Knowledge of the particle number is critical in many of our applications. In trying to rationalize membrane ‘clogging’ by particles for example, it is wise to compare the particle density to pore density at the membrane. When conjugating protein to NPs, it is important to work in a molar excess of protein. In using nanoparticles for visualization of membrane or gel integrity, it is surprising how difficult it can be to tune the dilution to get the right number in a field of view. Adding the same volume of micron-sized particles vs nanoparticles will cause a jump the number density over orders of magnitude and result in blank or overcrowded samples. For these applications and others, we find ourselves converting between standard preparation concentrations of % solids or mg/ml and molarity. The figure below does that conversion once-and-for-all for some of our most common samples.
The numbers file that created this is available here