We report a universal protocol for the in situ bioinspired green synthesis of metal (Pd, Pt, Ag and Au) nanoparticles (mNPs) on simultaneously reduced graphene oxide (rGO) sheets using a black pepper extract (BPE) for quantification and kinetic analysis of epidermal growth factor receptor (ErbB2) for application to breast cancer diagnostics. The phytochemicals present in BPE were found to assist the reduction, stabilization, and surface addition of mNPs onto rGO sheets. The antioxidants present in the BPE assist the formation of a "green corona" on the surface of derived G-mNPs@rGO (G-Pd@rGO, G-Pt@rGO, G-Ag@rGO, and G-Au@rGO) sheets as corroborated by DLS and FT-IR experiments. These bioinspired derivatives provided biocompatible surfaces, resulting in higher cell viability compared to that of chemically derived composites, C-mNPs@rGO (C-Pd@rGO, C-Pt@rGO, C-Ag@rGO, and C-Au@rGO). Toxicity was found to be drastically reduced for green-corona assisted derivatives of GO due to strong antioxidant properties of the phytochemicals present in BPE. In addition, a comparative analytical study of the quantification and kinetics of breast cancer biomarkers using both G-mNPs@rGO and C-mNPs@rGO nanocomposites was carried out. The G-mNPs@rGO nanosheets can be employed for ultrasensitive detection of ErbB2 concentration from 1.0 fM to 0.5 μM. © 2017 The Royal Society of Chemistry.