Creation of Novel Nano-Bio Conjugates for Life Sciences Using Gas-Liquid Phases Plasmas
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Creation of Novel Nano-Bio Conjugates for Life Sciences Using Gas-Liquid Phases Plasmas Toshiro Kaneko and Rikizo Hatakeyama Department of Electronic Engineering, Tohoku University, Sendai 980-8579, Japan ABSTRACT The gold nanoparticles (AuNPs) conjugated with carbon nanotubes (CNTs) and/or biomolecules such as DNA are synthesized using a novel plasma technique combined with introduction of ionic liquids or aqueous solution for application to life sciences. First, we successfully generate the gas-liquid interfacial discharge plasma (GLIDP) using an ionic liquid, in which the large sheath electric field is formed on the ionic liquid and the plasma ion irradiation to the ionic liquid with high energy is realized. Second, it is found that the high energy ion irradiation to the ionic liquid is effective for the synthesis of the AuNPs. Furthermore, the controlled ion irradiation to the ionic liquid including a carboxyl group can realize the density-controlled synthesis of the AuNPs on the CNTs by dissociation of the ionic liquid and the controlled functionalization of the CNTs by the dissociated carboxyl group. Third, the size- and morphology-controlled AuNPs covered with DNA are synthesized using the GLIDP with aqueous solution, where DNA prevents the AuNPs from further clustering, resulting in the small-sized AuNPs. The synthesized AuNPs conjugated with DNA can be encapsulated into the CNTs using the DC electric field. The CNTs work as vectors to deliver DNA into living cells because the CNTs have the unique ability to easily penetrate cell membranes with low cytotoxicity. INTRODUCTION One of the promising plasma processes for life sciences is a creation of nano-bio conjugates applied to drug delivery systems, gas sensors, field-effect transistors, and so on. In particular, the synthesis of various kinds of nanoparticles using gas-liquid phase plasmas [1, 2] is advantageous in that toxic stabilizers and reducing agents are unnecessary and the process is continuous during the plasma irradiation. In these methods, although it has been reported that the metal salt is reduced by electrons or active hydrogen, the optimal plasma conditions in terms of the synthesis rate, size control, and simplicity remain unclear because the high voltage discharge operated at atmospheric pressure and the consequential dynamic behavior of the gas-liquid interface prevent us from analyzing the precise properties of the plasma at the interfacial region. We have generated novel gas-liquid interfacial discharge plasmas (GLIDPs) under a low gas pressure condition [3, 4] by utilizing the unique properties of ionic liquids [5] which allow a fully-ionized plasma state, extremely low vapor pressure, and high heat capacity. In this paper, the dynamic behavior of charged particles and dissociation of the ionic liquid as a result of the GLIDPs are discussed under conditions ranging from low gas pressures to atmospheric pressure [6]. Recently, on the other hand, highly-ordered structures of metal nanoparticles have attracted much attention due to their h
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