Researchers synthesized reduced graphene oxide (rGO) using Parthenium hysterophorus weed leaf extract through a hydrothermal-assisted carbonization method. The resulting nanomaterial was confirmed to have crystallinity and geometry through X-ray diffraction. The nanomaterial was used as an electrochemical biosensor for dopamine and was highly sensitive with low detection limits and excellent reproducibility, outcompeting many metal-based nanocomposites. This study suggests that waste plant biomass can be a potent source for synthesizing metal-free carbon-based nanomaterials.