What is the right research microscope for me? This article gives you a brief overview of the major features you should have in mind when choosing an optical research microscope.

An optical microscope is often one of the central devices in a life-science research lab. It can be used for various applications which shed light on many scientific questions. Thereby the configuration and features of the microscope are crucial for its application coverage, ranging from brightfield through fluorescence microscopy to live-cell imaging.

This article provides a brief overview of the relevant microscope features and wraps up the key questions one should consider when selecting a research microscope.

Contents

• What kind of specimen do you use?
• In what dimensions do you think?
• Which contrast method suits best for your sample?
• What about the light source?
• Do you want to document or publish your results?
• Video: Advantages of a 19 mm FOV
• Do you want to manipulate your cells on the microscope?
• What is your budget?
• Who will use the microscope?

What kind of specimen do you use?

One of the first things to consider when selecting a research microscope is the type of specimen you want to explore. For fixed samples mounted on a thin glass slide, you can use an upright microscope. Living cells demand special characteristics of the microscope because they are kept in relatively large cell culturevessels filled with cell culture media.

Only an inverted configuration, with the objective below and the condenser above the specimen, facilitates the essential free space and the required proximity of the objective to the specimen. At the same time an inverted microscope keeps a good accessibility to the cells, e.g. to add micromanipulators.

In addition, living cells require an adequate environment to survive. Temperature and CO2concentration have to be kept at certain levels. A climate chamber with the corresponding controllers is necessary to fulfill this task.

Figure 1: Left: Glass slide to mount fixed samples e.g. histological sections. Right: Petri dish for cell culture usage.

 Figure 2: Left: An upright microscope features the objective above and the condenser below the specimen. Right: On an inverted microscope this set-up is turned around giving the users more space plus the required proximity of the objective to the specimen.

Microscopic specimen spread out into three dimensions: length, width, and height. Whereas some specimens, such as histological sections, are imaged only in xy-direction, there are other applications demanding acquisition also in z-dimension. To image 3D volumes e.g. of living cells, a motorized objective revolver is recommended which is able to guide your sample stepwise through the focus.  The imaging software should be able to reconstruct the single images for 3D visualization.

For living cells you have to add the dimension time. In this case, for example system stability is another critical feature. Due to the fact that temperature changes influence the imaging system during acquisition, effective counter measures are essential. An automatic focus adjustment such as the Adaptive Focus Control (AFC) counteracts these thermal influences and always finds the predefined focus.

Figure 3: The Adaptive Focus Control (AFC) automatically stabilizes the microscope focus also during long-term time-lapse acquisition. A sensor detects movements of an LED light beam (850 nm) which occur if the cover glass carrying the specimen changes its position e.g. due to thermal activity.

The majority of cells – especially animal cells – investigated with a microscope don’t have enough intrinsic contrast to see fine details. Researchers use contrast methods to fix this problem. Whereas phase contrast (PH) and differential interference contrast (DIC) manipulate the light passing through the specimen to add contrast, you can also stain it with fluorescent dyes (Immunofluorescence) respectively use fluorescent proteins.

According to the contrast method the microscope needs specific equipment; e.g. phase contrast needs special objectives whereas DIC utilizes certain prisms which have to be switched into the light path. For fluorescence microscopy you need special filter cubes allowing the correct light wave lengths to access and exit the specimen.

Figure 4: Series of neuronal cells acquired with different contrast methods. From left to right: Brightfield, DIC, Phase contrast, Fluorescence

 Figure 5: The Leica WF FRAP module (black box on the left) can be connected with the inverted research microscope Leica DMi8 via the Infinity Port.

One important question is how much money you can spend. Some microscope suppliers offer predefined configurations which are fit to special applications. But what if you don't need all of the preconfigured components you pay for? That's why a free configuration of components can be cheaper than buying a predefined microscope system.

Furthermore, the requirements for a microscope might change with time. In this case an upgradable system has certain advantages. With a predefined and fixed configuration you can find yourself tied to a limited amount of applications. Upgradability gives you the freedom to grow with changing demands.

Taking these points into account, a modular microscopy platform, such as the Leica DMi8, enables the researcher to start with an affordable microscope system which can be upgraded later on and grow with his demands.

Figure 6: Thanks to its modularity, the Leica DMi8 can be configured according to the researchers needs. Moreover it can be upgraded later on, if the requirements have changed.