Multilayer integrated structure for selective detection of Ochratoxin A

This work presents the design, fabrication and characterization of a system based on thin film technology for the selective detection of the natural fluorescence of Ochratoxin A. To this aim, the system optically couples an amorphous silicon photosensor with a long pass multi-dielectric filter, deposited on glass substrates. In particular, the filter rejects the wavelengths coming from the excitation source (centered at 340 nm) and transmits the emission spectrum (centered at 465 nm) of the mycotoxin, reducing therefore the background noise. The basic structure of the a-Si:H photosensors is a p-type/intrinsic/n-type stacked junction, deposited by Plasma Enhanced Chemical Vapor Deposition at temperatures ranging from 210 to 300 °C. Its responsivity at 465 nm is equal to 185 mA/W. The long pass filter is an interferential filter, constituted by alternating layers of TiO₂ and SiO₂. It has been designed by using a freeware software, and deposited by electron beam Physical Vapor Deposition at 250 °C. A very good agreement between modeled and experimental data of transmittance and reflectance has been achieved. In particular, transmittance of the filter varies by almost four orders of magnitude between 360 nm and 400 nm, showing its suitability in rejecting the excitation light.