The atomic force microscope (AFM) has been used in many ways to extract information from biologic specimens. Now Gerry Leatherman, Edgar Durantini, Devens Gust, Tom Moore, Anna Moore, Simon Stone, Ziniu Zhou, Peter Rez, YangZhang Liu, and Stuart Lindsay have used conduction atomic force microscopy (CAFM) to demonstrate that a molecule of carotene can function as a molecular wire.

Leatherman et al., synthesized carotene and then examined the molecules with the scanning tunneling microscope (STM), They could image spots that averaged 2 nm in diameter, although the size of the spots varied widely due to the geometry of the probe tip. Interestingly, the number of spots increased with the concentration of carotene, but the average size of the spots did not change. This made it clear that they were able to image carotene molecules with the STM, and that the carotene did not form large aggregates.

Nanofabrication is upon us. But engineers require measurements of physical properties of their materials in order to use them appropriately. Because the size of the object is in the nanometer scale, tiny measuring devices are required. Furthermore, there is the problem of reading these tiny devices. Zhong Lin Wang, Philippe Poncharal, and Walter de Heer at Georgia Tech have solved this problem by using the transmission electron microscope (TEM) to read off the measurements.

A special device was designed to fit inside the TEM, allowing for simultaneous visualization and manipulation of a nanostmcture. The nanostructure that Wang ef al, used was the carbon nanotube which could be clearly visualized by the TEM and has a well-defined structure. Specifically, they used multiwalled nanotubes with diameters of 5 to 50 nm and lengths of 1 to 20 μm. The device they designed for in situ microscopy was a modified specimen holder that allowed carbon nanotubes to be mounted in a conducting medium and positioned across from a counter electrode, which was a droplet of mercury or gold/ platinum balls.

The atomic force microscope (AFM), the workhorse of scanning probe microscopes, has become even more versatile. Anneliese Raab, Wenhai Han, Dirk Badt, Sandra Smith-Gill, Stuart Lindsay, Hansgeorg Schindler, and Peter Hinterdorfer have demonstrated that the AFM, in the dynamic force mode, can use antibodies as a probe. Dynamic force microscopy uses a magnetized tip that is oscillated in an alternating magnetic field as the tip scans the surface. This provides a very gentile interaction that can be recorded as a high resolution topographic image. Raab et al., showed that more information can be obtained from the specimen.

Regulated secretion occurs when the ceil detects a signal, vesicles containing the secretory product fuse with the plasma membrane of the cell, and the contents are released into the extracellular space. This mechanism is called exocytosis. Many laboratories around the world have studied exocytosis for the past couple of decades, and we know a lot about the many steps that are involved. The cytoskeleton appears to play a role in allowing vesicles to approach the plasma membrane, and many other proteins are in the cascade between reception of the signal and the release of the secretory products.

The atomic force microscope (AFM) has been shown to be very versatile. Fu-Ren Fan and Allen Bard have extended this versatility by imaging biologic molecules based on electrochemical reactions, referred to as scanning electrochemical microscopy (SECM). Imaging in this mode required the specimen to be covered with a thin film of water. An electrical potential of about 3 volts was maintained between the tungsten tip and an electrode near the specimen, so that electrochemical reactions that occurred within the aqueous medium resulted in a detectable current (a few picoamps).

As you can appreciate, the film of water was critical. Fan and Bard accomplished this by having the specimens on a mica chip in a environment with high relative humidity. The mica was coated with gold on one side to create the reference/counter electrode. When the SECM was operated on a dry mica chip, very small currents were measured.

The atomic force microscope (AFM) is well known for its outstanding spatial resolution, but it is becoming increasingly useful as the instrument for force spectroscopy. In the force spectroscopy mode, the AFM can measure tiny tension forces, in the piconewton (pN) range. Daniel Müller, Wolfgang Baurmeister, and Andreas Engel have used the AFM in both the imaging and force spectroscopy modes to pull proteins out of membranes in a controlled fashion.

Müller et al. used Deinococcus radiodurans, a bacterium best known for its high resistance to radiation (as its Genus name implies), as their test subject. They extracted a highly regular membrane from the bacterium, the hexagonally packed intermediate (HPl) layer. They mounted the HPI on mica, so that the hydrophilic outer surface of the HPI adsorbed strongly to the mica, exposing the hydrophobic inner surface to the silicon nitride AFM stylus.

Imagine a raft in a canal between point A and point B. On that raft is a visible (fluorescent) cargo. Also, attached to that raft is a motor that will propel the raft only from A to B (anterograde transport). When the raft gets to point B, another motor is attached that can propel the raft, and its cargo, and the anterograde motor, back to point A (retrograde transport). Within a cell, the canals are microtubLiles, and a lot is known about anterograde and retrograde transport in some systems, but these phenomena have not been directly observed in a living, intact animal. Until now, that is. In a pair of very interesting papers, the laboratory of Jonathan Scholey has shown us convincing micrographs of anterograde and retrograde transport in an important animal model.

Laser tweezers take advantage of the forces around converging beams of light to exert slight pressures on small structures. Whereas these optical devices have allowed for some elegant studies of cell biology, wouldn't it be great if we had mechanical tweezers that offered even better manipulation? In a recent paper, Philip Kim and Charles Lieber demonstrated a fabulous device they called “nanotweezers.“

Logically, they used nanotubes as the key structural component for their nanWith nanotubes serving as the tines of the tweezers, Kim and Lieber devised a very clever arrangement for the hub. They took a standard glass tube, 1 mm in diameter, and pulled it to a tapered end of about 100 nm.otweezers. Carbon nanotubes are particularly strong for their size, they conduct electricity, and they can be fabricated as small as 1 nanometer (nm) in diameter. With nanotubes serving as the tines of the tweezers, Kim and Lieber devised a very clever arrangement for the hub. They took a standard glass tube, 1 mm in diameter, and pulled it to a tapered end of about 100 nm. They then evaporated a very thin coat of chromium and then gold on one side, then rotated the rod 180° and deposited metal on the other side. Each coated side operated as an independent electrode.

When you read the header to this article, you probably thought I made a mistake. Doesn't he mean atomic force microscope, the familiar AFM? And isn't that microscope in our present, not in our future? Well, I'm not confused. The reference is to a beam of atoms that some day may be used in an atomic microscope, just like a beam of electrons is used in an electron microscope. It would be even more accurate to refer to an “atomic de Broglie microscope,” but that's a rather awkward label.

We are all familiar with the 4 groups of human blood types; 0, A, B, and AB. Each group is characterized by specific molecules on the surface of the red blood cells (RBCs). Recently, Michel Grandbois, Wolfgang Dettmann, Martin Benoit, and Hermann Gaub have modified the atomic force microscope (AFM) to use the different affinities of these molecules to produce an image.

A key step was to specifically functionalize the scanning probe tip of the AFM. What this means is to covalently attach an active molecule to the tip. The active molecule they used was a Iectin derived from the snail Helix pomatia (this is the same snail valued by the French as escargot). This Iectin binds specifically to molecules found on the surface of RBCs in blood group A (N-acetylgalactosamine-terminated glycolipids), but these molecules are not found in blood group O. But if the Iectin was bound directly to the AFM tip, nonspecific adsorption to the specimens would occur.

Miniaturization of electronic components is now reaching the level of whole instruments, and not just parts like transistors. Thomas George recently reported on a tiny electron microscope column a “few millimeters thick and about a centimeter square”, which would work in air. The secret being an electron- transparent membrane sealing in the column's vacuum. This is exciting news for folks working in areas such as acarid chaetotaxy that would benefit from a pocket-size electron microscope. However, it's limited by a micrometer-scale resolution limit.

Help is on the way, however. In separate reports in Applied Physics Letters, Driskill-Smith et al at. published “The 'nano-triode:’ A nanoscale field-emission tube”, and Dean and Chalamala published “The environmental stability of field emission from single-walled carbon nanotubes.“

Since, as everyone knows, an electron microscope's electron gun is a triode vacuum tube, the application is obvious. Everyone old enough to remember vacuum tubes, I should say.

This article is the second of a series transcribed from the discussion taped during the Facility Management session at M&M 2000. It is printed with permission of the Microscopy Society of America. Bulleted paragraphs indicate comments by individuals attending the session.

Strictly speaking, it is impossible to authenticate any painting to the extent of naming the artist who produced that object. One can only increase the likelihood thereof. In one celebrated case I felt I had fully proved that Manets palette had indeed been used to paint a particular painting but a “scholar” on whose reaction the art world depends for final acceptance of authenticity only said “someone” could have borrowed Manets palette one fine day and painted that picture. In a second celebrated case I was able to prove, but not convince, the world that a particular painting (Shroud of Turin) was, in fact, a painting and not an artifact produced by some other mysterious means, e.g., some sort of photographic process or resurrection itself.

Aldehydes are the most commonly used fixatives. They serve to stabilize the fine structural details of cells and tissues prior to examination by light or electron microscopy. Research workers, technicians, pathologists and others who regularly use aldehyde fixatives frequently do not appreciate the nature and properties of these compounds or the reasons for choosing to fix a specimen in formaldehyde, glutaraldehyde or a mixture of the two. Misconceptions are widespread also about formalin and paraformaldehyde, the commercial products from which formaldehyde-containing solutions are made.

We have recently been shopping for a confocal microscope and have found a simple way to test the capabilities of the various units that have been demonstrated to us. Some of the important aspects that we were looking for in our “ideal” multi-user system were:

1. 1) Ease of use.

2. 2) The ability to obtain good X-Y, X-Z and hence X-Y-Z resolution, and the accurate display of these images.

3. 3) The depth within the sample at which the system can resolve structures (this of course depends mostly on the lenses used), but is still an important criteria as it reflects on the system as a whole.

4. 4) “extras” such as a transmission detector and reconstruction/ analysis/image manipulation software.

In a criminal case, such as vehicle theft or vehicle hijacking, where a vehicle has been dismantled, the forensic scientist is many times faced with the problem of establishing the history of a specific auto body part. The normal method for doing this is by performing paint analysis. There are, however, a few shortcomings to paint analysis. In this paper another technique for determining the history of a body part is discussed, namely the comparison of surface replicas.

Photographic chemistry has long been a complex combination of inorganic metal-halide and organic chemistries and polymer science. We at the P.R.I, have managed to add biology to this stew.

Silver has long been known as a toxicelement to microbes, and so used as a drug to kill bacteria. But there are bacteria that can survive in environments high in silver. It has been reported that some bacteria can accumulate up to 25% of their dry biomass as silver, and so acquire resistance to the toxic effects of silver. Also, a recent article in the Proc. Nat. Acad.Sci. describes the intracellular deposition of silver grains in such shapes as hexagons and equilateral triangles.