Size-selective analyte detection in an integrated optical Young interferometer biosensor

Abstract

Integrated optical interferometric (IOI) biosensors are extremely sensitive label-free biosensors. The applicability of these sensors is however strongly hampered by the large background that originates from both bulk refractive index changes and non-specific binding of molecules to the sensor surface. In this thesis we demonstrate new methods to discriminate between substances based on their size, using a Young interferometer biosensor with simultaneous detection of multiple wavelengths. This method allows to discriminate specific binding from non-specific binding and/or bulk changes (which occurs in the whole evanescent field of ≈ 200 nm which is used for detection) and thereby improves the performance of the sensor. Numerical calculations are used to optimize sensor design and the detection method. This thesis also shows the design, realization and characterization of the self-build setup. Moreover, experimental data with this setup is presented, where binding of beads (size ≈ 85 nm, representing specific binding) is discriminated from binding of protein A (size ≈ 2 nm, representing non-specific binding) and bulk refractive index changes induced by D-Glucose. Furthermore, simulations show that combinations of multiple wavelengths and polarizations can improve the method and proof-of-principle experiments show the realization size-selective detection based on multiple wavelengths and polarizations. The measured data are analysed carefully and show that timing differences between bulk changes and binding of proteins can be discriminated from each other. We anticipate that this method will increase the general applicability of IOI biosensors and we present a forward look with possible new applications after applying constructive technology assessment on the method of size-selective detection.