ABSTRACT
The atomic force microscope (AFM) is capable of directly visualizing unstained biological samples in liquids at nanometre resolution. This chapter reviews the limiting factors of imaging speed, and key techniques for high-speed imaging. Proteins are inherently dynamic molecules that undergo structural changes and interactions with other molecules over a wide timescale range, from nanoseconds to milliseconds or longer. The dynamic PID controller can avoid parachuting in fact even when the set-point amplitude is increased up to 90% of the free oscillation amplitude. Regarding the feedback bandwidth, it is most important that the amplitude detection time and the cantilever's response time decrease in inverse proportion to the resonant frequency. The chapter demonstrates some examples of successful imaging of protein, focusing on dynamics in two-dimensional (2D) protein crystals and describes the potential of high-speed AFM for cell imaging. Monovacancy defects in the streptavidin 2D crystals were produced by increasing the tapping force onto the sample from the oscillating tip.
