PFOA) detection based on a fluorine-functionalized Ce-metal-organic framework (F-Ce-UiO-66-NH2) with oxidase-like activity, using 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate. This F-Ce-UiO-66-NH2 was synthesized through ligand exchange and post-modification with pentafluorobenzaldehyde (PFBA) on the basis of Ce-terephthalic acid (Ce-UiO-66), incorporating pentafluorophenyl groups that enhance the material's affinity for PFOA, leading to a more sensitive absorbance change in the presence of PFOA. Experimental and computational assays revealed that oxidase-like activity of F-Ce-UiO-66-NH2 primarily arises from hydroxyl radicals (•OH) generated through the conversion of superoxide radicals (•O2-). Furthermore, PFOA molecules were shown to undergo self-aggregation on the F-Ce-UiO-66-NH2 surface via fluorine-fluorine (F-F) interactions between PFOA molecules and the pentafluorophenyl groups as well as between PFOA themselves, blocking the active Ce sites and hindering the interaction of O2 and TMB with F-Ce-UiO-66-NH2, thereby diminishing its oxidase-like activity. Owing to these sophisticated mechanisms, this colorimetric sensor demonstrated a broad linear detection range from 0.5 to 210µM with a low detection limit of 0.41µM for PFOA, enabling precise quantification of PFOA concentrations in real environmental water samples. This work introduces a new strategy for constructing field-deployable colorimetric sensors based on F-F interaction, offering very valuable insights into the design and operational principle for PFAS detection.

Au@Fe3O4 Nanoparticle-Based Colorimetric Aptasensor for Noninvasive Screening of Colorectal Cancer via Detection of Parvimonas micra.

Colorectal cancer (CRC) is a common malignancy requiring early screening to improve patient outcomes. Current screening methods such as colonoscopy and fecal occult blood tests have several limitations including high cost, poor specificity, invasiveness, and inconvenience. Recent research has identified specific bacterial communities associated with CRC, notably Parvimonas micra (P. micra), which serves as a biomarker for early screening and diagnosis owing to its accumulation in the malignant tissues and feces of CRC patients. Herein, we employed the whole-bacterium systematic evolution of ligands by the exponential enrichment (SELEX) method to isolate high-affinity aptamers against P. micra using 17 selection cycles. These aptamers were subsequently bound to Au@Fe3O4 nanoparticles, and the interaction of P. micra and aptamers inhibited the peroxidase-like activity of Au@Fe3O4 nanoparticles, thereby blocking the 3,3',5,5'-tetramethylbenzidine (TMB) chromogenic reaction and resulting in a measurable reduction in absorbance. This colorimetric detection strategy demonstrated a linear response across a range of 100-108 CFU/mL for P. micra with a limit of detection of 11 CFU/mL. Using a colorimetric aptasensor, we assessed the abundance of P. micra in clinical fecal samples and found significantly higher levels in the feces of CRC patients as compared to that of healthy individuals, which was consistent with the quantitative polymerase chain reaction results. This study therefore represents the first successful identification of an aptamer with high affinity and specificity for P. micra, leading to the development of a highly specific and sensitive aptasensor for its detection. The presented approach has a significant potential for CRC screening and diagnosis.

Rapid visual detection of glutathione in vegetables and distinguishing multiple sulfur-containing compounds by smartphone-assisted sensor based on calcined PPy@CuNi-ZIF-67 nanozyme with enhanced oxidase-like activity.

In this work, polypyrrole-coated Cu, Ni co-doped ZIF-67 (PPy@CuNi-ZIF-67) was designed and prepared via a facile method. Calcined PPy@CuNi-ZIF-67 exhibited highly efficient oxidase-like activity and possessed excellent capacity to oxidize colorless 3,3',5,5'-tetramethyl benzidine (TMB) into blue oxidation products (oxTMB) within 4min. Glutathione (GSH) and sulfur-containing compounds can inhibit its oxidase-like activity. Based on this principle, an effective colorimetric method was developed in combination with a smartphone for efficient, sensitive, and visual detection of GSH. Under optimal conditions, good linearity was achieved in the range of 0.83-33.33μM, and the visual detection limit was 0.27μM. Moreover, based on the response difference of different sulfur-containing compounds to different chromogenic substrates, a new array sensor was constructed with three chromogenic substrates. The array sensor was proven to quickly distinguish five sulfur-containing compounds at a concentration as low as 8.3μM in combination with principal component analysis and hierarchical clustering analysis.

Ti-co-Ce oxide decorated chitosan fiber oxidase mimic identified for portable monitoring of S2-, CrO42- and Fe2+ assisted with a smartphone.

Environmental safety and protection is one of the most concerned topics nowadays. To conveniently monitor toxic S2-/CrO42- and to regulate bioactive Fe2+, Ti-co-Ce oxide decorated chitosan fiber (Ti-co-Ce ox@CC) was developed using microwave-assisted hydrothermal method. The integration of chitosan fiber and nano Ti-co-Ce oxide endowed Ti-co-Ce ox@CC with superior oxidase-like activity and improved water-dispersibility. It could quickly accelerate the oxidization of 3,3',5,5'-tetramethyl benzidine (TMB) with Vmax/Km of 6.67×10-8M·s-1/0.0178mM, much better than these (4.31×10-8M·s-1/0.0471mM) for Ti-co-Ce oxide only. Trace S2-, CrO42- or Fe2+ could selectively alter the oxidase-like activity with clear hyperchromic or hypochromic effect. Under the optimized conditions, there expressed excellent linear relationships between A652 and cS2-, cCrO42- or cFe2+ with ideal limits of detection (LOD) of 7.8×10-9M, 5.0×10-8M and 6.5×10-8M respectively. What's more, the red-green-blue (RGB) values analyzed by a smartphone also expressed nice linear relationships with satisfactory LODs of 3.8×10-8M, 7.7×10-8M and 9.2×10-8M for S2-, CrO42- and Fe2+. The proposed Ti-co-Ce ox@CC sensing platform will provide a promising potential for on-site intelligent identification of S2-, CrO42- and Fe2+ in practice.

Acetylcholinesterase-free colorimetric sensing platform for carbosulfan detection based on hollow PDA/MnO2 nanozyme.

Rapid and accurate detection of carbosulfan residues in vegetables is important for ensuring food safety. Herein, based on the unique hydrolysis behavior of carbosulfan, a nanozyme-based colorimetric sensing platform was proposed for detection of carbosulfan. Hollow polydopamine/MnO2 nanoparticles (H-PDA/MnO2 NPs) with excellent oxidase-like activity were synthesized, which can promote the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxidative product (oxTMB). Under acidic conditions, carbosulfan can be decomposed and produce reductive sulfide species (-SH), which are capable to disintegrate MnO2 NPs, resulting in decreased oxidase-like activity of H-PDA/MnO2 NPs. Based on the inhibitory effect on oxidase activity of H-PDA/MnO2 NPs, an acetylcholinesterase-free colorimetric assay was proposed for detection of carbosulfan with low limit of detection of 0.63ngmL-1. Integrating test swabs with smartphone, a portable colorimetric sensor was constructed, showing great potential for on-site detection. To demonstrate the feasibility of this method, carbosulfan in real vegetable samples were determined.

Applying hollow octahedron PtNPs/Pd-Cu2O nanozyme and highly conductive AuPtNPs/Ni-Co NCs to colorimetric -electrochemical dual-mode aptasensor for AFB1 detection.

Aflatoxin B1 (AFB1) is a secondary metabolite produced by Aspergillus flavus and Aspergillus parasiticus. This toxin is highly carcinogenic and toxic, posing a serious threat to human and animal health. AFB1 primarily enters the human body through contaminated food, particularly peanuts, corn, nuts, and wheat. These foods are easily contaminated with AFB1 during planting, harvesting, storage, and processing. Therefore, the establishment of an accurate and sensitive method for the detection of AFB1 is essential to safeguard food safety and human health. This study applied catalytic hairpin assembly (CHA), hybridization chain reaction (HCR), hollow octahedron PtNPs/Pd-Cu2O bifunctional nanozyme, and AuPtNPs/Ni-Co NCs to develop a colorimetric-electrochemical dual-mode aptasensor for AFB1 detection. Here, Pd-Cu2O corner-etched octahedra with cavities and oxygen vacancy defects were first designed, followed by the synthesis of PtNPs/Pd-Cu2O through the loading of PtNPs to enhance the peroxidase-like activity of Pd-Cu2O. PtNPs/Pd-Cu2O effectively catalyzed the generation of blue oxidation products from 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2). It also enhances the redox reaction of methylene blue (MB) at the electrode and improves the electrochemical signal. AuPtNPs/Ni-Co NCs possess a large specific surface area and excellent conductivity, enhanced the redox signal of MB. Additionally, the aptasensor combined the enzyme-free amplification strategies of CHA and HCR to improve sensitivity. The aptasensor reached limit of detection (LOD) 0.76pg/mL in electrochemical mode and 0.49pg/mL in colorimetric mode. The designed colorimetric-electrochemical dual-mode aptasensor exhibits high selectivity, specificity, stability, and reliability. The dual-mode aptasensor had been successfully applied to the spiked analysis of edible oils, peanuts, and cornmeal, demonstrating excellent recovery rates. Therefore, the dual-mode aptasensor had a wide application prospect in the field of quality supervision and food safety.

Signal-off colorimetric and signal-on fluorometric dual-mode aptasensor for ultrasensitive detection of Salmonella Typhimurium using graphitic carbon nitride.

Food safety is severely burdened by the prevalence of foodborne pathogens and the diseases they cause, necessitating the development of rapid, easy-to-use, highly sensitive, and reliable detection methods. Here, a signal-off colorimetric and signal-on fluorometric dual-mode detection method for Salmonella Typhimurium (S. typhimurium) was developed based on its unique interaction with aptamer DNA and graphitic carbon nitride (GCN). In the absence of a target Salmonella species, 6-carboxyfluorescein (FAM)-labeled aptamers are adsorbed on the surface of GCN primarily via a π-π interaction, resulting in reduced fluorescence of FAM through GCN-mediated quenching as well as improved peroxidase-like activity of GCN to generate intense blue color through facilitated electrostatic attraction between the negatively charged aptamer and positively charged 3,3',5,5'-tetramethylbenzidine (TMB) substrate. The introduction of S. typhimurium to the sample solution causes the detachment of the aptamer from GCN due to its higher affinity for S. typhimurium than GCN, thereby rapidly reducing the colorimetric signal and recovering the fluorescence. We successfully determined the number of S. typhimurium using this method in a remarkably short duration (10-30min), highlighting its rapidity. The limit of detection values for S. typhimurium were as low as 8 and 3CFU/mL when using colorimetric and fluorometric methods, respectively. Moreover, this method can be used to detect S. typhimurium spiked in real vegetable extract and milk with high reproducibility and reliability. This method serves as a convenient route to the rapid, sensitive, selective, and reliable detection of pathogens from complex food samples, with the potential to replace conventional yet laborious methods currently in use.

Immobilization of horseradish peroxidase on UiO-66-NH2 for colorimetric and fluorometric sensing of nitrite.

Immobilized enzymes play a crucial role in analytical sensing due to their exceptional stability and considerable commercial importance. In this study, a stable Zr-based metal-organic framework (UiO-66-NH2) was prepared as an immobilization platform for horseradish peroxidase (HRP) through covalent binding. HRP@UiO-66-NH2 retained 75% of its activity after 10 cycles. Subsequently, a colorimetric/fluorometric dual-mode sensing strategy using HRP@UiO-66-NH2 was developed for nitrite detection. HRP@UiO-66-NH2 facilitated the transformation of the non-colored compound 3,3',5,5'-tetramethylbenzidine (TMB) into its blue oxidized form. When nitrite is added, oxidized TMB (ox-TMB) specifically engaged with nitrite (NO2-) to generate diazotized TMB, leading to a color shift from blue to yellow. Concurrently, NO2- reacted with the amino groups of HRP@UiO-66-NH2, forming diazonium compounds and suppressing the fluorescence of HRP@UiO-66-NH2. The limits of detection were 0.21 μM and 0.19 μM for the colorimetric and fluorometric strategies, respectively. Furthermore, a portable kit for detecting nitrite was created by integrating gelatin with HRP@UiO-66-NH2. The kit could visually identify nitrite from 10-400 μM in colorimetric mode and 0-400 μM in fluorometric mode. This method provides an innovative approach for nitrite sensing, paving the way for new research into multifunctional immobilized enzymes and their potential uses in biochemical sensing applications.

Preparation of CHS-Fe3O4@@ZIF-8 peroxidase-mimic with an ultra-thin hollow layer for ultrasensitive electrochemical detection of kanamycin.

Ahighly sensitive and selective electrochemical biosensor was developedfor the detection of kanamycin using a core-hollow-shell structured peroxidase-mimic nanozyme, CHS-Fe₃O₄@@ZIF-8. The synthesized CHS-Fe3O4@@ZIF-8 was characterized with scanning electron microscopy, transmission electron microscopy, andX-ray photoelectron spectroscopy. Itwasfound that the CHS-Fe3O4@@ZIF-8 exhibits excellent peroxidase-like activity due to its ultra-thin hollow layer. Besides, CHS-Fe3O4@@ZIF-8 functionalized with complementary chains of kanamycin aptamer was anchored to the electrode surface via complementary base pairing with the kanamycin aptamer. Upon the presence of kanamycin, a strand displacement reaction was triggered leading to a reduction in the number of the CHS-Fe3O4@@ZIF-8, which slowed down the catalytic reaction of the substrate 3,3',5,5' -tetramethylbenzidine (TMB) facilitated by CHS-Fe3O4@@ZIF 8. Differential pulse voltammetry (DPV) was employed to measure and record changes in peak current resulting from catalytic oxidation product formation (oxidation product of TMB). The electrochemical signal exhibited a linear relationship with logarithmic variations in kanamycin concentration within a range spanning from 10 to 8000pM and achieved an impressive detection limit as low as 7.52pM. Furthermore, successful detection of kanamycin content in serum samples using this sensor demonstrated its good specificity and reproducibility. These findings indicate that theconstructed electrochemical kanamycin sensor holds significant potential for practical applications. The biosensor demonstrated high selectivity, distinguishing kanamycin from other antibiotics, and exhibited good reproducibility, making it reliable for practical applications. The successful detection of kanamycin in serum samples further underscores the sensor's potential for real-world applications, particularly in monitoring antibiotic residues in food products and clinical diagnostics.

Multifunctional Nanozyme with Aptamer-Based Ratiometric Fluorescent and Colorimetric Dual Detection of Prostate-Specific Antigen.

The adsorption of DNA probes onto nanomaterials represents a promising bioassay technique, generally employing fluorescence or catalytic activity to generate signals. A significant challenge is maintaining the catalytic activity of chromogenic catalysts during detection while enhancing accuracy by overcoming the limitations of single-signal transmission. This article presents an innovative multimodal analysis approach that synergistically combines the oxidase-like activity of Fe-N-C nanozyme (Fe-NC) with red fluorescent carbon quantum dots (R-CQDs), further advancing the dual-mode analysis method utilizing R-CQDs@Fe-NC. In this system, R-CQDs integrate with Fe-NC to provide a steady reference red fluorescence signal, while Fe-NC serves as the catalytic active site. The adsorption of 6-carboxyfluorescein-labeled aptamers (FAM-apt) significantly enhanced the electron transfer capability of R-CQDs@Fe-NC, enhancing its catalytic performance and resulting in increased oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Concurrently, the green fluorescence of FAM-apt diminishes due to energy competition, photoinduced electron transfer, and the internal filtration effect by R-CQDs@Fe-NC, while the red fluorescence from R-CQDs@Fe-NC remains stable. Upon recognizing and binding to prostate-specific antigen (PSA), FAM-apt detaches from the surface of R-CQDs@Fe-NC. This leads to simultaneous variations in both the fluorescence signal of the system and the colorimetric signal of TMB. Based on these properties, a colorimetric/fluorescence dual-mode detection method for PSA was established, with detection limits of 0.054 and 0.16 ng/mL, respectively. Furthermore, a smartphone-based sensing device facilitated rapid and convenient detection. This study presents a multisignal output sensing strategy and a simple capillary sensing device, presenting a promising approach for PSA diagnostic analysis and the potential detection of other biomarkers.

Colorimetric Detection of Dopamine Based on Peroxidase-like Activity of β-CD Functionalized AuNPs.

Catalytically active nanomaterials, or nanozymes, have gained significant attention as alternatives to natural enzymes due to their low cost, ease of preparation, and enhanced stability. Because of easy preparation, excellent biocompatibility, and unique optoelectronic properties, gold nanoparticles (AuNPs) have attracted increasing attention in many fields, including nanozymes. In this work, we demonstrated the applicability of beta-cyclodextrin functionalized gold nanoparticles (β-CD-AuNPs) as enzyme mimics for different substances, including TMB and DA. We found that β-CD-AuNPs can catalyze the H2O2-mediated oxidation of DA. The dopamine signal-off sensor was developed by taking advantage of the peroxidase-like activity of β-CD-AuNPs towards TMB and DA, where both 3,3',5,5'-tetramethylbenzidine (TMB) and dopamine (DA) may compete for the binding sites with β-CD-AuNPs. As a result, the presence of dopamine can be detected even through the naked eye (up to the concentration of 3.75 µM) and using a spectrophotometer (up to the concentration of 1.0 µM) by monitoring the disappearance of the blue color of the oxidized form of TMB in the presence of dopamine. Furthermore, no obvious disappearance of color was observed at lower concentrations of interferences including ascorbic and uric acid. Given the versatility of cyclodextrin to host large numbers of analyte molecules, we envision that a similar principle can be applied for the detection of other analyte molecules of biological, medical, and environmental significance.

Rapid detection of hydrogen peroxide and nitrite in adulterated cow milk using enzymatic and nonenzymatic methods on a reusable platform.

Cow milk is readily adulterated due to its complex properties that can emulsify many adulterants. Among the commonly used adulterants in cow milk are hydrogen peroxide (HP) and nitrite. Commercially available HP is added to extend cow milk's shelf life, while nitrite enters through the tap or pond water added to increase cow milk's volume. HP disrupts human free radical balance, while nitrite can cause methemoglobinemia. This study aims to rapidly detect these adulterants on-site by developing a point-of-care kit. A modified streptavidin-horseradish peroxidase (Strep-HRP)-tetramethylbenzidine (TMB) assay was used for designing the biosensor for HP detection. The Strep-HRP complex was immobilized on 8-well polystyrene strips with glutaraldehyde crosslinking. TMB was used as the substrate to detect HP at concentrations of 0.04% (v/v) and higher. Nitrite was detected using a modified Griess assay, wherein for the biosensor, the Griess reagent was coated on polystyrene strips with polyethylene glycol (PEG) used as the stabilizer to identify nitrite concentrations of 32 μg mL-1 and above. The Strep-HRP and Griess assay strips prepared in this investigation were stable for 25 and 10 days, with three times reusability for HP and twice for nitrite detection. Both strips were accurate, up to 95%, for detecting HP and nitrite in cow milk samples.

Preparation and activity of UiO-66 immobilized by horseradish peroxidase

UiO66 is a MOF crystalline material with a hollow octahedral structure, formed by zirconium ions and terephthalic acid. Owing to its outstanding stability and adjustable pore size, UiO66 holds great potential in gas storage, separation, and catalytic reactions. In order to expand the application range of UiO66, two modified UiO66 materials, UiO66-NH2 and UiO66-(COOH)2, were prepared. UiO66-NH2 was modified via Post-Synthetic Modification (PSM) by changing the reaction conditions and adding different modifiers, successfully achieving surface functionalization of UiO66-NH2 to obtain UiO66-NH2-COOH material. UiO66-NH2-COOH and UiO66-(COOH)2 were loaded with horseradish peroxidase (HRP) for catalyzing the reaction between H2O2 and 3,3′,5,5′-tetramethylbenzidine (TMB). Via the results of UV-vis, it was found that UiO66-(COOH)2 loaded with HRP had better catalytic effects than only HRP.

A SERS/colorimetric biosensor based on AuNSs@Ag core-shell Prussian blue nanozyme for non-interference and rapid detection of Staphylococcus aureus in milk.

AAuNSs@PB@Ag-Apt surface-enhanced Raman scattering (SERS) probehas been developedby embedding Prussian blue (PB) between Au core and Ag shell. The PB SERS probe illustrates strong SERS activity in the Raman silent region of 2070 cm-1, and has a zero background signal, ensuring high sensitivity for the detection ofStaphylococcus aureus(S. aureus).Moreover, the assemble SERS probe exhibits the catalytic function of peroxidase (POD), enabling the catalysis of 3,3',5,5'-tetramethylbenzidine (TMB) for colorimetric detection. Additionally, we prepared lectin-functionalized magnetic nanoparticles (F-MNPs-ConA) that demonstrate superior adsorption capabilities towards S. aureus, achieving an impressive adsorption valueof up to 98.62%. The F-MNPs-ConA/S. aureus/AuNSs@PB@Ag-Apt sandwich structure constructed by the above SERS probe and magnetic nanoparticles achieves highly sensitive detection of S. aureus. The detection range is 1 × 100 ~ 1 × 108 CFU·mL-1, and the detection limit (LOD) is 1 CFU·mL-1. Notably, this method can be integrated into smartphones, facilitating rapid and on-site detection of S. aureus. Compared withsimilar biosensors, this biosensor offers distinct advantages, including a wide detection range and a low detection limit. The reliability of the biosensor was confirmed by its application in milk, where the recovery ranged from 93.66 to 120.8%. The dual-mode SERS/colorimetric detection, non-interfering nature, magnetic enrichment, and reusability of the biosensor make it a promising tool for point-of-care testing (POCT).

Electronic structure modulation of ultrathin PtRuMoCoNi high-entropy alloy nanowires for boosting peroxidase-like activity and sensitive colorimetric determinationof isoniazid and hydrazine.

Self-supported ultrathin PtRuMoCoNi high-entropy alloy nanowires (HEANWs) were synthesized by a one-pot co-reduction method, whose peroxidase (POD)-like activity and catalytic mechanism were elaborated in detail. As expected, the PtRuMoCoNi HEANWs showed excellent POD-like activity. It can quickly catalyze the oxidization of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue OXTMB through decomposition of H2O2 to superoxide radicals. Notably, isoniazid and hydrazine effectively scavenge the as-produced superoxide radicals and reduce the blue OXTMB, showing high reduction ability and antioxidant property. Thus, the PtRuMoCoNi HEANW-derived colorimetric method was developed for determination of isoniazid and hydrazine, which exhibited the linear ranges of 1.5 to 50μM and 25 to 200μM coupled with the lower detection limits of 2.3 and 12.6μM for isoniazid and hydrazine, respectively. The excellent analytical performance mainly results from the synergistic catalytic effect of the multiple metals and distinctive ultra-thin nanowires. This work provides a simple and rapid colorimetric method for the determination of isoniazid and hydrazine in actual samples.

Integrated Microneedles and Hydrogel Biosensor Platform: Toward a Diagnostic Device for Collection and Dual-Mode Sensing of Monkeypox Virus A29 Protein.

The outbreak of the monkeypox epidemic underscores the importance of developing a rapid and sensitive virus detection technique. Microneedles (MNs) offer minimally invasive sampling capabilities, providing a solution for the development of integrated extraction and diagnostic portable devices. Here, we report an integrated MNs and hydrogel biosensor (IMHB) platform, composed of an electronic device, an MN patch, and a hydrogel patch. The IMHB allowed for specific extraction of monkeypox virus (MPXV) directly from lesional skin and virus detection in both electrochemical and colorimetric modes. A bifunctional signal probe 3,3',5,5'-tetramethylbenzidine (TMB) was loaded in a hydrogel patch, providing measurable signals for dual-mode sensing. Additionally, a control area was designed in this platform to collect blank samples from normal skin, enabling ratio analysis and quality control functions. This dual-mode ratiometric sensing strategy exhibited a wide range of 10-1000 ng/mL for MPXV A29 protein, with detection limits of 0.1632 and 0.3017 ng/mL for electrochemical and colorimetric assay, respectively. The developed IMHB platform provides a novel way for rapid on-site determination of MPXV, demonstrating the potential for quick intervention in the early stages of infectious diseases.

Copper‐Loaded Nitrogen‐Rich Mesoporous C3N6 Based Nanozymes for Calorimetric Detection of Glutathione and Glucose

AbstractBiomolecular sensing is routinely implemented in healthcare industries for disease diagnostics. Copper nanoparticles efficiently mimic peroxidase, which is needed for efficient glucose and glutathione sensing. However, bare copper nanoparticles are toxic to humans, therefore, anchoring materials are needed to prevent health hazards. Among the carbon‐based anchoring materials, graphene and its derivatives have already been implemented. However, due to poor C–Cu interaction, copper incorporation is inefficient in those systems, which necessitates the exploration of new suitable anchoring platforms. Nitrogen‐rich carbon nitride C3N6 with edge nitrogen atoms and plenty of in‐built vacancy sites in its lattice, apart from its facile synthesis, low cost, scalable production, and non‐toxic nature; offers excellent candidature for this purpose. Cu‐loaded mC3N6 (Cu‐mC3N6) nanozyme is synthesized employing hard silica template SBA‐15 and aminoguanidine hydrochloride and hydrated copper nitrate. First, peroxidase‐like activity is investigated for Cu‐mC3N6 nanozyme with chromogenic 3,3′,5,5′‐ tetramethylbenzidine (TMB) dye, followed by calorimetric detection of glutathione and glucose. Edge nitrogen active sites in the mC3N6 accommodate higher copper loading, resulting in enhanced peroxidase‐like activity and glutathione biosensing performance with a low detection limit of 0.42 ppm. It is believed that the present research will inspire the development of future‐generation nanozymes.

Microbe-mediated synthesis of defect-rich CeO2 nanoparticles with oxidase-like activity for colorimetric detection of L-penicillamine and glutathione.

To enhance production efficiency, curtail costs, and minimize environmental impact, developing simple and sustainable nanozyme synthesis methods has been the focus of relevant research. In this report, graphite-coated CeO2 nanoparticles (CeO2 NPs) with multiple defects (Ce3+ defects, oxygen vacancies and carbon defects) were synthesized via the culture filtrate of the extremely radioresistant bacterium Deinococcus wulumuqiensis R12 (D. wulumuqiensis R12). The as-prepared CeO2 NPs exhibit remarkable oxidase (OXD)-like activity, efficiently catalyzing the oxidation of the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) to form oxTMB, even in the absence of H2O2. The electron-rich bioactive substances in the supernatant were demonstrated to modulate the electronic state of the Ce atom and played a key role in the formation of multiple defects, thereby enhancing the OXD-like activity of CeO2 NPs. Based on the inhibitory effect of sulphydryl groups (-SH) on the TMB-CeO2 system, a colorimetric strategy for the detection of both L-penicillamine (L-PA) and glutathione (GSH) was devised and successfully applied in real sample analysis. The linear ranges of L-PA and GSH detection were found to be 10-500 μM and 9-200 μM with the limits of detection (LODs) at 8.53 and 5.19 μM, respectively. This work provides a straightforward, eco-friendly and nontoxic method for the synthesis and defect construction of CeO2 NPs with OXD-like activity.

Substrate Specificity of Adenine-Cu-PO4 Nanozyme: Ascorbic Acid Oxidation and Selective Cytotoxicity.

Though nanozymes are becoming promising alternatives to natural enzymes due to their superior properties, constructing nanozyme with high specificity is still a great challenge. Herein, with Cu2+ as an active site and adenine as a ligand, Adenine-Cu-PO4 is synthesized in phosphate-buffered saline. As an oxidase mimic, Adenine-Cu-PO4 could selectively catalyze oxidation of ascorbic acid (AA) to dehydroascorbic acid, but not universal substrates (3,3',5,5'-tetramethylbenzidine (TMB), 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and 2,4-dichlorophenol (2,4-DP)), small biomolecules (dopamine, glutathione, glucose, galactose), other vitamins (vitamin A acid, vitamin B1, vitamin K1) and even dithiothreitol (a common interference of AA). Such the specific AA catalytic oxidation is revealed that Adenine-Cu-PO4 selectively binds with AA through hydrogen bonds, accompanied with catalyzing AA oxidation, and concurrently O2 transferring to H2O2 via O2⋅-, further to H2O via ⋅OH. Based on the produced reactive oxygen species, with AA as a pro-oxidant, Adenine-Cu-PO4 nanozyme efficiently triggers severe intratumor oxidative stress to induce tumor cell death. This work opens a new avenue to design intrinsic nanozymes with high specificity, and also presents a promising application in the field of AA oxidation induced cancer therapy.

Pt@ZnCo2O4 Microspheres as Peroxidase Mimics: Enhanced Catalytic Activity and Application for L-Cysteine Detection.

Compared to natural enzymes, the development of efficient artificial simulated enzymes, such as those based on bimetallic materials with high catalytic activity and good stability, is an important way until now. Herein, we employed ZnCo2O4 microspheres as carriers to synthesize Pt-doped composites with different amounts using a one-pot method. The morphology and structure of the synthesized materials were characterized using XRD, SEM, BET, FT-IR, XPS, and Zeta potential techniques. It was found that Pt0 adhered well to the surface of ZnCo2O4 microspheres, with a 12.5% Pt doped ratio exhibiting abundant oxygen vacancies, excellent substrate affinity, and high peroxidase-like activity. Using fluorescent probes and electrochemical methods, the peroxidase-like catalytic mechanism has been explored that Pt@ZnCo2O4 microspheres can accelerate the electron transfer between H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB). Based on the optimal loading ratio of 12.5% of Pt@ZnCo2O4, a colorimetric sensor for visual detection of L-cysteine (L-Cys) was constructed, exhibiting a wide linear range of 0.1~50 µM and a low detection limit of 0.0163 µM. The sensor possesses good selectivity, reusability, and usage stability, which can be well applied to the determination of L-Cys in health product capsules with recovery rates of 96.9%~103.7% and RSD of 1.07%~6.50%. This work broadens the application prospects of spinel materials such as ZnCo2O4 in the field of biological analysis and also provides inspiration for the development of new artificial simulated enzymes.