aquatic science

CytoBuoy and aquatic science

Aquatic science was the main target field for the development of our products since 1986. Currently the CytoBuoy cytometers have the largest range of deployment options, the largest range of particle sizes and concentrations and the largest range of analysis options available.

Challenges

The two main challenges of this field in comparison to biomedical applications are:
  • the enormous range in particle types, sizes, their concentrations and physiological states. This requires an instrument for a wide range of particle sizes and concentrations and high 'information per particle' level.
  • dynamic ecosystems requiring sampling at "critical scales": the temporal and/or spatial scales at which data must be collected in order to resolve patterns and processes (including early warning). In practice this means the flow cytometer will go on ships, under water and on moorings, and should allow a high level of autonomous operation combined with high speed and high throughput.

Info x coverage

Briefly those two challenges require an instrument that combines a high level of information content AND a high level of frequency in sampling times and/or space (coverage). Whereas traditional flow cytometers analyze thousands of cells per second acquiring only a few fluorescence and light scattering numbers per cell, the recording of full photos at similar count rates would yield an unmanageable data flow. The CytoBuoy instruments use silico-imaging as basic data format: data-extensive but highly informative optical fingerprints obtained by fluid driven laser scanning of individual particles. Libraries of these fingerprints allow the automatic classification and enumeration of groups and species from large data sets as well as online warning for target (HAB) species.

Analysis principle

The power of the flow cytometric analysis principle is that the cells are passing a laser beam one by one at high speed and their individual light scattering and fluorescence properties are recorded to form an optical 'fingerprint' for each cell. This separates the flow cytometric method from bulk methods for fluorescence spectra and/or size spectra for bulk volumes of water where it is much harder to discriminate between the contributions of the various groups in the water since the readings are collected for all particles at once. Flow cytometry allows easy recognition of the different groups in the sample and quantification of their abundance as well as their optical properties (size, pigment) - even the detection of a few rare cells from within a high number of cells from a blooming species.

Aquatic science modifications

We have been working on adapting the 'medical' laboratory-based type of instrument for aquatic science for the last 20 years. This includes first the problem of phytoplankton cell size range - which we have expanded to the small size (picoplankton) as well as to the large size (big diatoms, chains and filaments etc - max diameter is 800 um and length can be several mm). This also solves the problem of instrument clogging with running field samples through the instrument - no need anymore to fractionate/filter the sample - concentrating is not needed also. The volumetric sample dosing allows the direct reading of concentrations whereas the automatic flow rate adjustment assures optimum data quality for sediment rich and/or eutroph to oligotroph conditions.

Then we have added a scanning feature which means the electronics 'follow' digitally the output of the scatter and fluorescence detectors whilst a particle is flowing through the laser beam. This means you automatically get an accurate length reading of each particle as well as the divison of their 'body parts' along their length axis (all particles are stretched out in the flow direction automatically by the sheath fluid which enhances the comparison potential and data processing). This means you will actually see where the heterocysts are in the Anabaena filaments, and you can count the number of cells per chain for many species (paper on Skeletonema). This type of scan data combines high recognition power with high data acquision and processing speed essential for the 'critical scales' approach.

To be able to take the instrument on a cruise and put it in/under water we have completely redesigned the flow cytometer to get (much) smaller and modular. The basic instrument we call the CytoSense which is a scanning flow cytometer that can hold 2 lasers and up to 10 optical detectors in a 30x45cm cylinder (ØxH) of only 15KGs. The instrument is fully computer programmable and you can read out the data files over internet if needed. The same instrument can be placed in a moored buoy (CytoBuoy) or a high pressure submersible housing (CytoSub) which makes it possible to do your field measurements on real live samples (without filtering - fixatives - transportation - waiting), anywhere, anytime.

Additional modules and options are an imaging (video) module on the CytoSense for targetted imaging to assist with the identification of species; a sorting module; a extra wide flow cell version to allow the analysis of zooplankton up to 1.5 mm, and a second laser version to increase the species recognition power based on 2-laser excitation and fluorescence emission in various bands. Please contact us for advice for your specific research interests.

Applications

screening of phytoplankton cultures, natural samples, detection of rare species, population dynamics research, general phytoplankton monitoring, assesment of biodiversity, bio-indicators, HAB's (harmful algal blooms), grazing, (micro)zooplankton, protection of aquaculture, bathing water, resource water, lake restoration, alarm for herbicides, invasive species control and bio-effect monitoring, marine optics and lake or sea truth for remote sensing.