The atomic force microscope (AFM) has been shown to be very versatile. Fu-Ren Fan and Allen Bard have extended this versatility by imaging biologic molecules based on electrochemical reactions, referred to as scanning electrochemical microscopy (SECM). Imaging in this mode required the specimen to be covered with a thin film of water. An electrical potential of about 3 volts was maintained between the tungsten tip and an electrode near the specimen, so that electrochemical reactions that occurred within the aqueous medium resulted in a detectable current (a few picoamps).

As you can appreciate, the film of water was critical. Fan and Bard accomplished this by having the specimens on a mica chip in a environment with high relative humidity. The mica was coated with gold on one side to create the reference/counter electrode. When the SECM was operated on a dry mica chip, very small currents were measured.