Nanodiamond imaging: molecular imaging with optically detected spin resonance of nitrogen-vacancy centers in nanodiamonds

Nanodiamond imaging is a new molecular imaging modality that takes advantage of nitrogen-vacancy (NV) defects in nanodiamonds to image the distribution of nanodiamonds within a living organism with high sensitivity and high resolution. Nanodiamond is a nontoxic material that is easily conjugated to biomolecules, such that the distribution of nanodiamond within a living organism can be used to elicit physiological information. Unlike the tracers used in other molecular imaging modalities such as positron emission tomography (PET) and single photon emission computed tomography (SPECT), nanodiamonds are stable and thus allow longitudinal imaging of the same organism over a long time span. Unlike fluorescence-based molecular imaging that has a resolution degraded by photon scattering, the resolution of nanodiamond imaging is defined by the strength of a magnetic gradient. <br/> To form an image, a magnetic field-free region is created, such as exists halfway between two identical magnets with north poles facing each other. Optical excitation pumps the NVs into a bright fluorescence state, and microwaves transfer them to a dark state, but only for those NVs within the field-free region and resonant with the microwaves. By rastering the field-free region across the sample, the changes in fluorescence yield the nanodiamond concentration. Images of nanodiamond phantoms within chicken breast have been recorded with a prototype system. By modifying the nanodiamond particles and enhancing the imaging system, it should be possible to approach 100 &mu;m resolution and to increase the sensitivity to a 10 nanomolar carbon concentration per root Hz in a mm³ voxel.