Nitrogen-doped carbon nanotubes decorated poly (L-Cysteine) as a novel, ultrasensitive electrochemical sensor for simultaneous determination of theophylline and caffeine.

In present study, a novel and facile electrochemical sensor based on glassy carbon electrode (GCE) modified with nitrogen-doped carbon nanotubes (N-CNT) decorated with poly (L-Cysteine) (PLCY) were fabricated and applied for the simultaneous voltammetric determination of theophylline (THEO) and caffeine (CAF). The morphology and structure of multilayer film modified on the surface of glassy carbon electrode were investigated successfully by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and Raman Spectroscopy. And the properties of the modified electrode were investigated by Chronocoulometry (CC), Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV) were utilized to investigate the electrochemical behavior of THEO and CAF on the composite film modified electrode. The results showed that the determination towards THEO and CAF can be operated at the same potential window with the oxidation current peak separated and non-interfering respectively. Compared to the bare GCE, the PLCY/N-CNT/GCE can signally meliorate the electrocatalytic activity towards the oxidation of THEO and CAF with a remarkably increase in the anodic peak currents of 495.94% and 465.48%. Under the optimal conditions, the fabrication multilayer film sensor had excellent performances in determination towards THEO and CAF with a wide linear dynamic range from 0.10 to 70.0μM and 0.40-140.0μM, low detection limit (S/N = 3) of 0.033μM and 0.20μM, respectively. The PLCY/N-CNT/GCE sensor also had advantages as easy-made, high-sensitivity, stability and reproducibility. Moreover, it was successfully used to analyze the THEO and CAF in green tee, oral theophylline sustained release tablets and energy drink sample with a satisfactory result.