The development of personal monitoring devices with the size of a human palm so that people can carry or wear with them has been of importance over a decade. Many small apparatuses to be able to detect the chemical and biological agent have been developed and commercialized, but the portable and wearable device to detect small particles, especially with the size of nanometer has not been developed yet up to our knowledge. In the present work, a new miniature device which is small enough for the application to a personal ultrafine particle monitoring sensor is described. The enlargement of particle size through heterogeneous condensational growth is used for the whole system. And, for miniaturization, microscale multiphase fluid control and microstructured surface modification technologies are employed. In order to evaluate the performance of the developed device, the condensational growth of ultrafine aerosol particles in a minichannel made of capillary structure was investigated through a laser sheet visualization technique. The main body of the device was constructed by cutting a commercially produced capillary structure. The physical dimension of the developed device is less than 1/10 of the smallest design commercially available. The polydisperse aerosol particles with the mean diameter of 20nm and concentration of more than 60,000 particles/cc and purified water as condensing fluid were used for test. The image of condensed droplets grown by the device was compared with those of standard size PSL particles. The experimental results show that the entered ultrafine particles successfully grew to micron size droplets through the developed condensation chamber and then could be counted with the optical detection system. Furthermore, the counting efficiency and the change of average size of condensed droplets were also investigated with the operating condition.

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