  Magnetic resonance imaging (MRI) is a non-invasive and label-free technique
widely used in medical diagnosis and life science research, and its success has
benefited greatly from continuing efforts on enhancing contrast and resolution.
Here we reported nanoscale MRI in a single cell using an atomic-size quantum
sensor. With nitrogen-vacancy center in diamond, the intracellular protein
ferritin has been imaged with a spatial resolution of ~ 10 nanometers, and
ferritin-containing organelles were co-localized by correlative MRI and
electron microscopy. Comparing to the current micrometer resolution in current
state-of-art conventional MRI, our approach represents a 100-fold enhancement,
and paves the way for MRI of intracellular proteins.
