Label-free electrochemical IgE aptasensor based on covalent attachment of aptamer onto multiwalled carbon nanotubes/ionic liquid/chitosan nanocomposite modified electrode.

A simple, sensitive and label-free aptamer-based biosensor for the detection of human immunoglobulin E (IgE) is developed using the electrochemical transduction method. A special immobilization interface consisting of multiwalled carbon nanotubes/ionic liquid/chitosan nanocomposite (MWCNTs/IL/Chit) is utilized to improve the conductivity and performance characteristics of the biosensor as well as to increase the loading amount of aptamer DNA sequence. A 5'-amino-terminated aptamer is covalently attached onto MWCNTs/IL/Chit modified glassy carbon (GC) electrode via a linker of glutaraldehyde (GA). Methylene blue (MB) is used as an electrochemical indicator which is intercalated into the aptamer through the specific interaction with its guanine bases. In the absence of IgE, MB bound to the aptamer produces a strong differential pulse voltammetric (DPV) signal. But when IgE exists, the intercalated MB releases from the aptamer, resulting an obviously decreased DPV signal. This phenomenon can be applied for human IgE detection. The peak current of MB linearly decreases with the concentration of IgE over a range of 0.5-30 nM with a detection limit of 37 pM. By using Bovine serum albumin (BSA) and lysozyme, the excellent specificity of this sensing system for the detection of IgE is also demonstrated. Finally, the proposed aptasensor is successfully used to IgE analysis in human serum sample. The obtained result is well agreed with the value obtained by the standard ELISA method. The herein described approach is expected to promote the exploitation of aptamer-based biosensors for protein assays in biochemical and biomedical studies.