Functionalized ultra-fine bimetallic PtRu alloy nanoparticle with high peroxidase-mimicking activity for rapid and sensitive colorimetric quantification of C-reactive protein

Nitric oxide-triggering activity of gold-, platinum- and cerium oxide-nanozymes from S-nitrosothiols and diazeniumdiolates

Cardiovascular diseases pose a significant global health challenge, contributing to high mortality rates and impacting overall well-being and quality of life. Nitric oxide (NO) plays a pivotal role as a vasodilator, regulating blood pressure and enhancing blood flow-crucial elements in preventing cardiovascular diseases, making it a prime therapeutic target. Herein, metal-based nanozymes (NZs) designed to induce NO release from both endogenous and exogenous NO-donors are investigated. Successful synthesis of gold, platinum (Pt) and cerium oxide NZs is achieved, with all three NZs demonstrating the ability to catalyze the NO release from various NO sources, namely S-nitrosothiols and diazeniumdiolates. Pt-NZs exhibit the strongest performance among the three NZ types. Further exploration involved investigating encapsulation and coating techniques using poly(lactic-co-glycolic acid) nanoparticles as experimental carriers for Pt-NZs. Both strategies showed efficiency in serving as platforms for Pt-NZs, successfully showing the ability to trigger NO release.

A rapid and facile immunoassay for C-reactive protein using PDMS-based digital magnetofluidics

BACKGROUND

C-reactive protein has been reported as a biomarker of inflammation caused by acute injury, infection or tissue damage and also a prediction marker of cardiovascular diseases. Commonly, the gold standard for the detection of CRP is enzyme-linked immunosorbent assays (ELISAs). Normally, traditional immunoassays in multiwell plates typically suffer from prolonged assay time due to slow mass transport controlled by diffusion. Herein, a PDMS based magnetofluidic approach has been applied for a rapid and facile immunoassay using a sandwich enzyme-linked immunosorbent assay (ELISA) for the analysis of CRP.

RESULTS

Due to the superhydrophobic PDMS, droplets of reagent and sample solutions were obtained when pipetting all solutions onto the PDMS substrate. These droplets were individually controlled by an external magnet to perform the assays. Magnetic beads immobilized with a capture antibody were not only used for immunomagnetic separation (IMS) of the captured CRP from the sample matrix, but also used as a carrier for droplet movement on the magnetofluidic device, expediting the immunoassay procedure, especially washing steps. The immunoassay of CRP was successfully performed within 1 h with a limit of detection of 0.015 mg L-1 in the concentration range of 0.1-10 mg L-1. The recovery percentages of CRP spiked in human serum were found in the range of 90-114 % with %RSD of less than 5 %, indicating acceptable accuracy and precision.

SIGNIFICANCE

By individually controlling the droplet movement using an external magnet, all steps of immunoassays were simply and rapidly performed. In addition, the microfluidic format allows for small volumes of reagents and samples and rapid assay kinetics. Therefore, the proposed magnetofluidic approach has shown its potential of becoming a rapid, facile and cost-effective method to perform traditional immunoassays in a variety of applications. In addition, the proposed approach is also particularly well-suited for analyses/reactions with multiple steps.

Fast Reaction of the Prussian Blue Based Nanozyme "Artificial Peroxidase" with the Substrates: Pre-Steady-State Kinetic Approach

This letter introduces the pre-steady-state kinetic approach, which is traditional for evaluation of elementary constants in molecular (enzyme) catalysis, for nanozymes. Apparently, the most active peroxidase-mimicking nanozyme based on catalytically synthesized Prussian Blue nanoparticles has been chosen. The elementary constants (k1) for the nanozymes' reduction by an electron-donor substrate (being the fastest stage according to steady-state kinetic data) have been determined by means of stopped-flow spectroscopy. These constants have been found to be dependent on both the size of the nanozyme and the reducing substrate redox potential. For the smallest nanozymes (32 nm in diameter), log(k1) linearly decays with an increase of the substrate redox potential (cotangent value ≈125 mV). On the contrary, for the largest nanozymes with a diameter above 150 nm, k1 is almost independent of it. Moreover, for the substrate with the lowest redox potential (K4[Fe(CN)6]), the rate constant under discussion (k1) is almost independent of the nanozymes' size. Perhaps, the rate of the intrananozyme electron transfer causing bleaching becomes comparative or even lower than that of the nanoparticle interaction with the fastest substrate. Anyway, the elementary constant of nanozyme reduction with potassium ferrocyanide (k1) reaches the value of 1 × 1010 M-1 s-1, which is 3-4 orders of magnitude faster than for enzymes peroxidases. The obtained results obviously demonstrate that the pre-steady-state kinetic approach is able to discover novel advantages of nanozymes from both fundamental and practical points of view.

Ratiometric electrochemical immunosensor for simultaneous detection of C-myc and Bcl-2 based on multi-role alloy composites

A ratiometric electrochemical immunosensor is proposed for simultaneous detection of cellular-myelocytomatosis oncoprotein (C-myc) and B-cell lymphoma 2 (Bcl-2) via the potential-resolved strategy. It relied on multi-role co-loaded alloy composites (CLACs) and poly(3,4-ethylenedioxythiophene) (PEDOT)-graphene oxide (GO)-multiwalled carbon nanotubes (MWCNTs) (PGM) modified electrodes. CLACs with good catalytic and enzyme-like properties were synthesized in one step by loading tetramethylbenzidine (TMB) or methylene blue (MB) into Pt-Pd alloy and used as label materials. After immunological reactions, CLACs showed distinguishable dual differential pulse voltammetry signals at  - 0.26 V and 0.38 V, corresponding to C-myc and Bcl-2, and the PGM had an electrochemical signal at 1.2 V, which could be used as a reference signal to construct a ratiometric sensor. CLACs had a satisfactory synergistic effect with the PGM, and eventually achieved quadruple signal amplification. Thus, benefiting from multiple magnification and ratiometric self-calibration functions, sensitive detections of C-myc and Bcl-2 were achieved, with detection limits as low as 0.5 and 2.5 pg mL-1, respectively. Additionally, when the designed method was applied to blood samples from lymphoma patients, results consistent with the ELISA kit were obtained. This will open avenues for constructing multiple protein detection sensors.

Au-X (X=Pt/Ru)-decorated magnetic nanocubes as bifunctional nanozyme labels in colorimetric, magnetically-enhanced, one-step sandwich CRP immunoassay

Scientific interest in the investigation and application of multifunctional nanomaterials in medical diagnostics has been increasing. The employment of magnetocatalytic immunoconjugates as both analyte-capturing agents and enzyme-like catalytic labels may enable rapid preconcentration and determination of relevant antigens. In this work, we synthesized and comprehensively characterized two types of noble metal-decorated magnetic nanocubes (MDMCs) which were subsequently applied in the one-step, sandwich nanozyme-linked immunosorbent assay (NLISA). Magnetic cores allow for rapid separation from complex samples of biological origin. The catalytically active shell composed of Au-decorated Pt or Ru can effectively mimic the activity of horseradish peroxididase, retaining at the same time the ability to form stable bioconstructs through self-assembly of thiolated ligands. As a result, hybrid multifunctional nanoparticles were synthesized and used to detect C-reactive protein (CRP) in serum samples. We have also paid considerable attention to the mechanistic studies of the formation of sandwich immunocomplexes with nanoparticle labels by means of immunoenzymatic methods and surface plasmon resonance. Analytical parameters of the Pt-MDMCs-labeled NLISA (detection limit LOD = 0.336 ng mL-1, recovery = 98.0%, linear response window covering two logarithmic units) turned out to be superior to the classical, one-step ELISA based on a horseradish peroxidase. In addition, our method offers further possibility of sensitivity adjustment by changing the parameters of magnetic preconcentration, together with good long-term stability of MDMCs conjugates and their good resistance to common interferences. We believe that the proposed simple synthetic protocol will guide a new approach to applying metal-decorated magnetic nanozymes as versatile and multifunctional labels for application in subsequent pre-analytical analyte concentration and immunoassays towards clinical applications.

Determination of lysophosphatidylcholine using peroxidase-mimic PVP/PtRu nanozyme

Lysophosphatidylcholine (LPC) can be used as a biomarker for diseases such as cancer, diabetes, atherosclerosis, and sepsis. In this study, we demonstrated the ability of nanozymes to displace the natural derived enzyme in enzyme-based assays for the measurement of LPC. Synthesized polyvinylpyrrolidone-stabilized platinum-ruthenium nanozymes (PVP/PtRu NZs) had a uniform size of 2.48 ± 0.24 nm and superb peroxidase-mimicking activity. We demonstrated that the nanozymes had high activity over a wide pH and temperature range and high stability after long-term storage. The LPC concentration could be accurately analyzed through the absorbance and fluorescence signals generated by the peroxidation reaction using the synthesized nanozyme with substrates such as 3,3',5,5'-tetramethylbenzidine (TMB) and 10-acetyl-3,7-dihydroxyphenoxazine (Ampliflu™ Red). LPC at a concentration of 0-400 µM was used for the analysis, and the coefficient of determination (R²) was 0.977, and the limit of detection (LOD) was 23.1 µM by colorimetric assay. In the fluorometric assay, the R² was 0.999, and the LOD was 8.97 µM. The spiked recovery values for the determination of LPC concentration in human serum samples were 102-115%. Based on these results, we declared that PVP/PtRu NZs had an ability comparable to that of the native enzyme horseradish peroxidase (HRP) in the enzyme-based LPC detection method.

Mesoporous platinum nanoparticles as a peroxidase mimic for the highly sensitive determination of C-reactive protein

The generation of a mesoporous structure in platinum nanoparticles can effectively enhance physical and chemical properties. In this study, mesoporous platinum nanoparticles (MPNs) were synthesized by a soft template-mediated one-pot chemical method. To develop a mesoporous structure, Pluronic F-127 was employed. The Pluronic F-127 surfactant forms self-assembled micelles, and the micelles act as the pore-directing agents in the synthesis of nanoparticles. Scanning electron microscopy results revealed that the MPN had a uniform size of 70 nm on average and a distinct mesoporous structure. The development of a concave mesoporous structure on the surface of the MPNs can increase the surface area and facilitate the efficient transport of reactants. The synthesized MPNs exhibited peroxidase-like activity. Furthermore, the MPNs showed excellent catalytic efficiency compared to HRP, due to the high surface area derived from the presence of the mesoporous structure. The peroxidase-like MPNs were applied to the enzyme-linked immunosorbent assay (ELISA) of C-reactive protein (CRP). The MPN-based ELISA exhibited sensitive CRP detection in the range from 0.24 to 7.8 ng/mL with a detection limit of 0.13 ng/mL. Moreover, the recoveries of the CRP concentrations in spiked human serum were 98.6% and 102%. These results demonstrate that as a peroxidase mimic, the MPNs can replace the natural enzymes in conventional ELISA for sensitive CRP detection.

Recent advances in nanomaterials-based optical sensors for detection of various biomarkers (inorganic species, organic and biomolecules)

This review briefly emphasizes the different detection approaches (electrochemical sensors, chemiluminescence, surface-enhanced Raman scattering), functional nanostructure materials (quantum dots, metal nanoparticles, metal nanoclusters, magnetic nanomaterials, metal oxide nanoparticles, polymer-based nanomaterials, and carbonaceous nanomaterials) and detection mechanisms. Further, this review emphasis on the integration of functional nanomaterials with optical spectroscopic techniques for the identification of various biomarkers (nucleic acids, glucose, uric acid, oxytocin, dopamine, ascorbic acid, bilirubin, spermine, serotonin, thiocyanate, Pb²⁺ , Cu²⁺ , Hg²⁺ , F^- , peptides, and cancer biomarkers (mucin 1, prostate specific antigen, carcinoembryonic antigen, CA15-3, human epidermal growth factor receptor 2, C-reactive protein, and interleukin-6). Analytical characteristics of nanomaterials-based optical sensors are summarized in Tables, providing the insights of nanomaterials-based optical sensors for biomarkers detection. Finally, the opportunities and challenges of nanomaterials-based optical analytical approaches for the detection of various biomarkers (inorganic, organic, biomolecules, peptides and proteins) are discussed.

Prussian blue: from advanced electrocatalyst to nanozymes defeating natural enzyme

The pathway from the advanced electrocatalyst to nanozymes defeating natural enzyme is reviewed. Prussian blue, being the most advantageous electrocatalyst for hydrogen peroxide reduction, is obviously the best candidate for mimicking peroxidase activity. Indeed, catalytically synthesized Prussian blue nanoparticles are characterized by the catalytic rate constants, which are significantly (up to 4 orders of magnitude) higher than for enzyme peroxidase. Displaying in addition the enzymatic specificity in terms of an absence of oxidase-like activity, catalytically synthesized Prussian blue nanoparticles can be referred to as nanozymes. The latter provide the most versatile method for surface covering with the electrocatalyst, allowing to modify non-traditional materials like boron-doped diamond. For stabilization, Prussian blue core can be covered with nickel hexacyanoferrate shell; the resulting core-shell nanozymes still defeat natural enzyme in terms of activity. Discovering the catalytic pathway of nanozymes "artificial peroxidase" action, we have found the novel advantage of nanozymes over the corresponding biological catalysts: their dramatically (100 times) improved bimolecular rate constants.

Maximizing the peroxidase-like activity of Pd@PtxRu4-x nanocubes by precisely controlling the shell thickness and their application in colorimetric biosensors

Although the application of nanoscale artificial enzymes in various industries is an attractive way to circumvent the intrinsic drawbacks of natural enzymes, their catalytic constant (K_cat) as a critical reaction parameter is far from satisfactory. Presented here is the rational design and fabrication of a unique peroxidase mimic catalyst based upon Pd@Pt_xRu_4-x (1 ≤ x ≤ 3) prepared by coating PtRu alloy as conformal, ultrathin shells on Pd nanocrystals. Benefiting from an optimal Pt/Ru ratio and well-defined {100} facets, together with confining the Pt-Ru alloy to a shell of averagely 3.3-atomic-layer thick (i.e. Pd@Pt-Ru_3.3L), the nanocrystals exhibit the highest catalytic activity and kinetics (1.2 × 10⁶ s^-1), resulting in a significant increase of catalytic activity compared with the classical PtRu nanozyme (3.6 × 10³ s^-1) and horseradish peroxidase (4.0 × 10³ s^-1), respectively. The following density functional theory calculations demonstrate that the origin of the superior catalytic performance could be attributed to the modulation of the adsorption behavior of the key reaction intermediates on the surface. As a proof of concept, its peroxidase mimicking ability is adopted for sensing glucose and glutathione molecules in human serum, with a long linear range and high selectivity. This work opens new horizons for the future development of advanced catalysts based upon alloy nanocrystals for various applications.

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.

Biomimetic -mineralized multifunctional nanoflowers for anodic-stripping voltammetric immunoassay of rehabilitation-related proteins

C-reactive proteins (CRPs; an acute-phase protein) in patients with initial acute cerebral infarction neurological rehabilitation prediction have a significant correlation. In this work, a simple and sensitive anodic-stripping voltammetric (ASV) immunosensing system was innovatively designed for the quantitative screening of target CRPs using biomimetic-mineralized bifunctional antibody-Cu₃(PO₄)₂ nanoflowers as molecular tags. In this system, a monoclonal anti-CRP antibody-anchored microtiter plate was utilized to specifically capture target CRPs from the sample. For detection, a sandwiched immunoreaction mode was employed with the antibody-Cu₃(PO₄)₂ nanoflowers in the presence of analytes. Subsequent ASV measurement of copper ions (Cu²⁺) released under acidic conditions from the bifunctional nanoflowers was conducted at an in situ prepared mercury film electrode. The introduction of hybrid nanoflowers greatly increased the loading amount of copper ions on the molecular tag, thereby amplifying the detectable signal of electrochemical immunoassay. Meanwhile, factors influencing the analytical properties of the electrochemical immunoassay were investigated in detail. By combining the high-efficiency nanohybrids with signal amplification, the dynamic concentration range of electrochemical immunoassay spanned from 0.01 ng mL^-1 to 100 ng mL^-1 toward the target CRP. The limit of detection was calculated to be 0.0079 ng mL^-1 at 3S_blank criterion. Intra- and interassay imprecisions (relative standard deviations: RSDs) were less than or equal to 6.72%. Good anti-interference ability, long-term storage stability, and acceptable accuracy for the evaluation of human serum specimens were observed during a series of procedures to determine the target protein. In addition, the bifunctional nanoflower-based immunosensing system offers promise for the simple, cost-effective analysis of disease-related proteins.