The A 3 adenosine receptor (AR) is a G protein-coupled receptor (GPCR) overexpressed in the membrane of specific cancer cells. Thus, the development of nanosystems targeting this receptor could be a strategy to both treat and diagnose cancer. Iron-filled carbon nanotubes (CNTs) are an optimal platform for theranostic purposes, and the use of a magnetic field can be exploited for cancer magnetic cell sorting and thermal therapy. In this work, we have conjugated an A 3 AR ligand on the surface of iron-filled CNTs with the aim of targeting cells overexpressing A 3 ARs. In particular, two conjugates bearing PEG linkers of different length were designed. A docking analysis of A 3 AR showed that neither CNT nor linker interferes with ligand binding to the receptor; this was confirmed by in vitro preliminary radioligand competition assays on A 3 AR. Encouraged by this result, magnetic cell sorting was applied to a mixture of cells overexpressing or not the A 3 AR in which our compound displayed indiscriminate binding to all cells. Despite this, it is the first time that a GPCR ligand has been anchored to a magnetic nanosystem, thus it opens the door to new applications for cancer treatment.