Kyo-Seon Kim

Controlled synthesis and biomolecular probe application of gold nanoparticles

In addition to their optical properties, the ability of gold nanoparticles (Au NPs) to generate table immobilization of biomolecules, whilst retaining their bioactivities is a major advantage to apply them as biosensors. Optical biosensors using Au NPs are simple, fast and reliable and, recently, they have been moving from laboratory study to the point of practical use. The optical properties of Au NPs strongly depend on their size, shape, degree of aggregation and the functional groups on their surface. Rapid advances in the field of nanotechnology offer us a great opportunity to develop the controllable synthesis and modification of Au NPs as well as to study on their properties and applications. The size-controlled growth of Au NPs requires the isotropic growth on the surface of Au nuclei whereas anisotropic growth will induce the formation of Au NPs of varying shape. Functionalized Au NPs provide sensitive and selective biosensors for the detection of many targets, including metal ions, small organic compounds, protein, DNA, RNA and cell based on their optical, electrical or electrochemical signals. In this review, we will discuss the size- and shape-controlled growth and functionalization of Au NPs to obtain Au nanoprobes. The basis of the optical detection of Au nanoprobes and their applications in nucleic acid, protein detection and cell imaging are also introduced.

Functionalization of magnetic nanoparticles for biomedical applications

Interest in utilizing magnetic nanoparticles for biomedical treatments originates from their external controllability of transportation and movement inside biological objects and magnetic heat generation. Advances in nanoparticle and nanotechnology enable us to produce magnetic nanoparticles of specific morphology and to engineer particle surfaces to manipulate their characteristics for specific applications. Intensive investigations and developments have been carried out in improving the quality of magnetic particles, regarding their size, shape, size distribution, their magnetism and their surface. The magnetic nanoparticles with appropriate surface chemistry can conjugate various biomaterials such as drugs, proteins, enzymes, antibodies, or nucleotides to be used for numerous in vivo applications including MRI contrast enhancement, immunoassay, hyperthermia, drug delivery, and cell separation. Here we review both the key technical principles of magnetic nanoparticle synthesis and the ongoing advancement of biomedical treatments using magnetic nanoparticles, specifically, the advancement in controlled drug delivery and hyperthermia.

Effects of Process Variables on NOx Conversion by Pulsed Corona Discharge Process

We investigated the effects of several process variables (initial concentrations of NO, NH3, and H2O and electron concentration) on NOx conversion by the pulsed corona discharge process (PCDP). In the PCDP, most of the NO is converted into NO2 and, later, into HNO3 which reacts with NH3 to form NH4NO3 particles. We solved the model equations of chemical species in the PCDP considering 23 chemical species and 54 chemical reactions. As the initial NO concentration increases or electron concentration decreases, it takes a longer reactor length to remove the NOx by the PCDP. As the initial H2O, it takes a shorter reactor length to remove the NOx. As the initial NO and H2O and electron concentration decreases, or as the initial NH3 concentration increases, it takes a longer reactor length to consume the NH3 by the particle formation reactions. The information on the effects of several process variables on the plasma chemistry in NOx conversion can be the basis guideline to develop a more efficient PCDP and this study can be extended to obtain the information on particle characteristics of ammonium salts.

Effects of Gas Flow on Particle Growth in Silane RF Discharges

The effects of gas flow on particle growth in silane RF discharges in a plasma chemical vapor deposition (PCVD) reactor with a shower-type powered electrode are studied using an in situ two-dimensional polarization-sensitive laser-light-scattering method. Particle growth depends on both the production of short-lifetime radicals and the loss of neutral clusters in the radical production region around the plasma/sheath boundary near the powered electrode. Gas flow of a velocity above about 6 cm/s is effective in suppressing particle growth because of increase in loss of neutral clusters. Moreover, particles larger than 120 nm in size that flow to the plasma/sheath boundary near the grounded electrode are found to pass through the sheath. This implies that such particles may deposit on film surfaces for PCVD reactors with the shower-type powered electrode.

The changes in particle charge distribution during rapid growth of particles in the plasma reactor.

The changes in particle charging were investigated during the rapid growth of particles in the plasma reactor by the discrete-sectional model and the Gaussian charge distribution function. The particle size distribution becomes bimodal in the plasma reactor and most of the large particles are charged negatively, but some fractions of small particles are in a neutral state or even charged positively. As the particles accumulate in the plasma reactor, the amount of electrons absorbed onto the particles increases, while the electron concentration in the plasma decreases. As the mass generation rate of small particles (monomers) decreases or as the initial electron concentration increases, the electron concentration in the plasmas increases and the particle charge distribution is shifted in the negative direction and the fraction of particles charged negatively and the average number of electrons per particle increase. With the decrease in monomer diameter, the electron concentration decreases in the beginning of plasma discharge, but, later, increases. For high mass generation rate of monomers or for low initial electron concentration or for small monomer diameter, the fraction of particles in a neutral state increases and the particle size distribution becomes broader.

Particle growth and transport in silane plasma chemical vapour deposition

The model equations for particle formation, growth and transport were proposed for silane plasma chemical vapour deposition and were solved numerically. We included the plasma chemistry of silane, particle nucleation by cluster formation, aerosol dynamics and transport of chemical species and particles. The evolutions of gaseous species and particles along the reactor were presented for several conditions of process variables such as reactor pressure, total gas flow rate and electric field strength. To reduce the CPU time in numerical simulation, we used lower values of electric field strength in the sheath region then the actual values and analysed the effects of electric field strength qualitatively. It was found that the concentration profiles of positive ions show peaks at the centre of the plasma reactor, whereas most of the negative ions are located in the bulk plasma region owing to the electrostatic repulsion from the sheath region. Most of the particles in the plasma reactor are located around the sheath boundaries, owing to the balance of the electrostatic force and the ion drag force. As the reactor pressure increases, the contaminant concentration and diameter increase in the plasma reactor. The lower the total gas flow rate the higher the particle concentration and the larger the particle diameter. The particle concentration and diameter in the plasma reactor increase abruptly as the electric field strength in the sheath region increases.

Modeling of rapid particle growth by coagulation in silane plasma reactor

The rapid particle growth by coagulation of particles in silane plasma reactor was analyzed, considering the Gaussian distribution function for particle charges. The model equations for particle growth were based on the experimental observations that the large predator particles of a few hundred nms are quite monodisperse and are composed of many small, tiny protoparticles of a few nms. The effects of process conditions such as protoparticle size, residence time, and mass generation rates of predator and protoparticles on particle growth in plasma reactor were analyzed theoretically. Based on the Gaussian distribution function of particle charges, most of the large predator particles in plasma reactor are found to be charged negatively, but some fractions of small, tiny protoparticles are in neutral state or even charged positively. Significant amount of negative charges in plasma reactor exist on the protoparticles. The predator particles charged negatively are believed to coagulate very fast with the pr...

Modeling of the evolutions of negative ions in silane plasma chemical vapor deposition for various process conditions

The evolutions of negative ions in the silane plasma chemical vapor deposition (PCVD) reactor for semiconductor processing were analyzed, considering the effects of chemical reactions, fluid convection, diffusion and electrical migration. The 23 plasma chemical reactions and 18 chemical species which might be important for the evolutions of negative ions were considered in this analysis. The governing equations were solved numerically. Most of the negative ions are located in the bulk plasma region and the concentrations of negative ions are almost zero in the sheath regions, as they are expelled from the sheath regions to the bulk plasma by electrostatic repulsion. The concentrations of negative ions at the downstream sheath boundary were higher than those at the upstream sheath boundary due to the effect of convection. As the reactor pressure increases, the concentrations of neutrals and positive ions increase, but the concentrations of negative ions decrease, based on the reaction chemistry proposed in this study. As the electric field strength increases, the negative ion concentrations increase, because more negative ions are contained in the bulk region by the stronger electrostatic repulsive forces.

The Factors Affecting the Particle Distributions Inside the Silane PCVD Reactor for Semiconductor Processing

The distributions of particles inside the silane plasma chemical vapor deposition (PCVD) reactor were theoretically investigated by analyzing the transport phenomena of particles for various plasma conditions. We included the effects of fluid convection, particle diffusion, and external forces (ion drag, electro static, and gravitational forces) onto the particles to analyze the movements of particles inside the plasma reactor. Initially, we assumed that the particles are uniformly distributed inside the plasma reactor and showed how these particles move and how they are distributed for various plasma conditions. The dominant force for the particle movement is the electrostatic force in the sheath region and the ion drag force in the bulk plasma region. Both the electrostatic and ion drag forces are towards the sheath boundaries and most of the particles are concentrated in the regions near the sheath boundaries by the balance of both forces, but the particle concentrations in the sheath region and in the bulk plasma region are almost 0. The particle concentrations at the down stream sheath boundary become higher than at the upstream sheath boundary by the effect of fluid convection. As the electric field strength increases, the particles are pushed more strongly towards the bulk plasma region and the peaks of particle concentrations are shifted more away from the electrodes. As the particle diameter increases from 0.1 mu m to 10 mu m, the relative importance of fluid convection on the particle movement becomes more significant than those of particle diffusion, ion drag force, and electrostatic force and the particle concentrations at the down stream sheath boundary increase, while those at the upstream sheath boundary decrease. It is found that the movements of negative ions as well as the positive ions are also important for determining the ion drag force onto the particles in silane PCVD.

Production of Monodisperse Nanoparticles and Application of Discrete-Monodisperse Model in Plasma Reactors

The particle growth in plasma reactor were investigated by using the discrete-monodisperse (D-M) model for various process conditions. The monodisperse large sized particle distribution predicted by the D-M model are in good agreement with the large sized particles by the discrete-sectional model and also in the experiments by Shiratani et al. (1996). Some fractions of the small size particles are in a neutral state or even charged positively, but most of the large sized monodisperse particles are charged negatively. As the mass generation rate of monomers increases, the large sized particles grow more quickly and the production rate of nanoparticles of 100nm by plasma reactor increases. As the initial electron concentration or the monomer diameter increases, it takes longer time for the large sized particles to grow up to 100nm, but the large sized particle concentration of 100nm increases and the resulting production rate of large sized particles of 100nm increases. As the residence time increases, the time for the large sized particles to grow up to 100nm decreases and the large sized particle concentration of 100nm increases and, as a result, the production rate of large sized particles of 100nm increases. We propose that the plasma reactor can be a good candidate to produce monodisperse nanoparticles.