Scanning Near-field Optical Microscope Designed for Operation in Liquids

We report on the construction of a scanning near-field optical microscope (SNOM), which has been designed to permit imaging at the solid/liquid interface. The probe consists of a tapered fibre tip and the so called lateral shear force is used for the tip-sample distance regulation. The liquid environment causes damping of the tip vibration and lowering of the resonance frequency by approx. 20% which can not be explained by the model of a harmonic oscillator. We demonstrate the optical and topographical resolution of the instrument utilizing test grids for atomic force microscopy. First results of in-situ observation of adsorption of human serum albumin proteins at a thin film of polystyrene from aqueous buffer solution are presented.