Nanomolar simultaneous determination of Ascorbic acid, Epinephrine, Acetaminophen, L-Tryptophan and L-Tyrosine on a glassy carbon electrode coated with γ-MnO2/PPy/RGO nanocomposite

Ascorbic acid (AA), Epinephrine (EPI), Acetaminophen (ACT), L-Tryptophan (Trp) and LTyrosine (Tyr) are biochemical compounds which play important roles in various biological processes. Usually, they are co-existing substances in biological matrices. Altering the concentration of these species cause to several diseases, so their determination in human fluids such as blood plasma is much essential. These facts have encouraged chemists to develop faster, simpler, and more sensitive techniques such as electrochemistry to meet the various demands using chemically modified electrodes. This is the first report of simultaneous determination of these compounds. Graphene has been used for the sensitive determination of various drugs molecules, due to their excellent conductivity because of π-π staking and synergetic effects with other materials [1,2]. Polypyrrole has been considered as one of the most promising electrode materials to enhance the sensing sensitivity because of its low cost, easy synthesis, relatively high conductivity and good electrochemical/mechanical properties [3-5]. Among various metal oxides, manganese dioxides (MnO2) have drawn great attention because of its high activity, non-toxicity, low cost, beneficial physicochemical property, relatively environmentally benign and good electrochemical properties [6]. The morphology and structure of the nanocomposite were characterized by the field emission scaning electron microscopy (FE-SEM), Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and raman spectroscopy. Among the bare (GCE), RGO/GCE, PPy/RGO/GCE and γ-MnO2/PPy/RGO/GCE modified electrode namely γ- MnO2/PPy/RGO/GCE exhibited much higher electrocatalytic activities toward oxidation of AA, EPI, ACT, Trp and Tyr. The measurements were carried out in pH 7.0 PBS, by Cyclic voltammetry (CV) at a scan rate of 100 mV/s, Differential pulse voltammetry (DPV) at a scan rate of 50 mV/s and Amperometry. The modified electrode gave five separated oxidation peaks 53 at 150 mV, 410 mV, 600 mV, 780 mV and 990 mV for AA, EPI, ACT, Trp and Tyr respectively. Under optimum conditions, DPV indicated linear relationships between oxidation peak current and AA, EPI, ACT, Trp and Tyr concentrations in the ranges of 1-360 μM, 0.5- 410 μM, 0.4-470 μM, 2-190 μM and 0.2-105 μM with detection limits of 0.04 μM, 0.032 μM, 0.033 μM, 0.018 μM and 0.008 μM respectively. Under optimum conditions, amperometry indicated linear relationships between oxidation peak current and AA, EPI, ACT, Trp and Tyr concentrations in the ranges of 2-450 μM, 1-540 μM, 0.8-660 μM, 3-220 μM and 0.5-160 μM with detection limits of 0.1 μM, 0.084 μM, 0.075 μM, 0.056 μM and 0.035 μM respectively The sensor provided a good performance for the simultaneous determination of AA, EPI, ACT, Trp and Tyr by not only greatly enhanced their current responses, but also resolved the overlapping peak potentials as well as decreased the over potentials. In addition, the sensor was successfully applied for the determination of these species in human blood real samples.