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Field Sensor for In-Situ Detection Of Marine Bacterial Bio��lms Novel Sensor Concept Enables Time-Resolved Detection of Bacteria By Matthias Fischer ��� Martin Wahl ��� Dr. Gernot Friedrichs I n marine environments, nearly all surfaces become rapidly covered by microorganisms, forming a bioflm. Following a biochemical conditioning phase, the bioflm formation starts within the very frst minutes when pioneer bacteria cells adhere to the submerged surface. Marine bioflms cause serious technical problems by settling on ship hulls and their water conduits, navigational equipment, stationary port structures, industrial pipelines and tidal power plants. They cause severe damage by increasing the drag, roughness and friction resistance of submerged objects, and accelerate biocorrosion of metals. In natural ecosystems, however, bacterial bioflms serve as a unique living habitat and enable or prevent additional biofouling by micro-organisms and macroorganisms. Bioflms on the surfaces of marine organisms can substantially change their ecology and wellbeing. To gain insight into bioflm formation kinetics and dynamics, continuous and in-situ monitoring of bioflm establishment in the marine habitat is desirable, but the required temporal and spatial resolution is diffcult to achieve. A photograph of the bioflm sensor without waterproof housing. (Bottom) Schematic longitudinal cross-sectional view of the cylindrical sensor head with the main components and a color-coded region illustrating the excitation of the UV-LED and fuorescence detection effciency pattern. Bioflm Sensor Concept For marine applications, sensor requirements differ considerably from those for highly sophisticated laboratory instrumentation. The aim was to develop a robust and reliable ready-to-use sensor to detect bioflm formation dynamics in situ, online and nondestructively in the marine environment. The sensor concept should allow for autonomous operation over several months, as well as selective detection, i.e., distinguishing between organic and inorganic material. A suffcient penetration depth is desired to account for the 3D structure of bioflm, which typically constitutes highly patchy cell clusters up to several-hundred micrometers in diameter. To ensure a representative sensor signal of the inhomogeneous bioflm, a large detection area of 1 square centimeter is required, while keeping a low detection limit and a wide dynamic range to quantify the entire growth range, from initially adsorbed bacteria cells up to a complex bioflm community. All organisms contain natural intracellular fuorophores, which can be utilized for fuorescence-based detection methods as they provide high sensitivity and selectivity, fast response time and the capability of monitoring large areas in situ without sample contact. The natural protein fuorescence of bacteria, stemming, for instance, from amino and nucleic acids, has long been known to indicate biomass and metabolic activity. At wavelengths in the ultraviolet (UV) range, intrinsic protein fuorescence originates mainly from the aromatic amino acids tyrosine, phenylalanine and tryptophan. Due to a very low quantum yield of phenylalanine and common quenching mechanisms of the emission of tyrosine, the native fuorescence in proteins is dominated by tryptophan. The indole chromophore of tryptophan can be selectively measured by optical excitation at a wavelength of 280 nanometers with detection of the corresponding peak fuorescence centered around 350 nanometers. www.sea-technology.com FEBRUARY 2013 / st 49