Atomic force microscopy : theory and practice in bacteria morphostructural analysis

The production of the first "microscope" between the end of the sixteenth and the beginning of the seventeenth century was a true breakthrough in the advance of civilization (1). Without the microscope, the natural, biological, medical, and other sciences would not be what they are today. After the optical microscope, a second breakthrough in the analysis of surface morphology occurred in the 1940s with the development of the scanning electron microscope (SEM). Instead of light (photons) and glass lenses, electrons and electromagnetic lenses (magnetic coils) are used to explore the sample. Optical and scanning (or transmission) electron microscopes are classified as "far field microscopes" because the distance between the sample and the point at which the image is obtained is long in comparison with the wavelengths of the photons or electrons involved. In this case, the image is a diffraction pattern and its resolution is wavelength limited (2, 3): in optical microscopy, resolution is determined by the Nyquist relation to the wavelength of the light used (typically about 1 μm); in a general purpose SEM, it is limited by the properties of the electromagnetic lenses (typically about 50Å) (4).