Iron doped graphitic carbon nitride with peroxidase like activity for colorimetric detection of sarcosine and hydrogen peroxide

Copper nanocubes as low-cost enzyme mimics in a sarcosine-sensing reaction cascade

The development of simple, inexpensive, deployable clinical diagnostics could have a global impact on public health by making measurements of patient health status more widely accessible to patients regardless of socioeconomic status. Here, we report a novel biosensor for sarcosine using a colorimetric readout created by a hybrid catalyst system using copper nanocubes and the enzyme sarcosine oxidase. The enzyme catalyzes the reaction of sarcosine to generate H2O2, which the copper nanocubes then use as a substrate to create free radicals that convert colorless 3,3',5,5'-tetramethylbenzidine (TMB) to its blue, oxidized form. The sensor showed good substrate affinity for Cu nanocubes and yielded a wide linear response range (0-140 μM) for sarcosine detection, with high selectivity against various interfering species. The limit of detection and limit of quantification were found to be 1.43 μM and 4.7 μM, respectively. We showed that the biosensor maintains function in a complex serum sample matrix, suggesting potential utility in clinical applications. Finally, we demonstrated a prototype based on light emitting diodes (LEDs) and a light-dependent resistor (LDR) for unambiguous visual interpretation using an inexpensive microcontroller potentially suitable for use outside of traditional clinical or analytical laboratories.

2D Fe/Co-MOF/SOX cascade reactors for fast noninvasive detection of sarcosine level in prostate cancer urine

Sarcosine plays a key role in screening for early prostate cancer. However, the several already reported peroxidase mimics immobilized with sarcosine oxidase (SOX) utilized to detect uriary sarcosine still have some limitations such as complex synthesis process, using of expensive heavy metals to mimic enzyme activity and long color development time. Herein, an inexpensive peroxidase-like 2D Fe/Co-MOF nanosheet was prepared by a simple solvent modulation method. The resultant 2D Fe/Co-MOF nanosheets have strong peroxidase activity, with its Vmax value for H2O2 of 15.3 × 10-8 M/s, being 1.76 times that of HRP. Then, using the 2D Fe/Co-MOF as a peroxidase model for anchoring natural SOX to construct 2D Fe/Co-MOF/SOX , which can act as a cascade reactor for detection of sarcosine. Considering the above properties, a platform for the detection of sarcosine was built based on a colorimetric method. Because of presence of the high ratio of Fe2+ caused by the electron transfer from Co2+ to Fe3+, large specific surface area and plentiful active sites, 2D Fe/Co-MOF/SOX with TMB (3,3',5,5'-tetramethylbenzidine) colorimetric reagent could have fast color development and can be applied conveniently and fastly in an early screening tool for prostate cancer patients. The sarcosine could be quantified by peroxidase activity with a detection range of 1-400 μM and a limit of detection (LOD) of 0.324 μM. More importantly, the average sarcosine concentration of 21.367 μM and 1.871 μM was detected in patient's and normal urine (n = 5), respectively, which showed an excellent screening effect and a great potential in early prostate cancer.

Bimetal loaded graphitic carbon nitride with synergistic enhanced peroxidase-like activity for colorimetric detection of p-phenylenediamine

In recent years, great progress has been made on the study of nanozymes with enzyme-like properties. Here, bimetallic Fe and Ni nanoclusters were anchored on the nanosheets of nitrogen-rich layered graphitic carbon nitride by one-step pyrolysis at high temperature (Fe/Ni-CN). The loading content of Fe and Ni on Fe/Ni-CN is as high as 8.0%, and Fe/Ni-CN has a high specific surface area of 121.86 m2 g-1. The Fe/Ni-CN can effectively oxidize 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2, and exhibits efficient peroxidase-like activity, leading to a 17.2-fold increase compared to pure graphitic carbon nitride (CN). Similar to the natural horseradish peroxidase (HRP), the Fe/Ni-CN nanozyme follows catalytic kinetics. The Michaelis-Menten constant (Km) value of the Fe/Ni-CN nanozyme for TMB is about 8.3-fold lower than that for HRP, which means that the Fe/Ni-CN nanozyme has better affinity for TMB. In addition, the catalytic mechanism was investigated by combination of free radical quenching experiments and density-functional theory (DFT) calculations. The results show that the high peroxidase-like activity is due to the easy adsorption of H2O2 after bimetal loading, which is conducive to the production of hydroxyl radicals. Based on the extraordinary peroxidase-like activity, the colorimetric detection of p-phenylenediamine (PPD) was constructed with a wide linear range of 0.2-30 μM and a low detection limit of 0.02 μM. The sensor system has been successfully applied to the detection of residual PPD in real dyed hair samples. The results show that the colorimetric method is sensitive, highly selective and accurate. This study provides a new idea for the efficient enhancement of nanozyme activity and effective detection of PPD by a bimetallic synergistic strategy.

A robust Fe-based heterogeneous photocatalyst for the visible-light-mediated selective reduction of an impure CO2 stream

The transformation of CO2 into value-added products from an impure CO2 stream, such as flue gas or exhaust gas, directly contributes to the principle of carbon capture and utilization (CCU). Thus, we have developed a robust iron-based heterogeneous photocatalyst that can convert the exhaust gas from the car into CO with an exceptional production rate of 145 μmol g-1 h-1. We characterized this photocatalyst by PXRD, XPS, ssNMR, EXAFS, XANES, HR-TEM, and further provided mechanistic experiments, and multi-scale/level computational studies. We have reached a clear understanding of its properties and performance that indicates that this highly robust photocatalyst could be used to design an efficient visible-light-mediated reduction strategy for the transformation of impure CO2 streams into value-added products.

Multifunctional N, Fe-doped carbon dots with peroxidase-like activity for the determination of H2O2 and ascorbic acid and cell protection against oxidation

Multifunctional N, Fe-doped carbon dots (N, Fe-CDs) were synthesized by the one-step hydrothermal method using ferric ammonium citrate and dicyandiamide as raw materials. The N, Fe-CDs exhibited peroxidase-like (POD) activity by catalyzing the oxidization of 3,3',5,5'-tetramethylbenzidine (TMB) to the green oxidation state ox-TMB in the presence of hydrogen peroxide (H2O2). Subsequently, based on the POD activity of N, Fe-CDs, an efficient and sensitive colorimetric method for the detection of H2O2 and ascorbic acid (AA) was established with a limit of detection of 0.40 µM and 2.05 µM. The proposed detection method has been successfully applied to detect AA in fruit juice, vitamin C tablets, and human serum samples and has exhibited excellent application prospects in biotechnology and food fields. Furthermore, N, Fe-CDs also showed a protective effect on the cell damage caused by H2O2 and could be used as an antioxidant agent.

Nanozymes: A comprehensive review on emerging applications in cancer diagnosis and therapeutics

Nanozymes, a new class of nanomaterials-based artificial enzymes, have gained huge attraction due to their high operational stability, working efficiency in extreme conditions, and resistance towards protease digestion. Nowadays, they are effectively substituted for natural enzymes for catalysis by closely resembling the active sites found in natural enzymes. Nanozymes can compensate for natural enzymes' drawbacks, such as high cost, poor stability, low yield, and storage challenges. Due to their transforming nature, nanozymes are of utmost importance in the detection and treatment of cancer. They enable precise cancer detection, tailored drug delivery, and catalytic therapy. Through enhanced diagnosis, personalized therapies, and reduced side effects, their adaptability and biocompatibility can transform the management of cancer. The review focuses on metal and metal oxide-based nanozymes, highlighting their catalytic processes, and their applications in the prevention and treatment of cancer. It emphasizes their potential to alter diagnosis and therapy, particularly when it comes to controlling reactive oxygen species (ROS). The article reveals the game-changing importance of nanozymes in the future of cancer care and describes future research objectives, making it a useful resource for researchers, and scientists. Lastly, outlooks for future perspective areas in this rapidly emerging field have been provided in detail.

Recent advances in the colorimetric and fluorescence analysis of bioactive small-molecule compounds based on the enzyme-like activity of nanomaterials

Nanomaterials with enzyme-like activity have been widely used in the construction of colorimetric and fluorescence sensors due to their advantages of cost-effectiveness, high stability, good biocompatibility, and ease of modification. Furthermore, the colorimetric and fluorescence sensors, which are effective approaches for detecting bioactive small-molecule compounds, have been extensively explored due to their simple operation and high sensitivity. Recent significant researches have focused on designing various sensors based on nanozymes with peroxidase- and oxidase-like activity for the colorimetric and fluorescence analysis of different analytes. In this review, recent developments (from 2018 to present) in the colorimetric and fluorescent analysis of bioactive small-molecule compounds based on the enzyme-like activity of nanomaterials were summarized. In addition, the challenges and design strategies in developing colorimetric and fluorescent assays with high performance and specific sensing were discussed.

Facile Fabrication of Wood-Derived Porous Fe3C/Nitrogen-Doped Carbon Membrane for Colorimetric Sensing of Ascorbic Acid

Fe3C nanoparticles hold promise as catalysts and nanozymes, but their low activity and complex preparation have hindered their use. Herein, this study presents a synthetic alternative toward efficient, durable, and recyclable, Fe3C-nanoparticle-encapsulated nitrogen-doped hierarchically porous carbon membranes (Fe3C/N-C). By employing a simple one-step synthetic method, we utilized wood as a renewable and environmentally friendly carbon precursor, coupled with poly(ionic liquids) as a nitrogen and iron source. This innovative strategy offers sustainable, high-performance catalysts with improved stability and reusability. The Fe3C/N-C exhibits an outstanding peroxidase-like catalytic activity toward the oxidation of 3,3',5,5'-tetramethylbenzidine in the presence of hydrogen peroxide, which stems from well-dispersed, small Fe3C nanoparticles jointly with the structurally unique micro-/macroporous N-C membrane. Owing to the remarkable catalytic activity for mimicking peroxidase, an efficient and sensitive colorimetric method for detecting ascorbic acid over a broad concentration range with a low limit of detection (~2.64 µM), as well as superior selectivity, and anti-interference capability has been developed. This study offers a widely adaptable and sustainable way to synthesize an Fe3C/N-C membrane as an easy-to-handle, convenient, and recoverable biomimetic enzyme with excellent catalytic performance, providing a convenient and sensitive colorimetric technique for potential applications in medicine, biosensing, and environmental fields.

Protein Nanotubes Assembled from Imidazole-Grafted Horseradish Peroxidase Nanogels

Protein assembly, a common phenomenon in nature, plays an important role in the evolution of life. Inspired by nature, assembling protein monomers into delicate nanostructures has emerged as an attractive research area. However, sophisticated protein assemblies usually need complicated designs or templates. In this work, we successfully fabricated protein nanotubes in a facile way by coordination interactions between imidazole-grafted horseradish peroxidase (HRP) nanogels (iHNs) and Cu2+. The iHNs were synthesized by polymerization on the surface of HRP by employing vinyl imidazole as a comonomer. By direct addition of Cu2+ into iHN solution, protein tubes were therefore formed. The size of the protein tubes could be adjusted by changing the added Cu2+ amount, and the mechanism behind the formation of protein nanotubes was elucidated. Furthermore, a highly sensitive H2O2 detection system was established based on the protein tubes. This work provides a facile method to construct diverse sophisticated functional protein nanomaterials.

Single Atom Iron-Doped Graphic-Phase C3 N4 Semiconductor Nanosheets for Augmented Sonodynamic Melanoma Therapy Synergy with Endowed Chemodynamic Effect

Sonodynamic therapy (SDT) is a non-invasive therapeutic modality with high tissue-penetration depth to induce reactive oxygen species (ROS) generation for tumor treatment. However, the clinical translation of SDT is restricted seriously by the lack of high-performance sonosensitizers. Herein, the distinct single atom iron (Fe)-doped graphitic-phase carbon nitride (C3 N4 ) semiconductor nanosheets (Fe-C3 N4 NSs) are designed and engineered as chemoreactive sonosensitizers to effectively separate the electrons (e- ) and holes (h+ ) pairs, achieving high yields of ROS generation against melanoma upon ultrasound (US) activation. Especially, the single atom Fe doping not only substantially elevates the separation efficiency of the e- -h+ pairs involved in SDT, but also can serve as high-performance peroxidase mimetic enzyme to catalyze the Fenton reaction for generating abundant hydroxyl radicals, therefore synergistically augmenting the curative effect mediated by SDT. As verified by density functional theory simulation, the doping of Fe atom significantly promotes the charge redistribution in the C3 N4 -based NSs, which improves their synergistic SDT/chemodynamic activities. Both the in vitro and in vivo assays demonstrate that Fe-C3 N4 NSs feature an outstanding antitumor effect by aggrandizing the sono-chemodynamic effect. This work illustrates a unique single-atom doping strategy for ameliorating the sonosensitizers, and also effectively expands the innovative anticancer-therapeutic applications of semiconductor-based inorganic sonosensitizers.

Construction of fluorescence and colorimetric tandem dual-mode sensor by modulating fluorescence and oxidase-like activity via valence switching of cerium-based coordination polymer nanoparticles for sarcosine detection

A fluorescence and colorimetric tandem dual-mode sensor was established by modulating fluorescence and oxidase-like activity via valence switching of cerium-based coordination polymer nanoparticles (Ce-CPNs) for the detection of sarcosine (Sar) which is considered as a potential biomarker for the diagnosis of prostate cancer (PCa). In the present research, sarcosine oxidase (SOX) specifically catalyzes the oxidation of Sar to yield H₂O₂ which can rapidly oxidize Ce(III)-CPNs to generate Ce(IV)-CPNs in appropriate alkaline solution. The generated Ce(IV)-CPNs create a markedly weakened fluorescent signal at 350 nm, while they can induce oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate blue TMBox through emerging good oxidase-like activity. The sensing platform can realize accurate, stable, and high-throughput detection of Sar because of the tandem dual signal output mechanism. More attractively, the chromogenic hydrogel sensing device using smartphone photographing has achieved perfect results for the on-site sensing of Sar in urine specimens without large experimental equipments, demonstrating its considerable clinical application potential in the early diagnosis of PCa.

Dual-Loading of Fe3O4 and Pd Nanoparticles on g-C3N4 Nanosheets Toward a Magnetic Nanoplatform with Enhanced Peroxidase-like Activity for Loading Various Enzymes for Visual Detection of Small Molecules

Enzyme mimics now play a significant role in biochemistry. Especially, peroxidase mimics have been widely used for developing colorimetric sensors of blood glucose. The peroxidase mimics previously reported could not be recycled for reusing and may generate scattering to cause unwanted optical interference when it was used for fabricating colorimetric sensors. We herein prepared a broad-applicable and reusable magnetic enzyme-loading nanoplatform with enhanced peroxidase-like activity by simultaneously loading Fe₃O₄ nanoparticles (Fe₃O₄NPs) and palladium nanoparticles (PdNPs) on graphitic carbon nitride (g-C₃N₄) nanosheets (Fe₃O₄NPs/PdNPs/g-C₃N₄). The prepared Fe₃O₄NPs/PdNPs/g-C₃N₄ possesses stable and enhanced peroxidase-like activity and good enzyme-loading capacity and can be used to load various natural enzymes to form highly-efficient and stable double-active nanozyme for fabricating colorimetric sensors for the visual detection of small molecules. Especially, the magnetic feature facilitates the magnetic separation of Fe₃O₄NPs/PdNPs/g-C₃N₄ from sample solution, which is in favor of recycling and eliminating the optical interference caused by nanozyme in colorimetric sensors. The prepared Fe₃O₄NPs/PdNPs/g-C₃N₄ has been successfully used to load glucose oxidase (GOx) and cholesterol oxidase (Chox) to form magnetic peroxidase-GOx and peroxidase-Chox double-active nanozymes, which can be used to fabricate colorimetric methods for the detection of glucose and cholesterol, respectively, with a visual detection limit of 15 μM and a spectrometry detection limit of 1.0 μM. With the developed glucose and cholesterol detection methods, we have successfully detected glucose and cholesterol in serum with a recovery of 98-104% and a RSD (n = 5) < 5%. With high peroxidase-like activity, good stability, reusable features, and broad applicability of loading enzyme, the developed magnetic Fe₃O₄NPs/PdNPs/g-C₃N₄ provided a promising approach for fabricating cost-effective, sensitive, and simple colorimetric sensors for the visual detection of various small molecules.

Structure engineering of silicon nanoparticles with dual signals for hydrogen peroxide detection

Fluorescent silicon nanoparticles (SiNPs) were synthesized by a one-step, simple, and green method with 3-Aminopropyltriethoxysilane (APTES) and ascorbic acid (AA) as reaction agents. Subsequently, the SiNPs and AgNPs nanocomplex (SiNPs@AgNPs) was constructed as the probe for hydrogen peroxide (H₂O₂) detection. The fluorescence of SiNPs was quenched due to the surface plasmonic-enhanced energy transfer between SiNPs and AgNPs. Meanwhile, the color tends to be yellow due to the existence of AgNPs. As the AgNPs were etched by H₂O₂, the fluorescence recovers and color fadings. Based on the well-designed structure, the "off-on" fluorescence sensing and "on-off" color sensing platforms for H₂O₂ were fabricated. The as-synthesized materials were characterized by Fourier transform infrared (FT-IR) spectroscopy, dynamic light scattering (DLS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Fluorescence and UV-vis absorption spectra were used to evaluate the optical performance. The fabricated sensor exhibited a linear range of 1.0-100.0 μM, with a limit of detection of 0.36 μM for the fluorescence sensing of H₂O₂. Additionally, a linear range of 1.0-50.0 μM and a limit of detection of 0.45 μM were displayed for the detection of H₂O₂ by colorimetric assay. The feasibility in complex medium of the fabricated fluorescent and colorimetric dual-signal sensor was evaluated by the detection of H₂O₂ in phosphate buffer saline (PBS) and lake water samples.

Nanoreactor of sarcosine oxidase-embedded ZIFs activates fluorescent response for diagnosis of prostate cancer

A fluorometric method was developed to detect sarcosine based on SOX@ZIF-8, which possessed great linearity, specificity, and easy operation.

Transferrin guided quasi-nanocuboid as tetra-enzymic mimics and biosensing applications

Given the promising prospect of nanozymes system with multi-enzyme mimetic activities, it is also a challenge for designing a controllable nanostructure as multi-enzymes mimics by protein-guided strategy. Here, transferrin (Trf)-directed manganese oxide with 3D nanomorphology was developed. Trf-Mn₃O₄ quasi-nanocuboids (NCs) was obtained by improved conditions for biomineralization, which employing Trf as biotemplate and Mn²⁺ as metal source in alkaline solution. Fortunately, not only was the controllable structure discovered, but Trf-Mn₃O₄ NCs also showed tetra-enzyme mimic activities involving peroxidase-, ascorbic acid oxidase-, catalase- and superoxide dismutase-mimic activities. Further, the catalytic properties and steady-state kinetic of Trf-Mn₃O₄ NCs was explored, systematically. Moreover, we develop simple colorimetric sensor based on the peroxidase-mimic activity of Trf-Mn₃O₄ NCs for the detection of gallic acid (GA) with the linear range within 0.1-40 μΜ, and the limit of detection was 41.2 nM (S/N = 3). Besides, a novel fluorimetric sensor for the detection of AA based on the ascorbic acid oxidase-mimic activity was proposed with the linear range of 0.5 μM-10 μM (R² = 0.9906) and 10 μM-5 mM (R² = 0.9927), and LOD of 0.24 μM (S/N = 3) was obtained. Both the proposed sensors showed outstanding detection performance, accuracy and repeatability, which realized the detection of GA and AA in real sample, respectively. The as-synthesized tetra-enzymic mimics not only enriched the species of nanozymes, particularly for the nanozymes with multi-enzyme mimic activities, the proposed sensors showed promising potential applications for biosensor in complex samples.

Two-dimensional biomaterials: material science, biological effect and biomedical engineering applications

To date, nanotechnology has increasingly been identified as a promising and efficient means to address a number of challenges associated with public health. In the past decade, two-dimensional (2D) biomaterials, as a unique nanoplatform with planar topology, have attracted explosive interest in various fields such as biomedicine due to their unique morphology, physicochemical properties and biological effect. Motivated by the progress of graphene in biomedicine, dozens of types of ultrathin 2D biomaterials have found versatile bio-applications, including biosensing, biomedical imaging, delivery of therapeutic agents, cancer theranostics, tissue engineering, as well as others. The effective utilization of 2D biomaterials stems from the in-depth knowledge of structure-property-bioactivity-biosafety-application-performance relationships. A comprehensive summary of 2D biomaterials for biomedicine is still lacking. In this comprehensive review, we aim to concentrate on the state-of-the-art 2D biomaterials with a particular focus on their versatile biomedical applications. In particular, we discuss the design, fabrication and functionalization of 2D biomaterials used for diverse biomedical applications based on the up-to-date progress. Furthermore, the interactions between 2D biomaterials and biological systems on the spatial-temporal scale are highlighted, which will deepen the understanding of the underlying action mechanism of 2D biomaterials aiding their design with improved functionalities. Finally, taking the bench-to-bedside as a focus, we conclude this review by proposing the current crucial issues/challenges and presenting the future development directions to advance the clinical translation of these emerging 2D biomaterials.

A Review on Metal- and Metal Oxide-Based Nanozymes: Properties, Mechanisms, and Applications

Since the ferromagnetic (Fe3O4) nanoparticles were firstly reported to exert enzyme-like activity in 2007, extensive research progress in nanozymes has been made with deep investigation of diverse nanozymes and rapid development of related nanotechnologies. As promising alternatives for natural enzymes, nanozymes have broadened the way toward clinical medicine, food safety, environmental monitoring, and chemical production. The past decade has witnessed the rapid development of metal- and metal oxide-based nanozymes owing to their remarkable physicochemical properties in parallel with low cost, high stability, and easy storage. It is widely known that the deep study of catalytic activities and mechanism sheds significant influence on the applications of nanozymes. This review digs into the characteristics and intrinsic properties of metal- and metal oxide-based nanozymes, especially emphasizing their catalytic mechanism and recent applications in biological analysis, relieving inflammation, antibacterial, and cancer therapy. We also conclude the present challenges and provide insights into the future research of nanozymes constituted of metal and metal oxide nanomaterials.