Magnetic sensing of iron in biomolecules using diamond nitrogen vacancy centers*

Iron is an essential yet toxic redox active element that is found in many cells, including neurons and glial cells. Several techniques have been used to quantify iron in neurons and cells; however, most are incapable of high-resolution imaging inside a single cell. Magnetic field sensors based on diamond nitrogen vacancy (NV) centers have emerged as a powerful tool for detecting magnetic signal in iron-containing biological samples with a good combination of spatial resolution and sensitivity [1-3]. In this study we use NV based T₁ relaxometry technique [2] to map iron in cytochrome C (Cyt C) proteins. Cyt C plays an important role in the electron transport chain of mitochondria and it is in the Fe(III) paramagnetic state under ambient conditions. We measure Cyt C under different concentrations and locations of the 10-nm NV doped diamond chip. We show a reduction of the NV T₁ from few milliseconds to hundreds of microseconds, explained by the spin noise from the intracellular iron spins. We discuss plans of imaging Cyt C and other iron-containing proteins on nanostructured diamond chip integrated with gratings. [1] A. Ermakova, et al., Nan. Lett. 13(7), 3305 (2013). [2] P. Wang, et al., Sci. Adv. 5(4), eaau8038 (2019). [3] I. Fescenko, et al., Phy. Rev. App. 11(3), 034029 (2019).