Three microalgal species (Dictyosphaerium chlorelloides(D.c.), Scenedesmus intermedius (S.i.) and
Scenedesmussp. (S.s.)) were encapsulated in silicate sol–gel matrices and the increase in the amount
of chlorophyll fluorescence signal was used to quantify simazine. Influence of several parameters on the
preparation of the sensing layers has been evaluated: effect of pH on sol–gel gelation time; effect of algae
density on sensor response; influence of glycerol (%) on the membrane stability. Long term stability was
also tested and the fluorescence signal from biosensors remained stable for at least 3 weeks. D.c. biosen-sor presented the lowest detection limits for simazine (3.6gL−1
) and the broadest dynamic calibration
range (19–860gL−1
) with IC50125±14gL−1
. Biosensor was validated by HPLC with UV/DAD detec-tion. The biosensor showed response to those herbicides that inhibit the photosynthesis at photosystem
II (triazines: simazine, atrazine, propazine, terbuthylazine; urea based herbicides: linuron). However, no
significant increases of fluorescence response was obtained for similar concentrations of 2,4-D (hormonal
herbicide) or Cu(II). The combined use of two biosensors that use two different genotypes, sensitive and
resistant to simazine, jointly allowed improving microalgae biosensor specificity