microscopy (3)

Microscope Overview
- Instrument that magnifies tiny objects for observation.
- Essential for viewing small cells.

Key Figures in Microscopy
- Robert Hooke: English microscopist; first to use cork stoppers, observed "cells" from cork.
- Antonie van Leeuwenhoek: Dutch scientist; examined pond water, discovered "animalcules" and described various forms of bacteria.

Components of Light Microscope
- Light Source: External or built-in, illuminates specimen.
- Condenser Lens: Substage lens gathers rays, enhances visibility of tiny specimen parts.
- Objective Lenses: Collect light rays, form enlarged images; real images for altered light, background light for unaltered.
- Ocular Lens: Magnifies the image formed by the objective.
- Focusing Knob: Adjusts focus, determining image clarity on retina.
- Total Magnification: Product of objective and ocular lens magnifications.

Resolution
- Ability to distinguish between two close points.
- Limited by diffraction; light appears as small disks instead of points.
Limits and Aberrations
- Minimum resolution value: < 0.2µm (200nm), sufficient for larger organelles.
- 7 types of aberrations must be addressed for effective lens production.

Visibility
- Factors impacting observation success.
- Contrast: Difference in appearance between object and background.
Staining Techniques
- Feulgen Stain: Specific for DNA, colors chromosomes; not usable on living cells.
- Requires hydrolysis in acid; toxic nature of stain.

Characteristics
- Bright background with contrasted specimen image.
Whole Mount: Intact objects or slices of organisms for viewing.
Fixation: Process of killing cells using chemical solutions; common fixatives: formaldehyde, alcohol, acetic acid.

Paraffin Embedding
- Use of Wax: Dissolvable in solvents for clear viewing.
- Staining processes followed by coverslip mounting with matching refractive index.

Phase-Contrast Microscopy
- Enhances visibility of transparent objects via refractive index differences.
- Useful for observing cell dynamics and intracellular components.
Fluorescence Microscopy
- Focuses on specific molecules (fluorophores) within cells.
- Light filters excite and visualize specific protein locations using fluorescent antibodies.
Laser Scanning Confocal Microscopy
- Invented by Marvin Minsky; allows imaging of thin planes in thick specimens using lasers.
Super-Resolution Fluorescence Microscopy
- Developed by Betzig, Moerner, and Hall; awarded Nobel Prize in 2014.
- Uses PA-GFP to enhance spatial resolution beyond traditional limits.
Stochastic Optical Reconstruction Microscopy (STORM)
- Works with photoswitchable fluorescent proteins for high-resolution localization below 20nm.
Light Sheet Fluorescence Microscopy
- Non-invasive imaging technique for live embryos over time using thin light sheets for reduced photodamage.
Lattice Light Sheet Microscopy
- Introduced by Eric Betzig; allows 3D imaging of live organisms with minimal damage over time.

Functionality
- Produces images via transmitted electrons, greater resolution than light microscopy.
Specimen Preparation
- Critical fixation methods required to preserve cellular structure; common fixatives: glutaraldehyde, osmium tetroxide.

Cryofixation
- Rapid freezing method to preserve cell macromolecules; minimizes artifact formation.
Ultrarapid Freezing: Involves plunging small specimens in extremely low-temperature liquids or utilizing high-pressure methods for larger specimens.

Negative Staining & Shadow Casting
- Heavy metal stains yield bright structures against dark backgrounds; shadow casting visualizes isolated particles.
Freeze-Fracture Replication
- Splits tissues and allows for detailed imaging of cellular structures.
Scanning Electron Microscopy (SEM)
- Utilizes reflected electrons to examine surfaces of biological specimens; requires critical-point drying for preservation of structure.