Magnetic relaxometry study of cytochrome C using nitrogen vacancy centers in diamond

Cytochrome C (Cyt-C) is a water-soluble protein with a single heme group, pivotal in the mitochondrial electron transport chain, where the heme group remains in the Fe⁺³ paramagnetic state, generating fluctuating magnetic fields [1]. Detecting these stochastic fields is challenging, yet the nitrogen-vacancy (NV) center offers a unique opportunity to measure these weakly random magnetic fields through spin-lattice (T₁) relaxometry [2]. In this study, we perform NV-T₁ relaxometry measurements on a diamond chip doped with a 8-nm thick NV-layer without the presence of Cyt-C, yielding a relaxation time of approximately 1.2 ms. Subsequently, by varying the concentration of Cyt-C from 2.6 µM to 54 µM on the diamond surface, we observe a reduction in the T₁ time to 850 µs and 150 µs, respectively. This decrease is attributed to spin-noise originating from Fe⁺³ spins within the Cyt-C proteins [3]. Additionally, we conduct imaging of Cyt-C nanoclustered proteins on a microstructured diamond chip equipped with gratings, enabling us to detect the presence of 1.44 × 10⁶ to 1.7 × 10⁷ Fe⁺³ spins per µm² [3]. [1] I. Bertini, et al., Chem. Rev. 106 (1), 90–115 (2006). [2] P. Wang, et al., Sci. Adv. 5(4), eaau8038 (2019). [3] S. Lamichhane, et al., arXiv:2310.08605 (2023).