Detection of Vitamin D in Food Supplements Using A Simple Modification of Electrochemically Reduced Graphene Oxide/Screen-Printed Carbon Electrodes

Abstract

Vitamin D (ergocalciferol and cholecalciferol) is a fat–soluble vitamin that is important for proper functioning of human metabolism which promotes calcium absorption for bone mineralization and prevent hypocalcemic tetany. Graphene is a two-dimensional nanomaterial offers superior properties of high surface area, high electrical conductance and great electrochemical properties. The development of electrochemically reduced graphene oxide (ERGO) for vitamin D detection is possible due to the non–polar property of ERGO and vitamin D. Initially, pre–treatment of the bare screen–printed carbon electrode (SPCE) was performed using cyclic voltammetry (CV) scan (–1.3 V to 0.4 V; 5 cycles) in 0.25 M potassium chloride (KCl) prior to the drop–casting of graphene oxide (GO) (5 μL, 0.7 mg/mL) on the sensor. Subsequently, a similar technique was applied on the GO/SPCE producing ERGO/SPCE. Several parameters of ERGO/SPCE have been optimized including GO concentration, CV cycle number and type of diluent. The developed sensor exhibits a linear detection of oxidation response of vitamin D, proportional to its concentration (0.50–8.0 mg/L; R2=0.9849 for N=5). This result was qualitatively evaluated with one type of food supplement and the detection of vitamin D displays a promising result for hand–held future device application.