Looking at algae through a microscope – a thing of the past?

Looking at algae through a microscope: a thing of the past?

Observing algae with lens-free imaging in real time

How motile are my microalgae? How many are in my culture? Who else is there? When working with microalgae cultures many producers take daily samples to know how the culture is fairing. Placing a drop onto a slide and observing the culture under the microscope is a standard procedure, as is measuring the optical density or doing cell counting. What if we could skip these steps? Our partners from IMEC developed a new lens free imaging module to do exactly that.

What is lens-free imaging?

Traditional microscopes use magnifying lenses. They bend the light that reflects off objects, making the objects appear larger when this light reaches our eyes. These lenses are essential for achieving micro-scale resolution needed to observe objects that are only a fraction of a millimetre in size. However, they also introduce several limitations. The need for magnification reduces the field of view. And, the size and configuration of the lenses make automation and compact design challenging. Additionally, the requirement for precise optical focusing makes traditional microscopes less suitable for continuous, on-field measurements.

Lens-free imaging (LFI) does not use magnifying lenses. The LFI device only consists of a light source and a CMOS image sensor (think digital camera). The light source illuminates the sample, generating an interference pattern, a sort of hologram. The image sensor captures this hologram, and algorithms reconstruct and enlarge the image of the sample from it. In LFI, algorithms replace magnifying lenses. They make the area that can be observed 20 times bigger, when compared to a traditional microscope with the same resolution.

LFI captures microalgae that are different in size in a single hologram and can later bring all of them in focus digitally by changing the parameters of the reconstruction algorithms. Focus is thus no concern during imaging.

With LFI, you can reconstruct different images from one hologram. It creates two types of pictures:

one that shows how much light the sample absorbs (intensity image, similar to brightfield microscopy)
another that shows tiny details in the shape and structure of the sample (phase image similar to phase-contrast microscopy).

You can also shine different colours of light on the sample to get colour-related details. Because LFI can take pictures very quickly, it can even switch between lights while something, like a microalga, moves across the view. This helps you see small colour differences between individual cells.

Image of Synechocystis Salina captured with LFI (left) and marked area (in red) reconstructed to intensity image (top right) and phase image (bottom right)

Why does REALM use lens-free imaging for microalgae-cultivation?

We are developing a new, continuous, automatic and cost-effective system to cultivate microalgae. As we go along in our cultivation, we often need to check and tweak the photobioreactors’ set-up. This is being done in different locations throughout Europe. The lens-free imaging module developed by our project partner IMEC offers several advantages.

Risk-Free: As the device is lens-free, it eliminates the risk of breaking any lenses.
Efficiency: It offers fast image capture and a wide field of view.
Portability: The device is portable and lightweight, making it easy to handle and transport.
User-Friendly: It features easy and fast configuration, making it accessible for quick setup.

Without the optical lenses, the module does not need alignment and is of more compact size. This makes the device smaller and more robust than traditional microscopes. We can easily take the small black box, move it around in the lab, integrate it into different systems, switch it on, connect it to a laptop and get started. This flexibility helps us during the development of our cultivation system, but not only that.

With the LFI module we can observe the culture and check all the information that you would usually determine in small lab tests remotely; a core aspect of our cultivation system. With REALM, we envision a small black box next to the photobioreactor, which will capture real-time images of the microalgae inside the photobioreactor using LFI, bringing information on the number of microalgae, biomass, or contaminants in the photobioreactor to screens from anywhere. And furthermore, this information can be integrated into our analysis platform along with info from other online sensors and weather data to further optimise the cultivation of microalgae.

Especially in open cultivation systems, microalgae cultivation often faces a wide variety of contaminants. The LFI device can detect these emerging contaminants and enable fast responses, ensuring more efficient and secure cultivation processes by preventing total culture collapse and loss.

How it is going with our LFI microalgae observation?

We are optimising the image processing of LFI to estimate the concentration of the microalgae and detect contaminants in the culture more precisely. Improved image processing is important to achieve the continuous monitoring of the culture in real-time.

The current version of the LFI setup is a portable, stand-alone device designed for high-throughput imaging. It can quickly collect large amounts of data, which is useful for analysing and improving microalgae research. The system has already been put to use at the University of Almeria and Necton since March 2023.

Lense-free imaging module developed by IMEC for the monitoring of microalgae cultures

Using our current capabilities, we can effectively detect and count culture cells, distinguish non-cells such as air bubbles, debris, and contaminants from actual cells. We can also differentiate between cells in polycultures, distinguishing Chlorella spp. from Scenedesmus spp., for example. This will help us evaluate the health and productivity of our cultures in continuous production systems automatically and remotely.