Maki Hiraoka

Silicon Based System for Single-Nucleotide-Polymorphism Detection: Chip Fabrication and Thermal Characterization of Polymerase Chain Reaction Microchamber

A single nucleotide polymorphism (SNP) is a difference in the DNA sequence of one nucleotide only. We recently proposed a lab-on-a-chip (LoC) system which has the potentiality of fast, sensitive and highly specific SNP detection. Most of the chip components are silicon based and fabricated within a single process. In this paper, the newly developed fabrication method for the silicon chip is presented. The robust and reliable process allows etching structures on the same chip with very different aspect ratios. The characterization of a crucial component to the LoC SNP detector, the microreactor where DNA amplification is performed, is also detailed. Thanks to innovative design and fabrication methodologies, the microreactor has an excellent thermal isolation from the surrounding silicon substrate. This allows for highly localized temperature control. Furthermore, the microreactor is demonstrated to have rapid heating and cooling rates, allowing for rapid amplification of the target DNA fragments. Successful DNA amplification in the microreactor is demonstrated.

High pressure pump as lab on chip component for micro-fluidic integrated system

We developed a miniaturized pump (8 mm diameter, 1 mm thickness) which generates a flow rate of 2 µL/min at a pressure of 3 MPa. It consists of a stack of several conductive polymer (CP) layers intercalated with electrolyte layers. The stack is housed in a polycarbonate case specially conceived for integration in a lab-on-chip device. The actuator operates at a bias lower than 2V. A maximum strain of 13% is measured in the single CP layer when it expands against atmospheric pressure; this strain is reduced by only a factor of 3 when pressure increases to 15 MPa. Using the stacked actuator, a maximum strain of 5% is measured.

Electrochemical sensor with dry reagents implemented in lab-on-chip for single nucleotide polymorphism detection

We developed an electrochemical (EC) sensor having dry reagents to detect pyrophosphoric acid (PPi) produced as a by-product of a polymerase-chain-reaction (PCR) amplicon for single nucleotide polymorphism (SNP) detection. The EC sensor is implementable in a lab-on-chip (LoC) system, and a sensor chip having side-wall electrical connections that enable electrical contacts from the top of the LoC has been developed. We also developed separated on-chip placement of dry reagents divided into three groups in a sensor cavity to suppress background current when there is no PPi. Using this chip, we successfully demonstrated SNP detection in the ABO gene from human blood samples, in combination with the allele-specific PCR amplification method using our developed LoC system.

Miniaturized pumps and valves, based on conductive polimer actuators, for lab-on-chip application

We developed a new type of conductive polymer (CP) actuator, specifically designed for miniaturized pumps and valves for lab-on-a-chip (LoC) applications. CP films soaked in an electrolyte solution reversibly change their thickness upon bias application. A large stroke actuator was fabricated by stacking several CP layers, bonded together by means of epoxy dots. The CP deposition process was optimized for obtaining the low surface roughness required for stacking. The maximum strain of stacked actuators and of individual layers was identical (13%), indicating that the dot gluing process eliminates strain losses previously observed in multi-layers actuators. Pumps and valves were fabricated and mounted on a microfluidic chip.

Development of multilayer conducting polymer actuator for power application

In late years many kinds of home-use robot have been developed to assist elderly care and housework. Most of these robots are designed with conventional electromagnetic motors. For safety it is desirable to replace these electromagnetic motors with artificial muscle. However, an actuator for such a robot is required to have simple structure, low driving voltage, high stress generation, high durability, and operability in the air. No polymer actuator satisfying all these requirements has been realized yet. To meet these we took following two approaches focusing on conducting polymer actuators which can output high power in the air. (Approach 1) We have newly developed an actuator by multiply laminating ionic liquid infiltrated separators and polypyrrole films. Compared with conventional actuator that is driven in a bath of ionic liquid, the new actuator can greatly increase generated stress since the total sectional area is tremendously small. In our experiment, the new actuator consists of minimum unit with thickness of 128um and has work/weight ratio of 0.92J/kg by laminating 9 units in 0.5Hz driving condition. In addition, the driving experiment has shown a stable driving characteristic even for 10,000 cycles durability test. Furthermore, from our design consideration, it has been found that the work/weight ratio can be improved up to 8J/kg (1/8 of mammalian muscle of 64J/kg) in 0.1Hz by reducing the thickness of each unit to 30um. (Approach 2) In order to realize a simplified actuator structure in the air without sealing, we propose the use of ionic liquid gel. The actuation characteristic of suggested multilayered actuator using ionic liquid gel is simulated by computer. The result shows that performance degradation due to the use of ionic liquid gel is negligible small when ionic liquid gel with the elasticity of 3kPa or less is used. From above two results it is concluded that the proposed multilayerd actuator is promising for the future robotic applications because it has advantages of high work/weight ratio and in-the-air operation, in addition to advantages of conventional polymer actuators.