From magnifying glass to high-resolution microscopy on-chip
The invention of the microscope in the late 16th century signaled the beginning of a whole new dimension in science. For the first time, researchers were able to look at nature’s basic building blocks, discovering cell structures, microbes, bacteria, etc. At the beginning of the 20th century, a new kind of microscopy emerged, which enabled scientists to focus on specific kinds of cell structures by letting them light up or ‘fluoresce’. Fluorescence microscopy has evolved to become an indispensable tool in biology and medicine. It is routinely used in clinical trials, to diagnose health disorders and in DNA sequencing.
In the last few decades, microscopy techniques have improved drastically. In 2014, three scientists even received a Nobel Prize for breaking the classical resolution limit of fluorescence microscopy. The recent cost reduction of DNA sequencing was also spearheaded by a shift to fluorescence-based detection and dense parallel read-out.
Despite the enormous progress that has been made in terms of resolution, the standard microscope actually still looks fairly similar to its 16th century predecessor: high-resolution microscopes tend to be expensive, bulky devices that require highly skilled operators. As a consequence, they can only be found in specialized labs, which limits their accessibility.
But the next big step in microscopy is coming and will be the development of high-resolution lens-free microscopy on a single chip. Imec researcher Niels Verellen recently received an ERC Starting Grant of 1.5. million euros (for five years) to develop an on-chip fluorescence microscope that is extremely compact and outperforms current standard microscopes in terms of resolution and field-of-view.
A lens-free microscope: why?
Though it may seem odd to develop a microscope without a lens, lens-free imaging microscopy is not a new field. Imec has already developed a compact on-chip solution for bright-field microscopy that is ready to be customized for specific use cases ranging from the inspection of cell cultures in incubators, particle or blood cell counts, to scratch & defect detection in industrial inspection systems.
Niels Verellen (senior photonics researcher & project leader): “The current solution that imec has been working on is an alternative for bright-field microscopy, i.e. the oldest and most standard kind of microscopy. But for many applications in medicine and biology, such as DNA sequencing or any kind of test that targets a specific molecule, you need fluorescence microscopy. The technique imec developed for lens-free bright-field microscopy can’t be readily adapted to enable high resolution fluorescence microscopy as well, because it uses the interference pattern of the illumination light to create a holographic reconstruction that effectively takes over the task of the lens. In fluorescence microscopy, the fluorescence emission is incoherent, so we need to use a completely different approach.”
A compact lens-free fluorescence microscope offers significant advantages in comparison to lens-based microscopes. The first one is fairly obvious: smaller is just more convenient. But on-chip devices also have other assets. Standard microscopes need tedious manual alignment, almost the way a piano needs tuning. This ‘tuning’ needs to be done by a highly skilled operator. For on-chip microscopes, the alignment would only have to be done once, i.e. when it is being produced in the cleanroom. Another big advantage would of course be the cost: by removing much of the hardware and by making the microscope CMOS compatible, it could potentially be mass produced.
The end goal: smaller form factor, better resolution
Each year about 3000 young researchers compete to receive an ERC Starting Grant, a grant designed to support promising researchers and to stimulate scientific excellence across Europe. With a success rate of about 10-12%, being one of the selected participants is quite an achievement. In the next five years, Niels Verellen will lead a team of researchers to develop an on-chip technique for fluorescence microscopy that is high-resolution, fast, robust, zero-maintenance, inexpensive and ultra-compact.
Niels Verellen: “By the end of this 5-year period, we want to have a proof of concept that indicates that our technique works and meets the required specs in terms of resolution and field-of-view. More specifically, we’re aiming for a 5 cm2 device with a target resolution of 100 nanometer.” In other words: a microscope that basically fits into your pocket, but still outperforms the standard microscope with a 150-200 nanometer resolution that you find in specialized labs today.
Building a new concept with state-of-the-art building blocks
To design the ultra-small microscope, the researchers will build on the most recent advancements in integrated photonics and CMOS image sensors, using existing building blocks to create a whole new concept. Niels Verellen: “Imec is the best, if not the only, place to do this kind of research because it has such a unique platform for visible photonics that is CMOS compatible. Thanks to the EU funded PIX4life project, we also have an open-access pilot line for biophotonics at imec.” So the challenge is not necessarily engineering new components, but combining them in a clever way to create new functionalities and developing image reconstruction models for high-resolution microscopy.
Niels Verellen: “All lens-based and existing state-of-the art lens-free microscopy solutions have in common that they use the propagation of light in 3D space to illuminate a sample. In our solution, however, the light will be confined to the 2D world of a single chip. Therefore, we need to find a way to render a complete high-resolution image within the constraints of only two dimensions. We know how to do this in theory, but it is a completely new approach that I expect will prove to be quite challenging. That being said, we are confident that it is possible. At the moment, we have already done some preparatory work with simple models and those have indicated that the basic components of our technique work.”
Towards faster, more accessible testing and research
The new microscope may be small, its societal impact would not. With this technology, advanced high-resolution fluorescence microscopy would become more widely available and affordable. In the medical field, this would imply that DNA sequencing could be done faster (higher throughput) and cheaper. But the on-chip microscope would be especially interesting in biological research and drug testing. Because the microscope is smaller and more affordable, more of them would be available in the lab. As a consequence, experiments could be set up in a different way: studying more parameters simultaneously in real-time. As such accelerating the understanding of diseases and development of precision medicin and therapies.