Magnetic resonance (MR) is one of the most important techniques for characterizing compositions, structure and dynamics of molecules. Over the past several years, quantum sensing with Nitrogen-Vacancy (NV) center has opened a new door for magnetic resonance spectroscopy of a single molecule. In my talk, I will mainly introduce several new experimental results on both of methods and biology applications. (I) Zero-field electron spin resonance (ESR) spectroscopy on nanoscale. We successfully measured the zero-field ESR spectrum of a few electron spins, by precisely tune the energy levels of NV centers to be resonant with the target spins, and directly resolved the hyperfine coupling constant. This work break the sensitivity limitation and open the door of practical applications of the zero-field ESR. (II) ESR spectroscopy of a single protein in poly-lysine and a single DNP duplex in aqueous solution. The work represents a step forward towards magnetic resonance investigation of biomolecules in their native environments at the single-molecule level. (III) We realized one-dimensional and two-dimensional nuclear magnetic resonance spectroscopy of two coupled nuclear spins and resolved its structure.
 Fazhan Shi, et al., Single-DNA electron spin resonance spectroscopy in aqueous solutions, Nature Methods 15, 697 (2018)
 Fei Kong, et al., Zero-field electron spin resonance spectroscopy on na-noscale, Nature Communications 9, 1563 (2018)
 Fazhan Shi, et al., Single-protein spin resonance spectroscopy under ambient conditions, Science 347, 1135 (2015)
 Fazhan Shi, et al., Sensing and atomic-scale structure analysis of single nuclear spin clusters in diamond, Nature Physics, 10, 21-25 (2014)
 Tobias Staudacher, et al., Nuclear magnetic resonance spectroscopy on a (5nm)3 volume of liquid and solid samples, Science, 339, 561 (2013)
 Zhiping Yang, et al., Two-dimensional nanoscale nuclear magnetic resonance spectroscopy enhanced by artificial intelligence, arXiv:1902.05676 (2019)