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 waterbloo m phytoplankton Microcystis aeruginosa has been developed. Excitation wavel engths of 620 and 440 nm were used, the former for detecting the cyanobacte ria themselves, and the latter for subtracting the interference due to euka ryotic algae present in the sample. The fluorescence of the cyanobacteria a nd eukaryotic algae was measured at 645 and 680 nm, respectively. A linear relationship between phycocyanin fluorescence was established for the speci es examined in the range of 10(-4) to 10(0) g/ml(-1) chlorophyll a. Further more, upon ultrasonic treatment of a colony of cyanobacteria, the relations hip between fluorescence intensity and cell concentration was improved, App lied to real samples in Lake Kasumigaura, Japan, after ultrasonication, thi s fluorometric method could detect waterbloom. This system is capable of th e 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. Furthermore, a device based on this system was used for the continuous in situ monitoring of phycocyanin in lake water . (C) 2000 John Wiley & Sons, Inc.