Colorimetric gas detection by the varying thickness of a thin film of ultrasmall PTSA-coated TiO2 nanoparticles on a Si substrate

Urmas Joost; Andris Šutka; Meeri Visnapuu; Aile Tamm; Meeri Lembinen; Mikk Antsov; Kathriin Utt; Krisjanis Smits; Ergo Nõmmiste; Vambola Kisand

doi:10.3762/bjnano.8.25

Colorimetric gas detection by the varying thickness of a thin film of ultrasmall PTSA-coated TiO₂ nanoparticles on a Si substrate

Beilstein J Nanotechnol. 2017 Jan 24:8:229-236. doi: 10.3762/bjnano.8.25. eCollection 2017.

Authors

Affiliations

¹ Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia.
² Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia; Laboratory of Functional Materials Technologies, Riga Technical University, Paula Valdena 3/7, 1048 Riga, Latvia.
³ Institute of Solid State Physics, University of Latvia, Kengaraga 8, Riga LV-1063, Latvia.

Abstract

Colorimetric gas sensing is demonstrated by thin films based on ultrasmall TiO₂ nanoparticles (NPs) on Si substrates. The NPs are bound into the film by p-toluenesulfonic acid (PTSA) and the film is made to absorb volatile organic compounds (VOCs). Since the color of the sensing element depends on the interference of reflected light from the surface of the film and from the film/silicon substrate interface, colorimetric detection is possible by the varying thickness of the NP-based film. Indeed, VOC absorption causes significant swelling of the film. Thus, the optical path length is increased, interference wavelengths are shifted and the refractive index of the film is decreased. This causes a change of color of the sensor element visible by the naked eye. The color response is rapid and changes reversibly within seconds of exposure. The sensing element is extremely simple and cheap, and can be fabricated by common coating processes.

Keywords: TiO2 nanoparticles; colorimetric gas sensing; p-toluenesulfonic acid (PTSA).