Progress in high resolution atomic force microscopy in biology

Abstract

The atomic force microscope (AFM) was invented by Binnig, Quate and Gerber less than 10 years ago (Binniget al. 1986). In their first prototype, a piece of goldfoil was used as the cantilever, with a crushed diamond tip mounted at the end. On the back of the cantilever, a tunnelling junction was used to monitor the deflection of the cantilever (the gold-foil) when the specimen was scanned with the tip in contact with the surface. Thus, the surface topography of the specimen was obtained with a resolution critically dependent on the sharpness of the tip provided the deformation of the specimen was not serious. Even with such a crude set-up, they managed to obtain a lateral resolution of ˜ 30 Å and a vertical resolution of better than 1 Å on an amorphous A12O3surface. The operating principle of such an instrument is deceptively simple. However, such an arrangement was inconvenient for routine operations and unsuitable for imaging hydrated specimens, because the tunnelling junction is easily contaminated in air and works poorly in aqueous solutions (Alexanderet al. 1989). As a result, the application of this type of AFM to biological samples was rare (Engel, 1991).

High resolution surface structure of E. coli GroES oligomer by atomic force microscopy

“…However, it was more difficult to achieve a uniform coverage on the mica surface, which would be required for high resolution AFM [26]. As we found, in addition to the incubation time and buffer conditions, the concentration of GroES also had profound effect on the surface coverage.…”

“…It is seen that the specimen was nearly closely packed, but no long range order was found, indicating that two-dimensional crystals were not formed under these conditions. Although the resolution in AFM is not well defined and is strongly dependent on the nature of the specimen [26,28], the smallest surface features resolvable in these images suggest a spatial resolution of 10 A or better. For example, the end of the 'spike' near the central channel has a width of 8-10 ,~, representing one of the highest resolution AFM images achieved so far [28][29][30], which is significantly higher than that achieved with EM of two-dimensional crystals [18].…”

“…Because of the variable conformations observed by EM, it was even suggested that GroES could have a flexible structure or a symmetry other than the seven-fold [18]. Since the atomic force microscopy (AFM) has been shown to be capable of obtaining high resolution surface structures of several oligomeric bacterial proteins (for recent reviews, see [24][25][26]), we have applied this method to determine the surface structure of GroES under aqueous solutions. We show that the subunit structure can be clearly resolved in the AFM images without image processing/averaging.…”

High‐resolution atomic‐force microscopy of DNA: the pitch of the double helix

“…One of the primary interests in atomic force microscopy (AFM) in biology has been the potential of high resolution imaging [1][2][3][4][5][6]. and this potential was recently demonstrated with several protein specimens at 1-2 nm resolution [7][8][9][10].…”

Improvement of DNA‐visualization in dynamic mode atomic force microscopy in air

“…Since its invention in 1986 (Binnig et al 1986), atomic force microscopy (AFM) has become an important tool for high-resolution structural and functional studies of biological materials such as membranes, proteins, and nucleic acids (Bustamante and Rivetti 1996, Engel 1991, Hansma and Hoh 1994, Lal and Scott 1994, Shao and Yang 1995, but an increase in resolution remains important. The first studies had been done at ambient conditions in air with contact-mode AFM, that is, mechanical contact between tip and sample occurs.…”