Characterization Methods for Planar Microelectrode Arrays
Yilmaz, Kardelen (2023)
2023
Bioteknologian ja biolääketieteen tekniikan maisteriohjelma - Master's Programme in Biotechnology and Biomedical Engineering
Lääketieteen ja terveysteknologian tiedekunta - Faculty of Medicine and Health Technology
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Hyväksymispäivämäärä
2023-06-26
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202306196836
https://urn.fi/URN:NBN:fi:tuni-202306196836
Tiivistelmä
Understanding the electrophysiology of electrically active cells is a key issue, as it is highly linked to the functioning of many vital organs of living organisms. With the advancements in technology, it recently is possible to produce devices, including arrays of microscale electrodes, to record and stimulate electrically active cell behavior. Microelectrode arrays (MEAs) are nowadays commonly used in research, they provide ample amount of data regarding electrically active cell behavior. However, the devices themselves and the related methods of characterization to describe the behavior and measurement quality of MEAs are seldom studied. How the device itself affects the nature of measurement and how it contributes to/hinders the data-gathering process is less focused on.
This thesis investigates some of the characterization methods for MEAs, with the purpose of reaching an evaluation procedure to characterize and define MEA quality and function after microfabrication. For this thesis, a new batch of MEAs was produced and their characteristics were examined. Other MEAs of different design and production dates were also examined to form a comparison. Different evaluation methods and the viability of these methods are presented. Electrical impedance spectroscopy and single frequency impedance analysis were the methods included in this thesis. Procedures completed in parallel with microscopy to observe visual changes. Moreover, a novel environmental conditioning test was introduced and tested out. The test involved the samples (two MEAs were tested) being placed onto an incubator and taken out regularly to have impedance measurements repeated over an extended period of time (100 hours). The experiment aimed to imitate a cell experiment as closely as possible without introducing cells to the system. The test seemed to cause visual and impedimetric changes, more so in one of the compared MEAs. As a result, the analysis and re-characterization of MEAs are advised after each cell experiment.
Moreover, over repeated impedance characterizations same size same material electrodes, some electrodes seemed to have more increase in the impedance magnitude over time. This drift also was observed through imaging of the electrodes. The imaging of the MEAs at different stages after their production revealed that there could be visual differences amongst electrodes of different impedimetric qualities. Electrodes with worsened impedance characteristics were observed to be a darker color compared to electrodes that holds a lower impedance magnitude value. An initial characterization protocol was suggested as a result of these tests. Furthermore, effects of the electrode size and material over the impedance was examined, and as a result, it was observed that circular electrodes with bigger diameter have lower impedance magnitude as expected. Circular electrodes with smaller diameter were observed to have less stable EIS measurements and higher impedance magnitudes.
This thesis investigates some of the characterization methods for MEAs, with the purpose of reaching an evaluation procedure to characterize and define MEA quality and function after microfabrication. For this thesis, a new batch of MEAs was produced and their characteristics were examined. Other MEAs of different design and production dates were also examined to form a comparison. Different evaluation methods and the viability of these methods are presented. Electrical impedance spectroscopy and single frequency impedance analysis were the methods included in this thesis. Procedures completed in parallel with microscopy to observe visual changes. Moreover, a novel environmental conditioning test was introduced and tested out. The test involved the samples (two MEAs were tested) being placed onto an incubator and taken out regularly to have impedance measurements repeated over an extended period of time (100 hours). The experiment aimed to imitate a cell experiment as closely as possible without introducing cells to the system. The test seemed to cause visual and impedimetric changes, more so in one of the compared MEAs. As a result, the analysis and re-characterization of MEAs are advised after each cell experiment.
Moreover, over repeated impedance characterizations same size same material electrodes, some electrodes seemed to have more increase in the impedance magnitude over time. This drift also was observed through imaging of the electrodes. The imaging of the MEAs at different stages after their production revealed that there could be visual differences amongst electrodes of different impedimetric qualities. Electrodes with worsened impedance characteristics were observed to be a darker color compared to electrodes that holds a lower impedance magnitude value. An initial characterization protocol was suggested as a result of these tests. Furthermore, effects of the electrode size and material over the impedance was examined, and as a result, it was observed that circular electrodes with bigger diameter have lower impedance magnitude as expected. Circular electrodes with smaller diameter were observed to have less stable EIS measurements and higher impedance magnitudes.