Freshwater and marine algal blooms can be harmful – even fatal – to wildlife and humans alike, so the sooner that authorities can predict them, the better. A cheap and portable new device developed at UCLA could help them do so.

First of all, what causes algal blooms? The two main culprits are increased water temperature due to climate change, along with high nutrient levels caused by fertilizer runoff from farms and lawns. Both result in increased populations of phytoplankton (algae is a type of phytoplankton), which produce biotoxins.

These toxins deplete oxygen from the water, plus the plankton block sunlight from reaching fish and aquatic plants, causing them to die. Additionally, fish and animals living adjacent to the water can ingest the biotoxins, which humans will also occasionally inhale. This leads to damage of the nervous system, brain and liver, and ultimately to death.

Ordinarily, scientists check for impending blooms by collecting water samples and then taking them back to a lab. There, in a multi-step process, a microscope is used to measure phytoplankton concentrations. If those concentrations are found to be rapidly rising, then an algal bloom is likely imminent. Unfortunately, though, the sample-gathering and subsequent analysis do take some time, lessening the chances of successfully minimizing the effects of a bloom, or at least of providing an early warning.

That's where the new device comes in. Created by a team led by Prof. Aydogan Ozcan, it's a compact, inexpensive and portable version of what's known as a flow cytometer. Hooked up to a laptop computer, it can be used onsite at the shoreline, identifying types and concentrations of plankton in water samples within a matter of seconds.

Unlike a microscope or a conventional cytometer, which utilize costly optical lenses, it features a holographic imaging system assisted by artificial intelligence algorithms. "Images of the microscopic objects are reconstructed from their shadows, which in this case are holographic shadows created by the diffraction of light from individual objects," Ozcan explains to us.

This technology is what's responsible for its small size, and potentially low retail price. Whereas regular flow cytometers go for a reported US$40,000 to $100,000, the UCLA prototype was assembled from materials costing a total of less than $2,500.

In field tests conducted along the Los Angeles shoreline, it was found to measure concentrations of potentially-toxic algae as accurately as traditional systems used by the California Department of Public Health.

A paper on the research was recently published in the journal Light: Science and Applications.

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