A robust dithiocarbamate tether allows novel gadolinium units based on DOTAGA (q=1) to be attached to the surface of gold nanoparticles (2.6–4.1 nm diameter) along with functional units offering biocompatibility, targeting and photodynamic therapy. A dramatic increase in relaxivity (r1) per Gd unit from 5.01 mm−1 s−1 in unbound form to 31.68 mm−1 s−1 (10 MHz, 37 °C) is observed when immobilised on the surface due to restricted rotation and enhanced rigidity of the Gd complex on the nanoparticle surface. The single‐step synthetic route provides a straightforward and versatile way of preparing multifunctional gold nanoparticles, including examples with conjugated zinc–tetraphenylporphyrin photosensitizers. The lack of toxicity of these materials (MTT assays) is transformed on irradiation of HeLa cells for 30 minutes (PDT), leading to 75 % cell death. In addition to passive targeting, the inclusion of units capable of actively targeting overexpressed folate receptors illustrates the potential of these assemblies as targeted theranostic agents.

Two different octadentate gadolinium chelates based on DO3A and DOTAGA chelates (hydration number q = 1) have been used to prepare a series of bi-, tri-and tetrametallic d-f mixed-metal complexes. The piperazine-based dithiocarbamate linker ensures that rotation of the gadolinium chelates is restricted, leading to enhanced relaxivity (r1) values, which increase with overall mass and the number of gadolinium units. The r1 value (at 10 MHz, 25 °C) per Gd unit rises from 5.0 mM −1 s −1 for the Gd-DO3A-NH2 monogadolinium chelate to 9.2 mM −1 s −1 in a trigadolinium complex with a ruthenium(III) core. Using a 1.5 T clinical scanner operating at 63.87 MHz (25 °C), an 86% increase in relaxivity per gadolinium unit is observed for this multimetallic compound compared to clinically-approved Dotarem. The gadolinium complexes based on the DOTAGA chelate also performed well at 63.87 MHz, with a relaxivity value of 9.5 mM −1 s −1 per gadolinium unit being observed for the trigadolinium d-f mixed-metal complex with a ruthenium(III) core. The versatility of dithiocarbamate coordination chemistry thus provides access to a wide range of d-f hybrids with potential for use as high-performance MRI contrast agents.