Synthesis and modification of magnetic nanoparticles for highly sensitive sensing

Abstract

Magnetic nanoparticles (MNPs) have attracted widespread interest in analytical chemistry because of their unique physical properties and the ability to manipulate MNPs with a magnetic field. These properties have led to a proliferation of research into the use of MNPs in a wide-range of analytical and sensing applications. Presented in this thesis is a study into the synthesis and modification of magnetic iron oxide nanoparticles (MIONs) with the ultimate aim being their application towards enhanced chemical sensing systems. The first section of the thesis reports the aqueous-phase synthesis of MIONs and a detailed study into the controlled adsorption of polyethyleneimine (PEI) onto the MIONs. The combination of MIONs with a PEI coating allows for the selective magnetic sequestration and quantification of ultra-trace levels of free cupric ions. The importance of controlled PEI adsorption for tailoring colloidal properties, as well as ensuring maximal cupric removal capacity is demonstrated. The second section of the thesis focuses on the modification of PEI-coated MIONs with gold to enable their use in electro-analytical applications. Reported in this section is a new method that was developed for the aqueous synthesis of 50-150 nm gold-coated MIONs, with the ability to engineer the coverage of gold coating. In-depth characterisation of the gold-shell formation process was performed. This section is concluded with a study into the functionalisation of gold-coated MIONs using thiol molecules with different functional groups for use as linkers in the attachment of functional molecules. The third section of the thesis explores the concept of utilising gold-coated MIONs as active elements in the selective capture and direct electro-analytical quantification of analytes. This system of ‘dispersible electrodes’ combines the ability to magnetically manipulate the dispersible electrodes, with enhanced electrical conductivity due to the gold coating. The ability of the system to reduce response times and improve detection limits of electrochemical sensors by bringing the sensor to the analyte rather than the conventional paradigm of bringing the analyte to the sensor is demonstrated.