Digital Fluorescence Microscope Product Review: EVOS FL and Celena S

Please Note:  As of 5/1/2017,  the iRiS™ Digital Imaging System has been renamed as the CELENA^® S Digital Imaging System.

By Sean Yu

Introduction

This review is my personal experience from testing the digital cell imaging systems: the EVOS FL^TM and the new CELENA^® S^TM.  The EVOS system has been on the market for a number of years and originally was developed by America Microscope Group (AMG) in 2009.  The EVOS is currently sold by Life Technologies (now a part of Thermo Fisher Scientific). The EVOS product line has a series of product lines ranging from the basic (EVOS XL) to mid-level EVOS FL and high end EVOS FL Auto. The EVOS family has been a dominant product in the digital microscope market segment.  The CELENA^® S Digital Cell Imaging System has recently been introduced to the North America market by Logos Biosystems.  In this article, I describe the instrument layouts and design, provide comparisons of image quality produced by each system, overall feature comparisons, and user experience comparisons.

Optics, Image viewing, and Focusing

The two systems, EVOS FL and CELENA^® S, have, overall, similar functionality, and similar specifications with regards to optics, monitoring, and fluorescence:

• Bright field and phase contrast optics with changeable objectives,
• Images are displayed on a monitor, no eye piece is needed
• Three color Epi-fluorescence capability with changeable filter modules

There are some differences in focusing and software capabilities:

• Manual focusing for the EVOS FL
• Motorized Focusing for the CELENA^® S
• The motorized focusing of the CELENA^® S allows Z-stack imaging
• CELENA^® S also has features such as time-lapse imaging, on-board image analysis software, and built-in 128 GB SSD hard drive.

Microscope Controls

EVOS FL

Stage and controls: EVOS has a solid, oval shaped base and on top of the base is the large square stage.  The manual focus knobs are on both sides of the base and the XY stage movement knobs are located on the side and the front of the stage.  Except for the front control knob, the focus and XY control knobs are well placed.  The front control knob may be prone to damage, as it protrudes from the front and may easily be knocked about.  The objective lens cycle wheel is located in the front of the base, allowing you to easily change between different objectives.  Cycling between filter cubes (module) is controlled by a lever moving back and forth behind the stage on the left side.  For me, this location made changing filters more difficult, since one has to reach out over the focusing and stage control knob.  If you are not careful it is easy to alter the stage control knobs as you are changing filters and can result in having to reposition and retake images, as happened to me.

Bright field and Phase contrast control and screen: EVOS’ phase contrast control unit sits on top of the stage, different CELENA^® S’ are organized on a wheel.  That made the unit quite compact.  This feature allows maximal clearance from the top, makes adjusting cell culture vessel and finding proper viewing spot much easier.  On the other hand, the small over structure also allow ambient light to interfere with fluorescence imaging, to solve that problem, a loose cover with dark filter is used to cover the slides/vessel while imaging; An integrated 15 inch screen is supported by a goose neck stand attached to the rear of the unit.  The USB port is located on the right side behind the stage.

CELENA^® S

Layout and controls: In contrast to the round base of the EVOS, the CELENA^® S is a rectangular unit with a cover that overhangs the stage and objectives.  The CELENA^® S diaphragm controls are on the top of the unit.  The full size cover and sliding diaphragm unit allow less ambient light to enter the optics while taking fluorescent images, but also make finding the viewing field more difficult.  The space under the cover is ample enough for the different size cell culture vessels.   There are two focusing knobs: macro on the left front and fine on the right front. Focusing also may be controlled on the screen with the mouse utilizing two sliding ledgers.  Switching between objective lenses is controlled by a sliding wheel in the front, similar to the EVOS FL. The filter modules are easily changed using a lever on the right sight of the unit.  The XY stage control also is located on the right side of the unit, toward the back.   The XY control mechanism is a stacked two knob configuration, similar to a traditional microscope. The CELENA^® S has several USB ports, a standard LED Monitor port, and an HDMI port making it easy to attach a wireless mouse, portable USBs, connect to internet, and/or attach a portable USB device.

Screen.  A separate LED screen is required for the CELENA^® S, allowing flexibility in the size and quality of monitor.  Overall, the monitor set-up makes it easier on the eye when viewing images, but does require more space.

Image quality

Using the same prepared fluorescence slide (FluoCells F369724, Life Technologies), I took a series of images using utilizing both systems.  Of course this is just one sampling, by no means a comprehensive measurement.  The images were taken with 10x and 20x objectives from the manufacturers.

There is no doubt that under the tested conditions, CELENA^® S images are more crisp (better resolution), brighter and have lower background.  To me, the difference in image quality is pretty significant.  Here are some examples of overlapping images taken by the two systems with the same slide from Molecular Probes (Life Technologies).  The quality difference may in part due to CELENA^® S being developed more recently and using new CMOS imaging sensor that has lower noise, higher dynamic range.  The EVOS FL I tested did use and\ older CCD sensor.  Of course, other factors such as instrument settings, quality and build of objective lens and other optical components may contribute to the image quality.

User Experience

Using EVOS FL

I found the EVOS FL’s user interface to be very easy to use, especially when observing live cells in cell culture vessels like a petri dish or 96 well plate.  Some really nice design features contribute to this experience:

• A small phase-contrast unit that is compactly designed at the top, allowing a better view of a culture vessel and easier positioning of the vessel.

• Large moving stage with control knobs located on both sides and the front of the stage.

• Large manual focusing knobs on both sides of the unit.Although the EVOS FL unit I used did not have a fine focusing knob, the ‘feel’ of focusing was very good.

• Software interface: The EVOS FL had a very good feature called “focusing and find”, which provides a live feed of the image to the monitor and allows the user to find the proper field of view and to correct the focusing of the image in response to any changes the of stage position.Re-focusing is immediate (or seems like it).The EVOS has another viewing feature called “actual”.In ‘actual’ mode, the unit displays a continuous timed exposure to show the actual image as it would appear in a capture image.

The one feature I did not like with the EVOS FL I tested was the location of the filter module control lever.  As mentioned above, I found its placement to be awkward to reach and found it difficult to switch filters without inadvertently moving the stage.

In summary, the EVOS FL is an excellent inverted microscope for routine cell culture usage, but not designed to obtain the highest quality images.

Using CELENA^® S

CELENA^® S’s large HD display really gives user a better view of fluorescence image and control functions on screen.  The user interface is simple and very intuitive   -- I was able to start using the instrument without reading the user manual. The mechanical controls on the unit are well placed at locations similar to a traditional microscope.  The focusing function is controlled by two knobs, coarse on the left and fine on the right.  The focusing is motorized, allowing on screen focus controls and image Z-stacking.  The mechanical specimen stage is controlled with a typical combinatory, stacked XY knob on the right side of the unit.

Feature Comparison

Summary

The CELENA^® S is designed to be an everyday use microscope capable of producing presentation/publication images.  I found the CELENA^® S to be easy to use with the ability to provide high quality images at a fraction of cost of confocal microscope.   With CELENA^® S’ onboard software and advanced imaging features such as Z-stacking/time lapse imaging, users can explore additional utilities that are usually only available in more expensive imaging systems (e.g. EVOS Auto, Cytell).  EVOS FL with its well-designed controls, is good daily use microscope more suitable, in my opinion, to obtain quick images such as with GFP transfected cells. The tested unit produced fluorescence images some users would likely find not to be of presentation/publication quality.