Abstract
The nano-friction force microscopy and the fluorescence microscopy were combined to study the effect of pH and ionic strength on the polydiacetylene (PDA) force-sensitivity at the nanoscale. We found that the increase in pH from 5.7 to 8.2 caused an enhancement in the force sensitivity by 8 folds. The elevation of NaCl concentration from 10 mM to 200 mM also made the PDA 5 times more force-sensitive. These results suggest that the PDA force sensitivity at the nanoscale can be conveniently enhanced by pre-stimulation with pH or ionic strength.