ABSTRACT
Even though SPMs (mainly STM and AFM) have existed for only a few decades, by any standard, they are still in the early-level experimental phase. Prior to SPMs, all molecular level images of biological systems were known from microscopic conditions much different than their ambient environments. For example, all x-ray microscopy is carried out under vacuum. All biological processes take place in aqueous environments, and therefore, STM and AFM have been found to be useful for these systems. For biological applications, the major aspects have developed extensively, including instrumental development, such as different operation modes, and the control of imaging environments.
