Biomedical subjects

Akio Oki

Publications and source records attributed to Akio Oki.

3 recordsLinked to original sources

PubMed2006

Study of water properties in nanospace.

Here we report an anomalous behavior of water, especially its viscosity and hydrodynamic flow, in a nanometer-confined space. As a typical model of a nanometer-confined space, the nanopillar chip, which was developed for DNA size-based separation was used, and single-particle tracking (SPT) technique was applied to investigate water viscosity and hydrodynamic flow in the nanopillar chip. The diffusion coefficients of nanospheres were almost one-third of the theoretical value derived from the Stokes-Einstein equation. This result gave indirect proof that water viscosity in a nanometer-confined space is higher than in a bulk solution. In order to improve resolution and throughput of the nanopillar chip for DNA separation, these potential factors affecting performance should be seriously considered.

Journal Article↗

PubMed2003

Low-voltage electroosmosis pump for stand-alone microfluidics devices.

Two types of low-voltage electroosmosis pumps were developed using microfabrication technology for usage in handy or stand-alone applications of the micrototal analysis systems (micro-TAS) and the lab-on-a-chip. This was done by making a thin (< 1 microm) region in the flow path and by only applying voltages near this thin region using electrodes inserted into the flow path. The inserted electrodes must be free from bubble formation and be gas-tight in order to avoid pressure leakage. For these electrodes, Ag/AgCl or a gel salt bridge was used. For patterning the gel on the chip, a hydrophilic photopolymerization gel and a photolithographic technique were optimized for producing a gel with higher electric conductivity and higher mechanical strength. For high flow rate application, wide (33.2 mm) and thin (400 nm) pumping channels were compacted into a 1 mm x 6 mm area by folding. This pump achieves an 800 Pa static pressure and a flow of 415 nL/min at 10 V. For high-pressure application, a pump was designed with the thin and thick regions in series and positive and negative electrodes were inserted between them alternatively. This pump could increase the pumping pressure without increasing the supply voltage. A pump with 10-stage connections generated a pressure of 25 kPa at 10 V.

Acrylic Resins↗

PubMed2002

pH Change of buffer solution in a microcapillary chip and its suppression.

During the electrophoresis separation of B- and T-cells from lymphocytes employing a microcapillary chip, they were found to become inactive in the reservoir after a short time. This was caused by the buffer solution becoming alkaline due to electrolysis. This was considered to take place in chips with small reservoir volumes. The pH change was confirmed by the ISFET (ion-sensitive field effect transistor) embedded in the chip. To suppress the pH change, two methods were studied. One is the insertion of a salt bridge just in front of and behind the capillary, thus introducing an electric potential but stopping flow of the acid and alkaline solutions into the capillary. The other is neutralization of the alkaline solution in the reservoir by injecting the acid solution produced in another capillary with the same structure by employing an electroosmotic flow (EOF) pump. Both methods achieved no pH change during electrophoresis measurements in the microcapillary.

Animals↗