by Dana Smith, PhD, Scientific Writer
Confocal microscopy is a powerful imaging technique used in various fields including biomedical sciences, materials science, and pharmaceutical research. A confocal microscope uses a combination of laser or focused light, scanning mirrors, pinhole filters, and fluorescence. With these components, a confocal microscope scans light across a sample to produce high quality images.
Confocal microscopy has advantages over conventional optical microscopy, while still being relatively easy to operate. In fact, confocal microscopes can bridge the gap between a conventional widefield microscope and a transmission electron microscope. Some of the main advantages of confocal microscopes include:
- 3D visualization: Confocal microscopes capture images at different focal planes. This type of image acquisition allows researchers to visualize the spatial arrangement within a sample. In biological applications, confocal microscopy can image the 3D architecture of cells and tissues.
- Improved focus and minimal background: Confocal microscopes use spatial filters to block any out-of-focus light, which prevents images from appearing blurry. The pinhole filter also reduces background noise to ensure that only relevant signal is captured during the imaging process.
- Improved contrast and resolution: By using laser illumination and pinhole filtering, confocal microscopy can produce images with excellent contrast and high resolution. These microscopes are an ideal choice for studying highly detailed structures such as subcellular components.
As previously mentioned, confocal microscopes collect sharply defined, clear images with low background because they gather discrete optical sections while eliminating out-of-focus light. The resulting image quality makes confocal microscopy an excellent tool for quantitative measurements and analyses. Additionally, researchers can use confocal microscopy for both live imaging and fixed samples, which makes it suitable for many different applications. If you are looking to purchase a confocal microscope, here is what to keep in mind while shopping:
Purchase considerations
When purchasing a confocal microscope, it is important to consider its application in your research. In general, experimental design can impact which microscope is the best fit. You should identify the particular imaging tasks that your research will require, such as live imaging or 3D reconstruction, to purchase a microscope that will best support those specific needs.
Sample characteristics can affect your confocal microscope choice, and it is critical to account for the size, type, and preparation of your samples. The samples that you plan to image with a confocal system will also influence the number of objectives and their working distance, the depth penetration of the microscope, and any potential fluorophores and optical filters.
Beyond experimental design, it is important to determine if the microscope you purchase is compatible with any of your existing imaging software. You may also want to consider purchasing from manufacturers and suppliers that can provide support and training for the confocal system.
Types of confocal microscopes
Classified by scanning methods, different types of confocal microscopes have their own unique advantages and drawbacks.
- Laser scanning confocal microscopes sweep a laser beam over the sample either point by point or by multiple points at a time. These systems are versatile and can be used for 2D, 3D, and 4D imaging. Laser scanning confocal microscopes use a pair of pinhole apertures to limit the size of the focal plane. As a result, they have excellent resolution and optical sectioning, even for relatively thick samples. With a laser scanning confocal microscope, the user can set the optical thickness, image in color, and use live or fixed tissues. However, this type of microscope has a slow imaging speed that may result in photodamage to the sample, including photobleaching of the fluorophores and phototoxicity of live cells.
- A spinning disk confocal microscope involves multiple points of light that are moved through the sample. Instead of a pair of pinholes like laser scanning confocal microscopes, this type of confocal microscope has hundreds of pinholes arranged in spirals on an opaque disk. The user can alter the disk rotation speed, pinhole diameter, and pinhole spacing to optimize and customize imaging. When spun, the pinholes scan the sample in rows to build the image, allowing for subsequent stacking and 3D visualization. This setup covers an entire field at a high rate, meaning that this type of confocal microscope has the advantages of imaging speed and a relatively low-light dose to prevent photobleaching and phototoxicity. However, this imaging speed comes at the cost of image resolution. Lastly, spinning disk confocal microscopes image multiple points at once so they require high-quality cameras to capture images from the sample.
- Hybrid scanning confocal microscopes represent an intermediate approach between single and multi-point scanning confocal microscopes. They combine the strengths of laser scanning and spinning disk technologies as they offer flexibility in imaging speed and resolution. These microscopes can cover more of the sample in one field of view, but increasing the imaging speed may lead to rapid photobleaching and lower resolution. Overall, hybrid systems are useful for researchers looking for versatility in their imaging workflow.
- Other advanced microscopes that use confocal technology include multiphoton confocal microscopes and spectral confocal microscopes. Multiphoton confocal microscopes use longer-wavelength lasers to penetrate deeper into samples. Common applications for this type of confocal microscope include deep-tissue imaging and live cell studies. A spectral confocal microscope can detect the spectral properties of emitted light, which allows researchers to identify different fluorescent dyes based on their emission spectra. This type of microscope is commonly used in multiplexing applications where multiple fluorescent markers are used.
Additional considerations
While understanding the different types of confocal microscopes is useful for deciding on the best option, cost is another key factor that can affect your choice. Generally, advanced systems and those with hybrid capabilities will tend to be more expensive. Laser based confocal microscopes are more expensive than a scanning disk confocal microscope because of their complex technology and point by point scanning mechanism. Finally, the need for certain components such as the type of camera, the number of objectives, and the types of optical filters factor into the final cost of the microscope.
Confocal microscopes are powerful tools that can improve the imaging involved in your research. Each type of confocal microscope—laser scanning, spinning disk, and hybrid scanning—has its own benefits and considerations so your selection needs to prioritize what type of image acquisition works best for your needs. Finding the right tradeoff between image speed, image resolution, and field of view is critical for guiding your decision to purchase a confocal microscope.
Confocal microscopy can be used across a wide range of applications from live imaging cells to analyzing materials through deep field penetration. No matter which you purchase, confocal microscopes can help support and improve your research program.
About the author
Dana Smith, PhD, completed her graduate training in Neurobiology at the University of Pittsburgh. She currently works as a medical writer, leveraging her expertise in translational research to create engaging and accessible content for both healthcare professionals and patients.