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Nano particle tracking

The rapid developments within nanoscience offers opportunities for studies in small scale biology and ecology, since nano-sized (10-9 m) objects are easily carried even by small (mm-scale) organisms without affecting their behavior. Moreover, other advantages with nano-sized tracking systems is that they can be used in aquatic ecosystems (i.e. in water) and that the same method can be applied to both consumer, e.g. zooplankton (mm-scale) and their algal, or even bacterial, food (µm scale).

The overall aim with the nano–related research is to be able to track individual animals, as well as their food, in their natural environment. In order to reach this aim we will initially work at laboratory scale and then, as the methodological developments proceed, expand to natural systems.

Nanoparticles are firmly attached to the Daphnias

These fluorescent probes have a strong stability, fluorescence and tunable wavelength. By changing the size of their core material they emit light at different wavelengths. Choosing from a variety of quantum dots (QD), and conjugating them with a protein called streptavidin (SA), it is possible to form a high affinity bond between the QD-SA conjugate and biotin labeled animals (as Daphnias). One can then track individual animals by labeling them with different QDs. After only a few days the Daphnia will molt and thus loose their fluorescence.

The set up

A collage with a photo of a water tank and two cameras and an illustration of how the cameras are viewing the daphnias in the tank.

The setup The setup (A) Picture of the stereo vision system, composed by two cameras (Cam1 and Cam2) that overlook the entire aquarium from different angles. (B) Air-cooled blue-light lamp used to excite the red and yellow fluorescent nanoparticles. (C) Schematic top view of the system with cameras positioned 90° from each other.

Movements of Daphnias

A black background with red and green wobbly lines.

After processing in ImageJ the animals movements are tracked in Matlab as in the example shown here. These individuals were recorded using two different QDs. One emitting in red (655 nm), and one in yellow (575 nm).

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