Due to their large chemically active surface and stability at high temperatures carbon nanotubes (CNTs) have been used as a support material for the dispersion and stabilization of metal and semiconductor nanoparticles (NPs). These hybrid materials have found several applications in catalysis, nanoelectronics, optics, nanobiotechnology, etc. Several ways have been described in the literature to immobilize NPs on CNTs and they can be divided into two main pathways: (a) the formation (and stabilization) of metal NPs directly on the carbon nanotube surface, and (b) the connection of chemically modified NPs to carbon nanotubes or to modified CNTs. A plethora of methods for the synthesis of different NPs have been very recently developed. This know-how is now available for the generation of a large variety of new hybrid products in combination with CNTs. A selection of representative examples of the synthesis, properties and applications of NP–CNTs is here reported and discussed.

We describe the synthesis of Gd(III)-doped carbon dots as dual fluorescence-MRI probes for biomedical applications. The derived Gd(III)-doped carbon dots show uniform particle size (3–4 nm) and gadolinium distribution and form stable dispersions in water. More importantly, they exhibit bright fluorescence, strong T1-weighted MRI contrast and low cytotoxicity.