Design and field application of a UV-LED based optical fiber biofilm sensor

► A fluorescence sensor has been developed for in-situ detection of large-area biofilms. ► Light collection by 540 tilted optical fibers results in a detection limit of 4000 cells/cm2. ► Field operation in aquatic environments for long-term data logging is possible. ► Biofilm formation can be monitored from first adhering cells to complex matured cell clusters.