Quantum Sensing of Paramagnetic Species Using Nitrogen-Vacancy Centers in Nanodiamonds for Biomedical Applications

Naturally occurring paramagnetic species, such as free radicals and metalloproteins, play an essential role in a multitude of critical physiological processes including metabolism, cell signaling and the immune response. These endogenous species can act as reporters of biological function and dysfunction. Synthetic paramagnetic probes also have an important role in biological sensing when targeted to specific sites enabling the study of functional information such as tissue oxygenation and redox status in living systems. There is also a need to develop methods to map the uptake of paramagnetic contrast agents used in Magnetic Resonance Imaging (MRI) at a cellular level.<br/>The work presented herein describes sensing methods that exploits the spin dependent emission of photoluminescence (PL) from an ensemble of Nitrogen Vacancy (NV) centers in diamond for rapid, non-destructive detection of paramagnetic species in biological systems. Sensing protocols based on the NV centre charge state switching and magnetic modulation of PL is also assessed providing a simple means to probe biological systems without the application of microwaves. Samples studied include paramagnetic salts in solution, liposomes and mamalian cells. Dynamic tracking of biochemical reactions is demonstrated alongside mapping of the cellular uptake of paramagnetic MRI agents including Gadobutrol, Gadolinium(III) texaphyrin and Manganese(II) texaphyrinby. Overall, this work introduces new protocols for quantum sensing of paramagnetic species using NVs in nanodiamonds for biomedical applications.