Electrochemical Impedance Modeling of Symmetric Electrodes for Aptasensing

This is the research topic for my master’s thesis, which serves as an integrated work for the related researches and projects that I have worked on. Relevant studies have been accepted as 4 journal papers (1st author x2, co-author x2) and 5 international conference papers (1st author x4, co-author x1). The list below shows all the related topics covered in my thesis:

(Ch. 3) Diffusion Impedance Modeling of Interdigitated Array Electrodes
(Ch. 3.4.6) Electrochemical Impedance Circuit Fitting Program
(Ch. 4) Impedimetric Aptasensing using a Symmetric Randles Circuit Model
(Ch. S.7) Real-time Impedimetric MUC1 Aptasensor using Microfluidic Symmetric Gold Electrode
(Ch. S.8) Real-time Impedance Detection Systems

Figure 1. Research framework for this thesis.

Abstract

The inhibition of tumor markers has been a popular research object among the academic society. They are often detected using simple and low-cost techniques such as electrochemical impedance spectroscopy (EIS), which aptamers are occasionally used as the sensing element for achieving high sensitivity and selectivity. This integrated method has flourished in recent years.

However, for electrochemical methods, a three electrode setup faces fabrication complexity, high cost and low yield rates during miniaturization. Two electrode impedimetric detection using interdigitated array (IDA) electrodes also faces a problem. Due to its geometry, there hasn’t been any studies that derive its diffusion impedance according to different bandwidths and gap widths. Therefore, this study makes a basis on impedimetric modeling of symmetric two electrode systems.

The first part focuses on the derivation and verification of an integral form of solution for IDA diffusion impedance. An equivalent circuit fitting program succeeded to accurately fit the EIS data and parameters such as the ratio of electrode bandwidth to gap width and diffusion coefficient can also be obtained by fitting the data from a single EIS experiment. This can aid researchers in relevant fields model their systems more accurately.

In the second part, a symmetric equivalent circuit model is developed, and it is applied it for impedimetric detection of thrombin and a tumor marker MUC1 with a fabricated aptasensor using standard Au electrodes (SGE) and IDA chips. The model is proved of correctness, and is applied for bio-detection. IDA chips are used for aptasensor fabrication for thrombin detection. The program designed in the first part is used for circuit fitting of EIS data, and accurate parameters are obtained. This sensor has the regenerability for six times of detection and the specificity is also confirmed.

Symmetric Au electrode systems have simple and low fabrication cost characteristics. Its integration with highly stable aptamers can contribute to mass production and customization in product commercialization. According to the above results, the author anticipates future developments in relevant medical diagnosis and point-of-care applications.

Selected Figures

Figure 1. (a) Redox mediator (species) associated binding event and its (b) ΔRct vs concentration signal relationship on an Au electrode.

Figure 2. Nyquist plot of EIS data of a bare Au IDA electrode (▲) and its fitted data (△). The electrode bandwidth (we) and gap width (wg) are 50μm. The equivalent circuit used is shown at the upper left corner, which is a Randles circuit that uses a constant phase element (CPE or Q) for modeling the double layer capacitance. The solution contains 0.1M KCl and 5mM Fe(CN)63-/4-. The frequency range of the data is 10-1~105Hz.

Figure 3. Simulation of time-dependent 2D concentration profile in an IDA unit cell. wewg = (top-left) 10-10, (top-right) 40-10 and (bottom) 10-40 (μm). The colored lines are simulated constant concentration contours and the black dashed lines are the predicted contours.

Figure 4. Nyquist plot for characterizing the fabrication, detection and regeneration process of thrombin impedimetric aptasensor using IDA chips. (a) Chip #1 and (b) chip #2. The first six steps are shown in the sequence from “Bare” to “2M NaCl 2nd” in the legend.

Figure 5. (a) Rct vs procedure steps for regenerability test using the IDA chips. (b) ΔRct (=Rct Rct,baseline) for specificity comparison of thrombin and HSA.

Related Publications

  1. (Upcoming conference with paper accepted) C.-Y. Lai, T.-H. He, W.-C. Huang, L.-C. Chen, MUC1 impedimetric aptasensing based on interdigitated array electrode chip using a novel diffusion element, 30th Anniversary World Congress on Biosensors, (2020).
  2. Master’s thesis: Electrochemical Impedance Modeling of Symmetric Electrodes and Interdigitated Array Chips for Aptasensing Applications

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes:

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>