A feasibility study for a label-free, multi-marker single sensor using electrochemical impedance spectroscopy (EIS), imaginary impedance, and a signal decoupling technique is reported. To our knowledge, this is the first reported attempt of using imaginary impedance for biomarker detection and multi-marker detection. The electrochemical responses of purified low and high density lipoproteins (LDL and HDL, respectively) were first individually characterized through the immobilization of their molecular recognition elements (MREs) onto gold disk electrodes (GDEs). The co-immobilization was performed by immobilizing the MREs of both LDL and HDL on the same GDE, which was then used to detect LDL and HDL simultaneously in mixed solution. Previous individual purified responses were then used to de-convolute the mixed response, when the two biomarkers were detected in mixed solutions. The optimal frequencies of LDL and HDL were found to be 81.38Hz and 5.49Hz, respectively, which shifted to 175.8Hz and 3.74Hz under co-immobilized conditions. After comparing the electrochemical signal in complex and imaginary impedance, imaginary impedance was found to be more suitable for multi-marker detection purposes. Since imaginary impedance is related to capacitance, electric displacement, relative permittivity, and effective capacitance were derived to elucidate the theory of optimal frequency. This work shows that EIS has the potential for multi-marker detection and can be extended to monitor other complex diseases such as diabetes mellitus for better management and diagnostic purposes.
Keywords: Cardiovascular disease; Electrochemical impedance spectroscopy; Imaginary impedance; Label free detection; Multi-marker detection; New method.
Published by Elsevier B.V.