High spatial resolution imaging with near-field scanning optical microscopy in liquids

The mechanism of tuning fork-based shear-force near-field scanning optical microscopy is investigated to determine optimal experimental conditions for imaging soft samples immersed in liquid. High feedback sensitivity and sta bility are obtained when only the fiber probe, i.e., excluding the tuning f ork prongs, is immersed in solution, which also avoids electrical shorting in conductive (i.e., buffer) solutions. Images of MEH-PPV were obtained wit h comparable spatial resolution in both air and water. High optical resolut ion (similar to 160 nm fwhm) was observed.