Chitosan-stabilized platinum nanoparticles as effective oxidase mimics for colorimetric detection of acid phosphatase

Deep convolutional neural network-based 3D fluorescence sensor array for sugar identification in serum based on the oxidase-mimicking property of CuO nanoparticles

Developing sensor arrays capturing comprehensive fluorescence (FL) spectra from a single probe is crucial for understanding sugar structures with very high similarity in biofluids. Therefore, the analysis of highly similar sugar' structures in biofluids based on the entire FL of a single nanozyme probe needs more concern, which makes the development of novel alternative approaches highly wanted for biomedical and other applications. Herein, a well-designed deep learning model with intrinsic information of 3D FL of CuO nanoparticles (NPs)' oxidase-like activity was developed to classify and predict the concentration of a group of sugars with very similar chemical structures in different media. The findings presented that the overall accuracy of the developed model in classifying the nine selected sugars was (99-100 %), which prompted us to transfer the developed model to predict the concentration of the selected sugars at a concentration range of (1-100 μM). The transferred model also gave excellent results (R2 = 97-100 %). Therefore, the model was extended to other more complex applications, namely the identification of mixtures of sugars in serum and the detection of polysaccharides in different media such as serum and lake water. Notably, LOD for fructose was determined at 4.23 nM, marking a 120-fold decrease compared to previous studies. Our developed model was also compared with other deep learning-based models, and the results have demonstrated remarkable progress. Moreover, the identification of other possible coexisting interference substances in lake water samples was considered. This work marks a significant advancement, opening avenues for the widespread application of sensor arrays integrating nanozymes and deep learning techniques in biomedical and other diverse fields.

Chitosan: A Green Approach to Metallic Nanoparticle/Nanocomposite Synthesis and Applications

Chitosan, a naturally occurring biopolymer derived from chitin, has emerged as a highly promising instrument for the production and application of metal nanoparticles. The present review delves into the several functions of chitosan in the development and operation of metal nanoparticles, emphasizing its aptitudes as a green reducing agent, shape-directing agent, size-controlling agent, and stabilizer. Chitosan's special qualities make it easier to manufacture metal nanoparticles and nanocomposites with desired characteristics. Furthermore, there is a lot of promise for chitosan-based nanocomposites in a number of fields, such as metal removal, water purification, and photoacoustic, photothermal, antibacterial, and photodynamic therapies. This thorough analysis highlights the potential application of chitosan in the advancement of nanotechnology and the development of medicinal and environmental solutions.

Synthesis, Structural Analysis, and Peroxidase-Mimicking Activity of AuPt Branched Nanoparticles

Bimetallic nanomaterials have generated significant interest across diverse scientific disciplines, due to their unique and tunable properties arising from the synergistic combination of two distinct metallic elements. This study presents a novel approach for synthesizing branched gold-platinum nanoparticles by utilizing poly(allylamine hydrochloride) (PAH)-stabilized branched gold nanoparticles, with a localized surface plasmon resonance (LSPR) response of around 1000 nm, as a template for platinum deposition. This approach allows precise control over nanoparticle size, the LSPR band, and the branching degree at an ambient temperature, without the need for high temperatures or organic solvents. The resulting AuPt branched nanoparticles not only demonstrate optical activity but also enhanced catalytic properties. To evaluate their catalytic potential, we compared the enzymatic capabilities of gold and gold-platinum nanoparticles by examining their peroxidase-like activity in the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Our findings revealed that the incorporation of platinum onto the gold surface substantially enhanced the catalytic efficiency, highlighting the potential of these bimetallic nanoparticles in catalytic applications.

Chitosan-assisted hydrogen adsorption and reversibility of Ni-doped hierarchical carbon scaffolds

We investigated the effects of chitosan (CS) on the hydrogen adsorption and reversibility of hierarchical carbon scaffold (HCS) loaded with Ni nanoparticles. As size-controllable, stabilizing, and shape-directing agents for the green synthesis of metal nanoparticles of CS, Ni nanoparticles with uniform distribution and shape are deposited onto HCS. The latter results in the superior specific surface area of Ni nanoparticles for hydrogen chemisorption. The best hydrogen adsorption capacities at room temperature under 20-70 bar H2 of 0.5-1.70 wt% H2 were obtained from 10 wt% Ni-doped HCS-CS. Although macropores of the HCS collapsed upon cycling due to hydrogen pressure applied during adsorption, average hydrogen capacities of 1.17 ± 0.05 wt% H2 (T = 25 °C and p(H2) = 50 bar) were maintained for 14 cycles. This is because not only uniform distribution and shape of Ni nanoparticles and microporous structures of the HCS were preserved upon cycling but also the interactions between Ni and heteroatoms (N and O) of the HCS and CS prevented particle agglomeration.

Construction of a dual-signal readout platform for effective glutathione S-transferase sensing based on polyethyleneimine-capped silver nanoclusters and cobalt-manganese oxide nanosheets with oxidase-mimicking activity

A novel dual-mode fluorometric and colorimetric sensing platform is reported for determining glutathione S-transferase (GST) by utilizing polyethyleneimine-capped silver nanoclusters (PEI-AgNCs) and cobalt-manganese oxide nanosheets (CoMn-ONSs) with oxidase-like activity. Abundant active oxygen species (O2•-) can be produced through the CoMn-ONSs interacting with dissolved oxygen. Afterward, the pink oxDPD was generated through the oxidation of colorless N,N-diethyl-p-phenylenediamine (DPD) by O2•-, and two absorption peaks at 510 and 551 nm could be observed. Simultaneously, oxDPD could quench the fluorescence of PEI-AgNCs at 504 nm via the inner filter effect (IFE). However, in the presence of glutathione (GSH), GSH prevents the oxidation of DPD due to the reducibility of GSH, leading to the absorbance decrease at 510 and 551 nm. Furthermore, the fluorescence at 504 nm was restored due to the quenching effect of oxDPD on decreased PEI-AgNCs. Under the catalysis of GST, GSH and1-chloro-2,4-dinitrobenzo (CDNB) conjugate to generate an adduct, initiating the occurrence of the oxidation of the chromogenic substrate DPD, thereby inducing a distinct colorimetric response again and the significant quenching of PEI-AgNCs. The detection limits for GST determination were 0.04 and 0.21 U/L for fluorometric and colorimetric modes, respectively. The sensing platform illustrated reliable applicability in detecting GST in real samples.

Enhanced the intrinsic oxidase-like activity of chiral carbon dots via manganese doping for selective catalytic oxidation

It is highly desirable to design and construct chemical catalysts with high activity and specificity as the alternatives of natural enzymes for industrial application. Chiral carbon dots (CDs), possessing both the intrinsic enzyme-like activity and specific recognition ability, are one of good candidates for enzyme-like catalysts. However, their catalytic activity is far from that of natural enzymes and needs to be enhanced. In this work, the modulation of the chiral structure and catalytic activity of chiral CDs with intrinsic oxidase-like activity was implemented by manganese (Mn) doping. Under the light condition, chiral CDs (l-Ser-CDs and d-Ser-CDs) derived from chiral serine (Ser) show weak catalytic activity and low selectivity toward the oxidation of L type of dopamine (l-DOPA), whereas the Mn functionalized chiral CDs (l-Mn-CDs or d-Mn-CDs) exhibit 6.9 times higher in catalytic activity and 2.9 times in selectivity ratio (SR) than Ser-CDs. Mn-CDs involve two-path catalytic process, in which the photogenerated electrons could reduce O2 to O2- as the active species and the holes would oxidize DOPA directly. Moreover, doping of Mn enables the CDs to generate more O2-. Besides, l-Mn-CDs have higher catalytic activity than that of d-Mn-CDs (+54.2 %), and the chiral Mn-CDs have stronger selective adsorption capacity towards chiral DOPA than Ser-CDs. Our work provides a new method for designing and preparing novel chiral artificial enzymes.

A colorimetric sensing strategy based on chitosan-stabilized platinum nanoparticles for quick detection of α-glucosidase activity and inhibitor screening

α-Glucosidase (α-Glu) is implicated in the progression and pathogenesis of type II diabetes (T2D). In this study, we developed a rapid colorimetric technique using platinum nanoparticles stabilized by chitosan (Ch-PtNPs) to detect α-Glu activity and its inhibitor. The Ch-PtNPs facilitate the conversion of 3,3',5,5'-tetramethylbenzidine (TMB) into oxidized TMB (oxTMB) in the presence of dissolved O2. The catalytic hydrolysis of 2-O-α-D-glucopyranosyl-L-ascorbic acid (AA-2G) by α-Glu produces ascorbic acid (AA), which reduces oxTMB to TMB, leading to the fading of the blue color. However, the presence of α-Glu inhibitors (AGIs) hinders the generation of AA, allowing Ch-PtNPs to re-oxidize colorless TMB back to blue oxTMB. This unique phenomenon enables the colorimetric detection of α-Glu activity and AGIs. The linear range for α-Glu was found to be 0.1-1.0 U mL-1 and the detection limit was 0.026 U mL-1. Additionally, the half-maximal inhibition value (IC50) for acarbose, an α-Glu inhibitor, was calculated to be 0.4769 mM. Excitingly, this sensing platform successfully detected α-Glu activity in human serum samples and effectively screened AGIs. These promising findings highlight the potential application of the proposed strategy in clinical diabetes diagnosis and drug discovery.

A dual-mode sensing system based on carbon quantum dots and Fe nanozymes for the detection of α-glucosidase and its inhibitors

In this research, a sensitive fluorometric and colorimetric dual-mode sensing platform based on nitrogen-doped carbon quantum dots (NCDs) and magnetic Fe nanoparticles with peroxidase-like activity (Fe nanozymes, Fe NZs) was established, and was further applied for the detection of α-glucosidase (α-glu) and its inhibitors. The ⋅OH that produced by H2O2 catalyzed by Fe NZs can oxidize the colorless diammonium 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) to green oxABTS, and a noticeable absorption peak at 417 nm appeared. Simultaneously, oxABTS can quench the fluorescence of NCDs at 402 nm via fluorescence resonance energy transfer (FRET). 2-O-α-D-glucopyranosyl-L-ascorbic acid (AAG) can be decomposed by α-glu to glucose and ascorbic acid (AA), AA can prevent the oxidation of ABTS, resulting in the absorption at 417 nm decreased. Moreover, the quenching effect of oxABTS on NCDs is weakened, and the fluorescence at 402 nm is restored. Therefore, based on the change of absorption at 417 nm and fluorescence at 402 nm, the fluorometric and colorimetric dual-mode sensing method can be used for the determination of acarbose and voglibose that are the inhibitors of α-glu.

Iron-doped carbon nitride with enhanced peroxidase-like activity for smartphone-based colorimetric assay of total antioxidant capacity

The facile detection of total antioxidant capacity (TAC) is limited by in-situ analysis, because it usually requires complex laboratory equipments. Here, a colorimetric assay for TAC detection is developed based on the peroxidase-like activity of iron-doped carbon nitride (Fe/NC) and the smartphone platform. The peroxidase-like activity of carbon nitride is greatly improved by the introduction of Fe atoms, and the active sites turn to Fe-Nx coordination groups in the Fe/NC. The inhibition mechanism of the chromogenic reaction for different kinds of antioxidants is also studied. The colorimetric assay is fabricated by the relationship of absorbance-color-antioxidant content and applied successfully to the TAC detection of several fruit juicesand commercial beverages. This work not only provides a promising approach for convenient in-situ TAC assay without the use of large instruments, but also expands the application of nanozymes in nutritional value assessment of foods.

Designing M13 Bacteriophage and Fe-Nanonest Self-Assembly System for Universal and Facile Preparation of Metal Single Atoms as Stable Mimicking Enzymes

Metal single-atom catalysts (MSACs) possess multiple advantages in chemical synthesis; their efficient fabrication routes, however, remain a challenge to date. Here, an interdisciplinary design using M13 bacteriophage virus as a biotemplate to carry Fe nanoclusters, which we figuratively call "Fe-nanonests", is proposed to enable facile and versatile synthesis of MSACs. The feasibility and generality of this self-assembly method was demonstrated by the observation of six different metal single atoms (MSAs) including Ag, Pt, Pd, Zn, Cu, and Ni. With Pd as a representative, key factors dominating the fabrication were determined. The Pd single atoms exhibited excellent horseradish peroxidase (HRP)-like activity, which was further improved by 50% via genetic editing of the M13 pVIII protein terminals. Excellent stability was also observed in the quantification of acid phosphatase, a cancer predictor. X-ray absorption near-edge structure spectroscopy has been applied to the analysis of Pd single atoms as well, and the Pd-N4 coordination explained the mechanism of high HRP-like catalytic activity. The MSAs synthesized by the M13 phage and Fe-nanonest self-assembly method show promising prospects in non-cold-chain medical detection applications.

Tailoring Phase Fraction Induced Saturation Polarization Delay for High-Performance BaTiO3-Based Relaxed Ferroelectric Capacitors

Electrostatic capacitors based on dielectric materials are essential for enabling technological advances, including miniaturization and integration of electronic devices. However, maintaining a high polarization and breakdown field strength simultaneously in electrostatic capacitors remains a major challenge for industrial applications. Herein, a universal approach to delaying saturation polarization in BaTiO3-based ceramic is reported via tailoring phase fraction to improve capacitive performance. The ceramic of 0.85(0.7BaTiO3-0.3Bi0.5Na0.5TiO3)-0.15Bi0.5Li0.5(Ti0.75Ta0.2)O3 delivers an ultrahigh recoverable energy density (Wrec) of 7.16 J cm-3 along with an efficiency (η) of approximately 90% at a breakdown electric field of 700 kV cm-1, outperforming the current BaTiO3-based ceramics and other lead-free ceramics. Meanwhile, the Wrec and η exhibit wide frequency, temperature, and cycling fatigue stability. Additionally, both an extremely fast discharge time of 115 ns and a large power density of 106.16 MW cm-3 are concurrently attained. This work offers a promising pathway for delaying saturation polarization design in order to create scalable high-energy-density ceramics capacitors and highlight the research prospects of pulse power applications.

Rational design of three-in-one Pt/MnO2/GO hybrid nanozyme with enhanced catalytic performance for colorimetric detection of ascorbic acid and cysteine

In this work, a novel three-in-one Pt/MnO₂/GO hybrid nanozyme with wide pH and temperature working range was rational prepared using simple hydrothermal and reduction strategy. The prepared Pt/MnO₂/GO displayed enhanced catalytic activity than single active component due to the excellent conductivity of GO, the increased active sites, the increased electron transfer capacity, the synergistic effect between each component and the decreased binding energy for adsorbed intermediates. Combing chemical characterization and theoretical simulation calculations, the O₂ reduction process on the Pt/MnO₂/GO nanozymes and the generated reactive oxygen species in the nanozyme-TMB system were thoroughly illustrated. Based on the excellent catalytic activity of Pt/MnO₂/GO nanozymes, a colorimetric strategy was proposed to detect the ascorbic acid (AA) and cysteine (Cys), and the experimental results indicated that detection range of AA was 0.35-56 μM with a LOD of 0.075 μM and detection range of Cys was 0.5-32 μM with a LOD of 0.12 μM. Good recoveries were achieved in the human serum and fresh fruit juice detection procedures, demonstrating the potential applications of Pt/MnO₂/GO-based colorimetric strategy in complex biological and food samples.

Amorphous mixed-valent Mn-containing nanozyme with cocklebur-like morphology for specific colorimetric detection of cancer cells via Velcro effects

Designing nanozymes with excellent catalytic activity through valence state engineering and defect engineering is a widely applicable strategy. However, their development is hindered by the complexity of the design strategies. In this work, we employed a simple calcination method to regulate the valence of manganese and crystalline states in manganese oxide nanozymes. The oxidase-like activity of the nanozymes was found to benefit from a mixed valence state dominated by Mn (III). And the amorphous structure with more active defect sites significantly enhanced the catalytic efficiency. Moreover, we demonstrated that amorphous mixed-valent Mn-containing (amvMn) nanozymes with unique cocklebur-like biomimetic morphology achieved specific binding to cancer cells through the Velcro effects. Subsequently, the nanozymes mediated TMB coloration through their oxidase-like activity, enabling the colorimetric detection of cancer cells. This work not only provides guidance for optimizing nanozyme performance, but also inspire the development of equipment-free visual detection methods for cancer cells.

Design of Smartphone-Assisted Point-of-Care Platform for Colorimetric Sensing of Uric Acid via Visible Light-Induced Oxidase-Like Activity of Covalent Organic Framework

Monitoring of uric acid (UA) levels in biological samples is of great significance for human health, while the development of a simple and effective method for the precise determination of UA content is still challenging. In the present study, a two-dimensional (2D) imine-linked crystalline pyridine-based covalent organic framework (TpBpy COF) was synthesized using 2,4,6-triformylphloroglucinol (Tp) and [2,2'-bipyridine]-5,5'-diamine (Bpy) as precursors via Schiff-base condensation reactions and was characterized with scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), Powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy, and Brunauer-Emmett-Teller (BET) assays. The as-synthesized TpBpy COF exhibited excellent visible light-induced oxidase-like activity, ascribed to the generation of superoxide radicals (O₂^•-) by photo-generated electron transfer. TpBpy COF could efficiently oxidase the colorless substrate 3,3',5,5'-tetramethylbenzydine (TMB) into blue oxidized TMB (oxTMB) under visible light irradiation. Based on the color fade of the TpBpy COF + TMB system by UA, a colorimetric procedure was developed for UA determination with a detection limit of 1.7 μmol L^-1. Moreover, a smartphone-based sensing platform was also constructed for instrument-free and on-site detection of UA with a sensitive detection limit of 3.1 μmol L^-1. The developed sensing system was adopted for UA determination in human urine and serum samples with satisfactory recoveries (96.6-107.8%), suggesting the potential practical application of the TpBpy COF-based sensor for UA detection in biological samples.

In Situ Synthesis of Horseradish Peroxidase Nanoflower@Carbon Nanotube Hybrid Nanobiocatalysts with Greatly Enhanced Catalytic Activity

Organic-inorganic hybrid nanoflowers (NFs) consisting of horseradish peroxidase (HRP) and copper II (Cu²⁺) are successfully synthesized with the involvement of carbon nanotubes (CNTs) by in situ and post-modification methods. Catalytic activities of in situ synthesized HRP-NF@CNT (HRP-NF@CNT-Is) and post-modification-synthesized HRP-NF@CNTs (HRP-NF@CNT-Pm) are systematically examined. The 30 mg CNTs incorporated HRP-NF@CNT-Is (HRP-NF@CNT-30Is) exhibits greatly increased catalytic activity and stability toward 3,3',5,5'-tetramethylbenzidine (TMB), thanks to the synergistic effect between HRP-NF and CNTs and the peroxidase-like activity of CNTs in the presence of hydrogen peroxide (H₂O₂). While HRP-NF@CNT-30Is retains almost 85% of its initial activity even after 10 cycles, HRP-NF (without CNTs) loses half of its initial activity at the same experimental conditions. We study how two experimental parameters, the pH values and temperatures, influence the catalytic activity of HRP-NF@CNT-30Is, in addition to the fact that HRP-NF@CNT-30Is is employed to detect the presence of H₂O₂ and glutathione (GSH) with colorimetric and spectrophotometric readouts. For instance, HRP-NF@CNT-30Is is used to sensitively detect H₂O₂ in the range of 20 to 300 μM with an LOD of 2.26 μM. The catalytic activity of HRP-NF@CNT-30Is is suppressed in the presence of GSH, and then an obvious color change from blue to nearly colorless is observed. Using this strategy, GSH is also sensitively determined in the range of 20-200 μM with an LOD of 11.2 μM. We expect that HRP-NF@CNTs can be used as a promising and novel nanobiocatalyst for various biomedical and industrial applications in the near future.

An electrochemical sensing platform based on carbon black and chitosan-stabilized platinum nanoparticles

The versatility of chitosan (Ch) biopolymer as a metallic nanoparticle stabilizing agent and excellent former of thin films on glassy carbon was explored in this work for the sustainable manufacture of novel electrochemical sensors based on carbon black (CB) and chitosan-stabilized platinum nanoparticles (Ch-PtNPs). Platinum nanoparticles highly stabilized by chitosan were easily synthesized at room temperature and characterized by HR-TEM, UV-vis, and voltammetry. Ch-PtNPs presented an average diameter of 2.7 nm, and typical voltammetric peaks of Pt in sulfuric acid medium were detected for films containing Ch-PtNPs. As a proof of concept, the CB-Ch-PtNP electrode was applied in the determination of hydrogen peroxide (H₂O₂) and the endocrine disruptor bisphenol A (BPA). Pronounced electrocatalytic activity towards H₂O₂ reduction was observed in the presence of Ch-PtNPs in the films, guaranteeing the non-enzymatic determination of H₂O₂ by chronoamperometry, with a limit of detection of 10 μmol L^-1. In the determination of BPA by differential pulse adsorptive anodic stripping voltammetry (DPAdASV), under optimal experimental conditions, a wide linear response range and a limit of detection at the nanomolar level (7.9 nmol L^-1) were achieved. In addition, excellent repeatabilities of sensor response and sensor fabrication, and accuracy in the analysis of natural water samples were obtained.

Fabrication of chitosan-MnO2‑iridium/nanoceria supported nanoparticles: Catalytic and anti-radical activities

Chitosan capped MnO₂‑iridium nanoparticles supported on nanoceria (Ch-MnO₂-Ir/CeO₂) were fabricated by using combination of colloidal solution and metal displacement galvanic methods. The oxidative degradation of acid orange 7 in aqueous solution by activated persulfate with the as-prepared nanoparticles was studied. The resulting Ch-MnO₂-Ir/CeO₂ with S₂O₈^2-, 80 % degraded 70.06 mg/L of acid orange 7 within 100 min, while at the same time, Ch-Ir, Ch-MnO₂, and Ch-Ir-MnO₂ remained inactive. CeO₂ increased the surface of the catalyst, and also improved the reactive oxygen species site of Ch-Ir-MnO₂ through the activation of S₂O₈^2- with CeO₂. The reversible redox cycle reaction, Ce (III) ↔ Ce (IV) and strong synergistic effect of MnO₂-Ir are responsible for the remarkable catalytic performance of Ch-MnO₂-Ir/CeO₂/S₂O₈^2- system. The degradation of acid orange 7 could be significantly retarded with inorganic (NO₃^- < Cl^- < SO₄^2- < H₂PO₄^- < HCO₃^-) and organic scavengers (ethanol < tertiary butanol < benzoquinone < phenol). Ch-MnO₂-Ir/CeO₂ exhibited excellent stability and reusability. Anti-radical activity of chitosan and Ch-MnO₂-Ir/CeO₂ was evaluated with 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical. The free radical properties increase with concentration of chitosan and Ch-MnO₂-Ir/CeO₂.

Visual detection of vitamin C in fruits and vegetables using UiO-66 loaded Ce-MnO2 mimetic oxidase

A nanocomposite (UiO-66/Ce-MnO₂) was fabricated by combining UiO-66 with cerium-doped manganese dioxide (Ce-MnO₂) for colorimetric detecting vitamin C (Vc). Compared with traditional artificial enzymes, the as-synthesized UiO-66/Ce-MnO₂ were simple to prepare and did not require the participation of other active substances. The doping of cerium increased the oxygen vacancies and the UiO-66 as a carrier improved the dispersibility. The formation of superoxide anion (O₂^-) and the inside Ce⁴⁺/Ce³⁺ and Mn⁴⁺/Mn³⁺ redox couples of UiO-66/Ce-MnO₂ endowed UiO-66/Ce-MnO₂ with a high catalytic capability, which could catalytically oxidize 3, 3', 5, 5'-tetramethylbenzidine (TMB) into oxidation state TMB (oxTMB) without H₂O₂, accompanying with color change and a prominent peak at 652 nm in UV-vis spectra. Based on the inhibitory effects of Vc on catalytic oxidation of TMB, detection of Vc can be achieved, exhibiting a linear relationship in the concentration of 1.13-17.01 μmol L^-1 with a low detection limit of 65.82 nmol L^-1. This system can also be detected by smartphone, the linear detection range is 12.47-22.67 μmol L^-1. Vc contents in fruits and vegetables detected by the sensor were in good agreement with the 2, 4-Dinitrophenylhydrazine colorimetry method (P > 0.05), indicating a reliable sensor for Vc detection.

Dual-mode colorimetric and fluorescence sensing system for the detection of captopril based on Fe/NC nanozymes and carbon dots

Metal nitrogen-doped carbon (MNC) nanozymes have received increasing attention in bio-catalysis filed due to adequate catalytic activity, outstanding stability and reusability. Herein, the Fe/NC nanozymes (Fe/NC NZs) with peroxidase-like activity was successfully synthesized and a fluorescence turn on and colorimetric dual-mode sensing system was developed for quantification of captopril (CP) based on Fe/NC NZs and orange-emitting carbon dots (O-CDs). The Fe/NC NZs as an enzyme mimic can efficiently catalyze the 3,3',5,5'-tetramethylbenzidine (TMB) chromogenic reaction, forming blue-colored oxidized TMB product (oxTMB) with the presence of H₂O₂, leading to the fluorescence quenching of O-CDs simultaneously via the inner filter effect (IFE). When CP was present, the blue oxTMB was reduced to colorless TMB, resulting in the inhibition of IFE and the recovery of fluorescence of O-CDs. The fluorescence increase of O-CDs and absorbance decrease of oxTMB depended on CP concentration. Good linear relationships of fluorescence and colorimetric sensing towards CP were obtained in the range from 1 to 50 μM, and the detection limits were 0.47 and 0.56 μM, respectively. Moreover, this as-constructed dual-mode sensor was used to detect CP in pharmaceutical products with satisfactory results.

Potential Environmental and Health Implications from the Scaled-Up Production and Disposal of Nanomaterials Used in Biosensors

Biosensors often combine biological recognition elements with nanomaterials of varying compositions and dimensions to facilitate or enhance the operating mechanism of the device. While incorporating nanomaterials is beneficial to developing high-performance biosensors, at the stages of scale-up and disposal, it may lead to the unmanaged release of toxic nanomaterials. Here we attempt to foster connections between the domains of biosensors development and human and environmental toxicology to encourage a holistic approach to the development and scale-up of biosensors. We begin by exploring the toxicity of nanomaterials commonly used in biosensor design. From our analysis, we introduce five factors with a role in nanotoxicity that should be considered at the biosensor development stages to better manage toxicity. Finally, we contextualize the discussion by presenting the relevant stages and routes of exposure in the biosensor life cycle. Our review found little consensus on how the factors presented govern nanomaterial toxicity, especially in composite and alloyed nanomaterials. To bridge the current gap in understanding and mitigate the risks of uncontrolled nanomaterial release, we advocate for greater collaboration through a precautionary One Health approach to future development and a movement towards a circular approach to biosensor use and disposal.

A Critical Review of Analytical Applications of Chitosan as a Sustainable Chemical with Functions Galore

Biomass and biowastes stand as sustainable and cost-effective environmentally benign alternative feedstock. Chitosan is a biocompatible, bioactive, and biodegradable biopolymer derived from chitin to achieve eight aspects out of the 12 green chemistry principles. Chitosan got significant attention in several fields including chemical analysis, in addition to chemical functionally, which enabled its use as adsorbent and its structural crosslinking using various crosslinkers. The physicochemical, technological, and optical properties of chitosan have been extensively exploited in analysis. Mainly, deacetylation degree and molecular weight are controlling its properties and hence controlling its functions. This review presents a structure, properties, and functions relationships of chitosan. It also aims to provide an overview of the different functions that chitosan can serve in each analytical technique such as supporting matrix, catalyst…etc. The contribution of chitosan in improving the ecological performance is discussed in each technique.

Visible Light-Responsive Sulfone-Based Covalent Organic Framework as Metal-Free Nanoenzyme for Visual Colorimetric Determination of Uranium

Covalent organic framework (COF) has been attracting considerable attention as a novel crystalline material owing to its extended π-electron conjugation and excellent spectral behavior. In this study, we present an imine-linked two-dimensional (2D) crystalline sulfone-based covalent organic framework (TAS-COF) synthesized by 2,4,6-triformylphloroglucinol (Tp) and 3,7-diaminodibenzo[b,d]thiophene (DAS) via a Schiff base condensation reaction. The benzothiophene sulfone endows the as-synthesized TAS-COF with excellent oxidase-like activity under visible light irradiation, ascribed to the generation of superoxide radicals (O2•−) by photo-generated electron transfer. TAS-COF can efficiently oxidase the colorless substrate 3,3′,5,5′-tetramethylbenzydine (TMB) into blue oxidized TMB (oxTMB) when exposed to visible light, and the presence of uranium (UO22+) leads to clear color fading due to the coordination between the imine of oxTMB and UO22+. A colorimetric strategy is thus developed for UO22+ determination with a detection limit of 0.07 μmol L−1. Moreover, a paper-based visual sensing platform is also constructed to offer simple and fast UO22+ content evaluation in water samples. The present study not only provides a promising strategy to prepare visible light-triggered COF-based metal-free nanoenzymes but also extends the applications of COF material in radionuclide detection.

Microwave-Assisted Green Synthesis of Carbon Quantum Dots Derived from Calotropis Gigantea as a Fluorescent Probe for Bioimaging

An eco-friendly, cost-effective, and convenient approach for synthesizing biocompatible fluorescent carbon quantum dots (CQDs) from the leaf extract of the medicinal plant Calotropis gigantea, commonly known as crown flower, has been demonstrated in this work. Fluorescence quantum yields of up to 4.24 percent were observed in as-synthesized CQDs. The size distribution of the as-synthesized CQDs varied from 2.7 to 10.4 nm, with a significant proportion of sp² and sp³ carbon groups verified by nuclear magnetic resonance analysis. The zeta potential of as-synthesized CQDs was measured to be -13.8 mV, indicating the existence of a negatively charged surface with incipient instability in aqueous suspension. Furthermore, as an alternative to organic or synthetic dyes, the development of simple, inexpensive, and non-destructive fluorescence-based staining agents are highly desired. In this regard, as-synthesized CQDs have shown remarkable fluorescent staining capabilities in this work and might be utilised as a suitable probe for optical and bio-imaging of bacteria, fungi, and plant cells.

Gold-Platinum Nanoparticles with Core-Shell Configuration as Efficient Oxidase-like Nanosensors for Glutathione Detection

Nanozymes, defined as nanomaterials that can mimic the catalytic activity of natural enzymes, have been widely used to develop analytical tools for biosensing. In this regard, the monitoring of glutathione (GSH), a key antioxidant biomolecule intervening in the regulation of the oxidative stress level of cells or related with Parkinson's or mitochondrial diseases can be of great interest from the biomedical point of view. In this work, we have synthetized a gold-platinum Au@Pt nanoparticle with core-shell configuration exhibiting a remarkable oxidase-like mimicking activity towards the substrates 3,3',5,5'-tetramethylbenzidine (TMB) and o-phenylenediamine (OPD). The presence of a thiol group (-SH) in the chemical structure of GSH can bind to the Au@Pt nanozyme surface to hamper the activation of O2 and reducing its oxidase-like activity as a function of the concentration of GSH. Herein, we exploit the loss of activity to develop an analytical methodology able to detect and quantify GSH up to µM levels. The system composed by Au@Pt and TMB demonstrates a good linear range between 0.1-1.0 µM to detect GSH levels with a limit of detection (LoD) of 34 nM.

Exploration of nanozymes in viral diagnosis and therapy

Nanozymes are nanomaterials with similar catalytic activities to natural enzymes. Compared with natural enzymes, they have numerous advantages, including higher physiochemical stability, versatility, and suitability for mass production. In the past decade, the synthesis of nanozymes and their catalytic mechanisms have advanced beyond the simple replacement of natural enzymes, allowing for fascinating applications in various fields such as biosensing and disease treatment. In particular, the exploration of nanozymes as powerful toolkits in diagnostic viral testing and antiviral therapy has attracted growing attention. It can address the great challenges faced by current natural enzyme-based viral testing technologies, such as high cost and storage difficulties. Therefore, nanozyme can provide a novel nanozyme-based antiviral therapeutic regime with broader availability and generalizability that are keys to fighting a pandemic such as COVID-19. Herein, we provide a timely review of the state-of-the-art nanozymes regarding their catalytic activities, as well as a focused discussion on recent research into the use of nanozymes in viral testing and therapy. The remaining challenges and future perspectives will also be outlined. Ultimately, this review will inform readers of the current knowledge of nanozymes and inspire more innovative studies to push forward the frontier of this field.

Biocompatibility of Platinum Nanoparticles in Brain ex vivo Models in Physiological and Pathological Conditions

Platinum nanoparticles (PtNPs) have unique physico-chemical properties that led to their use in many branches of medicine. Recently, PtNPs gathered growing interest as delivery vectors for drugs, biosensors and as surface coating on chronically implanted biomedical devices for improving electrochemical properties. However, there are contradictory statements about their biocompatibility and impact on target organs such as the brain tissue, where these NPs are finding many applications. Furthermore, many of the reported studies are conducted in homeostasis conditions and, consequently, neglect the impact of the pathologic conditions on the tissue response. To expand our knowledge on the effects of PtNPs on neuronal and glial cells, we investigated the acute effects of monodisperse sodium citrate-coated PtNPs on rat organotypic hippocampal cultures in physiological or neuronal excitotoxic conditions induced by kainic acid (KA). The cellular responses of the PtNPs were evaluated through cytotoxic assays and confocal microscopy analysis. To mimic a pathologic scenario, 7-day organotypic hippocampal cultures were exposed to KA for 24 h. Subsequently, PtNPs were added to each slice. We show that incubation of the slices with PtNPs for 24 h, does not severely impact cell viability in normal conditions, with no significant differences when comparing the dentate gyrus (DG), as well as CA3 and CA1 pyramidal cell layers. Such effects are not exacerbated in KA-treated slices, where the presence of PtNPs does not cause additional neuronal propidium iodide (PI) uptake in CA3 and CA1 pyramidal cell layers. However, PtNPs cause microglial cell activation and morphological alterations in CA3 and DG regions indicating the establishment of an inflammatory reaction. Morphological analysis revealed that microglia acquire activated ameboid morphology with loss of ramifications, as a result of their response to PtNPs contact. Surprisingly, this effect is not increased in pathological conditions. Taken together, these results show that PtNPs cause microglia alterations in short-term studies. Additionally, there is no worsening of the tissue response in a neuropathological induced scenario. This work highlights the need of further research to allow for the safe use of PtNPs. Also, it supports the demand of the development of novel and more biocompatible NPs to be applied in the brain.

Sensitive electrochemical biosensor for Uracil-DNA glycosylase detection based on self-linkable hollow Mn/Ni layered doubled hydroxides as oxidase-like nanozyme for cascade signal amplification

Nanozymes have been widely used in biosensors instead of natural enzymes because of low cost, high stability and ease of storage. However, few works use oxidase-like nanozymes to fabricate electrochemical biosensors. Herein, we proposed a sensitive electrochemical biosensor to detect uracil-DNA glycosylase (UDG) based on the hollow Mn/Ni layered doubled hydroxides (h-Mn/Ni LDHs) as oxidase-like nanozyme. Briefly, the h-Mn/Ni LDHs, which was prepared by a facile hydrothermal method, exhibited excellent oxidase-like activity because the hollow structure provided rich active sites and high specific surface area. Then, the signal probes were constructed by assembling the hairpin DNA (hDNA), single DNA1 and DNA2 on the h-Mn/Ni LDHs, respectively. In the presence of UDG, the uracil bases in the stem of hDNA were specifically excised, generating apyrimidinic (AP) sites and inducing the unwinding of the hDNA. Afterwards, the h-Mn/Ni LDHs@Au-hDNA/DNA1 was connected on the electrode via hybridization between unwinded hDNA and capture DNA (cDNA). Subsequently, the self-linking process allowed the retention of numerous h-Mn/Ni LDHs through simple DNA hybridization to amplify the signal of o-phenylenediamine (o-PD). Unlike many peroxidase-like nanozyme-based electrochemical biosensors, there is no need to add H₂O₂ during the experimental process, which effectively reduced the background signal as well as improved the stability of the biosensor. As expected, the biosensor exhibited excellent performance with a wide linear range and a low detection limit. This work highlights an appealing opportunity to develop a no H₂O₂ platform based on h-Mn/Ni LDHs for future application in biological analysis and clinical diagnosis.

Colorimetric and Fluorescent Dual-Modality Sensing Platform Based on Fluorescent Nanozyme

Compared with natural enzymes, nanozymes based on carbonaceous nanomaterials are advantages due to high stability, good biocompatibility, and the possibility of multifunctionalities through materials engineering at an atomic level. Herein, we present a sensing platform using a nitrogen-doped graphene quantum dot (NGQD) as a highly efficient fluorescent peroxidase mimic, which enables a colorimetric/fluorescent dual-modality platform for detection of hydrogen peroxide (H₂O₂) and biomolecules (ascorbic acid-AA, acid phosphatase-ACP) with high sensitivity. NGQD is synthesized using a simple hydrothermal process, which has advantages of high production yield and potential for large-scale preparation. NGQD with uniform size (3.0 ± 0.6 nm) and a single-layer graphene structure exhibits bright and stable fluorescence. N-doping and ultrasmall size endow NGQD with high peroxidase-mimicking activity with an obviously reduced Michaelis–Menten constant (K_m) in comparison with natural horseradish peroxidase. Taking advantages of both high nanozyme activity and unique fluorescence property of NGQD, a colorimetric and fluorescent dual-modality platform capable of detecting H₂O₂ and biomolecules (AA, ACP) with high sensitivity is developed as the proof-of-concept demonstration. Furthermore, the mechanisms underlying the nanozyme activity and biosensing are investigated.

Precise Subcellular Organelle Targeting for Boosting Endogenous-Stimuli-Mediated Tumor Therapy

Though numerous external-stimuli-triggered tumor therapies, including phototherapy, radiotherapy, and sonodynamic therapy have made great progress in cancer therapy, the low penetration depth of the laser, safety concerns of radiation, the therapeutic resistance, and the spatio-temporal constraints of the specific equipment restrict their convenient clinical applications. What is more, the inherent physiological barriers of the tumor microenvironment (TME), including hypoxia, heterogeneity, and high expression of antioxidant molecules also restrict the efficiency of tumor therapy. As a result, the development of nanoplatforms responsive to endogenous stimuli (such as glucose, acidic pH, cellular redox events, and etc.) has attracted great attention for starvation therapy, ion therapy, prodrug-mediated chemotherapy, or enzyme-catalyzed therapy. In addition, nanomedicines can be modified by some targeted units for precisely locating in subcellular organelles and boosting the destroying of tumor tissue, decreasing the dosage of nanoagents, reducing side effects, and enhancing the therapeutic efficiency. Herein, the properties of the TME, the advantages of endogenous stimuli, and the principles of subcellular-organelle-targeted strategies will be emphasized. Some necessary considerations for the exploitation of precision medicine and clinical translation of multifunctional nanomedicines in the future are also pointed out.

Ultrafine platinum nanoparticles confined in a covalent organic framework for enhanced enzyme-mimetic and electrocatalytic performances

Uniformly dispersed ultrafine platinum nanoparticles confined in a covalent organic framework (Pt/COF) have been designed and synthesized, which exhibit good catalytic activities in both enzyme-like and electrocatalytic catalysis. Benefiting from the space-confinement effect of pores in the COF matrix, the size of in situ grown Pt nanoparticles is as small as 2.44 nm with a narrow size distribution. Owing to the structure superiority, the Pt/COF catalyst exhibits much better peroxidase/oxidase-like activity than unsupported Pt nanoparticles and a physical mixture of the two components. Based on the inhibition of catalytic oxidation of the peroxidase substrate by Pt/COF, a sensitive colorimetric method is established for tannic acid sensing. Furthermore, the Pt/COF catalyst also exhibits better electrocatalytic activity and stability than commercial Pt/C catalyst towards the methanol oxidation reaction (MOR). This work demonstrates the promising application potential of COF-supported materials in both enzyme-mimetic and electrocatalytic catalysis.

Biosynthesis of Smaller-Sized Platinum Nanoparticles Using the Leaf Extract of Combretum erythrophyllum and Its Antibacterial Activities

Nanobiotechnology is a promising field in the development of safe antibiotics to combat the increasing trend of antibiotic resistance. Nature is a vast reservoir for green materials used in the synthesis of non-toxic and environmentally friendly nano-antibiotics. We present for the first time a facile, green, cost-effective, plant-mediated synthesis of platinum nanoparticles (PtNPs) using the extract of Combretum erythrophyllum (CE) plant leaves. The extract of CE served as both a bio-reductant and a stabilizing agent. The as-synthesized PtNPs were characterized using ultraviolet-visible (UV-Vis) absorption spectroscopy, high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and dynamic light scattering (DLS) techniques. The HR-TEM image confirmed that the PtNPs are ultrasmall, spherical, and well dispersed with an average particle diameter of 1.04 ± 0.26 nm. The PtNPs showed strong antibacterial activities against pathogenic Gram-positive Staphylococcus epidermidis (ATCC 14990) at a minimum inhibitory concentration (MIC) of 3.125 µg/mL and Gram-negative Klebsiella oxytoca (ATCC 8724) and Klebsiella aerogenes (ATCC 27853) at an MIC value of 1.56 µg/mL. The CE-stabilized PtNPs was mostly effective in Klebsiella species that are causative organisms in nosocomial infections.

Three-dimensional MoS2 nanoflowers supported Prussian blue and Au nanoparticles: A peroxidase-mimicking catalyst for the colorimetric detection of hydrogen peroxide and glucose

Well-dispersed Prussian blue (PB) and Au nanoparticles (Au NPs) loaded three dimensional MoS₂ nanoflowers (PB-Au@MoS₂ NFs) was synthesized by a simple and economical method. The structure, morphology and composition of the hybrid were characterized by XRD, SEM and EDS. Similar to the reported literature, MoS₂ nanoflowers showed peroxidase-like activity in catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). This peroxidase-mimicking activity could be enhanced with the introduction of PB and Au NPs. Herein, PB-Au@MoS₂ NFs could be used to establish a new platform for the determination of H₂O₂ and glucose by the chromogenic reaction. Wide linear ranges with 0-15 μM and 0-120 μM for H₂O₂ and glucose detection were finally obtained. The detection limits were as low as 0.25 μM and 3 μM (with signal to noise ratio of 3), respectively. The established platform was also used successfully for the determination of glucose in human serum and fruit juice samples with excellent sensitivity and stability.

Protein-Assisted Osmium Nanoclusters with Intrinsic Peroxidase-like Activity and Extrinsic Antifouling Behavior

Extensive studies have laid the groundwork for understanding peroxidase-like nanozymes. However, improvements are still required before their practical applications. On one hand, it is significant to explore highly reactive nanozymes. On the other hand, it is necessary to avoid fouling formed on the surface of nanozymes, which will affect their activity and the results of H₂O₂ sensors or H₂O₂-related applications. Herein, a strategy is reported to design osmium nanoclusters (Os NCs) with the existence of bovine serum albumin (BSA) through biomineralization. BSA-Os NCs were found to possess intrinsic peroxidase-like activity with a high specific activity (6120 U/g). Studies also found that the catalytic activity of BSA-Os NCs was better than those of reported protein-assisted metal nanozymes (e.g., BSA-Pt NPs and BSA-Au NCs). More significantly, BSA has been confirmed as a protective shell to give Os NCs extrinsic antifouling property in some typical ions (e.g., Hg²⁺, Ag⁺, Pb²⁺, I^-, Cr⁶⁺, Cu²⁺, Ce³⁺, S^2-, etc.), saline (0-2 M), or protein (0-100 mg/mL) conditions. Under optimal conditions, a colorimetric sensor was established to realize a linear range of H₂O₂ from 1.25 to 200 μM with a low detection limit of 300 nM. On this basis, remarkable features enable a BSA-Os NCs-based colorimetric sensor to detect H₂O₂ from complex systems with clear color gradients. Together, this work highlights the advantages of protein-assisted Os nanozymes and provides a paragon for peroxidase-like nanozymes in H₂O₂-related applications.

Nanozymes in Point-of-Care Diagnosis: An Emerging Futuristic Approach for Biosensing

Nanomaterial-based artificial enzymes (or nanozymes) have attracted great attention in the past few years owing to their capability not only to mimic functionality but also to overcome the inherent drawbacks of the natural enzymes. Numerous advantages of nanozymes such as diverse enzyme-mimicking activities, low cost, high stability, robustness, unique surface chemistry, and ease of surface tunability and biocompatibility have allowed their integration in a wide range of biosensing applications. Several metal, metal oxide, metal-organic framework-based nanozymes have been exploited for the development of biosensing systems, which present the potential for point-of-care analysis. To highlight recent progress in the field, in this review, more than 260 research articles are discussed systematically with suitable recent examples, elucidating the role of nanozymes to reinforce, miniaturize, and improve the performance of point-of-care diagnostics addressing the ASSURED (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and deliverable to the end user) criteria formulated by World Health Organization. The review reveals that many biosensing strategies such as electrochemical, colorimetric, fluorescent, and immunological sensors required to achieve the ASSURED standards can be implemented by using enzyme-mimicking activities of nanomaterials as signal producing components. However, basic system functionality is still lacking. Since the enzyme-mimicking properties of the nanomaterials are dictated by their size, shape, composition, surface charge, surface chemistry as well as external parameters such as pH or temperature, these factors play a crucial role in the design and function of nanozyme-based point-of-care diagnostics. Therefore, it requires a deliberate exertion to integrate various parameters for truly ASSURED solutions to be realized. This review also discusses possible limitations and research gaps to provide readers a brief scenario of the emerging role of nanozymes in state-of-the-art POC diagnosis system development for futuristic biosensing applications.

Construction of a Carbon Dots/Cobalt Oxyhydroxide Nanoflakes Biosensing Platform for Detection of Acid Phosphatase

Because abnormal acid phosphatase (ACP) can disrupt the normal physiological processes, determination of ACP level is extremely important for early diagnosis, treatment, and prognostic evaluation of diseases. Herein, a fluorescence platform for monitoring ACP level was established based on the assembly of red-emitting carbon dots (RCDs) on cobalt oxyhydroxide (CoOOH) nanoflakes. RCDs displayed excellent water solubility, pH stability, salt resistance, and photobleaching resistance. Interestingly, the fluorescence of the RCDs assembled on the surface of the CoOOH nanoflakes could be quenched due to the energy transfer caused by the nanoflakes. However, the ascorbic acid (AA) produced by the hydrolysis of ascorbic acid-2-phosphate trisodium salt (AAP) catalyzed by ACP could quickly and effectively reduce CoOOH nanoflakes, leading to the fluorescence recovery of the RCDs. Therefore, an "off-on" biosensor platform for rapid, sensitive, and selective detection of ACP was constructed with a limit of detection of 0.25 mU/L. With the assistance of the biosensor, the level of ACP in human serum samples was evaluated, and the spike recovery values ranged from 94.0% to 104.5%.