Sea Technology

FEB 2013

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Page 49 of 99

Double-logarithmic plots indicating the linear dependences of the fuorescence intensity with tryptophan concentration and bacteria cell number. Field Sensor Layout The portable fber-optic probe is contained in a waterproof housing (12 centimeters in diameter and 40 centimeters long) that is deployable to 50 meters depth. The sensor head comprises a substrate for bioflm establishment, the light source with an excitation flter on top, the collecting fber optics and a motor-driven cover plate. A UV transparent quartz window, equipped with a gas permeable and low-fuorescent foil for optimized bacterial growth, is employed as a settling substrate. The bioflm is 50 st / FEBRUARY 2013 back-illuminated and excited through the substrate using a 280-nanometer UV-LED with a narrow bandwidth interference flter. Eighteen bundles of 30 optical fbers each are arranged hemispherically around the LED to collect the emitted fuorescence light. The angle of the fbers is optimized to constrain the detected fuorescence volume to a layer close to the surface and for spatially uniform sensing of an effective area approximately 0.5 square centimeters. At the end of the combined fber bundles, the collected fuorescence emission is spectrally separated by a combination of two interference flters centered at 350 nanometers prior to detection on a photomultiplier tube operating in single-photon counting mode. The timing of the electronics, the readout of the detector and the data recording on a 1-gigabyte SD memory card is accomplished by a programmable microcontroller, making the sensor package ready for use as a feld data logger. A National Instruments Corp. LabVIEW-based graphical user interface allows the user to control the sensor settings, including the timing and sampling interval, via USB. Either a universal AC adaptor or seven nickel-metal-hydride rechargeable batteries with charge capacities of 4,500 milliampere hours at 1.2 volts could power the bioflm sensor unit. Bio��lm Measurement Sequence To measure the intrinsic fuorescence intensity of a marine bioflm under feld conditions, a light shield in the form of a black anodized cover plate is closed to block out direct sunlight. The remaining background intensity is measured

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