Single-protein spin resonance spectroscopy under ambient conditions

TLDR

Magnetic resonance reveals biomolecule structure and dynamics, yet detecting spectra from single biomolecules has remained elusive. The authors employ a single nitrogen‑vacancy center in bulk diamond as a sensor positioned near the protein. The study detects the electron‑spin resonance of a single spin‑labeled protein at ambient conditions, measures the spin‑label orientation and its modulation by protein motion, and demonstrates coherent spin driving—enabling future nuclear‑spin polarization and detailed structural studies.

Abstract

Magnetic resonance is essential in revealing the structure and dynamics of biomolecules. However, measuring the magnetic resonance spectrum of single biomolecules has remained an elusive goal. We demonstrate the detection of the electron spin resonance signal from a single spin-labeled protein under ambient conditions. As a sensor, we use a single nitrogen vacancy center in bulk diamond in close proximity to the protein. We measure the orientation of the spin label at the protein and detect the impact of protein motion on the spin label dynamics. In addition, we coherently drive the spin at the protein, which is a prerequisite for studies involving polarization of nuclear spins of the protein or detailed structure analysis of the protein itself.