Microbiology, 2021

2.3 • Instruments of Microscopy 55
Figure 2.25
A biofilm forms when planktonic (free-floating) bacteria of one or more species adhere to a surface, produce slime, and form
a colony. (credit: Public Library of Science)
Figure 2.26
In this image, multiple species of bacteria grow in a biofilm on stainless steel (stained with DAPI for epifluorescence
miscroscopy). (credit: Ricardo Murga, Rodney Donlan)
Scanning Probe Microscopy
A scanning probe microscope does not use light or electrons, but rather very sharp probes that are passed
over the surface of the specimen and interact with it directly. This produces information that can be assembled
into images with magnifications up to 100,000,000⨯. Such large magnifications can be used to observe
individual atoms on surfaces. To date, these techniques have been used primarily for research rather than for
diagnostics.
There are two types of scanning probe microscope: the scanning tunneling microscope (STM) and the atomic
force microscope (AFM). An STM uses a probe that is passed just above the specimen as a constant voltage
bias creates the potential for an electric current between the probe and the specimen. This current occurs via