Infectious diseases such as malaria remain a leading cause of death in many regions. This is partly because people there do not have access to medical diagnostic tools that can detect these diseases (along with a range of non-communicable diseases) at an early stage, when there is more scope for treatment.
It is a challenge that scholars have risen to, with the goal of democratizing health care for economically disadvantaged people around the world.
My colleagues and I have developed a new method for examining biological cells that is small enough to fit in a smartphone lens.
Although we have only tested it in the lab so far, we hope in the future this nanotechnology will enable disease detection in real medical environments using only a mobile device. We hope that our work will eventually help save millions of lives.
How to examine a biological cell
The ability to examine biological cells through optical microscopes is an essential part of medical diagnosis.
This is because specific changes in cells that can be observed under a microscope often indicate diseases. In the case of malaria, for example, the gold standard method of detection involves the use of microscopic images to identify specific changes in a patient’s red blood cells.
But biological cells are good at hiding. Many of its internal features are practically transparent and virtually invisible to conventional microscopes. To make these features visible, we need to apply tricks.
One way is to introduce some kind of chemical staining, which adds contrast to the transparent features of the cells.
Other methods use a process called “phase imaging”. Phase imaging exploits the fact that light, passing through the cell, contains information about the transparent parts of the cell – and makes this information visible to the human eye.
Conventional phase imaging methods rely on a combination of huge components such as prisms and interferometric settings, which cost thousands of dollars. Also, expensive and bulky equipment cannot be easily supplied in remote areas and economically disadvantaged countries.
A major scientific effort is currently being directed towards utilizing nanotechnology to replace traditional large optical components.
This is done by creating nanometer-thick devices with the potential for low-cost mass production. These devices could be integrated into portable devices, such as smartphone cameras, in the future.
In the specific case of phase imaging, scientists were previously only able to develop systems that:
- It relies on time-consuming computational post-processing, which makes the process more complicated and does not allow real-time imaging.
- It still uses mechanically moving or rotating parts. Due to the space requirements of these parts, they are not compatible with completely flat optical components and extremely small integration.
We have developed a device that can perform instantaneous phase imaging without these limitations. Our solution is only a few hundred nanometers thick, and can be integrated into camera lenses, in the form of a flat film on top of the lens.
How did we do it
We inserted a nanostructure into a very thin film (<200 nm) enabling phase imaging using an effect sometimes referred to as 'optical spin coupling'. The principle of operation is simple. A transparent object, such as a biological cell, is placed on top of the device. Light is shined through the cell and the previously invisible cell structure becomes visible on the other side. In our last post in ACS Photonics, we explain in detail how we have successfully demonstrated the use of this method in a laboratory setting, using artificially transparent objects. The bodies were only a few micrometers in size, and thus could be compared to biological cells.
Since this method enables phase imaging, but does not deal with magnification of small objects such as cells, it still currently requires bulky lenses to provide magnification. However, we are confident that our devices can be combined in the future with flat lenses, arising from other advances in nanotechnology.
Where can it lead us?
The challenge for the current device prototype is the manufacturing cost of around A$1,000. We used several expensive nanofabrication methods which are also used to make computer chips.
However, by taking advantage of the economies of scale associated with chip production, we believe we may achieve rapid, low-cost production of this device within the next few years.
So far we’ve only done this work in the lab. Seeing the technology becoming available in mobile medical devices requires collaboration with engineers and medical scientists who specialize in developing such tools.
Our long-term vision for the technology is to allow mobile devices to examine biological samples in a way that was not yet possible.
Aside from allowing remote medical diagnosis, it can also provide in-home disease detection, where a patient can obtain their own sample through saliva, or blood pricks, and send the image to a laboratory anywhere in the world.
New nano-imaging tool may allow disease diagnosis on smartphones
Lukas Wesemann et al, Real-time phased imaging using a metasurface with asymmetric transfer function, ACS Photonics (2022). DOI: 10.1021 / acsphotonics.2c00346
Introduction of the conversation
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