Layer-by-layer assembly of organic films and their application to multichannel surface plasmon resonance sensing

Abstract

This thesis provides a study of a single chip, multi-channel surface plasmon resonance (SPR) imaging system. The equipment has no moving parts and uses a single sensor "chip" onto which multiple channels can be incorporated. A light emitting diode is used as a photon source while a CCD camera forms the detector. The optical configuration has been designed to achieve a uniform illumination of the sample over a fixed area with a range of incident angles. Poly(ethylene imine), PEI, poly(ethylene-co-maleic acid), PMAE, poly(styrene sulfonate), PSS, and a cationic modified polyacrylic ester, PMADAMBQ, are used as the molecular "bricks" in layer-by-layer (LbL) self-assembled organic architectures. Reflectivity changes in real time are used to follow the adsorption steps during the deposition of the multilayer films. Sensing experiments are mainly focused on the first row transition metals such as iron (II), nickel (II), copper (II)and zinc (II). Sensing of anionic sodium dodecylbenzene sulphate, C(_12)H(_25)C(_6)H(_4)SO(_3)Na, and a reversible pH-dependent response for a PEI/PMAE/PMADAMBQ LbL film are also reported. Using a two bilayer structure, PEI/PMAE/PMADAMBQ/PMAE, a detection limit of less of one part per million for copper ions in solution is measured. Atomic force microscopy is used to elucidate the morphology of the organic films. In some cases, the visualization of isolated polymeric chains is demonstrated. It is proved that polyelectrolytes of different charge density form dissimilar structures. The outer surface of PEI/PSS bilayers appears to be more uniform than that of PEI/PMAE bilayers. This is believed to have an influence on the sensing performance of the LbL architectures. The use of the SPR sensing system for simultaneous interrogation of different polyelectrolyte thin films is demonstrated. Two different LbL self-assembled films, PEI/PSS and PEI/PMAE, are built-up on the same chip. Their response to a variety of metal ions is shown to be independent and reasonably reproducible. Moreover, consistent results are obtained when using sensing chips stored for a relatively long time.