Nanoparticles-based fluorescent conjugates for MRI contrast agents and bioimaging

Magnetic resonance imaging (MRI) is a useful tool in clinical diagnostic field because it has higher spatial resolution and contrast in soft tissue than other imaging procedures. The MRI method is based on the magnetic property of protons that align themselves in a very large magnetic field and the main MRI parameters are spin-lattice (T1) and spin-spin (T2) relaxation rates and times. The contrast agents are used to shorten relaxation times and can be classified in several ways based on their chemical nature, magnetic properties, biodistribution etc. The majority of MRI contrast agents, including the most widely used gadolinium-based ones, modify T1 relaxation. Although the toxicity of many gadolinium-based contrast agents is still under discussion. The superparamagnetic Fe₃O₄-nanoparticles, being much less popular and acting upon T2 relaxation, are getting growing interest as they are less toxic and capable for conjugation, which gives way to new promising multimodal agents for bioimaging.