The conventional synthetic methods for graphene oxide are based on the reaction of graphite with mixed strong oxidants, which involves the risk of explosion and toxic gases. Herein, we report a facile, safe, and green method to synthesize green graphene oxide (denoted as gGO) using sodium periodate as an effective oxidizing agent feature with lower Raman intensity (ID/IG = 0.65) and higher C/O atomic ratio (similar to 5.15). We also discuss the mechanism underlying the direct growth of MoS2 nanoroses (MoS2-NRs) on the in situ synthesized green reduced graphene oxide (grGO), in which the MoS2-NRs are assembled from few-layered MoS2 nanosheets. Due to the highly exposed active edge sites of MoS2-NRs and good electrical coupling with the underlying grGO, the resulting grGO/MoS2-NRs nanocomposite exhibits excellent electrocatalytic activity. Furthermore, the addition of L-proline assisted Au/Pd/Ag trimetallic nanoparticles to the nanocomposite provide a suitable label-free platform for direct antibody immobilization and increase the effective surface area. The as-prepared grGO/MoS2-NRs/AuPdAg nanocomposite was employed as a label-free immunosensing platform for the ultrasensitive detection of ochratoxin A, a food mycotoxin. The proposed immunosensor exhibits an excellent high detection range from 10 fg mL(-1) to 150 ng mL(-1) and limit of detection (LOD) of 5 fg mL(-1) (S/N = 3). (c) 2019 The Electrochemical Society.