Modified Gold-Coated Magnetic Nanoparticles: Development of an Amperometric ‘Calibration-Free’ Metal-Ion Sensor

摘要

In this thesis, several milestones in the development of an absolute ‘calibration-free’ sensor are described, using a sensing interface of modified, gold-coated magnetic nanoparticles (Au@Fe3O4). The Au@Fe3O4 sensing interface is comprised of a self-assembled monolayer of thioctic acid, whose distal end is activated with 1-(ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS) chemistry which allows coupling of a recognition element (here oligopeptides for metal ions using His-Ser-Gln-Lys-Val-Phe (HSQKVF) and Gly-Gly-His which have strong affinity for cadmium and copper respectively). The assembly of the sensing interface was confirmed by surface-enhanced Raman spectroscopy (SERS) and the transduction of the metal ions was by use of an electrochemical calibrated and calibration-free system.For the first time, SERS was employed as a characterisation tool in understanding the step by step fabrication of the sensing interface. Subsequently a Au@Fe3O4 sensing interface was used in voltammetric measurement of copper and cadmium as single species using a calibrated system. The use of HSQKVF modified Au@Fe3O4 nanoparticles to detect copper and cadmium simultaneously and, in a separate experiment, Gly-Gly-His to detect both copper and cadmium was also demonstrated. An absolute ‘calibration-free’ amperometric method was then developed using the Au@Fe3O4 sensing interface for single and two metal ions. The amount of metal ion extracted from an analyte solution of a given volume was measured directly from the charge passed during reduction of the ion. The charge was obtained from integrated areas under chronoamperograms, and by use of a kinetic model based on a first order reaction of a surface-confined redox system. The absolute method showed the ability to quantify the amounts of analyte from the measurement of charge passed. To estimate the uncertainty of the measurements, the Guide to the Expression of Uncertainty of Measurement (GUM) was adopted.