Spatiotemporal electrochemical detection in nanofluidic devices

The main focus of this thesis is to explore mass-transport processes for redox-active analytes in concentrated supporting electrolytes when they are driven by external pressure through nanofluidic channels with em-bedded electrodes. The principal devices employed in these experiments are so-called nanogap electrodes, which consist of two electrodes located in the floor and roof of the nanochannel. Electrochemical reactions taking place at the electrodes can profoundly disturb the concentration distribu-tion of analytes along the axial direction of the nanochannel in several manners. First, as elucidated in Chapter 4, changes in the redox state of molecules at different electrodes can cause significant variations in the distribution of analyte concentrations under steady-state conditions. Sec-ond, time-dependent changes in electrode potential can cause local, tran-sient fluctuations in the analyte concentration and the effects are made use of to develop a concept of electrochemical chromatography in Chap-ter 2 and 3. These represent a new class of phenomena in nanofluidics next to the more established electrokinetic and depletion-enrichment effects. In addition to the three core chapters, we explored further potential applications of electrochemistry in bioanalytical research. Chapter 5 decribes exploratory attempts to detect single conducting polymer mole-cules as they form a conducting pathway between two closely spaced electrodes. This approach can be further developed to become a transduc-tion mechanism in single-molecule detection assays suitable for detection of short DNA oligomers. Chapter 6 instead shows how electrochemical detection at microelectrodes can yield the same enzyme kinetic parame-ters as conventional photo-spectroscopy techniques, a preparatory work prior to studying the kinetics of single enzyme in nanogap devices.