The Emitter Detector Fiberoptics Unit PHYTO-EDF is connected to the standard Power-and-Control-Unit PHYTO-C of the PHYTO-PAM Phytoplankton Analyzer. All electro-optical components are contained in a single compact housing, with special fiberoptics (9-armed) forming the optical link to the sample. The fiberoptics can be mounted on a stand with base plate.
The compact emitter-detector box houses 4 different LED measuring light sources (470 nm, 520 nm, 645 nm and 665 nm), the actinic LED light sources (655 nm) and a photomultiplier detector. All LED light sources are equipped with miniature fiber couplers and short-pass filters (λ < 695 nm). The detector is protected by a special long-pass filter set (λ > 710 nm) which is optimized for low background signal.
The FIBER version is well-suited for highly sensitive assessment of photosynthetic activity on surfaces, as e.g. periphyton, microphytobenthos and microbial mats. Due to the use of a photomultiplier, large signals are obtained even at low sample densities. On the other hand, at high gain the photomultiplier has to be protected from ambient light. For this purpose, as well as for dark-acclimation of the sample, a darkening-box is provided which covers the sample and encloses the fiberoptics endpiece.
The latter consists of a 4 mm Ø perspex rod, the front of which is in contact with the sample surface via a thin layer of water. The perspex rod serves the purpose of mixing the different types of light and to guide the fluorescence to the detector fiber (1.5 mm Ø, in center of fiber bundle). While measurements are possible with the perspex rod being submerged in algae suspensions, the sensitivity is distinctly lower than with the MODULAR version or the PHYTO-PAM-II COMPACT version. For toxicological work , a 4 mm Ø quartz glass rod (EDF-Q) is available.
Functionally the four wavelength PHYTO-PAM Fiber version displays the same features as the MODULAR version. Chlorophyll fluorescence is excited by microsecond LED-light pulses alternating between four different wavelengths (measuring light) and the photosynthetic activity is assessed using red actinic light and saturation pulses.
The differently colored measuring light is absorbed to different extents by the three major types of phytoplankton (green algae, diatoms / dinoflagellates and cyanobacteria) leading to characteristic differences in the fluorescence responses.
After system calibration with the separate phytoplankton groups, the relative contents of these groups can be determined in unknown samples by computer-aided deconvolution using the PhytoWin software. The photosynthetic properties of these groups are characterized by their effective PSII quantum yields, relative electron transport rates (ETR) and light response curves.