The amount of aged solution sprayed depends on the EDL volume used. Four volumes are available: 19, 41.6, 93.6, 141.8 and 189.5 L. In the present work, for short aging times (20 and 100 ms), mediumsize EDL was used (93.6 L), delivering a total of 90 L per spray; for longer aging times, the biggest EDL was used (189.5 L), collecting 180 μL per spray. In all experiments, the total volume of the reaction mixture collected was 360 μL to ensure enough sample for filling the rotor. The filling volume of a standard 4 mm Zirconia solid-state NMR rotor is 80 L. More details of the mixing system are provided in the Supplementary Information Figure . The resulting frozen particles in cold isopentane are shown in Figure . Once the liquid droplets hit the cold isopentane, they solidify and sink immediately to the bottom of the Falcon tube. Sub-centimeter particles can be observed with the naked eye with some aggregation and deformation (Figure ). Most of the particles adopt a disc-like shape. Higher magnification observations were performed using a custom-built setup (Figure .) designed for imaging under temperature-controlled conditions (approximately -100 0 C). Around 2 mL of cold isopentane containing frozen particles was loaded into the sample holder and placed on a cold stage to keep the mixture chilled during imaging. The chamber was sealed with a cover and filled with cold nitrogen gas, which was used to maintain a sufficiently low temperature, ensuring that no particles melted during imaging. Round-shaped frozen particles are observed with an average diameter of 300-400 m (Figure -d and Figure ). Similar morphological observations have been made before for frozen droplets containing lysozymes prepared by similar spraying in cold isopentane. Maintaining the cold chain up to the NMR analysis is crucial, and thus, the NMR rotor packing is a critical step. A general solid-state NMR rotor packing scheme is shown in Figure . In detail, frozen particles are transferred to a homemade copper packing tool containing an NMR rotor (see details in Figure and SI5) and kept in a cold isopentane bath at -145 o C. To prevent any increase in sample temperature during packing, it is crucial to keep all packing tools cold, maintaining them below -145 o C. Once the rotor is filled, the packing funnel (holding the rotor) is placed on top of the Teflon holder containing a needle, allowing the rotor to be pushed up to a level of the top of the filling funnel while still submerged in cold isopentane (Figure ). The excess of solid and isopentane is then removed using a plastic pipette, and the level of rotor filling is checked to ensure sufficient space for the cap. The rotor is carefully removed from the funnel using cold tweezers and kept in the cold isopentane (Figure ). A zirconia cap is placed inside the cold copper packing funnel to mount it on a rotor. The rotor is then turned around and reinserted into the packing tool, where the cap is secured by gently pressing the rotor inside the filling funnel using cold tweezers (Figure ). Alternatively, the rotor cap can be mounted using a cold nitrogen gas setup (<-145 o C) (Figure ). Once the rotor cap is securely mounted, the rotor is removed from the copper funnel and stored in cold isopentane until further use in ssNMR analysis. Then, the rotor is transferred directly into the 4mm NMR probe cooled down at -120 0 C through vertical insertion from the top of the magnet. Such an approach enables reliable, successful insertions and imminent magic angle spinning of the rotor. We observed that excess isopentane from the outside of the rotor evaporates due to the strong flux of the insertion as well as bearing and drive gas into the coil.