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20 February 2014 Self-referenced label free biosensors based on differential fiber optic interferometry
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The measurement of refractive index (RI) is an important tool for label free biosensing in biomedical applications [1,2]. In this work, a LPG based fiber optic interferometric probe is used for thrombin detection. The aptamer raised against the thrombin was immobilized through an electrostatic immobilization method, using poly-L-lysine as cationic polymer. The functionalized probe was characterized and tested against thrombin. The system was validated with the detection of thrombin using an aptamer based probe (5’-[amine]GGTTGGTGTGGTTGG-3’) as a model system for protein detection. The shift corresponding to the affinity-assay between TBA and the thrombin was of about 56 pm. A differential readout interferometer based on a white light Mach-Zehnder configuration, with pseudo-heterodyne phase modulation is described. The system can be used to interrogate two similar LPGs based interferometers in a differential scheme. Considering the configuration where both devices are functionalized being one active (sensor) and the other one passive (reference) it is possible to accurately measure the behavior of the analyte of interest independent of non-specific binding events, bulk refractive index changes and temperature. Signal processing with low cost digital instrumentation developed in Labview environment allows a detectable change in refractive index of Δn ≈ 2x10-6 [3]. Coupling the sensing probe together with a passively functionalized reference probe in a differential system will enable pseudo-heterodyne interrogation and extremely sensitive phase detection of biological species.
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R. B. Queirós, C. Gouveia, M. Cristina L. Martins, and P. A. S. Jorge "Self-referenced label free biosensors based on differential fiber optic interferometry", Proc. SPIE 8938, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XIV, 89381K (20 February 2014);

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