Countercurrent laminar microflow for highly efficient solvent extraction.
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Journal Article↗
Biomedical subjects
Takehiko Kitamori
Publications and source records attributed to Takehiko Kitamori.
Application of a micro multiphase laminar flow on a microchip for extraction and determination of derivatized carbamate pesticides.
Determination of carbamate pesticides such as carbaryl, carbofuran, propoxur and bendiocarb was demonstrated on a microchip with newly designed microchannels developed for efficient solvent extraction. The pesticides were hydrolyzed to corresponding naphthols, coupled with p-nitrobenzenediazonium fluoroborate reagent, and then extracted into 1-butanol as colored azo derivatives and detected with a thermal lens microscope. Optimum flow rates for the aqueous and organic phases were evaluated in the continuous-flow chemical process established in the microchip. The calibration lines showed good linearity in the range of concentrations of 0.03 - 3 ppm (10(-7) - 10(-5) M) and a mass detection limit down to a nanogram level was achieved that is at least two orders of magnitude lower than the LODs for conventional spectrophotometric methods. Azo derivatives of the pesticides were successfully separated and identified by micellar electrokinetic chromatography (MEKC) using a sample prepared on a bulk scale.
Journal Article↗
Instantaneous carbon-carbon bond formation using a microchannel reactor with a catalytic membrane.
Instantaneous catalytic carbon-carbon bond forming reactions were achieved in a microchannel reactor having a polymeric palladium complex membrane. The catalytic membrane was constructed inside the microchannel via self-assembling complexation at the interface between the organic and aqueous phases flowing laminarly, where non-cross-linked polymer-bound phosphine and ammonium tetrachloropalladate dissolved, respectively. A palladium-catalyzed coupling reaction of aryl halides and arylboronic acids was performed using the microchannel reactor to give quantitative yields of biaryls within 4 s of retention time in the defined channel region.
Journal Article↗
Pressure-driven flow control system for nanofluidic chemical process.
We developed a novel flow control system for a nanofluidic chemical process. Generally, flow control in nanochannels is difficult because of its high-pressure loss with very small volume flow rate. In our flow control method, liquid pressure in a microchannel connected to the nanochannels is regulated by utilizing a backpressure regulator. The flow control method was verified by using simple structured microchip, which included parallel nanochannels. We found that the observed flow rate was three times lower than the value expected from Hagen-Poiseuille's equation. That implied a size-dependent viscosity change in the nanochannels. Then, we demonstrated mixing of two different fluorescent solutions in a Y-shaped nanochannel and also a proton exchange reaction in the Y-shaped nanochannel. The flow control method will contribute to further integration of nanochemical systems.
Microfluidics↗
Microchip-based liquid-liquid extraction for gas-chromatography analysis of amphetamine-type stimulants in urine.
A microchip-based liquid-liquid extraction for the gas chromatography analysis of urine for amphetamine-type stimulants has been developed. Partially modified microchannels with the capillarity restricted modification (CARM) method were employed for stabilizing the interface consisting of 1-chlorobutane and alkalized urine. Reliability of the microchip-based extraction was evaluated with respect to linearity, trueness and precision. As a practical demonstration, methoxyphenamine hydrochloride (50 mg) was administered to three healthy volunteers, and the concentration of methoxyphenamine in their urine was determined by both methods for comparison. This study showed the potential of pressure-driven microfluidics to contribute to the rapid automation analysis in forensic toxicology.
Adult↗
Supercooled micro flows and application for asymmetric synthesis.
Supercooled micro flow in microchannels was demonstrated. In order to clarify fundamental properties of the supercooling state in microchannels, freezing temperature was measured in the microchannels having widths ranging from 70 microm to 300 microm. The freezing temperature decreased with decreasing width of the microchannel when the microchannel wall was chemically modified with octadecylsilane group. The lowest freezing temperature was observed as -28 degrees C for water in the 70 microm wide microchannel. By contrast, the freezing temperature was -15 degrees C and did not depend on width when a microchannel with a bare glass surface was used. Next, the freezing point was measured with flow rates ranging from 0.1 to 2.0 microl min(-1) and no dependence on flow rate was observed. Then, the supercooled micro flow was applied to an asymmetric reaction in micro two-phase flow of aqueous and CH2Cl2 phases. As expected from thermodynamic prediction, enantiomeric selectivity increased in the supercooled state of water.
Catalysis↗
UV excitation thermal lens microscope for sensitive and nonlabeled detection of nonfluorescent molecules.
An ultrasensitive and nonlabeled detection method of nonfluorescent molecules on a microchip was developed by realizing a thermal lens microscope (TLM) with a 266-nm UV pulsed laser as an excitation light source (UV-TLM). Pulsed laser sources have advantages over continuous-wave laser sources in more compact size and better wavelength tuning, which are important for microchip-based analytical systems. Their disadvantage is difficulty in applying a lock-in amplifier due to the high (>10(4)) duty ratio of pulse oscillation. To overcome this problem, we realized a quasi-continuous-wave excitation by modulating the pulse trains at approximately 1 kHz and detecting the synchronous signal with a lock-in amplifier. The optimum pulse repetition frequency was obtained at 80 kHz, which was reasonable considering thermal equilibrium time. Furthermore, a permissible flow velocity in the range of 6.6-19.8 mm/s was found to avoid sensitivity decrease due to photochemical reactions and thermal energy dissipation. Under these conditions, we detected adenine aqueous solutions on a fused-silica microchip without labeling and obtained a sensitivity that was 350 times higher than that in a spectrophotometric method. The sensitivity was enough for detection on a microchip with an optical path length that was 2-3 orders shorter than that in conventional cuvettes. Finally, the UV-TLM method was applied to liquid chromatography detection. Fluorene and pyrene were separated in a microcolumn and detected in a capillary (50-microm inner diameter) with 150 times higher sensitivity than a spectrophotometric method. Our method provides highly sensitive and widely applicable detections for various analytical procedures and chemical syntheses on microchips.
Adenine↗
Circular dichroism thermal lens microscope for sensitive chiral analysis on microchip.
A novel chiral detector, a circular-dichroism thermal lens microscope (CD-TLM), was developed to realize sensitive and selective detection of small volume chiral samples on a microchip. To realize chiral recognition on TLM, an excitation beam was phase-modulated at a frequency of 1.2 kHz, and left-circularly polarized light (LCPL) and right-circularly polarized light (RCPL) were generated. Then, the differential light absorption between LCPL and RCPL, which is the CD effect, was detected as thermal lens signal intensity and phase. As a standard sample, optically active tris(ethylenediamine)cobalt(III) [Co-(en)3]3+I3- aqueous solutions were used for performance evaluations. First, we verified the basic principle for selective chiral analysis by comparing the signals in intensity-modulation and phase-modulation modes of the excitation beam. Also, we found that the g-factor, which is significant for determining enantiomeric excess, agreed well with the value obtained by the CD spectrometer. The limit of detection (LOD) for enantiopure [Co-(en)3]3+I3- was 6.3 x 10(-5) M (1.9 x 10(-7) abs) for (-)-Co(en)3(3+), and the sensitivity in absorbance units was more than 250 times higher than that in a CD spectrophotometer. Finally, we demonstrated enantiomeric excess determination on a microchip. The LOD was 1.7% (8.5 x 10(-7) abs) for (-)-Co(en)3(3+) and at least one order superior to the LOD of a CD spectrometer. The applicability of CD-TLM for sensitive chiral analysis on a microchip was verified, and CD-TLM is expected to be promising for microchip-based chiral synthesis and analysis systems.
Journal Article↗
AC electroosmotic micromixer for chemical processing in a microchannel.
A rapid micromixer of fluids in a microchannel is presented. The mixer uses AC electroosmotic flow, which is induced by applying an AC voltage to a pair of coplanar meandering electrodes configured in parallel to the channel. To demonstrate performance of the mixer, dilution experiments were conducted using a dye solution in a channel of 120 microm width. Rapid mixing was observed for flow velocity up to 12 mm s(-1). The mixing time was 0.18 s, which was 20-fold faster than that of diffusional mixing without an additional mixing mechanism. Compared with the performance of reported micromixers, the present mixer worked with a shorter mixing length, particularly at low Peclet numbers (Pe < 2 x 10(3)).
Diffusion↗
An actuated pump on-chip powered by cultured cardiomyocytes.
Cellular functions are frequently exploited as processing components for integrated chemical systems such as biochemical reactors and bioassay systems. Here, we have created a new cell-based microsystem exploiting the intrinsic pulsatile mechanical functions of cardiomyocytes to build a cellular micropump on-chip using cardiomyocyte sheets as prototype bio-microactuators. We first demonstrate cell-based control of fluid motion in a model microchannel without check valves and evaluate the potential performance of the bio-actuation. For this purpose, a poly(dimethylsiloxane) (PDMS) microchip with a microchannel equipped with a diaphragm and a push-bar structure capable of harnessing collective cell fluid mechanical forces was coupled to a cultured pulsating cardiomyocyte sheet, activating cell-based fluid movement in the microchannel by actuating the diaphragm. Cell oscillation frequency and correlated fluid displacement in this system depended on temperature. When culture temperature was increased, collective cell contraction frequency remained cooperative and synchronous but increased, while displacement was slightly reduced. We then demonstrated directional fluid pumping within microchannels using cantilever-type micro-check valves made of polyimide. A directional flow rate of nL min(-1) was produced. This cell micropump system could be further developed as a self-actuated and efficient mechanochemical transducer requiring no external energy sources for various purposes in the future.
Animals↗
Demonstration of a PDMS-based bio-microactuator using cultured cardiomyocytes to drive polymer micropillars.
Natural cellular functions are increasingly exploited for integrated chemical systems such as biochemical reactors and biosensors. We propose to utilize the intrinsic mechanical function of cardiomyocytes, converting chemical energy into mechanical energy. In this report, we demonstrate the working principle of our proposed poly(dimethylsiloxane) (PDMS) based cardiomyocyte bio-microactuator using fabricated PDMS micropillars driven to repetitive motion by attached pulsating cardiomyocytes. Sheets of PDMS embedded with an array of micropillars were fabricated and modified for cardiomyocyte attachment in culture. Primary neonatal rat cardiomyocytes were cultured on the array, attaching to the micropillars and substratum successfully, and exhibiting their typical spontaneous, pulsatile phenotype. Micropillars beat with the coupled cells spontaneously without any triggers. The beat frequency was 1.4 Hz at 37 degrees C and the displacement of the top of the pillar that beat most strongly in our observation was 2.8+/-0.2 microm. From this result, contractile forces of cultured cardiomyocytes were estimated to exceed 3.5 microN. The estimated force is far greater than that of a previously described hydrogel-based cardiomyocyte bio-microactuator (K. Morishima et al., in Micro Total Analysis Systems 2003, ed. M. A. Northrup et al., The Transducers Research Foundation, San Diego, CA, vol. 2, pp. 1125-1128). PDMS compatibility as a base material for bio-microactuator design using cultured cardiomyocytes was verified. This PDMS-based cell microactuator worked for about one week without exchange of the culture medium, and this system could be developed for various purposes in the future as self-actuated and efficient mechanochemical transducers without external energy source requirements.
Algorithms↗
Liquid filling method for nanofluidic channels utilizing the high solubility of CO2.
We developed a fabrication method and a liquid filling method for a nano chemical reactor that used Y-shaped nanochannels specially designed for mixing and reacting. In order to reduce the pressure loss and to utilize the characteristics of the nanochannel, inlet microchannels were fabricated just beside the nanochannels. We investigated an initial liquid filling method into the nanochannels that ensured there were no air bubbles that could cause a flow stack due to the capillary pressure. In our method, the micro- and nanochannels were filled with carbon dioxide and any remaining air during the initial liquid introduction was dissolved utilizing the high solubility of carbon dioxide. We propose that chemical reactions in nanospaces can be realized by utilizing these fabrication and liquid introduction techniques.
Journal Article↗
Quantitative detection and fixation of single and multiple gold nanoparticles on a microfluidic chip by thermal lens microscope.
A detection and fixation method of single and multiple gold nanoparticles on the wall of a microfluidic channel is demonstrated. A thermal lens microscope (TLM) with continuous-wave excitation (wavelength, 532 nm) and probe (wavelength, 670 nm) laser beams was used to realize the sensitive detection of heat generated by light absorption of individual gold nanoparticles (50 nm in diameter); fixation of the individual nanoparticles was realized simultaneously. The fixation mechanism was investigated and attributed to an absorption-based optical force. In addition to single nanoparticle detection, multiple-nanoparticle detection and fixation was demonstrated. An acceleration of fixation was observed when the number of fixed particles was increased. TLM is expected to be a powerful tool for both the quantitative detection and precise fixation of individual nanoparticles.
Journal Article↗
Miniaturized thermal lens and fluorescence detection system for microchemical chips.
We have developed a miniaturized two-way detection system using thermal lens and fluorescence spectroscopies for microchip chemistry. The system was composed of laser diode (LD) modules, fiber-based optics combined with a gradient index lens, and miniaturized detection units for thermal lens and fluorescence signals. The detection limits in the thermal lens and fluorescence spectroscopies were 6.3 x 10(-9)M for Ni(II) phthalocyanine tetrasulfonic acid and 3.0 x 10(-9)M for cy5, respectively. The performance of the system with the miniaturized thermal lens was equivalent to that of a conventional thermal lens microscope. The fluorescence sensitivity was comparable to sensitivities offered by conventional miniaturized systems.
Miniaturization↗
Monitoring of intercellular messengers released from neuron networks cultured in a microchip.
A cellular biochemistry analysis system was integrated on a quartz glass microchip with a microchamber for cell culture followed by a microchannel for detecting with a thermal lens microscope (TLM). Nerve cells from rat hippocampus were successfully cultured to form neural networks in the microchip. An aqueous solution of glutamate, which is known as a neurotransmitter, was introduced to stimulate the cultured neuron to release a retrograde messenger, arachidonate which is considered to be critical for neuronal plasticity, especially for long-term potentiation (LTP). After the introduction, the solution that flowed through the culture chamber was analyzed using the UV-TLM (excitation wavelength, 244 nm). The measured signal intensity was dependent on glutamate solution concentration, and the neurons were considered to release the retrograde messenger according to the glutamate concentration. This system is suitable for time-course monitoring of ultra trace amounts of chemicals released from very small amount of cultured cells.
Animals↗
Cell culture and life support system for microbioreactor and bioassay.
A microchip-based cell culture system was developed and a primary culture of rat hepatocytes was realized in the system. The microchip was made of glass plates and had a microchannel and a microculture flask inside. The flask inner surface was coated using collagen solution; then FBS and DMEM were added successively. Rat hepatocytes suspended in a medium was introduced into the microchip and incubated at 37 degrees C in a humidified atmosphere with 5% CO(2). Because of the shortage of dissolved oxygen, the cultured cells in the microchip resulted in a significant decrease in viability. To overcome this, a continuous medium flow oxygen and nutrition supplying system was designed and constructed. The system realized good cell growth for at least 4 days. Liver-specific functions, such as the synthesis of albumin and urea from hepatocytes were confirmed.
Albumins↗
Development of a microchip-based bioassay system using cultured cells.
We developed a novel bioassay system using a glass microchip and cultured cells. A microchamber for cell culture and microchannels for reactions and detection were fabricated on a Pyrex glass substrate by photolithography and wet etching techniques. Cell culture, chemical and enzymatic reactions, and detection were integrated into the microchip. To keep different temperatures locally in three areas of the microchip, we designed and fabricated a temperature control device. Nitric oxide released from macrophage-like cells stimulated by lipopolysaccharide was successfully monitored with the microchip, the temperature control device, and a thermal lens microscope. The total assay time was reduced from 24 to 4 h, and detection limit of NO was improved from 1 x 10(-6) to 7 x 10(-8) M compared with conventional methods. Moreover, the system could monitor a time course of the release, which is difficult to measure by conventional batch methods. We conclude that this system is promising for a rapid bioassay system with very small consumption of cells.
Animals↗
Surface modification method of microchannels for gas-liquid two-phase flow in microchips.
A capillarity restricted modification method for microchannel surfaces was developed for gas--liquid microchemical operations in microchips. In this method, a microstructure combining shallow and deep microchannels and the principle of capillarity were utilized for chemical modification of a restricted area of a microchannel. A hydrophobic--hydrophilic patterning in microchannels was prepared as an example for guiding gas and liquid flows along the respective microchannels. Validity of the patterning was confirmed by measuring aqueous flow leak pressure from the hydrophilic microchannel to the hydrophobic one. The leak pressure of 7.7-1.1 kPa agreed well with that predicted theoretically from the Young-Laplace equation for the microchannel depth of 8.6-39 microm. In an experiment to demonstrate usefulness and effectiveness of the method, an air bubble was first introduced into the hydrophilic microchannel and purged from the hydrophobic-hydrophilic patterned microchannels. Next, the patterning structure was applied to remove dissolved oxygen by contacting the aqueous flow with a nitrogen flow. The concentration of dissolved oxygen decreased with contact time, and its time course agreed well with numerical simulation. These demonstrations showed that the proposed patterning method can be used in general microfluidic gas-liquid operations.
Biomechanical Phenomena↗