Microplastics (MP) and nanoplastics (NP) are now recognized as one of the most pervasive and least understood forms of pollution in marine ecosystems. Their small size allows them to cross biological membranes, accumulate in cells, and interfere with fundamental metabolic processes. Yet, despite their growing environmental relevance, detecting these particles remains a major scientific and technological challenge. This is the gap the MOBILES project set out to address. In Deliverable D2.1, the team presents a compelling new approach: using marine diatoms as living, light‑responsive biosensors capable of rapidly identifying the presence of MP and NP within hours.
This work, led by the Cyprus University of Technology (CUT) demonstrates how naturally occurring marine diatoms can act as living sensors, translating plastic exposure into measurable optical signals.
Diatoms are photosynthetic microalgae whose light‑harvesting machinery is built around well‑organized pigment–protein complexes. Their chlorophyll a molecules sit at the heart of this system, responding to environmental stress with remarkable sensitivity. This sensitivity is usually a protective mechanism. But when MP and NP small enough to cross the semipermeable membrane enter the cell, they interact with the photosynthetic apparatus itself. And chlorophyll a responds in a way that is both measurable and diagnostic.
In healthy diatoms, the fluorescence emission peak around 680 nm is strong and stable. But once plastics enter the cell, this peak drops, reflecting a disturbance in the pigment’s photophysical environment. Meaning diatoms serves as biological system that converts invisible pollution into an optical fingerprint.
To the MOBILES project, it’s the foundation of a biotic sensor that can detect plastic pollution long before conventional analytical methods would even finish sample preparation.
However, before any biosensor can be built, the team needed to understand the optical behaviour of both the plastics and the organisms. Spectral libraries for plastics and diatoms were characterized:
Using Raman, FTIR, UV/Vis, fluorescence spectroscopy, and LIBS, the team mapped how each plastic type and each diatom species behaves optically. This mapping allowed the researchers to distinguish between the inherent optical properties of plastics, the baseline behaviour of diatoms, and the specific spectral changes caused by plastic-diatom interactions.
The team then exposed selected diatom species, including Cylindrotheca fusiformis, Phaeodactylum tricornutum, and Cyclotella cryptica, to MP and NP for periods ranging from 2 to 8 hours.
The result was consistent across species:
This means diatoms can serve as rapid, qualitative detectors of plastic contamination in water, without chemical pretreatment, without complex instrumentation, and without the need for laboratory‑grade sample preparation. For environmental monitoring, this is a major shift. Instead of waiting days for analytical results, a biological system can provide an early warning within a single afternoon.
With the goal to further reduce the detection time, the team discovered that adding ferricyanide, an external electron acceptor, amplifies the diatom’s optical response. When ferricyanide was added and in combination with excitation at 785 nm, the chlorophyll a peak dropped even more sharply, and much earlier. This innovation reduces detection time from 4–8 hours to just 2 hours, opening the door to near‑real‑time monitoring. It also suggests that diatom‑based sensing can be tuned and optimized, which lays a promising foundation for future research.
Deliverable D2.1 shows that diatoms are not only an interesting biological model, but also provide a practical pathway toward the EU’s Zero Pollution goals. Their optical response creates a biologically grounded, low‑cost detection method that avoids the barriers of traditional analytical chemistry. Instead of chromatography or mass spectrometry, diatom‑based sensing works without complex sample preparation, expensive instrumentation, or chemical pretreatment of plastics. It is a method that can be deployed where pollution actually occurs. Because diatoms naturally inhabit marine environments, their fluorescence and spectral behaviour can be integrated directly into in situ monitoring systems. The same biological response demonstrated in the laboratory can be embedded into portable fluorometric devices, microfluidic platforms, or even future autonomous sensing buoys; turning diatoms into a real‑time environmental sensor.
Using diatoms as biosensors brings also one additional benefit. They are not only able to signal current contamination but their UV/Vis spectral shifts, which persist after months of exposure, show that they can also retain the imprint of past pollution events. In this way, they function not only as detectors, but as biological archives, capturing both immediate and historical contamination patterns.
Several scientific and technological steps still remain opened. Right now, the detection of MP and NP via diatoms is only qualitative. Understanding dose–response relationships and species‑specific sensitivity will be essential for regulatory use.
In WP1 and WP2 will be explored how to embed diatoms-based detection into robust, field‑ready sensing devices.
Future work will also test other plastic types and environmental matrices. Key question will also be what happens when MP and NP interact with other pollutants, such as heavy metals, which are known to bind strongly to them.
Deliverable D2.1 – Diatoms‑based biosensor for bioplastic detection in water has been submitted and is available on Zenodo.
Deliverable D2.1
