Liu Zhao-Lin

Effects of Spherical Aberration on Optical Trapping Forces for Rayleigh Particles

The trapping force on Rayleigh particles in an optical tweezers system with an oil immersion objective is calculated by an electromagnetic model. The results indicate that the stability of particles trapped will be affected by spherical aberration, which is caused by refractive difference between objective oil and water solution, when the specimen manipulated is suspended in a water solution. The trapping force and depth of potential well will decrease and the minimum of laser power for ensuring the stability of particles trapped will increase with the enhanced trapping depth.

Mechanical Properties of Breast Cancer Cell Membrane Studied with Optical Tweezers

Membrane tethers are extracted from breast cancer cells using a force generated by an optical trap. It is experimentally obtained that the radius of tether is about 0.1 μm and the static tether force is about 8.5 pN. Calculations based on the experimental measurements give a bending modulus for the tether of 1.35×10−19 N.m and a surface membrane tension of 6.76×10−6 N/m in the breast cancer cell. The treatment with cytochalasin D results in the decreasing bending modulus and decreasing apparent surface tension. When the membrane protein caveolin is over-expressed, similar cases occur in bending modulus and apparent surface tension. In addition, the viscous resistance coefficient of the membrane is calculated to be 1.15 pN.s/μm according to the dynamic tether forces obtained under different pulling velocities.

Measurement of Breaking Force of Fluorescence Labelled Microtubules with Optical Tweezers

Under illumination of excitation light, the force that can make fluorescent dye-labelled microtubules break up is measured by using dual-beam optical tweezers. It is found that this force is about several piconewtons, which is two orders of magnitude smaller than that without fluorescence label. Microtubules can be elongated about 20% and the increase of the tensile force is nonlinear with the microtubule elongation. Some qualitative explanations are given for the mechanisms about the breakup and elongation of microtubules exposed to excitation light.

Broadening of Photoluminescence by Nonhomogeneous Size Distribution of Self-Assembled InAs Quantum Dots

The photoluminescence spectrum (PL) of InAs quantum dots (QDs) at 80 K is studied by comparison between the theoretical calculation and experimental measurement. The Gaussian line shape is used to approximate the size distribution of QDs. Its mean volume and the standard size deviation are well correlated with the peak and full width at half maximum (FWHM) of the PL spectrum. The experimental PL spectrum is well reproduced by the theoretical model based on the effect mass approximation including the size distribution without any adjustable parameters. Compared with the standard size deviation value σs = 9 × 10-2 determined by atomic force microscopic method a small value σs = 7 × 10-2 is obtained by the best fitting process from the measured and calculated PL spectra.

Membrane Tether Formation on a Cell Surface with Reservoir

We propose a mathematical model to analyse the membrane tether formation process on a cell surface with reservoir. Based on the experimental results, the membrane reservoir density of breast cancer cell was obtained, ? = 8.02. The membrane surface viscosity between membrane and environment ? is 0.021(pN.s/?m3), and the static force F0 = 5.71?pN.