Phytosynthesis of Palladium Nanoclusters: An Efficient Nanozyme for Ultrasensitive and Selective Detection of Reactive Oxygen Species

Hydrogen peroxide is a low-reactivity reactive oxygen species (ROS); however, it can easily penetrate cell membranes and produce highly reactive hydroxyl radical species through Fenton's reaction. Its presence in abnormal amounts can lead to serious diseases in humans. Although the development of a simple, ultrasensitive, and selective method for H2O2 detection is crucial, this remains a strategic challenge. The peroxidase mimetic activity of palladium nanoclusters (PdNCs) has not previously been evaluated. In this study, we developed an ultrasensitive and selective colorimetric detection method for H2O2 using PdNCs. An unprecedented eco-friendly, cost-effective, and facile biological method was developed for the synthesis of PdNCs. This is the first report of the biosynthesis of PdNCs. The synthesized nanoclusters had a significantly narrow size distribution profile and high stability. The nanoclusters were demonstrated to possess a peroxidase mimetic activity that could oxidize peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB). Various interfering substances in serum (100 mu M phenylalanine, cysteine, tryptophan, arginine, glucose, urea, Na+, Fe2+, PO43-, Mn+2, Ca2+, Mg2+, Zn2+, NH4+, and K+) were included to evaluate the selectivity of the assay, and oxidation of TMB occurred only in the presence of H2O2. Therefore, PdNCs show an efficient nanozyme for the peroxidase mimetic activity. The assay produced a sufficient signal at the ultralow concentration of 0.0625 mu M H2O2. This colorimetric assay provides a real-time, rapid, and easy-to-use platform for the detection of H2O2 for clinical purposes.