Development of a miniature capacitive sensor for liquid level measurement in organ-on-chip applications
Dhruba, Mehedi (2023)
Dhruba, Mehedi
2023
Master's Programme in Biomedical Sciences and Engineering
Lääketieteen ja terveysteknologian tiedekunta - Faculty of Medicine and Health Technology
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Hyväksymispäivämäärä
2023-06-22
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202306136726
https://urn.fi/URN:NBN:fi:tuni-202306136726
Tiivistelmä
Background and aim: Organ on chip (OOC) are multi-channel 3D microfluidic integrated circuits that mimic human mechanics, physiology and functions of a whole human organ and organ system. OOC devices offer a more realistic setting for studying biological responses to medicines and other stimuli because they imitate the shape and operation of human organs as microfluidic systems. However, for OOC devices to deliver exact and dependable findings, fluidic conditions must be precisely controlled. In organ-on-chip applications, liquid level monitoring is an important factor, especially in applications that use gravity-based pumping, which consists of an inlet and outlet chamber to measure and control the flow of the liquid. The aim of this thesis was to develop a capacitive interdigital sensor for organ-on-chip (OOC) applications that can measure liquid levels. Capacitive sensors were chosen due to their simplicity, linearity and easily accessibility. When the liquid level in the OOC device fluctuates, the sensor's capacitance varies, which can be measured. The size and shape of the sensor and the electrode geometry's design are important element for the sensor's sensitivity and accuracy.
Material and Method: After studying sensor geometry sensors were designed by AutoCAD and fabricated. The material for the substrate of the sensor was chosen PCB-FR4 because it is strong, water resistant and gives a good insulation layer. The sensor was fabricated and then soldered with copper wire then coated with Parylene C for the insulation layer and then tested with liquid DPBS (Dulbecco’s phosphate-buffered saline). Based on theory, 3 types of sensors, including different versions, were fabricated and tested and analyzed the data from the experiment. Type A consists of two single parallel electrodes with different dimensions and different gaps between electrodes. Type B consists of vertical finger electrodes with different dimensions for different versions based on 1-1-1 IDT sensor theory. Type C is horizontally placed finger electrodes where the gap between each electrode is same. In the experiment all the sensors then tested with different flow rate and the experiment were repeated to check the performance. Experiments were done both automatic and manual insertion and suction of liquid.
Results: In sensor characterization and comparison of data from different types of sensors, 1-1-1 IDT sensor Type B Version 3 had better average sensitivity compared to other versions of Type B as well as Type A and Type C sensors, including each version which was 3.92 pF/mm. The theoretical results of the sensor, like maximum capacitance and sensitivity, were almost close enough to the experimental results of the sensors, except there were some minor errors due to experimental limitations.
Conclusion: The sensor performance was quite good as it has high sensitivity, accuracy, and repeatability. Fabrication of the sensor is simple, fast, inexpensive, and easily accessible. The sensor can be customized as needed for the application. The findings show that the sensors are capable of accurately measuring liquid levels. Then sensor can be customized as needed for the application.
Material and Method: After studying sensor geometry sensors were designed by AutoCAD and fabricated. The material for the substrate of the sensor was chosen PCB-FR4 because it is strong, water resistant and gives a good insulation layer. The sensor was fabricated and then soldered with copper wire then coated with Parylene C for the insulation layer and then tested with liquid DPBS (Dulbecco’s phosphate-buffered saline). Based on theory, 3 types of sensors, including different versions, were fabricated and tested and analyzed the data from the experiment. Type A consists of two single parallel electrodes with different dimensions and different gaps between electrodes. Type B consists of vertical finger electrodes with different dimensions for different versions based on 1-1-1 IDT sensor theory. Type C is horizontally placed finger electrodes where the gap between each electrode is same. In the experiment all the sensors then tested with different flow rate and the experiment were repeated to check the performance. Experiments were done both automatic and manual insertion and suction of liquid.
Results: In sensor characterization and comparison of data from different types of sensors, 1-1-1 IDT sensor Type B Version 3 had better average sensitivity compared to other versions of Type B as well as Type A and Type C sensors, including each version which was 3.92 pF/mm. The theoretical results of the sensor, like maximum capacitance and sensitivity, were almost close enough to the experimental results of the sensors, except there were some minor errors due to experimental limitations.
Conclusion: The sensor performance was quite good as it has high sensitivity, accuracy, and repeatability. Fabrication of the sensor is simple, fast, inexpensive, and easily accessible. The sensor can be customized as needed for the application. The findings show that the sensors are capable of accurately measuring liquid levels. Then sensor can be customized as needed for the application.