The unification of isotachophoresis (ITP) and electric field gradient focusing (EFGF) is proposed, based on theoretical considerations and experimental evidence from previous literature. This... Show moreThe unification of isotachophoresis (ITP) and electric field gradient focusing (EFGF) is proposed, based on theoretical considerations and experimental evidence from previous literature. This unification increases the versatility of each EFGF method. A novel isotachophoretic separation method is developed which is based on one of the EFGF techniques, namely micro/nanofluidic concentration polarization devices, This novel method, coined depletion zone isotachophoresis (dzITP), requires a single electrolyte only, which is a simplification over conventional isotachophoresis. Moreover, positioning of focused analyte zones, selective release of individual analyte zones and continuous filtering based on ionic mobility differences is possible. Furthermore, it is shown that microvalves in PDMS chip devices can act as nanochannels upon closure, giving rise to a wide range of concentration polarization phenomena. Compounds can be concentrated over 1000-fold and subsequently be released. These techniques give novel possibilities for bioassays and sample preparation. Show less
In this thesis, nanochannels as well as nanofluidic phenomena are used to provide new and miniaturized bioanalytical tools for the life sciences. Isotachophoresis performed in nanochannels showed... Show moreIn this thesis, nanochannels as well as nanofluidic phenomena are used to provide new and miniaturized bioanalytical tools for the life sciences. Isotachophoresis performed in nanochannels showed the focusing and separation of analytes in a 0.4 picoliter volume, which is a volume in the order of a sample from a single cell. Depletion zone isotachophoresis (dzITP) is demonstrated which uses a nanofluidic phenomenon, concentration polarization, to enable isotachophoresis in a microchannel while using only a single electrolyte. A concept for surface enhanced Raman spectroscopy (SERS) sensor (SERSOR) is explored; a coating protecting the SERS surface from irreversible adsorption may enable dynamic measurements of biomolecules in solution in minute volumes. Working with nanochannels has led to the discovery of new unexpected fundamental phenomena: the very high surface to volume ratio in nanochannels causes acidification of solutions introduced in them, despite the presence of up to 1 mol/L of buffer. Also, extreme pressures of more than a 1000 bar may be induced in a nanochannel by what we named electrocavitation, an effects shown to impose a limit on further downscaling of ITP. Show less
