Probing local water contents of in vitro protein films by ultrasonic force microscopy

By means of ultrasonic force microscopy and lateral force microscopy we measure adhesion hysteresis and friction on protein films of bovine serum albumin and concanavalin A at local scales. Our investigations at different relative humidities (less than 5% and at 50% relative humidity) correspond to dehydrated and hydrated states of proteins. We demonstrate that a substantial increase of adhesion hysteresis with relative humidity is sensitive measure of protein–water binding capacity at local scales.