The bonding of glass substrates is necessary when constructing micro/nanofluidic devices for sealing micro- and nanochannels. Recently, a low-temperature glass bonding method utilizing surface activation with plasma was developed to realize micro/nanofluidic devices for various applications, but it still has issues for general use. Here, we propose a simple process of low-temperature glass bonding utilizing typical facilities available in clean rooms and applied it to the fabrication of micro/nanofluidic devices made of different glasses. In the process, the substrate surface was activated with oxygen plasma, and the glass substrates were placed in contact in a class ISO 5 clean room. The pre-bonded substrates were heated for annealing. We found an optimal concentration of oxygen plasma and achieved a bonding energy of 0.33–0.48 J/m2 in fused-silica/fused-silica glass bonding. The process was applied to the bonding of fused-silica glass and borosilicate glass, which is generally used in optical microscopy, and revealed higher bonding energy than fused-silica/fused-silica glass bonding. An annealing temperature lower than 200 °C was necessary to avoid crack generation by thermal stress due to the different thermal properties of the glasses. A fabricated micro/nanofluidic device exhibited a pressure resistance higher than 600 kPa. This work will contribute to the advancement of micro/nanofluidics.

Understanding the motion of colloidal particles flowing in small spaces is a general issue in various fields such as thermal engineering and micro/nanofluidics. In the present study, we investigated the motion of fluorescent submicrometer particles in a 3- μm microchannel by defocusing nanoparticle image velocimetry. An optical measurement system with controlled spherical aberration and an algorithm for processing defocused particle images with multiple diffraction rings were developed. By detecting the centroid position and the diameter of the outermost diffraction ring, which is proportional to the distance between the focal plane and the particle, the position of particles was determined with the spatial resolutions of 154–204 nm in the streamwise direction and 76–311 nm in the depthwise direction, which are comparable to or smaller than the optical diffraction limit. A reusable microfluidic device containing a size-regulated microchannel made of glass was developed, which is suitable for optical measurements and precise flow control. By controlling the strength of low-temperature glass bonding, detachment of the bonded glass substrates, washing, and reuse were achieved. Based on this method and technology, the velocity of particles with diameters of 199, 457, and 1114 nm was successfully measured in pressure-driven laminar flow. Results suggested that for larger particles comparable to the channel size, the particle velocity is slowed from the flow velocity by particle–wall hydrodynamic interactions. Therefore, the motion of colloidal particles in 100- μm spaces is considered to be affected by particle–wall hydrodynamic interactions, as well as 102- μm spaces reported previously.

Global warming is making it difficult to achieve the chilling requirement for the completion of endodormancy in protected peach cultivation. To stabilize peach production in the face of warming winters, we examined the use of rootstock low-chilling 'Okinawa' and endodormancy-breaking treatments. In pot culture, 'Hikawahakuhou' on 'Okinawa' rooted and flowered earlier than 'Hikawahakuhou' on 'Ohatsumomo'. Therefore, it was suggested that rootstock low-chilling 'Okinawa' influences the flowering of 'Hikawahakuhou'. In field culture, 'Hikawahakuhou' on 'Okinawa' led to commercial fruit quality and growth. In the field with 'Hikawahakuhou' on 'Okinawa', the application of either of two endodormancy-breaking treatments, hydrogen cyanamide sprayed after 400 to 600 chilling hours or nitrogen metabolism solution sprayed after 600 to 800 chilling hours, advanced both flowering and harvesting dates. Under continued global warming, the use of 'Okinawa' as a rootstock and endodormancy-breaking treatments will enable continued production of peach.

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