In this context, a novel, scalable and facile method for the green synthesis of graphene oxide (GO) to facilitate effective and safe oxidation of graphite using sodium periodate (NaIO4) is demonstrated. The optimized value of the oxidizing agent NaIO4 ensured effective oxidation, minimized defects on sp(2) C-C plane (I-D/I-G = 0.645) and increased C/O atomic ratio of similar to 5.146. Subsequently, we successfully synthesized the amino-functionalized reduced graphene oxide (NH2-rGO) and carboxylic surface modified AgPtPd (COOH-AgPtPd) trimetallic nanoparticles (TNPs), in order to fabricate a label-free electrochemical sensing platform using the conventional immersive layer-by-layer (LBL) assembly. The superior synergetic effect between LBL-assembled NH2-rGO and COOH-AgPtPd (COOH-AgPtPd/NH2-rGO) significantly boosts the electron transfer rate of the electrode as well as electrocatalytic efficiency. Therefore, the as-prepared COOH-AgPtPd/NH2-rGO nanocomposite-based sensing material was first employed for nonenzymatic electrochemical detection of H2O2, with a low detection limit of 0.2 nM. Moreover, COOH-AgPtPd/NH2-rGO nanocomposite can also be utilized as a sensing platform for label-free accurate electrochemical detection of prostate-specific antigen (PSA) over a large linear range of 4 fg mL(-1) to 300 ng mL(-1), with an ultra-low detection limit (LOD) of 4 fg mL(-1). (C) 2019 The Electrochemical Society.