One novel chemically modified electrode (CME) was prepared through fabricating polyethyleneimine/oxidized graphene multilayers on indium tin oxide (ITO) slide via layer-by-layer assembly followed by electrochemically depositing cobalt hexacyanoferrate. A large range of methods were used to characterize the morphology and electrochemical properties of the electrode including fieldemission scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, cyclic voltammetry, differential pulse voltammetry (DPV), electrochemical impedance spectroscopy and chronoamperometry. Under optimized conditions, the oxidation current of DPV (typically at 0.2 V vs. saturated calomel electrode) increased linearly in the range of 5 x 10(-5) to 2 x 10(-3) mol L-1. And the limit of detection and the limit of quantity were 4.6 x 10(-7) mol L-1 and 1.5 x 10(-6) mol L-1 (based on signal-to-noise ratio of 3 and 10), respectively. Average recoveries from (spiked) commercial mask were between 98.1% and 104.5% with relative standard derivations less than 3.14% (n = 3) at three spiked levels. The method was validated by HPLC. Furthermore, the possible mechanism of L-Cys detection was studied based on chronoamperometric experiments. (C) 2019 The Electrochemical Society.