A Study on a Multichannel Ordor Sensor Based on Color Information

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The aim of this research is to construct a multichannel odor-sensing system based on the color changes of dyes upon contact with odor gases. The response elements were composed of an array of dyes, 5,10,15,20-tetraphenyl-21H,23H-porphin and the Cu(II),Zn(II),Mn(II),Co(II),Fe(II) complexes, a Reichardt's dye, pH indicators (Thymol Blue, Methyl Orange, Methyl Red, Phenol Red, Phenolphthalein and Alizarin Yellow) and acceptors of charge transfer complexes, adsorbed on C18 and C2 reverse-phase TLC plates and a silica-gel one ; color images of the dye elements obtained with a scanner were analyzed to give the gray levels of red, green and blue components. Differences between the gray levels before and after exposure to various kinds of volatile organic compounds suggested that the proposed sensing system was capable of detecting target gases even in the presence of a large quantity of water vapor, and thus was applicable to many odor gases without any pretreatment. A principal component analysis discriminated between citrus fruits, kabosu, lemon, navel orange and grapefruits, and between regular coffees, canned coffees with sugar and canned black coffees, using the gray level differences of some pH-indicator image components as multivariable data. An optical fiber having an Alizarin Yellow/polyvinylpyrrolidone at the cladding part and a thin gold or silver film on an end surface was used as a sensing element; a decrease in the signal intensity of halogen-lamp light reflected from the fiber was observed at around 630 nm when the fiber was exposed to principal odor components of citrus fruits, linalyl acetate and linalool.