Abstract: An atomic force microscope in which a probe tip is oscillated at a resonant frequency and at amplitude setpoint and scanned across the surface of a sample, which may include an adsorbed water layer on its surface, at constant amplitude in intermittent contact with the sample and changes in phase or in resonant frequency of the oscillating are measured to determine adhesion between the probe tip and the sample. The setpoint amplitude of oscillation of the probe is greater than 10 nm to assure that the energy in the lever arm is much higher than that lost in each cycle by striking the sample surface, thereby to avoid sticking of the probe tip to the sample surface. In one embodiment the probe tip is coated with an antibody or an antigen to locate corresponding antigens or antibodies on the sample as a function of detected variation in phase or frequency.