We demonstrate an all-optical method for magnetic sensing of individual molecules in ambient conditions at room temperature. Our approach is based on shallow nitrogen-vacancy (NV) centers near the surface of a diamond crystal, which we use to detect single paramagnetic molecules covalently attached to the diamond surface. The manipulation and readout of the NV centers is all-optical and provides a sensitive probe of the magnetic field fluctuations stemming from the dynamics of the electronic spins of the attached molecules. As a specific example, we demonstrate detection of a single paramagnetic molecule containing a gadolinium (Gd3+) ion. We confirm single-molecule resolution using optical fluorescence and atomic force microscopy to co-localize one NV center and one Gd3+-containing molecule. Possible applications include nanoscale and in vivo magnetic spectroscopy and imaging of individual molecules.
@article{arxiv.1311.1801,
title = {All-optical sensing of a single-molecule electron spin},
author = {A. O. Sushkov and N. Chisholm and I. Lovchinsky and M. Kubo and P. K. Lo and S. D. Bennett and D. Hunger and A. Akimov and R. L. Walsworth and H. Park and M. D. Lukin},
journal= {arXiv preprint arXiv:1311.1801},
year = {2015}
}