Contrast agents (CAs) based on gadolinium (Gd), such as DotaremTM, are widely used in magnetic resonance imaging (MRI). The relatively low relaxivity (r1 = 3.94 mM-1 s-1 at 10 MHz, 37 °C) of the clinical standard, DotaremTM, leads to the need to administer large amounts of this agent, which raises toxicity concerns. Immobilisation of gadolinium-based CAs to large gold nanorods (GNRs) can lead to higher relaxivity and thus also reduce the administered dose. In addition to the platform provided by the gold nanostructure for the incorporation of many other functional units, the gold nanomaterial itself offers the potential for plasmonic effects to be exploited, such as photothermal therapy (PTT).

This thesis develops a reliable route to synthesise two types of GNRs functionalised with neutral and anionic monometallic Gd chelates as well as a cationic multimetallic Gd chelate. The functionalised GNRs were prepared successfully and fully characterised by a series of techniques to confirm the desired morphology, optical properties and successful attachment of the Gd chelates. Further studies showed that these Gd-functionalised GNRs were not cytotoxic at concentrations higher than those used in vivo (250 μM of gold) and also displayed very good cellular uptake and excellent colloidal stability within the clinical imaging timeframe.

The relaxivity values measured for the GNRs functionalised with monometallic and multimetallic Gd chelates developed in this work were found to be as high as 20.5 mM−1 s−1 and 60.0 mM-1 s-1 per Gd unit (at 10 MHz, 25 °C), respectively. These values represent a 4-fold and a 12-fold improvement on clinically-used Dotarem™. At 23 MHz and 25 °C, the relaxivity performance of the multimetallic Gd-functionalised GNRs reached an extremely impressive relaxivity value of 164.4 mM−1 s−1 per Gd unit, which, to our knowledge, is the highest reported for gold nanostructures functionalised with molecular Gd contrast agent units. The monometallic and multimetallic Gd-functionalised GNRs were also assessed in terms of their photothermal performance and were found to convert light efficiently into heat, while showing photothermal stability. The evaluation of the heating effect was investigated in terms of GNR concentration, power density and duration of irradiation, revealing an impressive capacity to heat the immediate surroundings to temperatures of around 60 °C above the starting temperature. The photothermal therapeutic effect was assessed in vitro, leading to almost complete destruction of the cells after only 5 minutes of irradiation. These results demonstrated the great potential of the Gd-functionalised GNRs as an effective MR imaging-guided PTT system.