Real-time measurement of photocatalytic reactions using a monolithic QCM array

This paper reports a real-time measurement of photocatalytic reactions by using a miniaturized quartz-crystal microbalance (QCM) array. The QCM was miniaturized and integrated on the same quartz plate using microfabrication techniques. Two QCMs were located close to each other, with one of the QCMs used as a reference sensor for the accurate and independent determination of mass change effects and environmental change effects. The QCM output was compensated for frequency shifts induced by ultra violet (UV) irradiation by subtracting the frequency shift of the reference sensor. The minimum detectable frequency shift under the irradiation was within 1 Hz. The measured photodecomposition speed of methylene blue dye on a TiO 2 -coated QCM agreed well with that evaluated by the standard optical testing method under dry condition. The developed method enabled us to measure the photodecomposition of a surfactant on a TiO 2 -coated QCM with sub-nanogram mass resolution in real time.