Detection of DNA by electrochemical impedance spectroscopy (EIS) has been reported by many authors and assays have been developed using lab setups. However, as for most detection assay methods there are issues to address to enable the development for the sensor market: Long time-to-result & high complexity for labelled assays and a lack of sensitivity and reproducibility for label-free assays. This work considers two different approaches to address the issues of time-to-result and assay complexity. The first part presents work on achieving rapid sequence-specific electrochemical detection of DNA hybridisation to complementary DNA on an electrode surface. To accomplish assay sensitivity to low DNA target concentrations, a signal amplification strategy is often necessary. One approach is to couple an enzyme to the hybridised target molecules and to deposit insoluble dyes in the subsequent enzymatic reaction, which enhances sensitivity through an increase in the impedance signal in presence of a redox mediator. The time typically taken for this process (20 – 40 min) precludes the use outside lab setups. Therefore, a protocol for sensitive detection in the presence of redox mediator is demonstrated on a practical timescale required for use in sensor applications. Based on these results a model for the fundamental understanding of the amplification reaction is presented which explains the retention of sensitivity at these enhanced timescales. This also enabled further optimisation of the assay for application in single base pair mismatch detection in biologically relevant sequences. Moreover, direct detection of the precipitate formation is demonstrated which enables real-time measurement of the enzymatic reaction without redox agent addition and with enhanced mismatch discrimination. The second part investigates the possibility to detect DNA non-sequence-specifically by non-Faradaic means. This approach aims at reducing assay complexity by establishing whether it is possible to sense the presence of polymeric DNA in solution by measuring changes in the properties of the electrochemical double layer without DNA surface hybridisation. In a sensor setup this approach could be linked to a polymerase chain reaction (PCR) to discriminate polymer from nucleotide monomer and thereby enable PCR progress to be monitored. In this work the response in the electrochemical double layer at the interface of blocked metal electrodes and solutions containing DNA are studied by means of EIS. Blocking layers were applied to the electrode surface to prevent unspecific adsorption of molecules and ions to the metal surface whilst preserving the sensitivity to detection of changes in the double layer. The characteristics of surface blocking layers on disposable electrodes are studied as they are key to understand the double layer properties at a blocked surface. A number of self-assembled monolayers are compared with respect to their temperature stability and their blocking characteristics at different potentials and ion concentrations. This established the basis to study the effect of the presence of, initially, a model polyelectrolyte and, ultimately, DNA on the double layer. Polyelectrolyte detection is successfully shown for the model polyelectrolyte, polyacrylic acid. DNA detection was more challenging and possible causes for deviation from the polyacrylic acid response are discussed.

<p> Early detection of pathogens in food and water samples is essential in containing and preventing the spread of various diseases, such as campylobacter jejuni or E-coli. In the food processing industry, fast and reliable methods for testing products against contamination would mean faster delivery and better food quality. The pairing specificity of complementary DNA strands provides a highly selective means of detecting pathogens based on their genomic content. Recently, a lot of research has been directed towards the use of mainstream semiconductor technology to build highly sensitive and cheap DNA hybridization sensors. Typically, the gate of a metal-oxide-semiconductor (MOS) transistor is removed, and probe single-stranded DNA molecules are added to the exposed insulator. Complementary DNA hybridization from a solution sample can then be sensed electrostatically by the underlying Field-Effect transistor (FET). </p> <p> The work in this thesis is concerned with the mathematical modeling of FET based biosensors, named BioFETs. Modeling will enable the assessment of the sensitivity of such devices, as well as the potential for using the BioFETs in creating fully electronic microarrays. The mathematical model presented here captures the effects of ionic charge screening of the DNA charges by counterions in the ambient solution, and the effects of surface adsorption that can also aid in the charge screening process. The effects of varying different parameters on the sensitivity of the BioFET are investigated, and the noise contributed by the FET structure is incorporated into the analysis to quantify the expected signal-to-noise ratio (SNR) ofthe BioFET. </p> <p> In order to gain further insight into the operation of the BioFET, linear approximations are applied to the different regions of the BioFET to arrive at an analytic expression that approximates its expected response to DNA hybridization. The approximations are verified by comparing them against the results obtained from the physical model. Finally, different circuit configurations are presented that allow for highly sensitive biosensors to be realized using the BioFET, and a description of a fabricated electronic DNA microarray chip in standard CMOS 0.8 μm is presented. </p> / Thesis / Master of Applied Science (MASc)

<p>In this thesis, I present the electrochemical studies of three dendrimeric polypropylene imine (PPI) nanomaterials and their applications as a platform in the development of a novel label free DNA nanobiosensor based on electrochemical impedance spectroscopy. Cyclic voltammetry (CV), differentia pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivities of the nanomaterials on glassy carbon electrode (GCE) as the working electrode.</p>

<p>In this thesis, I present the electrochemical studies of three dendrimeric polypropylene imine (PPI) nanomaterials and their applications as a platform in the development of a novel label free DNA nanobiosensor based on electrochemical impedance spectroscopy. Cyclic voltammetry (CV), differentia pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivities of the nanomaterials on glassy carbon electrode (GCE) as the working electrode.</p>

Philosophiae Doctor - PhD / In this thesis, I present the electrochemical studies of three dendrimeric polypropylene imine (PPI) nanomaterials and their applications as a platform in the development of a novel label free DNA nanobiosensor based on electrochemical impedance spectroscopy. Cyclic voltammetry (CV), differentia pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivities of the nanomaterials on glassy carbon electrode (GCE) as the working electrode. / South Africa

Ultraviolet (UV) radiation is a common DNA damaging agent. Major DNA lesions, such as cyclobutane pyrimidine dimers (CPDs) and pyrimidine-(6-4)-pyrimidone (6-4PPs) photoproducts, are carcinogenic and mutagenic. UV induced DNA damage was investigated using a simple electrochemical DNA biosensor based on an ultra-trace graphite electrode (UTGE) and low molecular weight doble-stranded DNA (dsDNA) from salmon sperm. Biosensor was prepared using adsorption of dsDNA on a surface of the UTGE and then used to detect UV-induced DNA damage. Effects of UV radiation were investigated using a combination of several electrochemical technics: square-wave voltammetry (SWV) for direct monitoring of DNA base oxidation and cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), as non-direct methods, using redox-active indicator [Fe(CN)6]4-/3- . CV and EIS, which allow characterization of electrode surface, were used to optimize preparation of the dsDNA/UTGE biosensor. Prepared dsDNA/UTGE biosensor was exposed to UV radiation using UV lamp with two set wavelengths: UVC of 254 nm and UVA of 365 nm. UVC radiation was used to damage DNA. Relative signal decrease was 50% after 20 minutes of exposure to UVC radiation. UVA radiation was used to compare effects of different types of UV radiation. Obtained...

The interaction between three selected representatives of environmental pollutants - naphthalene, anthracene, and 2-aminoanthracene - and DNA was investigated using an electrochemical DNA biosensor based on a glassy carbon electrode (GCE) and low molecular weight DNA from salmon sperm (DNA/GCE). The interactions with DNA were monitored using square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS). For naphthalene, there was no DNA damaging interaction observed. In the case of anthracene, the formation of an intercalation complex [DNA-anthracene] was observed. However, its formation does not cause DNA strand breaks. The formation of similar intercalation complex was observed for 2-aminoanthracene [DNA-2-aminoanthracene], where we suppose on the basis of the results obtained that the intercalation of 2-aminoanthracene into the DNA double helix induces a tension and subsequent formation of single-strand breaks, which cause that the fragments of DNA fall away from the electrode surface. The intercalative interaction of DNA with anthracene a 2-aminoanthracene was used in the development of electrochemical methods for determination of these compounds at the GCE and DNA/GCE. At the development of the methods, DC voltammetry (DCV) and differential pulse voltammetry (DPV) were used....

Presented Ph.D. Thesis is focused on the development of analytical methods applicable for determination of selected xenobiotic compounds and for monitoring DNA damage they can induce. The main attention has been paid to the development and testing of non-toxic electrode materials for preparation of miniaturized electrochemical devices and novel electrochemical DNA biosensors. 2-Aminofluoren-9-one (2-AFN) was selected as a model environmental pollutant, which belongs to the group of hazardous genotoxic substances. Its carcinogenic and mutagenic effects may represent a risk to living and working environment. 2-AFN has one oxo group, where the cathodic reduction occurs, and one amino group, where the anodic oxidation occurs. The voltammetric behavior of 2-AFN in the negative potential region was investigated at a mercury meniscus modified silver solid amalgam electrode (m-AgSAE) representing a non-toxic and more mechanically robust alternative to mercury electrodes. This working electrode was subsequently used for the development of a newly designed miniaturized electrode system (MES), which has many benefits as the possibility of simple field measurements, easy portability, and the measurement in sample volume 100 µL. Moreover, a glassy carbon electrode (GCE) was used for further investigation of...