Label-free aptasensor for lysozyme detection using electrochemical impedance spectroscopy

Acknowledgments: Financial support for this work was provided by Spanish Ministry of Science and Innovation through projects CTQ2013-41577-P and CTQ2016-80170-P and by program ICREA Academia from Generalitat de Catalunya. Dionisia Ortiz-Aguayo thanks the support of Universitat Autònoma de Barcelona for the PIF fellowship.This research develops a label-free aptamer biosensor (aptasensor) based on graphite-epoxy composite electrodes (GECs) for the detection of lysozyme protein using Electrochemical Impedance Spectroscopy (EIS) technique. The chosen immobilization technique was based on covalent bonding using carbodiimide chemistry; for this purpose, carboxylic moieties were first generated on the graphite by electrochemical grafting. The detection was performed using [Fe(CN)]/[Fe(CN)] as redox probe. After recording the frequency response, values were fitted to its electric model using the principle of equivalent circuits. The aptasensor showed a linear response up to 5 µMfor lysozyme and a limit of detection of 1.67 µM. The sensitivity of the established method was 0.090 µM in relative charge transfer resistance values. The interference response by main proteins, such as bovine serum albumin and cytochrome c, has been also characterized. To finally verify the performance of the developed aptasensor, it was applied to wine analysis