Hamed M. El-Badry

The Structure of Rubber Latex

The techniques of micromanipulation have been extended to the field of colloidal chemistry and should prove of increasing importance in the study of colloids, particularly in the investigation of surface films.

Micropaleontology: Single-Mounting of Microfossils

Specially fashioned micropipets, mechanically guided in the field of the microscope, have been used by Anderson (5) for making single-grain preparations of various types of microfossils. These are first dispersed in a suitable liquid on an object slide, whereafter a specimen is selected under the microscope, taken up into the pipet, and transferred onto another slide. There, it is then covered with a suitable mounting medium and a cover slip. The technique permits rapid sorting and mounting of various microfossils such as pollen, spores, diatoms, and hystrichospherids. Single mounting of as many as 30 to 40 specimens per hour is possible (6). Semipermanent mounts in glycerol jelly or permanent mounts in Canada balsam may be made. The technique is more rapid and versatile than the widely used fishing operations such as those described by Klaus (137) and Madler (159), or those described by Faegri and Iverson (95) for mounting pollen grains.

Identification of Airborne Particles

Sampling and identification of particles suspended in the air are important for many fields of study of the atmosphere of the earth. Techniques of chemical micrurgy have been extensively applied by Cadle and associates in important studies of air pollution and related problems in the applied chemistry and physics of the atmosphere. These techniques were particularly useful in the determination of the composition of airborne particles collected from smog during investigations of the smog problem in the County of Los Angeles (47, 48). In the investigation of air pollution problems of Los Angeles County, the use of these micromanipulative techniques and other microscopic techniques was not limited to the investigation of substances collected from the atmosphere, but was also applied to the study of gasoline engine exhaust gases (48) to discover what substances were introduced into the atmosphere from this important source.

Apparatus for General Chemical Experimentation with Micrograms to Nanograms

Qualitative investigations (25, 28, 29, 30, 91) including separation and identification by confirmatory tests, semiquantitative estimations making use of the volumes of precipitates (25, 30, 92, 93), and gravimetric (88, 89) determinations with microgram to nanogram samples can be carried out by mechanical manipulations in tiny glass capillary cones, and are nowadays well established fields. Chemical operations with micrograms to nanograms in volumes of solutions of the order of one microliter to a few nanoliters are performed in tiny capillary cones of approximately one half to a few microliters capacity. Small amounts of reagents and wash liquids are held ready for use in reagent containers which, together with the cones, are held ready on a glass carrier inside a moist cell to hinder evaporation of the small volumes of solutions. Measurement of volume is carried out in the reagent containers or in special measuring capillaries mounted on the carrier. The moist cell is mounted on the stage of a low-power microscope and is moved by means of the revolving mechanical stage of the microscope. The transfer of liquids is achieved by a micropipet operated with a suitable syringe and mechanically moved by a micromanipulator which permits displacement of the micropipet along the three spatial coordinates. The micromanipulator together with the rotating mechanical stage of the microscope provides the means for adjusting the relative positions of capillary vessels and micropipet. The separation of solids from liquids in the capillary cones is achieved by centrifugation and decantation. The mechanical and optical facilities permit the performance and observation of all necessary operations with ease and confidence.

Working with Living Cells and Tissues

Operative work on the unstained and living animal and plant cells and tissues has long been the aim of investigators in various fields of biology. It should be mentioned that microbiologists were the first to conceive and apply micromanipulative techniques. The main objective, as already indicated, had been to provide means for experimental work in the microscopic field on living matter and for the study of the consequences of these experiments on the living structure rather than the mere observation of the dead and stained specimen.

Mounting Small Crystals for X-Ray Investigations

Operative work for various purposes on individual particles and single crystal specimens of very small dimensions must frequently involve mechanical manipulation under microscopic control. Thus, metal filings and mineral particles may be oriented for the purpose of taking electron micrographs. Micromanipulative techniques enabling proper and close mounting of very small single crystal specimens, with dimensions of about 100μm or much less, in a predetermined orientation have also gained much importance with the development of micro x-ray diffraction cameras. Such small crystals may also be ground, cut, and shaped with the aid of mechanical devices under microscopic observation. For x-ray studies, it may be required, for instance, to remove excessive amounts of glass or crystalline material from the crystal to be investigated, or to obtain cylindrical crystal specimens to simplify absorption corrections. By means of suitable micromanipulations (157, 180, 184, 234) such delicate operations may be performed on the tiny specimens, which may be irreplaceable, without fear of losing or destroying them through clumsy handling.

Microscopes for Use in Micromanipulation

Most of the principal types of optical microscopes have been used in the varied fields of micromanipulative work. Several instruments of different types, designs, and makes, which have been actually employed are indicated in appropriate places in this volume in connection with the particular assemblies and fields in which they have been tried.

Preparation of Samples of Non-Biological Materials

Micromanipulative methods are widely used for sampling and investigation of a great variety of material. In many instances, the amount of sample that may be available for investigation and which may be extracted from localized areas in metallurgical products, mineral grains, and other material may be only micrograms to nanograms in mass. Even when comparatively larger samples are available, the constituents of interest may occur only in nanogram amounts. Consequently, exceedingly sensitive methods are often required for sampling and investigation.

The Study of Fibers

Microdissection techniques involving the use of micromanipulator mounted microneedles have been applied to the study of the microstructures of simple ramie nitrate fibers (188), and paper pulp fibers (214).

Archeology and Art

In the field of archeology mechanical manipulation under the microscope should receive increased attention in connection with the investigation of valuable objects of art since it permits the use of very small samples for analysis.