Optical electronic nose based on porphyrin and phthalocyanine thin films for rice flavour classification

In this paper, we have developed an optoelectronic nose for rice classification based on measurement of changes in the optical absorption of organic thin films upon interactions with volatile analytes. The organic thin films based on metalloporphyrin (ZnTPP) and metallophthalocyanine (ZnOBPc) for gas sensing application were fabricated by spin coating technique. The optical properties of these thin films were tested with UV-VIS spectrophotometry. The surface topology of the films was observed by atomic force microscopy (AFM) technique which reveals that the film´s topology is homogeneous with nano-scale thickness. The sensing behavior of the films toward various volatile compounds representing the simulated aroma rice, such as 5% v/v hexanal, 5% v/v octanal and deionized water, was investigated under N₂ atmosphere at room temperature. The results have shown that ZnTPP and ZnOBPc thin film gas sensors can discriminate such volatile compounds. The optoelectronic nose was then applied to examine the odors of Jasmine rice, normal white rice and various of their mixtures. It was shown that ZnOBPc thin film can clearly classify the type of rice better than ZnTPP thin film. These results were confirmed by computational quantum mechanics based on density functional theory, which reveals that ZnOBPc molecule binds to the simulated rice aroma molecules better than ZnTPP molecule.