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In this paper design, simulations and preliminary experimental results for an
optical biosensor, using a Mach-Zehnder interferometer as basic configuration, are
presented. This type of sensor offered a lot of advantages such as compactness, real time
analysis, low cost and high sensitivity and the possibility of integration of electronic
detection components on the same chip. The integrated optical structure is sensitive to
refractive index change induced due to the interaction of the evanescent field with an
immobilised biological sample placed on one of the two arms of the interferometer (the
sensitive one). A window is open in the upper cladding of the waveguide. Changing the bio
specimen produces a variation of the refractive index of the cladding layer, which can be
observed through the phase shift difference between the light of the two interferometer
arms. SU-8 polymer was tested as the core of the optical waveguides, an epoxy-based negative photoresist material, which presented very good transmission properties providing low propagation losses and SiO2 and PMMA positive photoresist were utilised as lower, respective upper claddings. The Optiwave FDTD software was used for the simulation of the propagation of the electromagnetic field at λ=630 nm and for the optimisation of the Mach -Zehnder interferometer parameters. |
full paper (pdf, 272 Kb)