It depends on whether the peptide is hydrophobic or hydrophilic
For hydrophobic peptides, we recommend using organic solvents, such as DMSO, to dissolve it. If it's hydrophilic peptide, you can decide which solvent/buffer to use based on your application.
We suggest dissolving the peptide in pure solvent (water or organic solvent) then diluting in an assay buffer e.g. PBS. (We do not recommend directly dissolving lyophilized peptides in a buffer PBS. This is because the high salt contents in PBS can affect peptide's interaction with water, causing aggregation formation.)
For fluorescent peptides that are typically sensitive to light, we strongly recommend amber vials or cover the containers with foils to avoid light.
For long term storage, please keep the lyophilized peptides at -20C or lower. Once in solution, make aliquots to minimize freeze-thaw cycles and keep the stock solution in -20C or lower as well.