"Impedance based biosensor platform design and applications."
Early disease detection could help to adjust patient treatment to their specific needs. For example, one hour prior to a heart attack the body releases an elevated level of the protein CRP. If a special sensor, sensitive to this protein, is incorporated in a wearable device, such as a wrist watch, the attack could be detected and the patient could go to the hospital and receive the appropriate treatment.
Biosensors are analytical devices, which can specifically respond to an analyte, interpret the concentration and transform it to a measurable electrical signal. Currently, a lot of research is focused on tailoring the recognition layers for specific enzymes, cells, DNA or antibodies. Recent work in this field has led to synthetic sensors able to mimic a biological detection. These molecular imprinted polymers (MIP) offer significant advantages over biological layers, including robustness and long shelf life, making them ideal for integration with commercial devices.
However, the readout of these biomimetic layers still needs some research. One of the methods suited for this readout is Electrochemical impedance spectroscopy. This powerful, non-invasive measurement technique is a well- established method in the field of biological research. Although impedance analyzers are readily available, a combination of high cost, large form factor and lack of a user-friendly operating method makes them unsuited for home use or smart device integration. This work focusses on the portability of electrochemical impedance readout devices through miniaturization, multiplexing of multiple channels and advanced signal processing.
First chapter discusses the typical layout, the working principles of a biosensor and its fields of application. The second chapter elaborates on different design principles, measurement setups and methods for electrochemical impedance spectroscopy as well as giving some basic measurement considerations.
The third chapter focuses on the developed devices. First the adaptions made to a commercially available impedance chip are discussed. The experiences and problems encountered, during a systems performance test, are then used to design the BioZ°. This eight-channel device is custom made to operate on biological relevant frequencies while still having a large impedance measurement range. Subsequently this system is expanded with a multiplexer making it possible to measure up to ninety six channels quasi-simultaneously. To further
increase the measurement speed two different arbitrary wave forms, based on the NI USB-6251 DAQ platform are presented. The first waveform is composed from a number of identical sine waves while the second method adapts the waveform to have a constant signal to noise ratio. Lastly a fourth design focused on mobility is presented. For this purpose the commercially available Arduino DUE board is adapted to perform standalone impedance measurements while storing the data to an SD-card.
The fourth chapter validates these setups in three different biological applications. First the adapted 5933 board is tested in a wet cell DNA hybridization and denaturation setup. Next the BioZ° is used to detect the molecules histamine and nicotine on a molecular imprinted polymer. After extension with the impediplexer the BioZ° is tested in a proliferation setup. In order to find the optimal starting concentrations for drug testing, three different cell lines (CHO,BV2, HEK) are seeded, in different concentrations on a nineteen six well plate with gold electrodes at the bottom. Subsequently the effects of different stimulators and growth inhibitors is tested on these different cell lines. Next the arbitrary wave setup is tested on a wet cell and a MIP layer sensitive to the Ara h 1 molecule. Lastly the Arduino DUE is used to monitor the wet cell over time.
The impedance methods presented in this work could ultimately lead to the development of smart devices able to interact with biological sensors sensitive to diverse disease pathogens.,