Millions of tons of pesticides are applied worldwide annually in agriculture. Among them, herbicides such as triazines and ureas, originating from agricultural runoff, can contaminate soils and surface and ground waters with severe toxic effects on humans. Nowadays, different analytical techniques are available for the detection of these chemicals; however, most of them are expensive and time-consuming, especially in the case of routine analyses. For this reason, on the basis of results collected through many years of experience in the field of photosynthetic organisms, we designed a biosensor platform intended for the easy, low-cost, and fast prescreening of photosynthetic herbicides. The platform combines the possibilities of amperometric and optical transduction systems, which have proven to be highly sensitive (limits of detection = 10(-10)-10(-8) M). The use of genetically modified algae strengthens the power of the platform, allowing different subclasses of herbicides to be recognized. The system has been validated for the analysis of environmental water and is proposed to support laboratories involved in the control of water pollution.