In a in the Journal of the American Chemical Society, Vansuch et al.聽use聽cryo-annealing and electron paramagnetic (EPR) spectroscopy to probe an intermediate state in the catalytic cycle of nitrogenase. This work, led by our collaborators at NREL,聽begins with the illumination of CdS quantum dot - nitrogenase biohybrids, resulting聽in the photodriven transfer of electrons聽to the enzyme. The illumination is performed at 233 K,聽which limits catalytic turnover and poses the enzyme in an intermediate state. Next the biohybrids are "annealed"聽at 236 K, after which the time-dependent relaxation of the catalytic intermediates can be monitored with EPR.