The CNT Network Biosensor Array for a General Immunoassay Platform
Authors: Lim Jaeheung , Lee Hoseok , Choi Seongwook , Lee Won Cheol , Park Young June 
Published: February 2020

Our group has proposed the C-chip platform based on the CNT network decorated with the gold nanoparticle as the immobilization site for the probe molecules [1],[2]. According to the biomarker to be detected, the probe molecule may vary from DNA, aptamers and antibodies. Also, the C-chip platform adopts the individual sensor having an asymmetric two-electrode system composed of a small island electrode (called the drain) enclosed by a large electrode, which shares the common ground (or power source voltage). Thanks to the large area of the common enclosing electrode which is placed in the electrolyte, the potential of the electrolyte tends to be stabilized to the enclosing electrode potential thereby the reference electrode, usually adopted in the common electrochemical sensor, can be omitted.

 The beauty of the C-chip platform is easiness of the integration to the CMOS chip technology where the above mentioned electrode can be readily realized by the last step of a metal layer fabrication. In the CMOS chip, the electrodes are connected to the signal processing circuit [3].

 To enhance the sensitivity and overcome the non-specific binding problem in the electrical biosensor, especially when the sensor is applied to detect the biomarker in the serum including large concentration of the noisy background molecules, we have proposed the electrical pulse method where the electrical pulses with various magnitude, shape and frequency are applied to the drain electrode. We have shown that the method provides both the de-screening effect and the enhancement of the association rate of the probe-target binding during the detection [4].

 In this paper, we report our efforts to use the electrical pulse method for an application to an immune assay where the antibody-antigen binding is electrically detected. In addition, we report the surface treatments of the various part of the sensor which is composed with metal electrodes, CNT channel and the gold nanoparticle. This surface treatment reduces the nonspecific binding problem. And we will report the data using the Alpha fetoprotein (AFP) known as the biomarker for the hepatoma. An optimized application of the electrical pulse method is expected to improve both the sensitivity and non-specific binding effects.

 The electrical pulsing method coupled with the surface treatment, we are able to make the C-chip platform close to general electrical biosensor platforms for detecting DNA, proteins and peptides.

[1] D. W. Kim, G. S. Choe, S. M. Seo, J. H. Cheon, H. Kim, J. W. Ko, I. Y. Chung, and Y. J. Park, “Self-gating effects in carbon nanotube network based liquid gate field effect transistors,” Appl. Phys. Lett., vol. 93, no. 24, p. 243115, 2008.

[2] S. M. Seo, T. J. Kang, Y. Kim, N. Kim, J. Ahn, T. W. Kim, Y. H. Kim, S. H. Ryu, and Y. J. Park, “Electrode asymmetry driven self-gating effect on the electrical detection of protein,” Sensors Actuators B Chem., vol. 191, pp. 800–805, Feb. 2014.

[3] J. Ahn, J. Lim, S.-H. Kim, J. Yun, C. Kim, S. Hong, M. Lee, and Y. Park, “Double-side CMOS-CNT biosensor array with padless structure for simple bare-die measurements in a medical environment,” in 2015 IEEE International Solid-State Circuits Conference - (ISSCC) Digest of Technical Papers, 2015, pp. 1–3.

[4] J.-M. Woo, S. H. Kim, H. Chun, S. J. Kim, J. Ahn, and Y. J. Park, “Modulation of molecular hybridization and charge screening in a carbon nanotube network channel using the electrical pulse method.,” Lab Chip, vol. 13, no. 18, pp. 3755–63, Sep. 2013.