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All-optical Sensing of a Single-molecule Electron Spin
We demonstrated an all-optical method for magnetic sensing of individual molecules in ambient conditions at room temperature. Our approach was based on shallow nitrogen-vacancy (NV) centers near the surface of a diamond crystal, which we used to detect single paramagnetic molecules covalently attached to the diamond surface. The manipulation and readout of the NV centers was alloptical and provided a sensitive probe of the magnetic field fluctuations that stemmed from the dynamics of the electronic spins of the attached molecules. As a specific example, we demonstrated detection of a single paramagnetic molecule containing a gadolinium (Gd3+) ion. We confirmed single-molecule resolution through use of optical fluorescence and atomic force microscopy to co-localize one NV center andone Gd3+ -containing molecule. Possible applications included nanoscale and in vivo magnetic spectroscopy and imaging of individual molecules.