Nanodiamond as a new hyperpolarizing agent and its ¹³C MRS

In this work, we have hyperpolarized carbonaceous nanoparticles (D ≈ 10 nm), that is, "nanodiamonds", with 1.1% ¹³C (natural abundance) using dynamic nuclear polarization (DNP). The polarization buildup curve showed a signal enhancement with relative intensity up to 4700 at 1.4 K and 100 mW microwave power. ¹³C magnetic resonance spectra (MRS) were obtained from the sample at 7 T, and the signal decayed with a T₁ of 55 ± 3s. Notably, polarization was possible in the absence of added radical, consistent with previous results showing endogenous unpaired electrons in natural nanodiamonds. These likely contribute to the shorter T₁'s compared to those of highly pure diamond. Despite the relatively short T ₁, these observations suggest that natural nanodiamonds may be useful for in vivo applications.