A noble electrochemical sensor based on TiO@CuO-N-rGO and poly (L-cysteine) nanocomposite applicable for trace analysis of flunitrazepam.

Flunitrazepam or date rape medication with trade name of Rohypnol belongs to the benzodiazepines branch that is used as a sedative, anesthetic, anticonvulsant, muscle relaxant, and antianxiety drug. It is known as "drug of aggression" because of its very strong and long-lasting effects on the central nervous system. The sedative influence of flunitrazepam drug increases with alcohol drinking, which causes mental and motor disorders and causes the victim to become silent. Due to its criminals use, its accurate measurement is crucial. In this work, a novel electrochemical sensor based on TiO@CuO-N doped rGO, TiO@CuO-N-rGO, nano-composite and poly (L-cysteine), poly (L-Cys), is presented for trace analysis of flunitrazepam in aqueous solution. At first, TiO@CuO-N-rGO nano-composite was synthesized by the sol-gel method and characterized by Raman spectroscopy, Fourier transform infrared, field emission scanning electron microscope, and X-ray diffraction analysis. Then, the suspension of the TiO@CuO-N-rGO nano-composite was drop casted on the surface of the glassy carbon electrode (GCE/TiO@CuO-N-rGO). After that, electro-polymerization of l-cysteine on the GCE/TiO@CuO-N-rGO surface was performed by cyclic voltammetry (CV) method. The electrochemical characteristics of the GCE/TiO@CuO-N-rGO/poly (L-Cys) surface were evaluated in the solution of ferri/ferrocyanide by electrochemical impedance spectroscopy (EIS) and CV techniques. The increase in current, change in oxidation peak potential, and the appearance of two reduction peaks indicated higher electron transfer rate with well-performed electrochemical process of flunitrazepam at the modified electrode surface compared to the bare GCE. These improvements originate from the synergistic effect of TiO@CuO-N-rGO nano-composite and poly (L-Cys). Finally, a linear relationship was resulted between the oxidation peak current and the concentration of flunitrazepam in the wide concentration range of 1 nM to 50 μM with a detection limit of 0.3 nM.