Application of corn zein as an anchoring molecule in a carbon nanotube enhanced electrochemical sensor for the detection of gliadin

This research focused on the fabrication of an electrochemical sensor capable of detecting the protein ‘gliadin’, which is responsible for serious autoimmune disorder causing chronic diarrhea, fatigue, weight loss and anemia in people having celiac disease. The fabrication process involves the replacement of toxic synthetic chemicals that are used for anchoring of the capture antibody in the working electrode, by the natural polymer zein coupled with several nanoparticles including, carbon nanotubes, graphene oxide and Laponite®. Novel biodegradable coatings made from zein nanocomposites: zein-graphene oxide (Z-GO), zein-Laponite® (Z-LAP) and zein-multiwalled carbon nanotubes (Z-CNT) using drop casting nanocomposite technique were tested for fabricating the electrochemical sensors using cyclic voltammetry (CV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS). Pristine zein coated electrode did not generate any oxidation/reduction peaks in the cyclic voltammograms and showed high degree of impedance in the EIS curves. While addition of the three nanoparticles (CNT, LAP, GO) considerably improved the electrical signal, Z-CNT gave the highest and strongest signals compared to other nanomaterials. The active tip of the electrochemical sensor was functionalized through a sequence of layer by layer deposition of Z-CNT nanocomposite, and other linker molecules, where Z-CNT acts as a natural linker molecule with large number of functional groups that offers immobilization of capture antibody and target and ensures high performance. Both CV curves and SWV curves indicated successful sequential immobilization of gliadin antibody onto the Z-CNT coated electrode. The Z-CNT biosensor was successfully able to give CV signals for gliadin allergens for as low as 0.5 ppm, and was highly selective for gliadin, when tested against other food toxins like acrylamide and formamide, and the Z-CNT nanocomposite remained stable over a 30-day period.