Name: electron microscopy: tem vs sem
Uploaded: 2023-04-30T12:00:52.000Z
Duration: 1 min 25 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Life Science

SC.912.L.14

SC.912.L.14.4

Overview of Electron Microscopy

מיקרוסקופי אור משתמשים באור נראה כדי להאיר אובייקט, והעדשות שלהם יכולות להגדיל תמונה עד פי 2000. במקום אור, מיקרוסקופי אלקטרונים משתמשים באלומת אלקטרונים בעלת אורך גל קצר מאוד המאפשרת הגדלה של עצמים פי 2 עד 50 מיליון.
חוט להט פולט אלקטרונים יוצר את קרן האלקטרונים, ועדשות אלקטרוסטטיות ואלקטרומגנטיות ממקדות את הקרן על דגימה. הסביבה הפנימית של מיקרוסקופ אלקטרונים נשמרת תחת ואקום מכיוון שמולקולות אוויר יכולות להסיט את קרן האלקטרונים.
בהתאם לאינטראקציה של קרן האלקטרונים עם הדגימה, ניתן לחלק את מיקרוסקופ האלקטרונים לשני סוגים – מיקרוסקופ אלקטרונים תמסורת, או TEM, ומיקרוסקופ אלקטרונים סורק, או SEM.
ב-TEM, האלקטרונים מועברים דרך דגימה דקה ולאחר מכן משמשים ליצירת תמונה דו-ממדית. כאשר קרן האלקטרונים עוברת דרך הדגימה, ניתן לקבל מידע על הרכבה הפנימי ומבנהה באמצעות TEM.
ב- SEM, קרן האלקטרונים סורקת את פני השטח של הדגימה, ולאחר מכן האלקטרונים המוחזרים משמשים ליצירת מידע על הטופוגרפיה התלת-ממדית והרכב פני השטח.

סקירה כללית של מיקרוסקופיית אלקטרונים

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אורכי הגל של האור הנראה מגבילים בסופו של דבר את הרזולוציה התיאורטית המקסימלית של תמונות שנוצרו על ידי מיקרוסקופי אור. רוב מיקרוסקופי האור יכולים להגדיל רק פי 1000, ומעטים יכולים להגדיל עד פי 1500. אלקטרונים, כמו קרינה אלקטרומגנטית, יכולים להתנהג כמו גלים, אבל עם אורכי גל של 0.005 ננומטר, הם מייצרים רזולוציה גדולה משמעותית עד 0.05 ננומטר בהשוואה ל-500 ננומטר לאור נראה. מיקרוסקופ אלקטרונים (EM) יכול ליצור תמונה חדה המוגדלת עד פי 2,000,000. לפיכך, EMs יכולים לפתור מבנים תת-תאיים וכמה מבנים מולקולריים (לדוגמה, גדילים בודדים של DNA).

ישנם שני סוגים בסיסיים של EM - מיקרוסקופ אלקטרונים חודר (TEM) ומיקרוסקופ אלקטרונים סורק (SEM). ה-TEM דומה במקצת למיקרוסקופ האור הבהיר מבחינת אופן פעולתו. עם זאת, הוא משתמש בקרן אלקטרונים הממוקדת על הדגימה מלמעלה באמצעות עדשה מגנטית (ולא בעדשת זכוכית) ומוקרנת דרך הדגימה אל גלאי. אלקטרונים עוברים דרך הדגימה, ואז הגלאי לוכד את התמונה.

כדי שהאלקטרונים יעברו דרך הדגימה ב-TEM, הדגימה חייבת להיות דקה במיוחד (עובי 20-100 ננומטר). התמונה מופקת בגלל אטימות משתנה בחלקים שונים של המדגם. ניתן לשפר אטימות זו על ידי צביעה של הדגימה בחומרים כגון מתכות כבדות, שהן צפופות באלקטרון. TEM דורש שהקרן והדגימה יהיו בוואקום ושהדגימה תהיה דקה במיוחד ומיובשת.

SEMs יוצרים תמונות של משטחים של דגימות, בדרך כלל מאלקטרונים שנדחו מהדגימה על ידי קרן אלקטרונים. זה יכול ליצור תמונות מפורטות מאוד עם מראה תלת מימדי המוצג על צג. בדרך כלל, דגימות מיובשות ומוכנות עם מקבעים המפחיתים ארטיפקטים לפני שהן מצופות בשכבה דקה של מתכת כמו זהב. בעוד שמיקרוסקופיית אלקטרונית העברה דורשת חתכים דקים מאוד ומאפשרת לראות מבנים פנימיים כגון אברונים וחלקם הפנימי של ממברנות, ניתן להשתמש במיקרוסקופ אלקטרוני סורק כדי לראות את המשטחים של עצמים גדולים יותר (כגון גרגיר אבקה) וכן את המשטחים של דגימות קטנות מאוד.

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אורכי הגל של האור הנראה מגבילים בסופו של דבר את הרזולוציה התיאורטית המקסימלית של תמונות שנוצרו על ידי מיקרוסקופ אור. רוב מיקרוסקופ האור יכול ...

Education

JoVE Core

Cell Biology

ביולוגיה של התא

Unit 1

יחידה 1

Visualizing Cells, Tissues, and Molecules

ויזואליזציה של תאים, רקמות ומולקולות

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

electron microscopy: tem vs sem

Electron microscopy uses electrons instead of visible light to make images with much higher detail than a light microscope. Visible light limits the resolution of light microscopes, which usually magnify up to 1000X, and sometimes up to 1500X. Electrons have a much shorter wavelength, about 0.005 nm, so they can produce resolution as fine as 0.05 nm. An electron microscope can also magnify images up to 2,000,000X and reveal subcellular structures and some molecular structures, including single strands of DNA.

There are two main types of electron microscopes: the transmission electron microscope, or TEM, and the scanning electron microscope, or SEM. A TEM works in a way that is somewhat similar to a brightfield light microscope. It uses an electron beam focused from above with a magnetic lens, not a glass lens, and sends the beam through the sample to a detector. The detector captures the image after electrons pass through the specimen.

A TEM sample must be extremely thin, usually 20 to 100 nm thick, so electrons can pass through it. Different parts of the specimen block electrons by different amounts, which creates the image. Staining with electron-dense materials such as heavy metals can increase this contrast. TEM also requires a vacuum, and the sample must be ultrathin and dehydrated.

SEM is used to view the surface of a specimen. It forms images from electrons that are knocked off the sample by an electron beam. This produces very detailed images with a three-dimensional appearance on a monitor. Specimens are usually dried and treated with fixatives to reduce artifacts before they are sputter-coated with a thin layer of metal, such as gold. TEM is best for internal structures such as organelles and membrane interiors, while SEM is useful for surfaces, including larger objects like a pollen grain, as well as very small samples.

Electron Microscopy: TEM vs SEM

imaging biological samples with optical microscopy

imaging-biological-samples-with-optical-microscopy

How Light Microscopes Bring Samples Into View

Optical microscopy uses light and lenses to make tiny biological samples visible. Antonie van Leeuwenhoek built the first compound optical microscope in the 17th century to view blood cells, bacteria, and yeast cells. In 1830, Joseph Jackson Lister developed an essentially modern light microscope. During the 20th century, microscopes gained better magnification and resolution. A sample is placed on a glass slide and clipped onto the stage, which is the flat platform of the microscope. The...

phase contrast and differential interference contrast microscopy

phase-contrast-and-differential-interference-contrast-microscopy

Microscope Contrast for Live, Unstained Cells

Phase-contrast and differential interference contrast microscopy help scientists see live cells without stains. Both methods boost contrast so thin, transparent structures become easier to study under the microscope. Phase-contrast microscopes use interference between light that passes straight through a cell and light that is refracted by cell parts. The microscope uses an annular stop in the condenser to make a hollow cone of light. The objective lens also contains a phase plate with a phase...

fixation and sectioning

Microscope Slide Prep and Staining

Microscope slide preparation includes wet mounts, fixation, and staining. These steps help make specimens easier to see under a light microscope. They also help preserve cells and highlight important structures. A wet mount is the simplest slide preparation. The specimen is placed in a drop of liquid on the slide. A liquid sample can be added directly with a dropper, and a solid sample, such as a skin scraping, can be placed on the slide before the liquid is added. The liquid is sometimes...

immunofluorescence microscopy

Fluorescent Antibody Staining in Cells

Fluorescent antibody staining uses a fluorescence microscope to make cells and microbes visible in bright colors against a dark background. The microscope works with fluorochromes, which are fluorescent dyes that absorb energy from a light source and then give off visible light. Some fluorochromes are natural, such as chlorophylls. Others are added to the specimen to improve contrast. Common examples of fluorochromes include Texas red and FITC. The method can also use nucleic acid dyes such as...

immunocytochemistry and immunohistochemistry

immunocytochemistry-and-immunohistochemistry

Antibody Staining in Cells and Tissues

Immunocytochemistry (ICC) and immunohistochemistry (IHC) use antibodies to detect specific proteins or antigens in samples. ICC focuses on individual cells, such as blood cells and stem cells. IHC is used for tissue samples. These methods were first published by Albert Coons in 1941, when they were used to detect pneumococcal antigen in mouse tissue sections from mice infected with Pneumococcus. Both techniques can produce either a colored signal or a fluorescent signal. Enzyme-conjugated...

confocal fluorescence microscopy

Confocal Microscopy for Sharp Cell Images

Confocal microscopy is an advanced imaging method used to capture sharp fluorescence images. Its main advantage is that it blocks out-of-focus light from the sample with pinholes. That helps produce high-resolution images with strong contrast. Unlike a standard optical microscope, a confocal microscope uses a focused laser beam to scan the sample surface at different z-planes. This makes it especially useful for thick specimens, such as biofilms. These samples can often be examined alive and...

protein dynamics in living cells

Fluorescent Methods for Protein Movement

Protein movement in living cells can be measured with fluorescence-based methods such as FRAP, FRET, and PET. These techniques help scientists track how proteins move, interact, and change distance inside the cell. Fluorescent recovery after photobleaching, or FRAP, measures protein movement rates within the cell. In this method, a small region is exposed to a strong laser beam. The beam permanently bleaches fluorophore-tagged proteins in that area. Over time, bleached proteins diffuse away...

total internal reflection fluorescence microscopy

total-internal-reflection-fluorescence-microscopy

Surface-Only Imaging with TIRF Microscopy

Total internal reflection fluorescence microscopy, or TIRF, is a microscope method used to view fluorophores near a solid surface with a higher refractive index, such as a glass coverslip. It is useful when scientists want to study signals close to the cell surface. TIRF works when light from a medium with a lower refractive index, such as air, hits the glass coverslip at a critical angle. Instead of entering the glass, the light undergoes total internal reflection. This reflection creates an...

atomic force microscopy

Atomic Force Microscopy for Surface Mapping

Atomic force microscopy is used to map the surface details of materials. It can examine ceramics, glass, polymers, and biological samples. The method gives far more resolution than an optical imaging system and produces three-dimensional surface profiles instead of flat 2D images. The probe is the key part of an AFM setup. It includes the cantilever and tip assembly, and it is also the part that is replaced most often. Constant contact with samples wears down the tip, so probe choice depends...

super-resolution fluorescence microscopy

Sharper Cell Images with Fluorescence Microscopy

Super-resolution fluorescence microscopy gives sharper images than standard fluorescence microscopy by reducing the point spread function, or PSF. The PSF is the light pattern from a point source that makes it look blurred. Because of this blur, each fluorescent spot appears larger than it really is. Nearby fluorophores can also overlap through their PSFs and make the image less clear. Several super-resolution methods have been developed to improve image detail. Photoactivated localization...

overview of electron microscopy

Electron microscopy uses electrons instead of visible light to make images with much higher detail than a light microscope. Visible light limits the resolution of light microscopes, which usually magnify up to 1000X, and sometimes up to 1500X. Electrons have a much shorter wavelength, about 0.005 nm, so they can produce resolution as fine as 0.05 nm. An electron microscope can also magnify images up to 2,000,000X and reveal subcellular structures and some molecular structures, including single...

scanning electron microscopy

How SEM Reveals Surface Details

A scanning electron microscope (SEM) reveals the surface details of a sample with an electron beam. The beam scans across the sample in a two-dimensional pattern. SEM can image areas from about 1 centimeter down to 5 micrometers wide. SEM is useful for studying bacteria, viruses, tissues, and larger samples such as insects. Conventional SEM can produce magnification from 20X to 30,000X. It also offers spatial resolution of about 50 to 100 nanometers. The process starts when the electron gun...

transmission electron microscopy

How TEM Reveals Tiny Structures

Transmission electron microscopy uses electrons to reveal very small structures inside a specimen. The technique grew from the first electron microscope prototype developed in 1931 by physicist Ernst Ruska. He built on the idea that magnetic fields can direct an electron beam, just as lenses direct light in an optical microscope. In a transmission electron microscope, a hot tungsten element produces electrons. An electron gun then accelerates them with a potential difference, giving the beam...

preparation of samples for electron microscopy

preparation-of-samples-for-electron-microscopy

Electron Microscopy Sample Prep Methods

Electron microscopy sample prep methods help biological samples survive imaging in TEM and SEM. Before a specimen can be viewed, it must be fixed, or stabilized, so the electron beam does not damage it. It also must be dried well, or desiccated, because the microscope uses a vacuum. Fixation should happen as quickly as possible. Once a sample leaves its natural environment, its properties begin to change. In tissue samples, oxygen levels can drop and change the appearance of mitochondria. That...

immunogold electron microscopy

Immunogold Labeling in Electron Microscopy

Immunogold labeling in electron microscopy uses antibodies and tiny gold particles to find specific proteins in cells and tissues. The gold particles are very electron-dense, which means they show up clearly in electron microscope images. This gives researchers a high-resolution way to see where proteins are located and to compare their amounts under different stimulation conditions. The method can reveal proteins on the cell surface and inside cells. It has been used to study proteins...

cryo-electron microscopy

Cryo-EM for Native Biomolecule Imaging

Cryo-EM, or cryo-electron microscopy, lets scientists image biomolecules in their frozen, native state. It avoids the dehydration, fixation, and staining used in conventional electron microscopy, which can distort samples and create artifacts. It also reduces damage from the electron beam by using gentler imaging conditions. This method is useful when other structure tools have limits. X-ray diffraction needs a molecule to form a crystal, and that is not always possible. Even when...

electron microscope tomography and single-particle reconstruction

electron-microscope-tomography-and-single-particle-reconstruction

3D Imaging with Electron Microscopy

Transmission electron microscopy (TEM) can build 3D images of biological samples. It does this with electron microscope tomography and single-particle reconstruction. Tomography can show cell parts or small cells in vivo, while single-particle reconstruction is used for macromolecules and macromolecular complexes in vitro only. Electron tomography can be done in TEM or in STEM, which stands for scanning transmission electron microscopy. STEM is mainly used for thick biological specimens. It...

key terms and concepts

Learn how electron microscopy uses electrons for high-resolution images, and compare TEM and SEM for viewing internal structures and surface detail.

Electron Microscopy: TEM vs SEM | JoVE K12

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

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Describe the scientific theory of cells (cell theory) and relate the history of its discovery to the process of science.

SC.912.L.14.1

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Prokaryotes are small unicellular organisms that include the domains&#x2014;Archaea and Bacteria. Bacteria include many common organisms, such as ...

Cytoplasm

The cytoplasm consists of organelles and a framework of protein scaffolds called the cytoskeleton suspended in an aqueous solution, the cytosol. The ...

The Nucleus

The nucleus is a membrane-bound organelle that acts as a control center in a eukaryotic cell. It contains chromosomal DNA, which controls gene expression ...

Endoplasmic Reticulum

Endoplasmic ReticulumThe endoplasmic reticulum (ER) is an extensive network of membranous sacs and tubules in eukaryotic cells, continuous with the outer ...

Ribosomes

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that ...

Golgi Apparatus

As they leave the Endoplasmic Reticulum (ER), properly folded and assembled proteins are selectively packaged into vesicles. These vesicles are ...

Microtubules

There are three types of cytoskeletal structures in eukaryotic cells&#x2014;microfilaments, intermediate filaments, and microtubules. With a diameter of ...

Peroxisomes

Peroxisomes and mitochondria are two important oxygen-utilizing organelles in eukaryotic cells. Mitochondria carry out cellular respiration&#x2014;the ...

Gap Junctions

Multicellular organisms employ a variety of ways for cells to communicate with each other. Gap junctions are specialized proteins that form pores between ...

The Extracellular Matrix

In order to maintain tissue organization, many animal cells are surrounded by structural molecules that make up the extracellular matrix (ECM). Together, ...

Tissues

Cells with similar structure and function are grouped into tissues. A group of tissues with a specialized function is called an organ. There are four main ...

Plant Cell Wall

The plant cell wall gives plant cells shape, support, and protection. As a cell matures, its cell wall specializes according to the cell type. For ...

Plasmodesmata

The organs in a multicellular organism&#x2019;s body are made up of tissues formed by cells. To work together cohesively, cells must communicate. One way ...

What are Membranes?

A key characteristic of life is the ability to separate the external environment from the internal space. To do this, cells have evolved semi-permeable ...

Membrane Fluidity

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Fluid Mosaic Model

The fluid mosaic model was first proposed as a visual representation of research observations. The model comprises the composition and dynamics of ...

What is an Electrochemical Gradient?

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Osmosis

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Tonicity in Animals

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Secondary Active Transport

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Pinocytosis

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While endocytosis takes particles ...

Relate structure to function for the components of plant and animal cells. Explain the role of cell membranes as a highly selective barrier (passive and active transport).

SC.912.L.14.2

Cell Structure

Background
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Compare and contrast the general structures of plant and animal cells. Compare and contrast the general structures of prokaryotic and eukaryotic cells.

SC.912.L.14.3

Overview of Microscopy Techniques

The early pioneers of microscopy opened a window into the invisible world of microorganisms. In 1830, Joseph Jackson Lister created an essentially modern ...

Introduction to Light Microscopy

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The wavelengths of visible light ultimately limit the maximum theoretical resolution of images created by light microscopes. Most light microscopes can ...

Phase Contrast and Differential Interference Contrast Microscopy

Phase-Contrast Microscopes
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Confocal Fluorescence Microscopy

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Introduction to Fluorescence Microscopy

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Compare and contrast structure and function of various types of microscopes.

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SC.912.L.14.6

A. Cells have characteristic structures and functions that make them distinctive.

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C. Life can be organized in a functional and structural hierarchy ranging from cells to the biosphere.

D. Most multicellular organisms are composed of organ systems whose structures reflect their particular function.

Electron Microscopy: TEM vs SEM

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