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The photoluminescence of rutile and anatase TiO2 has been investigated in the range of 360–890 nm at several temperatures. An unexpected intense near-infrared (1.53 eV) photoluminescence band was recorded for both phases. At low temperatures, the resulting bands form a substructure of equally spaced peaks irrespective of the phase. The spectra were interpreted in the framework of the single-configuration-coordinate model as the phonon-replica effect, originating from ionization of oxygen vacancies.

This work aims at a broad overview of the results obtained with metal-sulfide materials in the field of chemoresistive gas sensing. Indeed, despite the well-known electrical, optical, structural and morphological features previously described in the literature, metal sulfides present lack of investigation for gas sensing applications, a field in which the metal oxides still maintain a leading role owing to their high sensitivity, low cost, small dimensions and simple integration, in spite of the wide assortment of sensing materials. However, despite their great advantages, metal oxides have shown significant drawbacks, which have led to the search for new materials for gas sensing devices. In this work, Cadmium Sulfide and Tin (IV) Sulfide were investigated as functional materials for thick-film chemoresistive gas-sensors fabrication and they were tested both in thermo- and in photo-activation modes. Furthermore, electrical characterization was carried out in order to verify their gas sensing properties and material stability, by comparing the results obtained with metal sulfides to those obtained by using their metal-oxides counterparts. The results highlighted the possibility to use metal sulfides as a novel class of sensing materials, owing to their selectivity to specific compounds, stability, and the possibility to operate at room temperature.

Numerous medical studies show that tumor growth is accompanied by protein changes that may lead to the peroxidation of the cell membrane with consequent emission of volatile organic compounds (VOCs) by breath or intestinal gases that should be seen as biomarkers for colorectal cancer (CRC). The analysis of VOCs represents a non-invasive and potentially inexpensive preliminary screening technique. An array of chemoresistive gas sensors based on screen-printed metal oxide semiconducting films has been selected to discriminate gases of oncological interest, e.g., 1-iodononane and benzene, widely assumed to be biomarkers of colorectal cancer, from those of interference in the gut, such as methane and nitric oxide.

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Among the major challenges of medicine today there are screening and early detection of tumors (since the adenoma stage) in order to prevent their degeneration into malignant cancer and/or metastases. In particular, the colorectal cancer shows a high curability rate, up to 90%, if identified when in its benign stage. The Protocol discussed here is proposed to implement the clinical validation of a device consisting of an array of chemoresistive gas sensors made of semiconductor materials, able of identifying the difference between fecal exhalation of healthy subjects and of subjects suffering from high-risk colorectal polyps or tumors. The tests are compared to the results of fecal occult blood test and colonoscopy as a gold standard.

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