Nick H. S. Lee1, Michael L. Crichton1, Stephen J. Wilson2, Mark A. F. Kendall1 *

 

1Australian Institute for Bioengineering and Nanotechnology
2School of Information Technology and Electrical Engineering
University of Queensland
Brisbane, Queensland, Australia

 

Bioimpedance has been an active area of research in recent years for disease diagnosis due to its cost effectiveness, ease of implementation and relevance in a wide range of fields1. In essence, it describes tissue opposition to a known electrical current, typically applied via electrodes that interface with the tissue under measurement. However, most systems rely on wet gel electrodes placed on the surface to achieve this, which limit the resolution (spatially on the surface and with depth) that they are capable of interrogating. In this presentation, we will discuss an alternative approach – a microelectrode array (MEA) design that penetrate skin surface in a minimally invasive manner to achieve deeper bioimpedance sensing.

MEAs were manufactured with arrays of projections of 50 µm, 150 µm and 250 µm length, by deep reactive ion etching of silicon and subsequently metallised with platinum. These were then applied to Wistar rat skin ex vivo and their depth of penetration quantified by measuring deposited tracks of fluorescent microspheres in the skin. Bioimpedance measurements were performed using two MEAs applied to the skin spaced 30 mm apart (bipolar configuration) and 1 VRMS sinusoidal voltage from 5 Hz to 1 MHz applied across them.

Our MEAs (shown in Figure 1) penetrated to depths 34.68 ± 6.68 µm, 91.33 ± 20.54 µm and 86.84 ± 22.66 µm (using the 50 µm, 150 µm and 250 µm long MEAs, respectively). Compared at these depths, bioimpedance results showed that conventional wet gel electrodes exhibited higher impedance magnitude and phase lags compared to the skin-penetrating MEA. Between MEAs of different lengths, the 50 µm MEA recorded the highest impedance magnitude compared to its longer counterparts, which we hypothesise was due to it being in contact with the less hydrated epidermal layer.

The MEA approach shows promise as a potential bioimpedance mapping tool at targeted tissue depths, a clear advantage over the conventional wet gel electrodes.

 

References

1 Khalil S., Mohktar M. and Ibrahim F. Sensors 2014, 14, 10895-10928. The theory and fundamentals of bioimpedance analysis in clinical status monitoring and diagnosis of diseases.

 

Biographic Details

Name: Mr Nick Hong Seng Lee

Affiliation, Country: Australian Institute for Bioengineering and Nanotechnology, Australia

Phone: +61 7 334 64193 E-mail: nickhongseng.lee@uq.edu.au

Research interests: bioimpedance, medical device, skin cancer diagnosis, wearable technology