A UV-LED Based Optical Fiber Biofilm Sensor: Design, Calibration, and Field Application

Date/Time:

15 Mar 2012
11:15-11:40

Location:

South Galleries

Seminar Details
An optical fiber-based biofilm sensor has been developed in order to dynamically detect biofilm formation of bacteria and unicellular microorganisms in their natural marine environment. The device is based on the detection of natural fluorescence utilizing the intrinsic amino acid tryptophan of microorganisms constituting the biofilm. Promising sensor head geometries were modeled and optimized in terms of the spatial arrangement of the entire optical system and of the light emission and collection characteristics. The sensor head design is capable of detecting biofilms grown on a large surface of about 1 cm2 (patent pending: Fischer, Friedrichs, Wahl; DE 102011101934.4). The intrinsic fluorescence originating from biofilms disposed on a UV transparent substrate is excited by a 280 nm UV LED. The emitted fluorescence is collected and guided by 540 optical fibers to a photomultiplier tube operating in photon counting mode. Interference filters are utilized to spectrally separate the 350 nm emission from background and scattered excitation light. Calibration measurements show that tryptophan can be detected in the nanomolar range and at low cell coverages down to < 4000 bacteria cells/cm2. A wide dynamic range enables one to study biofilm growth from the first attachment of cells up to complex biofilms. In first field experiments, biofilm formation dynamics has been continuously monitored by exposing the sensor to Baltic Sea water over a period of several weeks. During these experiments, subsamples were collected for a comparison of the biofilm sensor readout with fluorescence microscopy images. Additionally, the composition of the bacterial community has been analyzed by fluorescence in situ hybridization using Cy3-labeled oligonucleotide probes. Overall, the biofilm sensor measurements clearly proved that straightforward continuous monitoring of biofilm formation in natural habitats is feasible. Moreover, the sensor holds potential for deep sea deployment.