Systematic Comparison of Platinum-Group Metal Nanomaterials as Efficient Enzyme-Mimetics in Biosensing

Since their discovery, nanomaterials of platinum group metals (PGMs) have been incorporated into technologies indispensable to the world today due to their tremendous stability, catalytic efficiency, and unique physiochemical properties. To meet society’s demand for the wide application of these rare metals, it is imperative to have a complete understanding of their formation, function, and application in industry. In biosensing, many PGM systems have been made which have been proven to substantially improve the sensitivity of bioassays. However, studies comparing the activities across PGMs are unavailable, leaving a gap in our understanding of how the choice of metal impacts nano-catalyst design. Understanding the catalytic activity of different PGMs is critical for the advancement of bioassays and across the population of PGM consumers.<br/>In this work, nanomaterials of PGMs (including Pt, Pd, Rh, Ir) are synthesized using an aqueous system stabilized by the surfactant sodium citrate. The prepared materials are characterized to reveal maximum likeness in morphology (electron microscopy), oxidation state (x-ray photoelectron spectra), surfactant (infrared spectra), and surface chemistry (x-ray diffraction) to ensure the difference in catalytic activity is due solely to the type of element present. The materials are systematically evaluated for enzyme-like peroxidase activity using the oxidation of 3 3' 5 5'-tetramethylbenzidine (TMB) by hydrogen peroxide as a model reaction. Traditional Michaelis-Menten kinetic analysis is utilized to derive parameters k_m and V_max which are used to calculate the molar k_cat of each PGM material. The synthetic procedures are scaled up and applied to the diagnostic platform enzyme-linked immunosorbent assay (ELISA) to confirm the trend in activity is seen on a industrially relevant, benchmark test.<br/>This research aims to advance the development of diagnostic platforms that rely on highly efficient PGMs to reach lower limits of detection as well as to provide the academic significance of uncovering the widely debated, but never proven, most active peroxidase PGM.