AFM tip. The results are striking and highlight the utility of CFM to detect
different functional groups on a surface.
Aside from being used to image surfaces and surface-bound material, AFM
has other applications. One unorthodox application of AFM in a nonimaging setting is in the recent development of a cell nanoinjector. In the
past, in order to introduce a substance into a living cell, the cell had to be
permeabilized with an electric current or chemical agent, or a bulky
micropipette had to be used as an injector. This process could result in
damage to the cell membrane, inducing undesirable side effects. However,
scientists have been able to attach delivery moieties such as a carbon
nanotubes to the end of an AFM tip for use as “nanoinjectors.” Because of
the tip’s small dimensions, the cell membrane is not irreversibly perturbed.
The substance (or cargo) to be injected into a cell is chemically attached
to the delivery moiety (through a disulfide linkage, for instance). A carbon
nanotube as a delivery moiety acts like a “nanoneedle” when it is attached
to the AFM tip, which is then used to inject the carbon nanotube (with the
molecular cargo) through the cell membrane. Inside the reducing environment of the cell interior, the disulfide linkage between the cargo and
the carbon nanotube is severed and the cargo is released into the cell. The
AFM tip then withdraws the nanoneedle from the cell interior. Because
the nanoneedle is of such small dimensions, the cell membrane is not
perturbed greatly and the cell remains unharmed. Furthermore, by using
the AFM machinery, excellent spatial precision in the placement of the
cargo can be achieved. Figure 8.33 shows a schematic diagram of a
nanoinjector and Figure 8.34 shows electron microscope images of the
nanoneedle before and after the attachment of molecular cargo. Although
the AFM-operated nanoinjector is admittedly limited to delivering cargo
to one cell at a time, it still promises to be a useful tool in a wide variety of
biological studies.
8.7.3 Transmission electron microscopy
Unlike the scanning probe microscopies, which utilize physical interactions between a sharp tip and a surface to create an image, electron
microscopy techniques use a beam of electrons to visualize a sample.
Because electrons have much smaller wavelengths than visible light,
electron microscopies are able to achieve resolutions far greater than
optical microscopies.
IMAGING NANOSTRUCTURES 317
different functional groups on a surface.
Aside from being used to image surfaces and surface-bound material, AFM
has other applications. One unorthodox application of AFM in a nonimaging setting is in the recent development of a cell nanoinjector. In the
past, in order to introduce a substance into a living cell, the cell had to be
permeabilized with an electric current or chemical agent, or a bulky
micropipette had to be used as an injector. This process could result in
damage to the cell membrane, inducing undesirable side effects. However,
scientists have been able to attach delivery moieties such as a carbon
nanotubes to the end of an AFM tip for use as “nanoinjectors.” Because of
the tip’s small dimensions, the cell membrane is not irreversibly perturbed.
The substance (or cargo) to be injected into a cell is chemically attached
to the delivery moiety (through a disulfide linkage, for instance). A carbon
nanotube as a delivery moiety acts like a “nanoneedle” when it is attached
to the AFM tip, which is then used to inject the carbon nanotube (with the
molecular cargo) through the cell membrane. Inside the reducing environment of the cell interior, the disulfide linkage between the cargo and
the carbon nanotube is severed and the cargo is released into the cell. The
AFM tip then withdraws the nanoneedle from the cell interior. Because
the nanoneedle is of such small dimensions, the cell membrane is not
perturbed greatly and the cell remains unharmed. Furthermore, by using
the AFM machinery, excellent spatial precision in the placement of the
cargo can be achieved. Figure 8.33 shows a schematic diagram of a
nanoinjector and Figure 8.34 shows electron microscope images of the
nanoneedle before and after the attachment of molecular cargo. Although
the AFM-operated nanoinjector is admittedly limited to delivering cargo
to one cell at a time, it still promises to be a useful tool in a wide variety of
biological studies.
8.7.3 Transmission electron microscopy
Unlike the scanning probe microscopies, which utilize physical interactions between a sharp tip and a surface to create an image, electron
microscopy techniques use a beam of electrons to visualize a sample.
Because electrons have much smaller wavelengths than visible light,
electron microscopies are able to achieve resolutions far greater than
optical microscopies.
IMAGING NANOSTRUCTURES 317