1.Ensure monodispersity: The sample preparation for BioSAXS measurements is similar to the methods used for other experimental biophysical techniques. The purity and monodispersity of the measured samples ensure the interpretability and highquality of scattering data. Hence, the homogeneity of the sample should be characterized using other techniques (e.g., SDS-PAGE, dynamic light scattering, size-exclusion chromatography, analytical ultracentrifugation, etc.) before SAXS measurement.

2. Sample volume: At BL19U2, the typical sample volume required for BioSAXS tests using an automated sample changer is 60μL with a concentration range from 1 to 10 mg/ml.

3.Standard sample: It is strongly recommended to prepare protein standards to evaluate the status of beamline setups at the beginning of the experiment. Lysozyme from hen egg white is typically used as a protein standard, which is available at BL19U2 on request.

4. laboratory on site: BL19U2 is equipped with a wet laboratory on site, which comprises the most typically used laboratory devices, reagents, and consumables. Those devices include a tabletop centrifuge, a Nanodrop spectrophotometer, an ultrasonic bath, a dynamic light scattering instrument, and other typical instruments (e.g., refrigerators, ultrapure water purifiers, pH meters, balances, and pipettes). They can be used freely for sample preparation and characterization before SAXS measurements.