| 1. |
- Kazoe, Yutaka, et al.
(författare)
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Quantitative characterization of liquids flowing in geometrically controlled sub-100 nm nanofluidic channels
- 2023
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Ingår i: Analytical Sciences. - : Springer Science and Business Media LLC. - 0910-6340 .- 1348-2246. ; 39:6, s. 779-784
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Tidskriftsartikel (refereegranskat)abstract
- With development of nanotechnologies, applications exploiting nanospaces such as single-molecule analysis and high-efficiency separation have been reported, and understanding properties of fluid flows in 101 nm to 102 nm scale spaces becomes important. Nanofluidics has provided a platform of nanochannels with defined size and geometry, and revealed various unique liquid properties including higher water viscosity with dominant surface effects in 102 nm spaces. However, experimental investigation of fluid flows in 101 nm spaces is still difficult owing to lack of fabrication procedure for 101 nm nanochannels with smooth walls and precisely controlled geometry. In the present study, we established a top-down fabrication process to realize fused-silica nanochannels with 101 nm scale size, 100 nm roughness and rectangular cross-sectional shape with an aspect ratio of 1. Utilizing a method of mass flowmetry developed by our group, accurate measurements of ultra-low flow rates in sub-100 nm nanochannels with sizes of 70 nm and 100 nm were demonstrated. The results suggested that the viscosity of water in these sub-100 nm nanochannels was approximately 5 times higher than that in the bulk, while that of dimethyl sulfoxide was similar to the bulk value. The obtained liquid permeability in the nanochannels can be explained by a hypothesis of loosely structured liquid phase near the wall generated by interactions between the surface silanol groups and protic solvent molecules. The present results suggest the importance of considering the species of solvent, the surface chemical groups, and the size and geometry of nanospaces when designing nanofluidic devices and membranes. Graphical abstract: [Figure not available: see fulltext.].
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| 2. |
- Morikawa, Kyojiro, et al.
(författare)
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Fused silica microchannel fabrication with smooth surface and high etching selectivity
- 2023
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Ingår i: Journal of Micromechanics and Microengineering. - : IOP Publishing. - 0960-1317 .- 1361-6439. ; 33:4
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Tidskriftsartikel (refereegranskat)abstract
- Channel fabrication technology has become increasingly important for microfluidic and nanofluidic devices. In particular, glass channels have high chemical and physical stability, high optical transparency, and ease of surface modification, so that there is increasing interest in glass microfluidic devices for chemical experiments in microfluidics and nanofluidics. For the fabrication of glass channels, especially those with a high aspect ratio (depth/width), lithography using a metal resist and dry etching have mainly been used. However, there are still issues involving the surface roughness of the etched channel and the low etching selectivity. In this study, a microchannel fabrication method with high etching selectivity that produces a smooth etched surface was developed. First, interference during dry etching by remaining Cr particles after the photolithography and Cr etching processes was assumed as the cause of the rough etched surface. Three different dry etching processes were introduced to verify this. In process 1 without removal of the Cr particles, the etched surface was not flat and had a 1 μm scale roughness. In process 2 where a cleaning process was included and high power etching was conducted, a smooth surface with a 1 nm scale roughness and a faster etching rate of 0.3 μm min−1 were obtained. For this high-power etching condition, the etching selectivity (fused silica/Cr) was relatively low at approximately 39-43. In process 3 with a cleaning process and low-power etching, although the etching rate was relatively low at 0.1 μm min−1, a smooth surface with 1 nm scale roughness (10 nm scale roughness deeper than 40 μm in the depth region) and a much higher etching selectivity of approximately 79-84 were obtained. The dry etching method presented in this study represents a significant contribution to microfluidics/nanofluidics for microchannel/nanochannel fabrication.
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| 3. |
- Sano, Hiroki, et al.
(författare)
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Nanofluidic analytical system integrated with nanochannel open/close valves for enzyme-linked immunosorbent assay
- 2023
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Ingår i: Lab on a Chip. - : Royal Society of Chemistry (RSC). - 1473-0197 .- 1473-0189. ; 23, s. 727-736
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Tidskriftsartikel (refereegranskat)abstract
- There have been significant advances in the field of nanofluidics, and novel technologies such as single-cell analysis have been demonstrated. Despite the evident advantages of nanofluidics, fluid control in nanochannels for complicated analyses is extremely difficult because the fluids are currently manipulated by maintaining the balance of driving pressure. To address this issue, the use of valves will be essential. Our group previously developed a nanochannel open/close valve utilizing glass deformation, but this has not yet been integrated into nanofluidic devices for analytical applications. In the present study, a nanofluidic analytical system integrated with multiple nanochannel open/close valves was developed. This system consists of eight pneumatic pumps, seven nanochannel open/close valves combined with piezoelectric actuators, and an ultra-high sensitivity detector for non-fluorescent molecules. For simultaneous actuation of multiple valves, a device holder was designed that prevented deformation of the entire device caused by operating the valves. A system was subsequently devised to align each valve and actuator with a precision of better than 20 μm to permit the operation of valves. The developed analytical system was verified by analyzing IL-6 molecules using an enzyme-linked immunosorbent assay. Fluid operations such as sample injection, pL-level aliquot sampling and flow switching were accomplished in this device simply by opening/closing specific valves, and a sample consisting of approximately 1500 IL-6 molecules was successfully detected. This study is expected to significantly improve the usability of nanofluidic analytical devices and lead to the realization of sophisticated analytical techniques such as single-cell proteomics.
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| 4. |
- Sano, Hiroki, et al.
(författare)
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Nanofluidic gas/liquid switching utilizing a nanochannel open/close valve based on glass deformation
- 2023
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Ingår i: Journal of Micromechanics and Microengineering. - 0960-1317. ; 33:8
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Tidskriftsartikel (refereegranskat)abstract
- There has been much progress in the field of nanofluidics, and novel applications, such as single-cell analysis, have been achieved. In such cases, controlling the location of the gas/liquid interface is vital and partial hydrophobic modification is frequently used to pin the position of this interface. However, because the fluid manipulating pressure in such devices is comparable to the Laplace pressure at the interface of approximately 0.1 MPa, the interface cannot be maintained stably. The present work demonstrates a method of controlling the gas/liquid interface using a hydrophobic nanochannel open/close valve. The high Laplace pressure at this valve (on the order of 1 MPa) fixes the location of the interface even during fluid manipulation. In addition, the interface can be moved at any time simply by closing the valve to generate an impulsive pressure higher than the Laplace pressure. A device incorporating this nanochannel open/close valve was fabricated, and the surface of the valve chamber was modified with hydrophobic molecules. Gas/liquid replacement in association with the operation of this valve was verified using microscopic observations. It was verified that this replacement was triggered by the valve operation, with a replacement time of 1.2 s. Using this process, gas/liquid switching can be performed when desired and this control method could expand the use of gas/liquid two-phase systems to realize further integration of chemical processes in nanofluidics.
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