Fabrication and optical measurements of a TiO₂-ALD evanescent waveguide sensor

In the present work, we report the design, fabrication and characterisation of an evanescent waveguide sensor. TiO₂ deposited by Atomic Layer Deposition (ALD) on silicon wafer is used as waveguide material. In order to enhance the surface interaction between sensor and target, we have fabricated the waveguide as a freestanding structure. The sensitivity of the sensor is evaluated by evaporation of several concentrations of ethanol and isopropyl alcohol diluted in water and found to be 0.85 and 1.34 dB/% (v/v), respectively. The sensor is meant to evaluate a patient condition after colon-surgery by sensing the presence of Escherichia coli in drain fluid. We carried out the deposition of a self-assembled monolayer on the waveguide as first layer of surface functionalisation using antibody to make the sensor the selective to E. coli. Preliminary optical investigations are presented.