GOLD NANOPARTICLE PATTERNING BY SELF-ASSEMBLY AND TRANSFER FOR LSPR BASED SENSING T. Ozaki, K. Sugano, T. Tsuchiya, O. Tabata Department of Micro Engineering, Kyoto University , Kyoto, JAPAN ADVISER: Dr .CHENG-SHINE-LIU REPORTER: SRINIVASU V P & HSIEH,HSIN-YI STUDENT ID: 9733881 & 9735803

OUTLINE Abstract Introduction Process overview Template assisted self assembly Results and discussion Transfer of nanoparticles LSPR characteristics of assembled Nanoparticle patterns Conclusion

Abstract Pattern formation Dot and line pattern Assembled particle pattern transfer Localized Surface Plasmon Resonance (LSPR)

Introduction Characteristics of nanoparticles Conventional nanopatterning techniques Advantages of proposed method 60-nm diameter gold nanoparticles

PROCESS OVERVIEW 1) Self-assembly step 2)Transfer step

Template assisted self assembly Mechanism of TASA Aqueous particle dispersion Capillary force

Result and discussion Effect of cross sectional shape Relation between yield and concentration The self-assembly yield is defined as the ratio of the total dot-patterned area to the properly assembled area.

SEM images of each cross-section before resist removal SEM images of each cross-section before resist removal. Shape A, B and Shape C were fabricated by SF6 and CF4 dry etching, respectively.

concentration of particle dispersion and a yield of self-assembly. Relation between a cross-sectional profile of a template pattern and a yield of self-assembly (the concentration of particle dispersion: 0.002 wt%) Relation between concentration of particle dispersion and a yield of self-assembly.

Capillary force

Template transfer process SiO2/Si substrate with assembled particles Uncured PDMS was poured onto the template (base compound : curing agent = 10:1) (3) Degassing for 30 min (4) Curing PDMS (60 ℃ for 4 hr) (5) Peel off PDMS

Au self-assemble on the template Transferred pattern on the PDMS (> 90% successful)

LSPR principle Noble metal nanoparticles exhibit a strong UV-vis absorption band that is not present in the spectrum of the bulk metal. This absorption band results when the incident photon frequency is resonant with the collective oscillation of the conduction electrons and is known as the localized surface plasmon resonance (LSPR). E(λ) = extinction (viz., sum of absorption and scattering) NA = area density of nanoparticles a = radius of the metallic nanosphere em = dielectric constant of the medium surrounding the metallic nanosphere λ = wavelength of the absorbing radiation εi = imaginary portion of the metallic nanoparticle's dielectric function εr = real portion of the metallic nanoparticle's dielectric function χ = 2 for a sphere (aspect ratio of the nanoparticle)

LSPR characteristics These mechanisms are: resonant Rayleigh scattering from nanoparticle labels in a manner analogous to fluorescent dye labels nanoparticle aggregation charge-transfer interactions at nanoparticle surfaces local refractive index changes This approach has many advantages including: a simple fabrication technique that can be performed in most labs real-time biomolecule detection using UV-vis spectroscopy a chip-based design that allows for multiplexed analysis

LSPR applications Sensor adsorption of small molecules ligand-receptor binding protein adsorption on self-assembled monolayers antibody-antigen binding DNA and RNA hybridization protein-DNA interactions

LSPR scattering spectrum Dot pattern aperture Schematic of dark-field microscope line pattern

Dark-field microscope Diagram illustrating the light path through a dark field microscope. Light enters the microscope for illumination of the sample. A specially sized disc, the patch stop (see figure) blocks some light from the light source, leaving an outer ring of illumination. The condenser lens focuses the light towards the sample. The light enters the sample. Most is directly transmitted, while some is scattered from the sample. The scattered light enters the objective lens, while the directly transmitted light simply misses the lens and is not collected due to a direct illumination block (see figure). Only the scattered light goes on to produce the image, while the directly transmitted light is omitted.

Scattering spectrums of line patterns w/o polarization line pattern w/o polarization Vacuum air methanol water ethanol hexane toluene xylene Refractive index 1.0 1.0008 1.329 1.330 1.36 1.3749 1.4963 1.498

Spectrum peak vs. refractive index Polarizing cube beamsplitter p-polarized light s-polarized light Non-polarized light non-polarized light p-polarized light s-polarized light

Conclusions Self-assembly nanoparticle pattern formation method can be realized more than 90% onto 200 x 200 dots. Dot and line patterns of gold nanoparticles in diameter of 60 nm were transferred on a flexible PDMS substrate. LSPR sensitivity will be possible by controlling patterns of the assembled nanoparticles. In the future, it is expected that this method will realize novel MEMS/NEMS devices with nanoparticles patterns on various 3D microstructures made of various materials via a carrier substrate.