In this study, a novel nano-molecularly imprinted polymer was synthesized and used to prepare modified carbon paste electrodes. A nano-molecularly imprinted polymer was synthesized by using silanized magnetic graphene oxide (Fe₃O₄/GO–SiO₂) as a nanofiller material with molecular recognition capacity. The surface of graphene oxide (GO) was silanized chemically to prevent the accumulation of GO sheets and also to reduce the interactions between GO and the polymer matrix. The presence of polar groups on the surface of GO layers improved their dispersibility in a polar solvent by using ultrasound, which facilitated their incorporation into methacrylic acid (MAA) as a functional monomer in the molecular imprinting process. The prepared nanocomposite was characterized by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The electrochemical sensor was tested by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques for the selective determination of thyroxin (T₄). The limit of detection and the linear range were found to be 3 × 10⁻⁹ M (S/N = 3) and 4 × 10⁻⁸ to 7 × 10⁻⁷ M T₄, respectively. Finally, the modified sensor was successfully applied in the measurement of T₄ in real samples.