Development of a fluorometric sensor for the measurement of phycobilin pigment and application to freshwater phytoplankton

A two-channel fluorometric sensor system for the detection of the waterbloom phytoplankton Microcystis aeruginosa has been developed. Excitation wavelengths of 620 and 440 nm were used, the former for detecting the cyanobacteria themselves, and the latter for subtracting the interference due to eukaryotic algae present in the sample. The fluorescence of the cyanobacteria and eukaryotic algae was measured at 645 and 680 nm, respectively. A linear relationship between phycocyanin fluorescence was established for the species examined in the range of 10⁻⁴ to 10⁰ g/ml⁻¹ chlorophyll a. Furthermore, upon ultrasonic treatment of a colony of cyanobacteria, the relationship between fluorescence intensity and cell concentration was improved. Applied to real samples in Lake Kasumigaura, Japan, after ultrasonication, this fluorometric method could detect waterbloom. This system is capable of the rapid determination of phycocyanin; the time required for one measurement cycle is approximately 25 min including sonication and rinsing for 5 min. The detection limit of this method is suitable for detecting phycocyanin in the early stage of waterbloom formation. Furthermore, a device based on this system was used for the continuous in situ monitoring of phycocyanin in lake water. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 53–61, 2000