Inexpensive 3D-Printed Microscope Can Spot Coronavirus in Blood

The digital holographic machine, faster than a PCR test, relies on deep learning

4 min read
A photo of a digital microscope

The digital microscope is comprised of a laser diode, a microscope objective lens, a glass plate to induce lateral shearing of the object wavefront, and an image sensor.

Tim O'Connor

A digital microscope that uses holography and deep-learning technology could detect COVID-19 in a drop of blood. A diagnosis could be made on the spot in a matter of minutes instead of the hours or sometimes days it can take for PCR test results to come back.

The system, which uses digital holographic microscopy, could be used in areas that lack health care facilities, as well as in hospitals whose labs are backlogged with tests.

That's according to one of the machine's developers, IEEE Fellow Bahram Javidi. He is the director of the Multidimensional Optical Sensing and Imaging Systems Lab at the University of Connecticut in Storrs. His collaborators were Dr. Bruce T. Liang,Timothy O'Connor and Dr. Jian-Bing Shen. Liang is dean of the university's school of medicine, O'Connor is a biomedical engineering grad student, and Shen is a physician at the university's medical center. The researchers' article on their preliminary findings, "Digital Holographic Deep Learning of Red Blood Cells for Field-Portable, Rapid COVID-19 Screening," was published in the 15 May issue of the Optical Society's Optics Letters.

An illustration of how the light emitted from the laser diode illuminates the red blood cellsThe light emitted from the laser diode illuminates the red blood cells, which is then magnified by the microscope objective lens. The glass plate creates reflections from both its front and back surfaces. The two reflected beams self-interfere to form a digital hologram.Tim O'Connor

Javidi told The Institute the project stemmed from his desire to help stop the spread of the coronavirus in parts of Africa, Asia, and elsewhere that have limited resources.

"I wanted to find a way to quickly test for the virus from a droplet of blood using an affordable, portable, and rapid disease-identification system," he says.

That's just what the researchers developed. The machine uses low-cost components that Javidi says can be easily obtained, including a camera, a laser diode, an objective lens, a glass plate, and a CMOS image sensor. The body of the microscope can be made using a 3-D printer.


TESTING A THEORY

A number of diseases can modify a person's red blood cells. Javidi, who is not a physician, wondered whether the same could be true of the coronavirus.

"The signatures would be very small—at the nanoscale level—but the changes in the red blood cells would still be there," he says.

He confirmed his theory with doctors at the UConn Health center. Hematologists studying COVID-19 had reported seeing changes in the blood cells of their patients, such as significantly lower hemoglobin and hematocrit levels. Furthermore, Javidi says, morphological changes have been reported in COVID-positive patients. He and his team also found recent research on COVID-19 patients that suggests statistically significant differences in the size and shape of red blood cells, especially in those with a severe case of the virus.

Javidi's research team decided to explore digital holographic microscopy, which is used in cell imaging, cell classification, and disease identification.

"DHM has drawn great interest due to its stain-free operation, numerical refocusing ability, and single-shot operation, lending itself as a powerful tool for biological sample investigation," the researchers wrote in their paper. "The technology has good vertical resolution—which helps researchers get a better sense of the morphology of cells. And because it relies on computers for much of the image processing, it is easy to use."

The technology has been able to identify malaria, diabetes, sickle-cell anemia, and other diseases through blood samples.

In the team's holographic microscope, light from the laser diode passes through the blood sample and is then magnified by an objective lens. Part of the light then bounces off the front of a glass plate and part off the back, creating two copies of the light that have passed through the sample. That creates a hologram that is then recorded by an image sensor. A technician is able to computationally work with the hologram to reconstruct a 3D profile of the sample.

"I wanted to find a way to quickly test for the virus from a droplet of blood using an affordable, portable, and rapid disease-identification system."

Individual cells are numerically reconstructed to retrieve the cells' phase profile due to the propagation and interaction of light through the cells, and then inputted into the deep-learning network to be classified.

Because no one feature of the cells was indicative of infection, the team measured a number of different features and fed them into the network to be classified.

Javidi's team worked with doctors at the university's health center to obtain the blood samples. The study looked at more than 1,400 red blood cells, with 840 of them coming from 10 patients who tested positive for the virus and 630 from 14 health care workers who tested negative. The microscope system found that 80 percent of the patients had the virus and that 13 of the 14 workers were virus-free.

The preliminary results were positive, but there were limitations to the research, Javidi says. It's not clear how effective the test will be for early detection, because the samples were taken from patients who had a moderate case of the virus.

Javidi says the next step is to continue to test blood samples of COVID-19 patients. He would like to widen the sample pool to include people outside the United States and is looking for collaborators.

He's seeking funding from the U.S. National Science Foundation.

You can learn more about the project from the lab'swebsite or by viewing this video.

The Conversation (0)

Get unlimited IEEE Spectrum access

Become an IEEE member and get exclusive access to more stories and resources, including our vast article archive and full PDF downloads
Get access to unlimited IEEE Spectrum content
Network with other technology professionals
Establish a professional profile
Create a group to share and collaborate on projects
Discover IEEE events and activities
Join and participate in discussions

The Inner Beauty of Basic Electronics

Open Circuits showcases the surprising complexity of passive components

5 min read
Vertical
A photo of a high-stability film resistor with the letters "MIS" in yellow.
All photos by Eric Schlaepfer & Windell H. Oskay
Blue

Eric Schlaepfer was trying to fix a broken piece of test equipment when he came across the cause of the problem—a troubled tantalum capacitor. The component had somehow shorted out, and he wanted to know why. So he polished it down for a look inside. He never found the source of the short, but he and his collaborator, Windell H. Oskay, discovered something even better: a breathtaking hidden world inside electronics. What followed were hours and hours of polishing, cleaning, and photography that resulted in Open Circuits: The Inner Beauty of Electronic Components (No Starch Press, 2022), an excerpt of which follows. As the authors write, everything about these components is deliberately designed to meet specific technical needs, but that design leads to “accidental beauty: the emergent aesthetics of things you were never expected to see.”

From a book that spans the wide world of electronics, what we at IEEE Spectrum found surprisingly compelling were the insides of things we don’t spend much time thinking about, passive components. Transistors, LEDs, and other semiconductors may be where the action is, but the simple physics of resistors, capacitors, and inductors have their own sort of splendor.

High-Stability Film Resistor

A photo of a high-stability film resistor with the letters "MIS" in yellow.

All photos by Eric Schlaepfer & Windell H. Oskay

This high-stability film resistor, about 4 millimeters in diameter, is made in much the same way as its inexpensive carbon-film cousin, but with exacting precision. A ceramic rod is coated with a fine layer of resistive film (thin metal, metal oxide, or carbon) and then a perfectly uniform helical groove is machined into the film.

Instead of coating the resistor with an epoxy, it’s hermetically sealed in a lustrous little glass envelope. This makes the resistor more robust, ideal for specialized cases such as precision reference instrumentation, where long-term stability of the resistor is critical. The glass envelope provides better isolation against moisture and other environmental changes than standard coatings like epoxy.

15-Turn Trimmer Potentiometer

A photo of a blue chip
A photo of a blue chip on a circuit board.

It takes 15 rotations of an adjustment screw to move a 15-turn trimmer potentiometer from one end of its resistive range to the other. Circuits that need to be adjusted with fine resolution control use this type of trimmer pot instead of the single-turn variety.

The resistive element in this trimmer is a strip of cermet—a composite of ceramic and metal—silk-screened on a white ceramic substrate. Screen-printed metal links each end of the strip to the connecting wires. It’s a flattened, linear version of the horseshoe-shaped resistive element in single-turn trimmers.

Turning the adjustment screw moves a plastic slider along a track. The wiper is a spring finger, a spring-loaded metal contact, attached to the slider. It makes contact between a metal strip and the selected point on the strip of resistive film.

Ceramic Disc Capacitor

A cutaway of a Ceramic Disc Capacitor
A photo of a Ceramic Disc Capacitor

Capacitors are fundamental electronic components that store energy in the form of static electricity. They’re used in countless ways, including for bulk energy storage, to smooth out electronic signals, and as computer memory cells. The simplest capacitor consists of two parallel metal plates with a gap between them, but capacitors can take many forms so long as there are two conductive surfaces, called electrodes, separated by an insulator.

A ceramic disc capacitor is a low-cost capacitor that is frequently found in appliances and toys. Its insulator is a ceramic disc, and its two parallel plates are extremely thin metal coatings that are evaporated or sputtered onto the disc’s outer surfaces. Connecting wires are attached using solder, and the whole assembly is dipped into a porous coating material that dries hard and protects the capacitor from damage.

Film Capacitor

An image of a cut away of a capacitor
A photo of a green capacitor.

Film capacitors are frequently found in high-quality audio equipment, such as headphone amplifiers, record players, graphic equalizers, and radio tuners. Their key feature is that the dielectric material is a plastic film, such as polyester or polypropylene.

The metal electrodes of this film capacitor are vacuum-deposited on the surfaces of long strips of plastic film. After the leads are attached, the films are rolled up and dipped into an epoxy that binds the assembly together. Then the completed assembly is dipped in a tough outer coating and marked with its value.

Other types of film capacitors are made by stacking flat layers of metallized plastic film, rather than rolling up layers of film.

Dipped Tantalum Capacitor

A photo of a cutaway of a Dipped Tantalum Capacitor

At the core of this capacitor is a porous pellet of tantalum metal. The pellet is made from tantalum powder and sintered, or compressed at a high temperature, into a dense, spongelike solid.

Just like a kitchen sponge, the resulting pellet has a high surface area per unit volume. The pellet is then anodized, creating an insulating oxide layer with an equally high surface area. This process packs a lot of capacitance into a compact device, using spongelike geometry rather than the stacked or rolled layers that most other capacitors use.

The device’s positive terminal, or anode, is connected directly to the tantalum metal. The negative terminal, or cathode, is formed by a thin layer of conductive manganese dioxide coating the pellet.

Axial Inductor

An image of a cutaway of a Axial Inductor
A photo of a collection of cut wires

Inductors are fundamental electronic components that store energy in the form of a magnetic field. They’re used, for example, in some types of power supplies to convert between voltages by alternately storing and releasing energy. This energy-efficient design helps maximize the battery life of cellphones and other portable electronics.

Inductors typically consist of a coil of insulated wire wrapped around a core of magnetic material like iron or ferrite, a ceramic filled with iron oxide. Current flowing around the core produces a magnetic field that acts as a sort of flywheel for current, smoothing out changes in the current as it flows through the inductor.

This axial inductor has a number of turns of varnished copper wire wrapped around a ferrite form and soldered to copper leads on its two ends. It has several layers of protection: a clear varnish over the windings, a light-green coating around the solder joints, and a striking green outer coating to protect the whole component and provide a surface for the colorful stripes that indicate its inductance value.

Power Supply Transformer

A photo of a collection of cut wires
A photo of a yellow element on a circuit board.

This transformer has multiple sets of windings and is used in a power supply to create multiple output AC voltages from a single AC input such as a wall outlet.

The small wires nearer the center are “high impedance” turns of magnet wire. These windings carry a higher voltage but a lower current. They’re protected by several layers of tape, a copper-foil electrostatic shield, and more tape.

The outer “low impedance” windings are made with thicker insulated wire and fewer turns. They handle a lower voltage but a higher current.

All of the windings are wrapped around a black plastic bobbin. Two pieces of ferrite ceramic are bonded together to form the magnetic core at the heart of the transformer.

This article appears in the February 2023 print issue.

{"imageShortcodeIds":[]}