Tomoki Tanemura

Manipulation system for nano/micro components integration via transportation and self-assembly

We developed, for the first time, the manipulation system based on optoelectronic tweezers (OET) which manipulates multiple nano/micro components on an arbitrary substrate with concurrent observation of the component motion. From the theoretical analysis, the manipulation force of a hundred pN order is expected to act on components. It was successfully demonstrated to manipulate a PMMA particle of 10 mum diameter on a photoconductive film.

Sequential and Selective Self-Assembly of Micro Components by DNA Grafted Polymer

We demonstrated that Deoxyribonucleic Acid (DNA) can be utilized as an intelligent adhesive activated by temperature control to realize sequential and selective self-assembly of 5 mm squared silicon micro components on a substrate. Two kinds of complementary DNA pairs whose melting transition temperature (Tm) and base sequence were designated appropriately were utilized to verify the feasibility of the proposed approach. It was successfully confirmed that sequential and selective assembly of micro components on the substrate can be realized below each Tm. Furthermore, DNA grafted polymer was proposed for the first time as a flexible spacer between micro components and a substrate to improve self-assembly yield and speed.

DNA mediated sequential self-assembly of nano/micro components

A novel sequential self-assembly process of nano/micro components applying deoxyribonucleic acid (DNA) hybridization was proposed for the first time and its validity was experimentally verified. In the proposed process, characteristics of DNA, such as hybridization specificity of complementary pairs of single-stranded DNA (ssDNA) into a double-stranded DNA (dsDNA), and the dependence of hybridization on ambient temperature (melting temperature Tm) plays a key role. These characteristics of DNA can be designed and synthesized by base-pair sequence of DNA. Three types of self-assembly experiments using two types of ssDNA with different Tm (65degC and 50degC) were carried out; 1.) between Au nanoparticles, 2.) between Au nanoparticle and Au coated substrate, and 3.) between silicon micro components (5times5times3 mum3) and Au coated substrate. Through these experiments, it was successfully verified that the sequence of the self-assembly can be controlled by controlling the ambient temperature. The reversibility of this process was also confirmed. However, the silicon micro components assembly on Au coated substrate was not confirmed.

DNA-grafted-polymer mediated self-assembly of micro components

Systematic experiments of DNA mediated sequential and selective self-assembly of 5 × 5 (μm2) silicon micro-components to a substrate using DNA-grafted-polymers as flexible binding spacers were carried out for the first time. The surfaces of the micro-components and sites on the substrate were modified by the same 30-mers single-stranded-DNA (ssDNA). The complementary ssDNA was grafted to a polymer to form DNA-grafted-polymer. Four types of DNA-grafted-polymer with two different ssDNA hybridization lengths and two different ssDNA fractions were prepared. From the measured time dependence of the number of self-assembled micro-components on the sites, the DNA-grafted-polymer technique proved to greatly enhance the assembly yield and time compared to direct self-assembly between micro-components and sites.

Multi-Gas Sensor by Infrared Spectrometer

In order to detect many types of gases (CO2, NOx, SOx, C2H5OH) in the automotive cabin by infrared absorption sensor, we developed a novel micro electro mechanical systems (MEMS) based Fabry–Perot spectrometer with an ultra wide wavelength range (3.20–8.40 μm) compared to previously reported spectrometers (typically 2.80–5.80 μm). The wavelength range of a Fabry–Perot spectrometer is known to increase by increasing the ratio of the refractive indices of the multilayer mirrors. Thus, a novel mirror structure was proposed replacing the low refractive index layer of SiO2 (nL = 1.44) with “air (nL = 1.00)” for a wider wavelength range. To fabricate the proposed structure, the internal stress of the four ultra-thin polycrystalline silicon films (ca. 320 nm) was controlled tensile by the deposition temperature. A gas sensor was fabricated using our developed spectrometer. It was found that the sensor detected CO2 and C2H5OH successfully.

Contact potential difference for sequential assembly and face alignment of submillimeter components

We demonstrated a new approach utilizing contact potential difference (CPD) based self-assembly for a future sequential assembly of nano/micro components and face alignment of submillimeter scale components. Two types of experiments realized by CPD were carried out; 1) sequential assembly of silica particles using Coulomb force induced by contacting a silver (Ag) probe on a platinum (Pt) substrate, and 2) face alignment of component with Ag on one face and Pt on the other face on a Pt substrate by CPD induced additional electrostatic adhesive energy. In the face alignment experiment, the measured adhesive energies of two different metal pairs (Pt-Ag and Pt-Pt) were one order smaller than the theoretical value. However, 83 % components were successfully aligned as Pt face up.