A sensitive tapered optical fiber tip combined with dielectrophoretic (DEP) trapping was used for rapid and label-free detection of bacteria in water. The angular spectrum of the optical field at the fiber tip was changed with the surrounding refractive index (RI). By measuring far-field intensity change at the defocus plane, the intensity sensitivity was up to 95 200%/RIU (RI unit), and the detection limit was 5.2 × 10^–6 RIU at 0.5% intensity stability. By applying an AC voltage to a Ti/Al coated fiber tip and an indium–tin-oxide glass, the DEP force effectively trapped the Escherichia coli (E. coli) near the fiber tip. Those bacteria can be directly measured from optical intensity change due to the increase of surrounding RI. By immobilizing the antibody on the Ti/Al fiber tip, the tests for specific K12 bacteria and nonspecific BL21 bacteria verified the specificity. The antibody-immobilized Ti/Al coated fiber tip with DEP trapping can detect bacteria at a concentration about 100 CFU/mL.

中文翻译：

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光学离焦法利用集中介电泳力的大肠杆菌纤维传感器

灵敏的锥形光纤尖端与介电电泳（DEP）捕集相结合，可用于快速，无标签地检测水中的细菌。光纤尖端处的光场的角光谱随周围的折射率（RI）而变化。通过测量散焦平面上的远场强度变化，强度灵敏度高达95 200％/ RIU（RI单位），在0.5％的强度稳定性下，检测极限为5.2×10 ^–6 RIU。通过在涂有Ti / Al的光纤尖端和氧化铟锡玻璃上施加交流电压，DEP力有效地捕获了大肠杆菌（E. coli））靠近光纤尖端。由于周围RI的增加，可以从光强度变化中直接测量那些细菌。通过将抗体固定在Ti / Al纤维尖端上，针对特定K12细菌和非特异性BL21细菌的测试证实了特异性。带有DEP捕获的固定有抗体的Ti / Al涂层光纤尖端可以检测浓度约为100 CFU / mL的细菌。