A method of detecting the presence of bioactive molecules in a fluid sample, comprising contacting a solution of a microorganism selected from the group consisting of a monocellular algae and a cyanobacteria with the fluid sample so as to obtain a formulation having a microorganism concentration of 200 000-1×107 cells/mL of fluid sample; incubating the formulation for 10 to 120 minutes at a pH of 7 to 12 and a temperature between 18 and 35° C.; and measuring the fluorescence emitted by the formulation, whereby a fluorescence emitted in the sample that is lower than that in a control sample is an indication that the sample contains a bioactive molecule.