Protein-Templated Controllable Noble Metal Nanoparticles Synthesis And Biomimetic Peroxidase Activities Study

Manufactured nanostructures that mimic enzymes are of great interest as they potentially have improved properties relative to native enzymes, such as greater resistance to extremes of pH and temperature and lower sensitivity to proteases. Several nanostructures that possess catalytic activities have been discovered. Examples include peroxidase-like activity of ferromagnetic nanoparticles, superoxide dismutase mimetic properties of ceria nanoparticles and hydrogenation catalyzing activities of ferritin encapsulated palladium nanoparticles. Such synthetic enzymes have potential applications in various fields, including biomedicine, energy storage and bioremediation.Ferritins are a well-studied family of proteins that play an important role in iron storage. They comprise 24 subunits that assemble into a hollow nanocage with an external diameter of 12 nm in diameter and an 8 nm diameter cavity. Physiologically, iron is stored within the protein shell in a compact mineral form and one protein shell can accommodate up to 4500 atoms of iron. The channels formed at the subunit junctions are required for the transport of iron and other metal ions into and out of the protein shell. Ferritins have successfully been used as a scaffold to synthesize various protein-inorganic hybrids.Platinum (Pt) is a most widely used catalyst in chemical industries. Colloidal Pt has been showed to catalyze the decomposition of hydrogen peroxide (H₂O₂), and Pt nanoparticles recently have been demonstrated to catalyze the scavenging of both H₂O₂ and superoxide anion (O2·-). Thus these characteristics resemble the enzymatic activities of catalase and superoxide dismutase (SOD). These two enzymes play important roles in maintaining redox balance in living organisms by scavenging excess reactive oxygen species (ROS). The overproduction of ROS can lead to oxidative stress, damage to virtually all biomolecules and ultimately may induce cell death.Compared to the numbers of studies in biomimetic syntheses of gold and silver, protein-guided formation of platinum, one of the most important nobel metals, is relatively underexplored. In this study we investigated the possibility of using the apoferritin (apoFt) protein shell as a nanoreactor to control the synthesis of size-tunable Pt nanostructures. ApoFt was used as a scaffold to synthesize of 1 to 2 nm Pt nanoparticles (Pt-Ft) inside its protein shell. Pt-Ft showed catalase-like activities as reported, as well as horseradish peroxidase (HRP)-like activities. Interestingly, Pt-Ft possessed these enzymatic activities with distinctive enzymatic properties, namely different responses to pH and temperature for different enzymatic substrates. Using 3,3',5,5'-tetramethylbenzidine (TMB) and 3,3'-diaminobenzidine (DAB) as substrates, we found that the optimal pH and temperature for the oxidation catalyzed by Pt-Ft were similar to that of native HRP (pH optimum 4; temperature optimum 37°C). However, this was not the case for the catalase-like activity of Pt-Ft, where the optimal pH and temperature were quite different from that of native catalase, being significantly higher in each case. Compared to other engineered nanoparticles, such as iron oxide and cerium oxide, Pt-Ft had a significantly smaller nanostructural core and unique peroxidase activities for different substrates. Metal oxide nanoparticles utilize different valence states (Fe²⁺/Fe³⁺ or Ce³⁺/Ce⁴⁺) for their catalytic activity, but Pt-Ft consists of mainly, if not entirely, zero-valent Pt nanoclusters, and the changes of valence states are between zero valence and oxidized Pt. Additionally, the ferritin shells make these nanostructures biocompatible and potentially more bioactive, for example, through their possible interactions with ferritin receptors.Quantum dots have physical and optical properties that make them useful tools for high-resolution labeling immunoassay. In this work, a rapid and simple method of quantitative immunoassay for Cardiac troponin I(cTnI)was developed by using quantum dots-labeled antibodies. The monoclonal antibodies of cTnI(2F11) could be labeled with CdTe quantum dots and the coupled product(CdTe-2F11)were characterized by SDS-PAGE. The result of immunofiltration assay indicated that the CdTe-2F11maintained the antibody activity. The cTnI at the different concentrations in NC membrane could react with CdTe-2F11 and be detected by using ImageMaster to analyze the fluorescence intensity of the immunodotting. The result showed that the detection limit of cTnI was 120ng, and there was a good linear relation between concentration of cTnI and the fluorescence intensity (R²=0.9966), in this study.