Biotemplated Platinum Nanozymes: Synthesis, Catalytic Regulation and Biomedical Applications.

Platinum (Pt) nanozymes with multiple intrinsic enzyme-mimicking activities have attracted extensive attention in biomedical fields due to their high catalytic activity, ease of modification, and convenient storage. However, the Pt nanozymes synthesized by the traditional method often suffer from uncontrollable morphology and poor stability under physicochemical conditions, resulting in unsatisfactory catalytic behavior in practical applications. To optimize the catalytic ability, biological templates have been introduced recently, which can guide the deposition of platinum ions on their surface to form specific morphologies and then stabilize the resulting Pt nanozymes. Given the promising potential of biotemplated Pt nanozymes in practical applications, it is essential to conduct a systematic and comprehensive review to summarize their recent research progress. In this review, we first categorize the biological templates and discussed the mechanisms as well as characteristics of each type of biotemplate in directing the growth of Pt nanozyme. Factors that impact the growth of biotemplated Pt nanozymes are then analyzed, followed by summarizing their biomedical application. Finally, the challenges and opportunities in this field are outlined. This review article aims to provide theoretical guidance for developing Pt nanozymes with robust functionalities in biomedical applications.

Handheld pH meter-assisted immunoassay for C-reactive protein using glucose oxidase-conjugated dendrimer loaded with platinum nanozymes.

A simple and feasible pH meter-based immunoassay is reported for detection of C-reactive protein (CRP) using glucose oxidase (GOD)-conjugated dendrimer loaded with platinum nanozyme. Initially, platinum nanozymes were loaded into the dendrimers through an in situ synthetic method. Then, GOD and monoclonal anti-CRP antibody with a high molar ratio were covalently conjugated onto carboxylated dendrimers via typical carbodiimide coupling. The immunoreaction was carried out with a competitive mode in a CRP-coated microplate. Along with formation of immunocomplex, the added glucose was oxidized into gluconic acid and hydrogen peroxide by GOD, and the latter was further decomposed by platinum nanozyme, thus accelerating chemical reaction in the positive direction. The produced gluconic acid changed the pH of detection solution, which was determined using a handheld pH meter. Under optimum conditions, the pH meter-based immunoassay gave a good signal toward target CRP from 0.01 to 100 ng mL-1. The limit of detection was 5.9 pg mL-1. An intermediate precision ≤ 11.2% was acquired with batch-to-batch identification. No nonspecific adsorption was observed during a series of procedures to detect target CRP, and the cross-reaction against other biomarkers was very low. Importantly, our system gave well-matched results for analysis of human serum samples relative to a referenced ELISA kit.Graphical abstract.

Tumor-Homing Phage Nanofibers for Nanozyme-Enhanced Targeted Breast Cancer Therapy.

Photodynamic therapy (PDT) eliminates cancer cells by converting endogenous oxygen into reactive oxygen species (ROS). However, its efficacy is significantly hindered by hypoxia in solid tumors. Hence, to engineer filamentous fd phage, a human-friendly bacteria-specific virus is proposed, into a nanozyme-nucleating photosensitizer-loaded tumor-homing nanofiber for enhanced production of ROS in a hypoxic tumor. Specifically, Pt-binding and tumor-homing peptides are genetically displayed on the sidewall and tip of the fd phage, respectively. The Pt-binding peptides induced nucleation and orientation of Pt nanozymes (PtNEs) on the sidewall of the phage. The resultant PtNE-coated tumor-homing phage exhibits significantly enhanced sustained catalytic conversion of hydrogen peroxide in hypoxic tumors into O2 for producing ROS needed for PDT, compared to non-phage-templated PtNE. Density functional theory (DFT) calculations verify the catalytic mechanism of the phage-templated PtNE. After intravenous injection of the PtNE-coated indocyanine green (ICG)-loaded tumor-homing phages into breast tumor-bearing mice, the nanofibers home to the tumors and effectively inhibit tumor growth by the PtNE-enhanced PDT. The nanofibers can also serve as a tumor-homing imaging probe due to the fluorescence of ICG. This work demonstrates that filamentous phage, engineered to become tumor-homing nanozyme-nucleating tumor-hypoxia-relieving nanofibers, can act as cancer-targeting nanozymes with improved catalytic performance for effective targeted PDT.

Oxygen-supplying ROS-responsive prodrug for synergistic chemotherapy and photodynamic therapy of colon cancer.

Introduction: The synergistic treatment of chemotherapy and photodynamic therapy (PDT) has remarkable potential in cancer therapy. However, challenges remain, such as unstable chemotherapeutic drug release, suboptimal targeting, and reduced efficacy of PDT under hypoxic conditions commonly found in solid tumors. Methods: To address these issues, we use camptothecin (CPT) and pheophorbide a (Pa) incorporated through the functional thioketal, which serves as the reactive oxygen species (ROS)-responsive trigger, to construct a ROS-responsive prodrug (CPT-TK-Pa). Subsequently, we co-loaded it with a platinum nanozyme (PtNP) in distearylphosphatidylethanolamine-polyethylene glycol (DSPE-PEG) to obtain the ROS-responsive prodrug nanoparticle (CPT-TK-Pa/Pt NP). Results and Discussion: Specifically, the incorporated PtNP within CPT-TK-Pa/Pt NP positively catalyzes the conversion of hydrogen peroxide (H2O2) to oxygen, thereby ameliorating the hypoxic state of the tumor. This enhanced oxygen generation could replenish the oxygen that is consumed by Pa during 660 nm exposure, enabling controlled CPT release and amplifying the photodynamic response. In vitro investigations reveal the potency of CPT-TK-Pa/Pt NPs in inhibiting colon tumor cells. Given its ROS-responsive release mechanism and enhanced PDT efficacy, CPT-TK-Pa/Pt NP has the potential to be a promising candidate for cancer therapy.

RGD peptide modified platinum nanozyme Co-loaded glutathione-responsive prodrug nanoparticles for enhanced chemo-photodynamic bladder cancer therapy.

Bladder cancer is one of the most common malignant tumors in the urinary system worldwide. The poor permeability and uncontrollable release of drug and hypoxia of tumor tissues were the main reasons leading to poor therapeutic effect of chemo-photodynamic therapy for bladder cancer. To solve the above problems, a tumor-targeting peptide Arg-Gly-Asp (RGD) modified platinum nanozyme (PtNP) co-loaded glutathione (GSH)-responsive prodrug nanoparticles (PTX-SS-HPPH/Pt@RGD-NP) was constructed. Firstly, a GSH-responsive prodrug (PTX-SS-HPPH) was prepared by introducing a disulfide bond between paclitaxel (PTX) and photosensitizer 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a (HPPH), which could realize the GSH-responsive release of the drug at the tumor sites. Also, the distearoylphosphoethanolamine-poly (ethylene glycol)-RGD peptide (DSPE-PEG-RGD) modified the prodrug to enhance the targeting and permeability ability to bladder cancer cells. Besides, to alleviate the hypoxia of tumor tissues, PtNP was introduced to produce oxygen (O2) and improve photodynamic therapy efficiency. The results showed that the PTX-SS-HPPH/Pt@RGD-NP could achieve GSH-responsive drug release in tumor microenvironment, enhance the drug accumulation time and permeability at tumor sites in T24 subcutaneous tumor model and T24 orthotopic bladder tumor model, and alleviate hypoxia in tumor tissues, thus realizing enhanced chemo-photodynamic therapy for bladder cancer, and providing new strategies and methods for clinical treatment of bladder cancer.

Power-free colorimetric biosensing of foodborne bacteria in centrifugal tube.

Early finding of pathogens is significant to avoid foodborne diseases. Here, a novel lab-in-centrifugal-tube colorimetric biosensor was reported for Salmonella typhimurium detection using immune nickel nanowires (NNWs) to form capture nets for specific bacterial separation, gold@platinum nanozymes (GPNs) to mark target bacteria for effective signal amplification, and a smartphone App to analyze color change for quantitative bacterial determination. A 3D-printed cylindrical magnetic separator with air pressure self-regulating structure and NNW capture nets was elaboratively constructed and assembled inside the disposable centrifuge tube to simply perform the bacterial separation, label, wash, coloration and detection. Under optimal conditions, Salmonella typhimurium could be quantitatively detected in 2 h with a low detection limit of 21 CFU/mL. The recovery of target bacteria in spiked pork samples ranged from 87.0% to 97.6% with the averaged recovery of 93.9%. This biosensor was Affordable, Sensitive, Specific, User-friendly, Rapid and robust, Equipment-free and Deliverable to end-users (ASSURED), and had shown the potential for point-of-care testing of foodborne pathogens to ensure food safety.

Photoenzymatic Activity of Artificial-Natural Bienzyme Applied in Biodegradation of Methylene Blue and Accelerating Polymerization of Dopamine.

Enzymes as biocatalysts have attracted extensive attention. In addition to immobilizing or encapsulating various enzymes for combating the easy loss of enzymatic activity, strengthening the enzymatic activity upon light irradiation is a challenge. To the best of our knowledge, the work of spatiotemporally modulating the catalytic activity of artificial-natural bienzymes with a near-infrared light irradiation has not been reported. Inspired by immobilized enzymes and nanozymes, herein a platinum nanozyme was synthesized; subsequently, the platinum nanozyme was grafted on the body of laccase, thus successfully obtaining the artificial-natural bienzyme. The three-dimensional structure of the artificial-natural bienzyme was greatly different from that of the immobilized enzyme or the encapsulated enzyme. The platinum nanozyme possessed excellent laccase-like activity, which was 3.7 times higher than that of laccase. Meanwhile, the coordination between the platinum nanozyme and laccase was proved. Besides, the cascaded catalysis of artificial-natural bienzyme was verified with hydrogen peroxide as a mediator. The enzymatic activities of artificial-natural bienzyme with and without near-infrared light irradiation were, respectively, 46.2 and 29.5% higher than that of free laccase. Moreover, the reversible catalytic activity of the coupled enzyme could be manipulated with and without a near-infrared light at 808 nm. As a result, the degradation rates of methylene blue catalyzed by the coupled enzyme and the platinum nanozyme were higher than that of laccase. Furthermore, accelerating polymerization of the dopamine was also demonstrated. Briefly, this facile strategy may provide a universal approach to control the catalytic activity of other natural enzymes.

Sodium Alginate Modified Platinum Nanozymes With Highly Efficient and Robust Oxidase-Like Activity for Antioxidant Capacity and Analysis of Proanthocyanidins.

Platinum nanozymes exhibiting highly efficient and robust oxidase-like activity are successfully synthesized and modified using sodium alginate (SA-PtNPs). According to a steady-state dynamic assay, Michaelis-Menton constant (K m ) is calculated as 11.6 µM, indicating that the affinity of SA-PtNPs toward the substrate, 3, 3', 5, 5'-tetramethylbenzidine (TMB), is high. It shows in the paper that SA-PtNPs exhibit a significant oxidant effect on substrate-O2 to produce O 2 • - as an oxidase mimic. Moreover, the oxidase-like activity fluctuated slightly under changes in environmental pH and incubation time, implying that SA can increase the dispersibility and stability of PtNPs. A colorimetric assay for oligomeric proanthocyanidins (OPC) was realized given how few explorations of the former there are. We found that the significant inhibitory effect of OPC on the oxidase-like activity is due to the competitive effect between OPC and TMB for binding to the active site of SA-PtNPs, resulting in a color change. Under optimal conditions, the logarithmic value of the chromogenic difference (ΔA450nm) to OPC concentration was linear (4-32.5 µM, r = 0.999) with a limit of detection (LOD) of 2.0 µM. The antioxidant capacity of OPC obtained by the Soxhlet extraction method from grape seeds was 2.85 U/mg. The recovery from the experiment in which OPC was added to grape seeds ranged from 97.0 to 98.6% (RSDs of 0.5-3.4%), suggesting a high accuracy in OPC detection. These findings are important because OPC is an internationally recognized antioxidant that eliminates free radicals in the human body and, therefore, may prevent a variety of diseases. Thus, we envisage that this Pt nanozyme-based assay may be prevalent for antioxidant capacity evaluation and analytical applications.

Platinum Nanozyme-Triggered Pressure-Based Immunoassay Using a Three-Dimensional Polypyrrole Foam-Based Flexible Pressure Sensor.

This work describes a novel and portable pressure-based point-of-care (POC) testing strategy for the sensitive and rapid detection of carcinoembryonic antigen (CEA) via a flexible pressure sensor constructed by three-dimensional (3D) polypyrrole (PPy) foam. Initially, platinum nanoparticles (PtNPs) were conjugated to the detection antibodies, which were used to form sandwich-type immunocomplexes with targets and capture antibodies in the reaction cell. Then, the carried PtNPs catalyzed the dissociation of hydrogen peroxide (H2O2) for the generation of oxygen (O2) in a sealed device, translating the biomolecule recognition event into gas pressure. With the increase of pressure, a flexible pressure sensor with 3D polypyrrole foam as the sensing layer was used to sensitively monitor the pressure variations in this system. Thus, the concentration of the target could be quantitatively determined by the pressure response. Under optimal conditions, the pressure-based immunosensor showed good sensing performance for CEA in the dynamic working range from 0.2 to 60 ng/mL with a detection limit of 0.13 ng/mL. The reproducibility, specificity, and accuracy compared with commercial enzyme-linked immunosorbent assay (ELISA) kit were also acceptable. Therefore, this work provides a promising approach for developing portable and sensitive POC testing in the future.

Platinum nanozyme-encapsulated poly(amidoamine) dendrimer for voltammetric immunoassay of pro-gastrin-releasing peptide.

An innovative electrochemical immunosensing platform was designed for the sensitive monitoring of lung cancer biomarker (pro-gastrin-releasing peptide; ProGRP) by using platinum nanoparticles encapsulated inside dendrimers (PtDEN) as enzymatic mimics for the signal amplification. PtDEN nanocomposites were prepared through a simple chemical reduction method with the assistance of NaBH4. Thereafter, PtDEN-labeled anti-ProGRP secondary antibody was launched for the detection of target analyte with a sandwich-type assay format on anti-ProGRP capture antibody-modified screen-printed carbon electrode. Accompanying formation of immunocomplex, the labeled PtDENs electrochemically oxidized 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide to produce a well-defined voltammetric signal within the applied potentials. Thanks to the high-efficient catalytic efficiency of platinum nanoparticles and high-loading ability of dendrimer, improved analytical features were acquired with PtDENs relative to platinum nanoparticles alone. Using PtDENs labeling strategy, the properties and factors influencing the analytical performance of electrochemical immunosensor were studied in detail. The strong bioconjugation of antibodies with the PtDENs caused a good repeatability and intermediate precision down to 7.64%. Under optimum conditions, the electrochemical immunosensor exhibited a dynamic linear range of 0.001-10 ng mL-1 ProGRP with a detection limit of 0.86 pg mL-1. Good selectivity and relatively long-term stability (>6 months) were achieved for target ProGRP. Significantly, the acceptable accuracy was gotten for analysis of ProGRP in human serum specimens referring to commercially available human ProGRP enzyme-linked immunosorbent assay (ELISA) method.