Biomedical subjects

Byung Jun Yoon

Publications and source records attributed to Byung Jun Yoon.

5 recordsLinked to original sources

PubMed2006

Control of particle-deposition pattern in a sessile droplet by using radial electroosmotic flow.

In this technical note, we report an experimental investigation of radial electroosmotic flow (EOF) as an effective means for controlling particle-deposition pattern inside an evaporating droplet, which has a potential application to biochemistry and analytical chemistry especially for sample preparation steps. Using the microelectrode, which consists of the circular electrode around the rim of droplet and the point electrode at the center of the droplet, we generate the radial electric field at the bottom of the electrolyte droplet. The electric field developed between the center electrode and the circular electrode causes a radial EOF in the vicinity of the bottom of the droplet. By changing the applied voltage, the strengths and directions of the radial EOF are controlled at one's own discretion, and thus, we can modify the solute distribution inside the droplet during evaporation. When the radial EOF compensates the natural outward flow at a suitable choice of electrical voltage, the particles are uniformly distributed at the entire droplet spot. Moreover, with strong radial EOF, all the particles are deposited at the center rather than at the rim. We also carry out a simple theoretical investigation of flow field inside the droplet with Smoluchowski slip velocity condition to show how the particles travel during evaporation.

Electroosmosis↗

PubMed2006

Electrophoretic mobility equation for protein with molecular shape and charge multipole effects.

We derive a simple formula for the free solution electrophoretic mobility of protein by including both molecular shape and charge distribution effects. The molecular shape of protein is described by a deformed sphere model, while the charge distribution is represented in terms of net charge, charge dipole, and charge quadrupole. The deformed sphere model approximates the radial coordinate of the protein surface as a simple quadratic equation based on the atomic coordinate data. Charge dipole does not affect the mobility of protein. Combined with the quadratic coefficients of the surface equation, charge quadrupole affects the mobility. When the charge quadrupole contribution is negligible, the mobility equation simplifies to the Henry equation in which the sphere radius is replaced with the hydrodynamic radius of protein. The deformed sphere model predicts correctly the hydrodynamic radius of protein from the atomic coordinate data. The hydrodynamic radius is not the radius of sphere of equal volume but the effective radius that correlates with the translational diffusivity of protein. To illustrate the utility of our mobility equation we study the electrophoresis of lysozyme and compare our results with previously published works.

Electrophoresis↗

PubMed2003

High-order field electrophoresis theory for a nonuniformly charged sphere.

An electrophoresis theory is developed for a rigid sphere in a general nonuniform electric field. The zeta potential distribution and the double-layer thickness are both arbitrary. The zeta potential of the sphere is assumed to be small so that the deformation of the double layer can be neglected. Explicit expressions for the translational and rotational velocities of the sphere are derived in terms of the multipole moments of the zeta potential distribution and the tensor coefficients of the applied electric field. The presence of the kth-order component in the electrical potential field applied to the sphere results in a translation of the sphere only when the sphere possesses the (k-1)th- or (k+1)th-order multipole moments of the zeta potential distribution. In addition, the kth-order component in the electrical potential field causes a rotation of the sphere only when the sphere possesses the kth-order moment of the zeta potential distribution. As an illustrative example for the utility of our theory, we theoretically devise an electrophoresis analysis scheme for estimating the dipole moment of a dipolar sphere by observing the electrophoretic translation of the sphere in a quadratic potential field.

Journal Article↗

PubMed2002

Electrophoretic motion of a slightly deformed sphere with a nonuniform zeta potential distribution.

Electrophoretic motion is analyzed for a rigid, slightly deformed sphere with a nonuniform zeta potential distribution. Hydrodynamics and electrostatics solutions for the deformed sphere with an arbitrary double-layer thickness are determined by using the domain perturbation method. The surface shape and the zeta potential distribution for the deformed sphere are expressed by using the multipole expansion representation. In terms of monopole, dipole, and quadrupole moments of the surface shape and the zeta potential distribution, explicit expressions are obtained for the translational and rotational electrophoretic mobility tensors. The ensemble average for the mobility of the deformed sphere with a uniform orientation distribution is also derived. The utility of the general mobility expression is demonstrated by studying the electrophoretic motion of axisymmetric and ellipsoidal particles. The translational and rotational mobilities of axisymmetric particles are both affected by the monopole, dipole, and quadrupole moments of the zeta potential. For ellipsoidal particles, however, the dipole moment of the zeta potential does not affect the translational mobility, while the rotational mobility depends only on the dipole moment. The mobility of the deformed sphere with either a thick or a thin double layer is also derived.

Journal Article↗

PubMed2001

Iterative Solution Method for the Linearized Poisson-Boltzmann Equation: Indirect Boundary Integral Equation Approach.

An iterative solution scheme is proposed for solving the electrical double-layer interactions governed by the linearized Poisson-Boltzmann equation. The method is based on the indirect integral equation formulation with the double-layer potential kernel of the linearized Poisson-Boltzmann equation. In contrast to the conventional direct integral equation approach that yields Fredholm integral equations of the first kind, the indirect integral equation approach yields well-posed Fredholm integral equations of the second kind. The eigenvalue analysis reveals that the spectral radius of the double-layer integral operator is always less than one. Thus, iterative solution schemes can be successfully implemented for solving the electrical double-layer interactions for very large and complex systems. The utility of the iterative indirect method is demonstrated for several examples which include spherical and spheroidal particles. Copyright 2001 Academic Press.

Journal Article↗