Microscopes are powerful tools for examining biological cells. Under the right conditions and magnification, cell components and activity become visible and diseases can be exposed. Microscopes can inform treatment and saves lives—if they are within reach. With an inexpensive, versatile, and portable new microscope design, researchers at the University of Connecticut (UConn) and the University of Memphis (U of M) are hoping to increase access to high-resolution microscopes.
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| A 3D animation generated from the 3D printed microscope. Video via Bahram Javidi/OSA |
As the researchers report in the OSA journal Optical Letters, their new design can resolve subcellular features in three-dimensional images and capture tiny fluctuations in biological cells over time. It’s research quality yet robust enough to carry to a patient’s bedside. The team was led by Bahram Javidi (UConn) and included Timothy O’Connor (UConn) and Ana Doblas (U of M).
Objects can be magnified by many different arrangements of mirrors, lenses, and optical components. For this project, the team wanted an arrangement that didn’t require extensive sample preparation (like staining or labeling) or laboratory-style control of environmental conditions like noise, but that produced useful 3D images. So, they turned to a modified version of a technique called digital holographic microscopy (DHM).
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| The high-resolution, low-cost microscope in use. Image via Bahram Javidi/OSA. |
The “digital” in DHM refers to the fact that instead of looking through an eyepiece directly at a sample, the microscope feeds data into a computer program and an image of the sample is generated on a screen. “Holographic” refers to the fact that the image is produced using the technique for making holograms. If you’re thinking Star Trek, Red Dwarf, or Avatar, you’re kind of on the right track. Holograms are 3D images of objects that you don’t need special glasses to see. Put simply, a hologram is created by illuminating an object with a laser beam and then recording how the light around the object is changed by the object.
In traditional DHM, you first illuminate a sample with a laser. Then, using a digital camera, you record the interference pattern created when light transmitted or reflected by the object interferes with an uninterrupted reference beam. That data is processed by a computer program and output as a 3D image of the sample. DHM is a great way to study cells, but here’s the problem—it requires a complicated setup and is really sensitive to vibrations. For these reasons, it’s usually done on a special optical table in the lab.
To make this technique viable outside of the lab, the researchers modified a traditional DHM setup. Instead of illuminating a sample with a traditional laser beam, their design uses a patterned or “structured” beam. The structure affects the interference pattern in such a way that you can double the resolution of the 3D image.
DHM and structured illumination microscopy (SIM) have been combined before, but in a way that required two separate light sources. The problem is that the more sources you have, the more sensitive the microscope is to vibrations. To get around this problem, the new design takes advantage of geometry in a way that requires only one light source. The researchers add structure to the illuminating beam by passing it through a diffraction grating (a clear cd) before it reached the object, which created an alternating light and dark pattern.
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Typical optical setup of DHM. Image credit: Egelberg (CC BY-SA 3.0).
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The researchers estimate that the microscope costs around several hundred dollars in parts, less if it could be manufactured in bulk. All of the optical parts are commercially available and the rest of the microscope can be printed with a 3D printer. The capabilities of 3D printing are key to the success of this design.
“3D printing the microscope allowed us to precisely and permanently align the optical components necessary to provide the resolution improvement while also making the system very compact,” said Javidi in a press release.
In addition to working out the design specifics, the team wrote a computer algorithm to process the data and reconstruct the images. Tests of their system showed that the SIM modification doubled the resolution of DHM, enabling microscope to resolve features as small as 0.775 micrometers (for comparison, the diameter of a red blood cell is about 5 micrometers). In addition, the microscope can expose changes in biological cells over time that happen on a scale as small as a few tens of nanometers.
Javidi and his team are exploring ways to further reduce the impact of environmental noise on the images and collaborating with international partners to see how well the microscope can diagnose conditions like diabetes, sickle cell disease, and malaria.
“This new microscope doesn’t require any special staining or labels and could help increase access to low-cost medical diagnostic testing,” says Javidi. “This would be especially beneficial in developing parts of the world where there is limited access to health care and few high-tech diagnostic facilities.”