Calculation of optical trapping forces on dielectric spheres at an oil-water interface with ray-optics model

The transverse trapping forces on a dielectric sphere located at an oil-water interface are theoretically investigated with the ray-optics model. The transverse trapping forces rely on the internal property of the particle-interface system, and increase with either the decrease of three phase contact angles at the oil- water interface or the use of oil phase with low refractive index. The numerical results also show that the transverse trapping forces can be improved by either decreasing the numerical aperture of the microscope objective or shrinking the diameter of the trapping laser beam.     

对恐怖袭击事件记录数据的量化分析与研究

恐怖主义是人类的共同威胁,利用数据挖掘可以为反恐防恐提供有价值的信息支持.基于数据挖掘的思路,从恐怖袭击事件中提取能描述危险程度的特征属性,构建量化分级模型,并考虑准确率评价指标进行优化.通过组内平方和法分析改进高斯混合模型(GMM),对恐怖组织进行聚类分析,侦查出潜在最相关的嫌疑人.建立相关模型结合统计分析,得到恐怖袭击发生的主要原因、时空特性和蔓延特性,并对未来全球反恐态势进行预测,帮助反恐组织提高反恐的精准性和打击能力.     

Observing Nanometre Scale Particles with Light Scattering for Manipulation Using Optical Tweezers

Nanometre-scale particles can be manipulated using optical tweezers, but cannot be directly observed. We present a simple method that nanoparticles can be directly observed using optical tweezers combined with dark field microscopy. A laser beam perpendicular to a tightly focused laser beam for trap illuminates specimen and does not enter objective, nanoparticles in focal plane all can be directly observed in dark field because of light scattering. It is implemented that the polystyrene beads of diameter lOOnm can be directly observed and trapped.     

Measurement of interaction force between RGD-peptide and Hela cell surface by optical tweezers

Since RGD peptides (R: arginine; G: glycine; D: aspartic acid) are found to promote cell adhesion, they are modified at numerous materials surface for medical applications such as drug delivery and regenerative medicine. Peptide-cell surface interactions play a key role in the above applications. In this letter, we study the adhesion force between the RGD-coated bead and Hela cell surface by optical tweezes. The adhesion is dominated by the binding of α5β1 and RGD-peptide with higher adhesion probability and stronger adhesion strength compared with the adhesion of bare bead and cell surface. The binding force for a single α5β1 -GRGDSP pair is determined to be 16.8 pN at a loading rate of 1.5 nN/s. The unstressed off-rate is 1.65 × 10-2s-1 and the distance of transition state for the rigid binding model is 3.0 nm.     

光线庞加莱球法构建的结构光场及其传输特性研究

结构光场在光信息传输、显微成像以及微粒俘获中有重要作用.本文基于光线庞加莱球法结合不同花瓣数的梅花曲线构建了一类结构光束.根据光线庞加莱球法可计算这类光束在束腰面上的光强与相位分布，以及光束内外焦散线的分布.这些焦散线的特征表明梅花形结构光束具有无衍射与自修复的特性.进一步采用角谱衍射法和光线追迹研究了这类光束在空间中的传输特性.当梅花花瓣数为0时，该光束退化为拉盖尔-高斯光束；当花瓣数为1时，内焦散线汇集到两点，使光束具有无衍射特性.通过光线庞加莱球法获得其光线在空间传播的轨迹，直观地展示了光束被遮挡后的自修复特性.此外，本文还展示了花瓣数为5的结构光束，其内焦散线为十角星结构，该光束同样具有自修复特性.通过修改梅花曲线参数或选择其他庞加莱球面曲线可以构造更加复杂的结构光场.     

基于自回归模型的光阱中粒子运动模拟

通过分析光阱中颗粒位移信号特性, 建立描述粒子受限布朗运动过程的自回归模型, 进而提出了一种基于自回归模型的光阱中颗粒运动信号模拟的新方法. 对半径为1 μm的粒子处于光阱刚度分别为10, 20, 50 pN/μm 光阱时的位移信号进行了模拟, 得到的模拟位移信号的自相关函数与理论值相一致. 为了进一步阐明自回归模型的有效性, 在相同光阱参数下, 分别采用自回归模型与蒙特卡罗方法模拟光阱中微粒的位移信号, 采用功率谱法分别对两种模拟方法所得的微粒位移标定光阱刚度, 结果表明自回归模型方法能够取得和蒙特卡洛法相同的精度. 因此, 本文为分析光阱中粒子的随机运动提出了一种新的模拟方法, 可以用来对光阱中的噪声及特性进行分析. 关键词： 光阱 布朗运动 信号模拟 自回归模型     

Manipulation of Nanoparticles Using Dark-Field-Illumination Optical Tweezers with Compensating Spherical Aberration

Based on our previous investigation of optical tweezers with dark field illumination [Chin. Phys. Left. 25（2008）329] nanoparticles at large trap depth are better viewed in wide field and real time for a long time, but with poor forces. Here we present the mismatched tube length to compensate for spherical aberration of an oil-immersion objective in a glass-water interface in an optical tweezers system for manipulating nanoparticles. In this way, the critical power of stable trapping particles is measured at different trap depths. It is found that trap depth is enlarged for trapping nanoparticles and trapping forces are enhanced at large trap depth. According to the measurement, 70-nm particles are manipulated in three dimensions and observed clearly at large appropriate depth. This will expand applications of optical tweezers in a nanometre-scale colloidal system.     

细菌自体荧光检测装置的研究与设计

细菌感染会造成伤口愈合延迟，增加患者和医疗卫生系统的负担，因此非常需要对伤口细菌进行及时检测和适当的处理。基于细菌自发荧光原理，设计了一种对伤口常见细菌快速检测成像的系统，可用于辅助识别伤口细菌负荷和判断感染情况，无需采样培养或染色鉴定。使用智能手机采集细菌荧光图像，以405 nm LED作为细菌激发光源，配合荧光图像信息提取和定量算法能够快速识别提取图像上的感兴趣区域并对荧光信号进行量化，定位细菌荧光信号区域。梯度浓度实验证实了荧光强度与细菌浓度高度相关，荧光强度与浓度之间存在线性关系，随着细菌浓度的降低，荧光信号强度呈下降趋势，系统最小检测限约为10⁵ CFU/mL。与传统细菌检测方法相比，本装置具有操作简单、检测速度快、成本低等特点，为伤口细菌检测提供了一种新的手段。