Sandwich-type electrochemical immunosensor for highly sensitive determination of cardiac troponin I using carboxyl-terminated ionic liquid and helical carbon nanotube composite as platform and ferrocenecarboxylic acid as signal label

Herein we report a sandwich-type electrochemical immunosensor for sensitive detection of cardiac troponin I (cTnI) using a new composite of carboxyl-terminated ionic liquid and helical carbon nanotubes (CIL-HCNTs) as platform and ferrocenecarboxylic acid (Fc-COOH) as signal label. The composite of CIL-HCNTs was prepared by a simple and convenient one-step ultrasound method and was then characterized by Fourier transform infrared spectroscopy, scanning electron microscope, cyclic voltammetry and chronocoulometry. CIL-HCNTs, possessing large surface area and high electrical conductivity, provide a good platform for anti-cTnI monoclonal antibody immobilization through the carboxyl groups of CIL-HCNTs. The Fc-COOH, as a signal label based on the oxidation process, was combined with the CIL-HCNT platform to construct the electrochemical immunosensor for cTnI determination. Under optimal conditions, the electrochemical immunosensor exhibited desirable performance for cTnI determination with a wide range of linearity from 0.01 to 60.0 ng mL−1 and a relatively low detection limit of 0.006 ng mL−1. Importantly, the immunosensor showed excellent specificity and acceptable reproducibility as well as satisfactory reliability for human serum sample analysis.