Excellent electronic and optical properties make Indium tin oxide (ITO) an attractive electrode substrate.¹ It is an alloy of indium oxide (In₂O₃) and tin oxide (SnO₂) in a weight ratio of 90:10. It is transparent as thin film, so, it is also good to be viewed under different types of microscopes used in cell-culture studies. Despite the commercial availability of finest quality ITO and some low-cost methods for direct deposition being in use by now, definition of patterns on them is still a concern. Placing its popularity and extensive usage aside, the manufacturing of ITO electrodes so far lacks a rapid, proficient, highly reproducible, flexible, cost-effective, easy patterning process that could surpass non-trivial, time consuming techniques as lithography. A promising advancement towards achieving these limitations was the use of lasers for the fabrication of the ITO electrodes and related structure. Even though several laser techniques are explored, with the exception of CO₂ lasers, none of the others provides the benefit of being widely available and comparatively inexpensive means for fabrication of microelectrode sensors. Presently, these are the highest-power continuous wave lasers available. With their high efficiency, they are usually employed in laser cutting, welding, drilling and surface treatment.²

A cost-effective method based on CO₂ laser irradiation for the preparation of ITO microelectrodes to find applications in the bio-sensing, impedance-based analysis, and more, is presented. Electrodes of different sizes and shapes were examined to identify the performance of the samples. They were later optimized to suit our applications for studies in three dimensional cell-cultures. For rectangular shaped electrodes, the smallest sizes optimized were 25, 50 and 100 µm wide. The figure attached shows cyclic voltammetry results illustrating the reproducibility of 100 µm electrodes with ferrocenedimethanol as the redox probe in potassium nitrate. However, smaller electrodes are not always desirable. For the cell-culture work, electrodes with area 1.75mm² were fabricated and characterized to get reproducible results. Initial measurements of impedance based cellular assays have been conducted first in DMEM medium and then in the cell culture medium to understand the parameters and study the adhesion of the cells on to the electrodes. Analysis of glucose sensing properties of the system have also been attempted. Further modifications of the electrode structure and characterizations for validation will be discussed.

References

1. Stadler A. et al. J.Materials, 2012, 5, 661-683
2. Wang Y. et al. J Energy Chem. 2021, 59, 642-665