  Nitrogen-vacancy (NV) magnetometry offers an alternative tool to detect iron
levels in neurons and cells with a favorable combination of magnetic
sensitivity and spatial resolution. Here we employ NV-T1 relaxometry to detect
Fe in cytochrome C (Cyt-C) nanoclusters. Cyt-C is a water-soluble protein that
contains a single heme group and plays a vital role in the electron transport
chain of mitochondria. Under ambient conditions, the heme group remains in the
Fe+3 paramagnetic state. We perform NV-T1 relaxometry on a functionalized
diamond chip and vary the concentration of Cyt-C from 6 uM to 54 uM, resulting
in a decrease of T1 from 1.2 ms to 150 us, respectively. This reduction is
attributed to spin-noise originating from the Fe spins present within the
Cyt-C. We perform relaxometry imaging of Cyt-C proteins on a nanostructured
diamond chip by varying the density of adsorbed iron from 1.44 x 10^6 to 1.7 x
10^7 per um^2.
