(77i) Tuning Nanostructures for Understanding Nanozymes in Biosensors

Natural enzymes are 3D protein machines, which require well-controlled conditions (temperature, pH, purity etc.) to function properly. These enzymes are used in a wide range of applications such as biosensing, tissue engineering, therapeutics and environmental protection, however, precisely controlling the operation and storage conditions can be difficult. Nanozymes, which are high surface area inorganic nanostructures that mimic enzyme functionality, have attracted increasing attention in recent years for their reasonable tolerance of variations in conditions. However, several contemporary challenges facing nanozyme technologies remain. First, most of the reported nanozymes are dispersed in solution, rendering the materials hard to recover and environmentally unfriendly. Second, nanozymes tend to have a low density of active sites, resulting in catalytic activity less than natural enzymes. To date, these bottlenecks have restricted the widespread application of nanozymes.

To resolve these issues, we deposited a new class of nanocolumnar Ni nanozymes. These nanozymes were deposited on silicon substrates by glancing angle deposition (GLAD). GLAD gives high surface area and porosity to these nanozymes, leading to a high concentration of catalytically active sites to mimic enzyme-like activity. Due to the nanozymes’ deposition on a solid substrate, these nanozymes are reusable, suggesting cost-efficiency. We reported peroxidase-like catalytic activities of nitrogen-doped Ni GLAD films and compared them with unmodified Ni film. Peroxidase-like activity was studied by accelerating the oxidation reaction of colorless 3,3’,5,5’-tetramethybenzidine (TMB) to a blue product (oxTMB) in the presence of hydrogen peroxide (H₂O₂). Surface characterization and morphology studies by XRD, XPS and SEM, confirm the presence of adsorbed N^3- ions as catalytically active centers for accelerating electron transfer. The absorbance of oxTMB solution was measured by UV-Vis spectroscopy at 652 nm. Low Michaelis-Menten constant (K_m (mM)) demonstrates the high effectivity of the catalyst. The K_m of the natural enzyme, unmodified Ni GLAD films, and nitrogen plasma modified Ni GLAD films were calculated to be 0.43, 0.22, and 0.17 respectively, which confirms high peroxidase like activity for our proposed modified nanozyme.

Overall, our approach demonstrated a reusable and efficient nanozyme technique to mimic natural enzymes’ peroxidase-like activity. We firmly believe this study will boost the mechanistic understandings of nanozymes to understand the depth for mimicking other possible catalytic activities of natural enzymes.