Algae diagnostics by matrix method of laser fluorimetry

Evgeny E. Ostroumov, Victor V. Fadeev
Physical Department, Moscow State University, Moscow, 119899, Russia
ostroumov@lid.phys.msu.su

Rainer Reuter
Physical Department, Carl von Ossietzky University, Oldenburg, 26111, Germany

ABSTRACT

In previous publications we proposed a “matrix” approach in pulsed laser fluorimetry of complex organic compounds. This approach synthesizes several methods, for instance, non-linear and kinetic fluorimetry. One measures a matrix of fluorescence intensity values I_fl,ij at different intensities of excitation light I_exc,i and at different delays t_j between the registration point and laser pulse - ||I_fl,ij(I_exc,i, t_j)||. Solving the inverse problem one can determine molecular photo-physical parameters.

Molecular parameters of the photosynthetic unit of such organisms like phytoplankton vary in a wide range for different algae species and for different environmental conditions. We showed in previous publications that an application of non-linear fluorimetry allows to determine two parameters: a fluorescence parameter Φ₀ and a parameter that equals the combination of three photo-physical parameters of chlorophyll a molecules in the light harvesting complex (LHC): A=στ²γn₀, where σ is the excitation cross section, τ is the excitation lifetime, γn₀ the maximal rate of singlet-singlet annihilation, and n₀ the local concentration of chlorophyll a molecules in LHC. It was experimentally established, that parameter A strongly depends on the state and species of the algae.

In this report an attempt to apply the matrix method to phytoplankton is presented. The main goal of the work is to increase the number of determined parameters and, therefore, to enhance the yield of laser fluorimetry in comparison to exclusively non-linear fluorimetry.

Fluorescence value matrixes ||I_fl,ij(I_exc,i, t_j)|| were obtained for several alga species at three environment conditions: low light, strong light and in the presence of the chemical inhibitor DCMU. The experimental technique consisted of measuring fluorescence kinetic curves at different excitation intensities I_exc,i in the range of 1.4•10²¹ - 7•10²² photons / cm²s. By means of these data 15x512 matrixes were formed. Saturation curves were obtained by integration of the matrix columns. Solving the inverse problem for these curves, values of the parameters Φ₀ and A were obtained. The inverse problem for kinetic curves and matrixes was investigated. After processing of the data, different parameter values for several species and states of the phytoplankton were obtained.

Last Update: 2005-04-7