Inhibition of protein adsorption to muscovite mica by monovalent cations.

One of the most challenging steps in biological atomic force microscopy (AFM) is to find conditions under which the sample will adsorb to a substrate. Here we show that a common constituent of biological buffers, monovalent cations, can inhibit the adsorption of a number of different proteins onto one of the best substrates for biological AFM, muscovite mica. The potency series for different cations to prevent adsorption is the same for every protein, K+ > Na+ > Li+, and, in each case, this inhibition could be overcome by increasing the concentration of proteins. These results thus suggest that reducing the extent of this inhibition by using lower concentrations of salt, higher concentrations of proteins, or Li+ in place of K+ and Na+ may be generally useful procedures to maximize the amount of protein on mica.