Nanoporous TiO2 anatase film has been investigated as sensitive layer in Surface Plasmon Resonance sensors for the
detection of hydrogen and Volatile Organic Compounds, specifically methanol and isopropanol. The sensors consist of a
TiO2 nanoporous matrix deposited above a metallic plasmonic grating, which can support propagating Surface Plasmon
Polaritons. The spectral position of the plasmonic resonance dip in the reflectance spectra was monitored and correlated
to the interaction with the target gases.
Reversible blue-shifts of the resonance frequency, up to more than 2 THz, were recorded in response to the exposure to
10000 ppm of H2 in N2 at 300°C. This shift cannot be explained by the mere refractive index variation due to the target
gas filling the pores, that is negligible.
Reversible red-shifts were instead recorded in response to the exposure to 3000 ppm of methanol or isopropanol at room
temperature, of magnitudes up to 14 THz and 9 THz, respectively. In contrast, if the only sensing mechanism was the
mere pores filling, the shifts should have been larger during the isopropanol detection.
We therefore suggest that other mechanisms intervene in the analyte/matrix interaction, capable to produce an injection
of electrons into the sensitive matrix, which in turn induces a decrease of the refractive index.