Nanodiamond-based hyperpolarization for in-situ magic-angle-spinning nuclear magnetic resonance spectroscopy of proteins

Diamond-based hyperpolarization of external molecular spins has a significant impact on the modality of the nuclear magnetic resonance (NMR) spectroscopy and its sensitivity. The current nitrogen-vacancy (NV) center-based hyperpolarization and optical detection technique however faces a challenge in its implementation at high external field conditions required for the analysis of complex chemical entities such as proteins. In this work, we demonstrate that the surface electrons of nanodiamonds can be an attractive alternative with a number of practical benefits to this end. We first show at a very high external field condition (16.4 T) and low temperature (30 K) that the 13C spin polarization 200-fold higher than the conventional NMR can be achieved for the external bio-molecules within ~3 nm from the diamond surface with no laser illumination and no lattice orientation dependence. This latter property enabled us to record sensitivity-enhanced high-resolution multi-dimensional NMR data on protein sample under continuous sample spinning. We also show that the smallness of the nanodiamond (~5 nm), stability to bio-reduction and richness in surface chemistry enables a molecular-specific delivery of the diamond particle to targeted protein amyloid fibers within crowded cellular environment for a selective hyperpolarization. Overall, this work opens up new avenues to highly sensitive and targeted in-situ MAS NMR spectroscopy, relevant to biology and other fields.