Tomomi Inaba

A continuous-flow microbial microreactor using microbes immobilized into a microporous carrier by dielectrophoresis

In this paper we demonstrate a continuous-flow microbial microreactor that immobilizes microbes into microporous carrier. First, bacteria are trapped into 3, 5, 10, 20-μm-diameter pores using positive dielectrophoresis (DEP). After non-immobilized bacteria are flushed, the continuous-flow microreactor generates reaction products when culture media including reactive substrate are supplied. Continuous-flow type reactors facilitate collecting and evaluating reaction products. We used the developed microreactor to characterize microbes belonging to Corynebacterium group by measuring generated lactic acid when glucose was supplied. The amount of lactic acid produced by a single bacterium was deduced and we found Corynebacterium variabile to be most productive among three tested members. The microbial reactor proposed herein is readily applicable to an efficient microbial screening platform.

Nanoimprinted holes to immobilize microbes

In this paper we demonstrate highly dense immobilization of bacteria into nanoimprinted holes. Nanoimprinting enables micro holes smaller than 2 μm in diameter with a high accuracy, which cannot be patterned using conventional UV photolithography. In our prior work, we developed a microbial reactor immobilizing bacteria into micro holes, which facilitated collection and evaluation of reaction products while the number of bacteria involved in the reaction could be quantified. However, the holes were made by photolithography and the minimum size was limited to be 3 μm in diameter. Large holes allow multiple bacteria to be immobilized in a hole, which resulted in errors in quantification. The number of bacteria immobilized in a nanoimprinted hole was found to have smaller deviation than in photolithographically formed holes. In addition, density of the immobilized bacteria was experimentally found to be largest in case of 2-μm-holes. The proposed processes will be of great help for precise evaluation of bacteria reaction.

Microfabrication of Super Absorbent Polymer Structure Using Nanoimprinting and Swelling Process

Micro-fabrication technologies have been extensively studied to achieve smaller sizes and higher aspect ratios. When the features have sizes of a couple of micrometers or below, nano-imprinting can be an effective method for micro-fabrication at low cost. However, it is difficult to achieve aspect ratio greater than 1. In this research, we propose micro fabrication of super absorbent polymer (SAP) as a new material for micro devices. SAP swells by adding deionized water, which can be used as a post patterning process to enhance the aspect ratio of micro structures. Micropatterning of SAP must be conducted under thoroughly dry conditions and we used nano-imprinting processes. We successfully augmented an aspect ratio of the nano-imprinted micro holes of SAP from 0.65 to 1.2 by the swelling process. The proposed patterning and swelling process of SAP can be applicable to micro-fabricate high-aspect-ratio structures at low cost for high performance lab-on-a-chip.

Bacteria manipulation using dielectrophoresis for efficient screening

In this paper we demonstrate a microfluidic device that immobilizes microbes into microporous carrier using positive dielectrophoresis (DEP). This device can characterize bacteria, while precisely controlling the reaction conditions and the number of bacteria involved in the biochemical reaction, and can effectively screen them to efficiently produce useful chemicals by fermentation, such as organic acids, antibiotic drugs, and foods. We chose microbes belonging to Corynebacterium group as samples. First, as preparing for using the microfluidic device, we experimentally deduced effective DEP frequency of 10 MHz, when live C. glutamicum was preferably driven to the areas with stronger electric fields. Second, we characterized the microfluidic device and found that the device could immobilize microbes into micro pores and evaluate the production capacity of a single bacrerium. As the demonstration, we used the developed device to characterize microbes under various environments and evaluate biological activity.