Irreversible adsorption of lysozyme to polishing marks on silica

Fluorescence microscopy, in combination with atomic force microscopy (AFM), reveals that rhodamine-labeled lysozyme adsorbs strongly from aqueous solu tion to polishing marks of nanometer depths on fused silica surfaces. The f luorescence and topographical images correspond closely. Fluorescence inten sity varies by as much as a-fold over the same region where the topography varies over 2.5 nm. Desorption of lysozyme from the surface occurs on rinsi ng with solutions of increased ionic strength or decreased pH, showing that reducing the Coulombic attraction enhances desorption. Different polishing marks behave differently with respect to desorption: the fluorescence patt ern on the surface changes when the ionic strength of the rinsing solution reaches 0.1 M, indicating that some polishing marks are more strongly adsor ptive than are others. The desorption depends on pH, which is consistent wi th the known variation in the charge of silica surface. A superpolished sil ica photomask, which has significantly fewer polishing marks on the nanomet er scale, has significantly less adsorption of lysozyme, suggesting that th e topography on the nanometer scale influences adsorption.