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Rotation of Irregularly Shaped Liposome using Optical Tweezers
하청일,박혁규,이행섭 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.II
In recent years, optical tweezers have been used in various fields as attractive tools for trapping and manipulating small particles such as colloidal particles, bacteria, red blood cells, etc. However, most theories and experiments relating to optical tweezers mainly focus on the function of trapping and transferring objects spatially. In this work, we study the rotational motion of irregularly shaped biological material which is not birefringent, in terms of forming birefringence and optical torque.
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하청일,김성진,박혁규 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.4
Transportation and delivery of microscopic materials in very small and complex systems such as biological organisms are mainly done by physical diffusion. This phenomenon in a fluid system with a low Reynolds number can be explained using the Stokes-Einstein relation <i>D</i> = <i>k<sub>B</sub>T</i>/β, where <i>D</i> is the diffusion coefficient, <i>T</i> is the temperature of the system, and β is the viscous friction coefficient of the background fluid. For a spherical particle with radius a in a fluid of viscosity η, β = 6πηa. As far as we know, all the experimental tests of this relation before ours measured only <i>D</i>, η, a, and <i>T</i> due to the experimental difficulties in measuring β directly. In this research, we tested this relation from a different perspective. The diffusion coefficient <i>D</i> and the viscous friction coefficient β were experimentally measured in the same system by using a position tracking method and an oscillating optical tweezers technique, respectively. We found that our experimental results supported the Stokes-Einstein relation very well.
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이동윤,하청일,박혁규 한국물리학회 2011 새물리 Vol.61 No.4
When using optical tweezers, determing the exact value of the trap stiffiness is very important. In this work, displacements of micron-sized particles were measured as a function of time by using two different methods; a passive method that measured the trap stiffness of the trapped particle at a fixed position by using optical tweezers and an active method that measured the trap stifffness by forcing the trapped particle to oscillate. When using the passive method, the trap stiffnesses, which were determined from the Boltzmann distribution and from the power spectrum, were measured as 1.06 pN/μm and 1.07 pN/μm, respectively. When using the active method, the trap stiffnesses,which were obtained from data on the amplitude and from phase information on the trapped particle by using an lock-in amplifier, were both measured as 0.91 pN/μm. These trap stiffness values obtained from the two different methods are compared, and the differences are discussed 광집게를 이용할 때 포획 탄성계수의 크기를 정확하게 아는 것이 매우중요하다. 현재 포획 탄성계수를 결정하는 여러가지 방법들이 알려져있다. 하지만 그 방법들로 측정한 포획 탄성계수의 정량적인 비교연구는부족하다. 본 연구에서는 마이크론 크기의 입자를 수 피코뉴턴(pN)의힘으로 고정한채 포획 탄성계수를 측정하는 방법(수동 방법; passive method)과 광집게로 포획한 입자를 강제로 흔들어서 포획 탄성계수를측정하는 방법(능동 방법; active method)을 비교 분석해 보았다. 수동방법으로 얻은 데이터는 볼쯔만 분포와 파워 스펙트럼을 통해 분석하여포획 탄성계수를 각각 1.06 pN/㎛, 1.07 pN/㎛를 얻었다. 능동방법으로 얻은 데이터는 락인엠프을 이용해서 노이즈를 제거한 후에입자의 운동 진폭과 위상 정보로부터 포획 탄성계수를 둘 다 0.91pN/㎛얻었다. 본 연구에서는 두가지 방법에 따른 포획 탄성계수측정에 장단점을 비교하고 새로운 활용 방안을 제시하였다.
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Observation of Colloidal Particle Dynamics Near a Flat Wall by Using Oscillating Optical Tweezers
박혁규,하청일,Daniel Ou-Yang 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.3
We study the hydrodynamics of a micron-sized spherical particle positioned nearby a flat wall by using oscillating optical tweezers that trap and oscillate the colloidal particle. In this situation,the presence of the flat wall complicates the flow field surrounding the particle, so the force felt by the moving particle is quite different from the three dimensional hydrodynamics drag force,known as Stokes’ drag. However, in biological processes, this condition is ubiquitous and governs the biological particle hydrodynamics. In this work, we describe observations of confined particles dynamics by using oscillation optical tweezers and compare the results with known theories and other experimental data.
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