Concepts of Microscopy

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Chapter: Pharmaceutical Microbiology : Identification of Microorganisms

It is worthwhile to mention here that before one looks into the different instruments related to microscopy one may have to understand the various vital and important cocepts.


Microscopy : The Different Instruments

 

Microscopy essentially deals with the following three cardinal goals, namely :

 

(i) Examination of ‘objects’ via the field of a microscope,

 

(ii) Technique of determining particle size distribution by making use of a microscope, and

 

(iii) Investigation based on the application of a microscope e.g.optical microscopyelectron microscopy.

 

Concepts

 

It is worthwhile to mention here that before one looks into the different instruments related to microscopy one may have to understand the various vital and important cocepts, such as :

 

Light microscopes usually make use of glass lenses so as to either bend or focus the emerging light rays thereby producing distinct enlarged images of tiny objects. A light micro-scope affords resolution which is precisly determined by two guiding factors, namely :

(a) Numerical aperture of the lens-system, and

(b) Wavelength of the light it uses :

However, the maximum acheivable resolution is approximately. 0.2 μm.

 

Light microscopes that are commonly employed are : the Bright field, Darkfield, Phase-contrast and Fluorescence microscopes. Interestingly, each different kind of these variants give rise to a distinctive image ; and, hence may be specially used to visualize altogether different prevailing aspects of the so called microbial morphology.

 

As a rather good segment of the microorganisms are found to be almost virtually colour-less ; and, therefore, they are not so easily visible in the Bright field Microscope directly which may be duly fixed and stained before any observation.

 

One may selectively make use of either simple or differential staining (see Section 4.6.1.1.) to spot and visualize such particular bacterial structures as : capsules, endospores and flagella.

 

The Transmission Electron Microscope accomplishes real fabulous resolution (approx. 0.5 nm) by employing direct electron beams having very short wave length in comparison to the visible light.

 

The Scanning Electron Microscope may used to observe the specific external features quite explicitely, that produces an image by meticulously scanning a fine electron beam onto the surface of specimens directly in comparison to the projection of electrons through them.

 

Advent of recent advances in research has introduced two altogether newer versions of microscopy thereby making a quantam jump in the improvement and ability to study the microor-ganisms and molecules in greater depth, such as : (a) Scanning Probe Microscope ; and (b) Scan-ning Laser Microscope.


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