The development of wireless DNA microelectrochemical microarray sensors is described. The operational principles of these sensors are based on bipolar electrochemistry. Bipolar electrodes are used to fabricate the wireless microarrays in this work. The systems are configured so that DNA sensing is carried out at the cathodic end of a bipolar electrode (BPE) and the result of the sensing experiment is reported at the anodic end of the BPE. There are two types of reporting platforms developed in this study. The first type relies on the emission of electrogenerated chemiluminescence (ECL). The system is configured so that ECL is emitted at the anodic end of the BPE when the target DNA is hybridized to the capture probe DNA immobilized on the cathodic end of the BPE. However, when there is no hybridization reaction occurs, there is no ECL emission on the electrode surface. The second type of reporting platform developed is based on silver electrodissolution at the anodic end of a BPE. When a reduction reaction occurs at the cathodic end of a BPE, it triggers oxidation and dissolution of silver deposited at the anodic end of the BPE. The loss of silver can easily be detected by the naked eye. This detection principle is used for DNA detection: when the target DNA is hybridized to capture probe DNA on the BPE, the BPE becomes shorter. However, if target DNA does not hybridize to the electrode surface, the length of the BPE remains the same. The BPE microarrays described in this work eliminate the need for complicated microfabrication procedures and instrumentation. For example, as many as 1000 BPEs can be simultaneously controlled using just two driving electrodes and a simple power supply. To fully utilize BPE microarrays for specific sensing tasks, a method based on robotic spotting was developed to modify the cathodic end of each BPE in the array. Because each BPE in a microarray is individually addressable, this development allows each BPE to perform a particular sensing operation. / text

The work deals with topic of bipolar electrodes of lead-acid accumulator. Theoretical part of the thesis presents of comtenporary knowledge of the topic as it is described in scientific literature. Experimental part deals with conductometric method that is used in corrosion rate measurement of experimental electrodes.

The development and characterization of bipolar electrode (BPE) focusing is described. BPE focusing is an electrokinetic equilibrium technique in which charged analytes are focused and locally enriched on an electric field gradient in the presence of a counter-flow. This electric field gradient is formed at the boundary of an ion depletion zone – the direct result of faradaic reactions occurring at the BPE in the presence of an externally applied electric field. Direct measurement of the electric field strength in the ion depletion region shows that the electric field is enhanced in this region and takes on a gradient shape, confirming the results of numerical simulations. Transient electric field measurements with simultaneous monitoring of a focused fluorescent tracer reveal that the field gradient forms rapidly upon application of the external field and remains stable over time with the tracer focused at a local field strength predicted by simple electrokinetic equations. These transient electric field measurements probe the effect of individual experimental parameters on the electric field gradient and the focused band. The results of these studies indicate that a steeper field gradient leads to enhanced concentration enrichment of the analyte. The slope of the gradient is increased with higher concentration of the running buffer and higher applied field strength. The addition of pressure driven flow across the microchannel moves the location of the field gradient and the position of the focused band. Further enhancement of enrichment is achieved through the suppression of Taylor dispersion after coating the microchannel with a non-ionic surfactant. The findings of these studies have motivated the transition of BPE focusing to smaller microchannels. A decrease in microchannel size not only decreases Taylor dispersion, but also provides access to higher buffer concentration and higher applied field strength, both of which enhance enrichment. The result is a three-order-of-magnitude increase in total analyte enrichment at a much higher enrichment rate. Furthermore, a dual channel configuration for BPE focusing is introduced which provides greater control over focusing conditions. Finally, the formation of ion depletion and enrichment zones at a BPE in a microchannel is shown to mimic ion concentration polarization (ICP) at micro-/nano-channel junctions. This is significant because this faradaic ICP provides a model to which traditional ICP can be compared and is achieved in a more easily fabricated device. In summary, the fundamental principles of BPE focusing are described. A greater understanding of the effect of experimental parameters on the focusing process leads to an unprecedented magnitude and rate of enrichment in a simple device architecture. / text

Philosophiae Doctor - PhD (Chemistry) / Electrochemiluminescence (ECL) is a light-emitting process generated by electrochemical redox reactions and has been widely used as an analytical tool, especially in the field of biosensing, that is, immunoassays and DNA-probe assays. Thus, the scope of this work was to develop a simple, sensitive ECL immunosensor for cardiac injury and to study and present insights into newly fabricated platforms for bioanalytical applications by using ECL as detection mechanism. / 2021-08-31

In this dissertation, three different microfluidic devices with bioanalytical applications are presented. From chapter to chapter, the bioanalytical focus will gradually become the development of a point-of-care sensor platform able to yield a reliable and quantitative response in the presence of the desired target. The first device consists of photolithographically-patterned gold on glass bipolar electrodes and PDMS Y-shaped microchannels for the controlled enrichment, separation from a mixture, and delivery of two charged dyes into separate receiving microchannels. The principle for the permanent separation of these dyes is based on the concept of bipolar electrochemistry and depended on the balancing/unbalancing of convective and electromigrating forces caused by the application of a potential bias, as well as the activation/deactivation of the bipolar electrodes. Two different bipolar electrode configurations are described and fluorescence is used to optimize their efficiency, speed, and cleanliness of delivery. The second device is a DNA sensor fabricated on paper by wax printing and folding to form 3D channels. DNA is detected by strand-displacement induced fluorescence of a single-stranded DNA. A multiplexed version of this sensor is also shown where the experiment results in “OR” and “AND” Boolean logic gate operations. In addition, the nonspecific adsorption of the reagents to cellulose is studied, demonstrating that significant reduction of nonspecific adsorption and increased sensitivity can be achieved by pre-treating the substrate with bovine serum albumin and by preparing all analyte solutions with spectator DNA. The third device, also made of paper, has a novel design and uses a versatile electrochemical detection method for the indirect detection of analytes via the direct detection of AgNP labels. A proof-of-concept experiment is shown where streptavidin-coated magnetic microbeads and biotin-coated AgNPs are used to form a composite model analyte. The paper device, called oSlip, and electrochemical method used are easily coupled so the resulting sensor has a simple user-device interface. LODs of 767 fM are achieved while retaining high reproducibility and efficiency. The fourth device is the updated version of the oSlip. In this case, the objective is to show the current progress and limitations in the detection of real analytes using the oSlip device. A sandwich-type immunoassay approach is used to detect human chorionic gonadotrophin (pregnancy hormone) present in human urine. Various optimization steps are performed to obtain the ideal reagent concentrations and incubation time necessary to form the immunocomposite in one step, that is, by mixing all reagents at the same time in the oSlip. Additionally, improvements to the electrochemical detection step are demonstrated. / text