Electron microscope Presentation (2).pptx

Electron microscope and it's two types

1. Electron Microscopy Introduction

2. Electron Microscopy Electron microscopy uses a beam of electrons instead of light to view specimens.
It provides ultra-high magnification and resolution (up to 1,000,000×).
Electrons have a shorter wavelength than light, allowing visualization of tiny structures like viruses, organelles, and molecules.

3. Need for Electron Microscope Light microscopes can only resolve up to 200 nm (0.2 µm).
Many biological structures (like ribosomes or viruses) are smaller than this limit.
Electron microscopes overcome this by using electrons (λ = 0.005 nm).

4. Principle of Electron Microscopy Based on wave nature of electrons (De Broglie hypothesis).
A beam of electrons is accelerated and focused by electromagnetic lenses.
The electrons interact with the specimen and produce an image on a fluorescent screen or detector.

5. Types of Electron Microscopy There are two main types: 1. Transmission Electron Microscope (TEM) 2. Scanning Electron Microscope (SEM)

6. Transmission Electron Microscope (TEM) Principle :
A beam of electrons passes through a thin specimen.
Denser parts absorb electrons → appear darker; lighter parts → brighter. Features :
2D image
Ultra-high resolution (up to 0.1 nm)
Used to study internal structure of cells and organelles

7. TEM — Biological Sample Preparation Primary fixation : 2–4% glutaraldehyde in buffer (stabilizes proteins) Post-fixation : 1% osmium tetroxide (stabilizes membranes & adds electron density) En -bloc staining (optional): uranyl acetate for contrast Dehydration : graded ethanol/acetone series → 30 → 50 → 70 → 90 → 100% Resin infiltration : epoxy resins ( Epon , Araldite) Polymerize (e.g., 60°C) → hard block Ultrathin sectioning : 50–90 nm on ultramicrotome ; collect on copper grids Grid staining : uranyl acetate + lead citrate (final contrast) Speaker note: For suspensions/viruses use negative staining or cryo -TEM (plunge-freeze).

8. Applications Viewing cell organelles (mitochondria, ribosomes, nucleus.
Virus and bacteria morphology
Nanomaterials and crystal structure analysis

9. Scanning Electron Microscope (SEM) Principle :
A focused beam of electrons scans the surface of specimen.
Electrons bounce back → detected → 3D image produced. Features: 3D surface view
Moderate resolution (1–10 nm)
Specimen coated with thin metal (gold/palladium)

10. Biological Sample Preparation Fixation : glutaraldehyde (and optional osmium) Rinse in buffer Dehydration : graded ethanol series Drying : Critical-Point Drying (CPD) OR HMDS chemical drying alternative Mounting : on aluminium stub using conductive adhesive/tape Sputter-coating : Au/ Pd or carbon (2–10 nm typical) to prevent charging Cryo -SEM : freeze and fracturing for hydrated/native surfaces Speaker note: Good coating + grounding reduces charging and improves topographic detail.

11. Applications Surface texture of cells, insects, metals, tissues
Material sciences, forensics, and industrial inspection

12. Advantages of Electron Microscopy Extremely high resolution & magnification
Reveals fine structural details
Wide range of applications (biology, nanotech, forensics)

13. Limitations Expensive and large equipment
Requires vacuum and skilled operator
Specimen must be dead and thin
Complex sample preparation

14. Applications in Science Cell biology – organelle structure
Virology – virus identification
Nanotechnology – nanoparticle study
Material science – surface and fracture analysis
Forensics – micro-evidence study