Development of a Miniaturized Dissolved Oxygen Sensor with Anti-Biofouling Coating for Water Monitoring
Experiments Results and Discussions
The optical scheme of MR optical DO sensor is shown in Fig. 1 (b). The fluorescence DO sensitive membrane was immobilized in a reservoir with total reflective (gold) surface at its bottom. A 455 nm laser was used as light source for generating fluorescence. A fluorescence-choosing band-pass filter is placed on top of the reservoir for not only preventing the excitation light from detected by a CCD sensor but also reflecting the excitation light into the reservoir again for MR purpose. After excitation, the generated fluorescence from membrane was collected by a convex lens and read by a commercially available spectrometer. The synthesis of DO sensitive membrane is guided by the following procedure: first, the PDMS elastomer (Dow Corning) was mixed with crosslinker at 10 to 1 weight ratio. Then 1 mg of the luminescent dye (Tris(bipyridine)ruthenium(II) chloride, Sigma Aldrich) was added to the polymer solution and stirred until uniformly mixed. The mixture was spin-coated on a three-inch silicon wafer at 4000 rpm for 30 second to obtain a membrane with 20 µm thickness. The DO sensing results suggest that the sensitivity is increased three times when using MR device as compared with the conventional setup.
Contact angles of PDMS surfaces before and after PEG grafting are shown in Fig. 2 (a). The results show that the contact angle of PDMS is reduced significantly after PEG grafting (from 106.4 to 24.3), which illustrates the facts that the hydrophobicity of PDMS is reduced and that the protein (hydrophobic) absorption is restricted as showed in Fig. 2 (b).
The MR DO sensing device shows three times higher sensitivity as compared with signal excitation optical DO sensing setup. The result suggests that the multi-reflection device is a good replacement of miniaturized optical DO sensor. PEG grafting results in our experiments also show good anti-protein absorption capacity which may be effective in eliminating the biofouling progress.
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