Preparation of L-Tryptophan Electrochemical Sensor Based on Graphene Oxide/Carbon Nanotubes Nanocomposite Modified Electrode

A single-layer graphene oxide (GO) was prepared by Hummers method, and then mixed with multiwalled carbon nanotubes (MWCNT) in ultrasound bath to form stable GO/MWCNT nanocomposites. A novel L-tryptophan (L-Trp) electrochemical sensor was fabricated based on GO/MWCNT modified glassy carbon electrode. The modified electrode was characterized by transmission electron microscope (TEM), cyclic voltammetry (CV) and alternating current impedance (EIS), and the electrochemical behaviors and kinetic properties of L-Trp on the modified electrode were also investigated. The experimental results showed that a sensitive oxidation peak of L-Trp appeared at GO/MWCNT modified electrode (E-pa = 0.956 V), and the oxidation reaction was an irreversible process containing two electrons and two protons transfer. This electrode process controlled by the adsorption step, and the standard rate constant was 9.613. x 10(-4) cm/s. Trace levels of L-Trp can be determined by this oxidation peak. In phosphate buffer of pH 6.0, the oxidation peak currents were linearly dependent on the L-Trp concentrations in the range of 1.00 x 10(-6) - 1.00 x 10(-4) mol/L with accumulation time of 25 s at 0.600 V and scan rate of 100 mV/s. The correlation coefficient was 0.995 and the detection limit was 3.50 x 10(-7) mol/L. The prepared electrochemical sensor had favorable stability and could be applied to the quick determination of L. Trp in human serum, and the recovery of standard addition was from 97.8% to 104.2%.