Gel tips for atomic force microscopy

A cantilever used for atomic force microscopy is modified with polymeric ge ls to provide the tip with abilities to hold or release molecules and to al ter its own characteristics in response to external stimuli. Nanometer-scal ed, cross-linked polymer layers are grafted on the surface of an ordinary s ilicon-based cantilever before the bulk reaction mixture becomes macroscopi c gel. A dry, 6 nm polyacrylamide grafted layer swells to about 30 nm in wa ter. The swelled tip could withstand repeated scanning and produce stable i mages. In the case of a hydrogel that undergoes volume phase transition by pH, a soft hydrophilic tip is transformed into a harder hydrophobic tip by changing pH, thus demonstrating that the nanometer-scaled, grafted network behaves in the same way as the bulk gel.