1-[(4-nitrophenyl)methyl]-4,4'-bipyridinium (N-PMB) was synthesized by refluxing 4,4′-bipyridine and 4-nitrobenzylchloride. A stable film of 1-phenylmethyl-4,4′-bipyridine (PMB) was successfully electrografted on glassy carbon electrodes by the reduction of the diazonium moieties generated in situ. High antifouling ability was obtained for the PMB modified electrode which makes it a useful sensor device for environmental waters monitoring. The modified electrode was used as an amperometric sensor for mediated hydrogen peroxide detection at -0.5 V. The calibration curve was linear from 5 to 60 μM H2O2 (R2=0.9978, n=7) with a detection limit of 0.25 μM. PMB modified electrodes was able to detect oxygen in river water with good sensitivity, selectivity and reproducibility.