Coordination polymers nanoparticles for bioimaging

Early diagnosis of patient diseases is subjected to the appropriate use of bioimaging techniques. For this reason, the development of contrast agents that improve and enhance the response of current clinical imaging practices is a pressing concern. Non-invasive bioimaging techniques most often need specific probes to follow and measure biological routes in living systems. These molecular imaging agents must exhibit: I) a remarkable contrast effect, i.e. a high signal-to-noise ratio under real physiological conditions, II) pronounced in vivo stability under the effect of numerous enzymes or proteases present in serum or targeted tissue equilibrated with a fast clearance from healthy organs and III) low cost and eco-friendly production. To overcome current drawbacks that hindrance the full development of the different bioimaging techniques, several groups are exploring nanoparticles as contrast agents. In this scenario, coordination polymer nanoparticles have emerged as a handy platform offering predesigned unique advantages thanks to their chemical flexibility, structural diversity and tailoring skills. Indeed, these systems reveal high metal cargos, low toxicity and multifunctional character by adequately selecting the combination of metal ions and ligands. Moreover, in a reminiscent way of organic polymeric nanoparticles, coordination polymer nanoparticles have also demonstrated its ability to encapsulate therapeutic-active molecules, thus combining diagnostic and therapeutic functionalities, the so-called Theranostic nanomedicine. For all these reasons, the use of this family of nanoparticles as imaging contrast agents has attracted broad interest over the last years with numerous examples being reported. Herein, we review main accomplishments in the area grouped according to the used technology, including magnetic resonance imaging, computed tomography, optical imaging, radioimaging or photoacoustic imaging.