Development of electrochemical methods for sensing at bipolar electrode arrays

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Borchers, Janis
Major Professor
Anand, Robbyn K
Hillier, Andrew
Lee, Young-Jin
Smith, Emily
Windus, Theresa
Committee Member
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This dissertation describes the development of electrochemical methods for sensing at bipolar electrode (BPE) arrays. Electrochemical sensors are in use in many aspects of everyday life from glucose meters to radon detectors. It is important to develop methods that continue to improve the sensitivity and reliability of these sensors. Much work has been done to improve how the electrochemical signal is processed, such as adapting the electronics to chips the size of a cell phone and using cell phones for imaging. The methods of transducing the signal are also growing, such as employing microfluidic platforms, using new materials to enhance the electrode signal, and improving the limits of detection. Point-of-care (POC) is an attribute that is also important with work with electrochemical sensors. POC sensors need to be portable, low cost, highly sensitive and selective, and have short analysis times to be effective. Delivering rapid results to patients allows for quicker diagnosis and the treatment process to begin sooner. The work in this dissertation focuses on electrochemical methods of sensing at BPE arrays. A BPE is an electronic conductor in an ionic solution. A potential is applied to the ionic solution by driving electrodes producing faradaic reactions at the two ends of the BPE. By applying the potential to the driving electrodes instead of the BPE directly, many BPEs can be arranged in an array format and are essentially considered wireless. BPE arrays require only a small DC power source making them ideal for adaption to POC testing. The methods discussed in this dissertation are focused on two main aspects, developing a means to extract information rich voltammetric information at a BPE array and a method to improve the sensitivity of BPE arrays. An underlying focus of the electrochemical methods is they are easily adaptable to POC needs. The first section of this work describes a linear array of BPEs in a ladder format. In this work, one end of the BPE facilitates a faradaic reaction that depends on the presence of an analyte. This reaction enables an electrically coupled process, at the other end - an electrogenerated chemiluminescence (ECL) reaction producing a visible signal. The opposing ends of the BPEs are positioned in two separate microfluidic channels separated by an insulator. The two ends are in contact with two different electrolyte solutions at distinct potentials. This arrangement generates an interfacial potential, which drives the electrically coupled anodic and cathodic reactions at opposing ends of the BPE. The discrete voltages imposed by the ladder arrangement, allow the BPE array to display the entire current-potential response simultaneously and in real time. The second section of this dissertation focuses on a method to improve the sensitivity of BPEs which have characteristically suffered from poor limits of detection when used in biological applications. This section of the dissertation has two aspects to it. First, amplification methods are reviewed with interdigitation of the sensing end of the BPE employed as the amplification strategy in this work. Interdigitated BPEs (IDBPEs) take advantage of the close proximity of two electrodes to facilitate redox cycling, which allows species that undergo reversible faradaic reactions to be reduced and oxidized repeatedly such that one molecule is able to transfer many electrons. This amplification of the current at the sensing end of each BPE generates an increase of the ECL signal on the reporting end thereby leading to improved sensitivity and limit of detection. Second, the IDBPE array is adapted to be used with dielectrophoresis (DEP) to capture, retain, and electrochemically analyze melanoma cells demonstrating the IDBPE array is able to be utilized in biological applications. In summary, the work in this dissertation describes the development of two electrochemical methods for sensing at BPE arrays. In addition, electrochemical analysis of melanoma cells is applied to the IDBPE array with the use of DEP for cell manipulation.
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