Discrimination of odorants of definite concentrations by using plasma-organic-film-coated QCR sensors

Odorant-discrimination experiments were conducted for the major single-odor substances in various types of botanical species such as fruits and flowers by using a gas-sensing system consisting of a sensor array of quartz crystal resonators (QCRs) and a pattern-recognition technique. The sensing devices were fabricated by radio-frequency sputtering of biomaterials or polymers on to the QCRs. The 22 tested odorants of definite concentration, 0.1–64 ppm, were well discriminated by principal component analysis, using the sensors steady-state and dynamic properties as parameters. From the 1-nearest-neighbor method, introduced to evaluate the discrimination capability, the best discrimination was obtained, using the frequency changes in QCRs for longer than 10 min and the time constant of adsorption at 5 min as parameters, with the success rate of 83%. This system is thus highly reliable for discriminating trace amounts of odorants.