Biosensing in a microelectrofluidic system using optical whispering-gallery mode spectroscopy

Label-free detection of biomolecules using an optical whispering-gallery mode sensor in a microelectrofluidic channel is simulated. Negatively charged bovine serum albumin is considered as the model protein analyte. The analyte transport in aqueous solution is controlled by an externally applied electrical field. The finite element method is employed for solving the equations of the charged species transport, the Poisson equation of electric potential, the equations of conservation of momentum and energy, and the Helmholtz equations of electromagnetic waves. The adsorption process of the protein molecules on the microsensor head surface is monitored by the resonance frequency shifts. Frequency shift caused by temperature variation due to Joule heating is analyzed and found to be negligible. The induced shifts behave in a manner similar to Langmuir-like adsorption kinetics; but the time constant increases due to the presence of the external electrical field. A correlation of the frequency shift, the analyte feed concentration in the solution, and the applied voltage gradient is obtained, in which an excellent linear relationship between the frequency shift and the analyte concentration is revealed. The applied voltage gradient enhances significantly the analyte concentration in the vicinity of the sensor surface; thus, the sensor sensitivity which has a power function of the voltage gradient with exponent 2.85 in the controlled voltage range. Simulated detection of extremely low protein concentration to the pico-molar level is carried out.     

Efficient capture of circulating tumor cells with a novel immunocytochemical microfluidic device

Ability to perform cytogenetic interrogations on circulating tumor cells (CTCs) from the blood of cancer patients is vital for progressing toward targeted, individualized treatments. CTCs are rare compared to normal (bystander) blood cells, found in ratios as low as 1:10⁹. The most successful isolation techniques have been immunocytochemical technologies that label CTCs for separation based on unique surface antigens that distinguish them from normal bystander cells. The method discussed here utilizes biotin-tagged antibodies that bind selectively to CTCs. The antibodies are introduced into a suspension of blood cells intending that only CTCs will display surface biotin molecules. Next, the cell suspension is passed through a microfluidic channel that contains about 9000 transverse, streptavidin coated posts. A CTC making contact with a post has the opportunity to engage in a biotin-streptavidin reaction that immobilizes the cell. Bystander blood cells remain in suspension and pass through the channel. The goal of the present study is to establish the technical performance of these channels as a function of antigen density and operating conditions, especially flow rate. At 18 μL/min, over 70% of cells are captured at antigen densities greater than 30 000 sites/cell while 50% of cells are captured at antigen densities greater than 10 000. It is found that lower flow rates lead to decreasing cell capture probabilities, indicating that some streamlines develop which are never close enough to a post to allow cell-post contact. Future modeling and streamline studies using computational fluid dynamics software could aid in optimization of channel performance for capture of rare cells.     

Applying an optical space-time coding method to enhance light scattering signals in microfluidic devices

An "optical space-time coding method" was applied to microfluidic devices to detect the forward and large angle light scattering signals for unlabelled bead and cell detection. Because of the enhanced sensitivity by this method, silicon pin photoreceivers can be used to detect both forward scattering (FS) and large angle (45-60°) scattering (LAS) signals, the latter of which has been traditionally detected by a photomultiplier tube. This method yields significant improvements in coefficients of variation (CV), producing CVs of 3.95% to 10.05% for FS and 7.97% to 26.12% for LAS with 15 μm, 10 μm, and 5 μm beads. These are among the best values ever demonstrated with microfluidic devices. The optical space-time coding method also enables us to measure the speed and position of each particle, producing valuable information for the design and assessment of microfluidic lab-on-a-chip devices such as flow cytometers and complete blood count devices.     

External and Internal Instantiation of Abstract Information Facilitates Transfer in Insight Problem Solving

Four studies were conducted to examine how instantiation of abstract statements facilitates solutions to insight problems. The first two experiments explored the effects of external instantiation (adding a concrete example to the abstract source information) on transfer. Providing an example along with the abstract source statement fostered transfer of analogous solutions. Moreover, adding a complete concrete instantiation to an abstract statement produced greater transfer than adding only specific items to illustrate the abstract terms. The second two experiments examined the effects of internal instantiation (encouraging learners to generate their own concrete examples of the abstract information) on transfer. This factor, too, facilitated problem solving. Generating examples to instantiate the abstract statement yielded even better transfer than simply informing participants of the relationship between the abstract statements and the target problems. These findings suggest that both external and internal instantiation facilitate transfer by promoting mental processes associated with implementing the source analogs.     

What every teacher needs to know...

作为一名教师, 你是怎样理解学习,以及如何学习这两个概念;你可曾有勇气去尝试全新的教学理念——做学生成长期的教练,不仅只传授实际知识,更乐于和学生一起分享学习的方法、技巧,以及终生受益的绝招。     

人类认知的局限与跨文化传播--一个致力于跨文化融洽交流的计划

本文就世界文化课程内容的具体设置,及联合大学与传媒以更好实现课程积极目标等问题进行了探讨.文中通过多层次的论证强调指出人们始终持有相异或相冲突的宗教、哲学以及意识形态,尚没有一种普世真理足以使世间所有人心悦诚服.即便是广泛接受和运用中的科学知识,其发展亦受阻于人类本身的局限而不可确定.尽管科学在前沿问题研究上竞争激烈,也仍然无法回答和消除所有的问题和差异.因此,从全球或泛人类立场观之,人类现有的知识与理解能力具有不确定和不完整的特点,而这样的特点浸透在所有的具体文化信仰之中.认识到共同局限性的人们--尤其是政界的领导人--亟需摒弃极端的文化分离思想,以更宽容理解的心态进行思考和行动,这样才能避免不同民族及不同国家间的不断冲突和互相伤害.     

这个世界没有最完美

亲爱的朋友,感谢你请我去你的新公司做客。公司虽然不大,但看得出你对它倾注了全部心思。你问我,对公司有什么样的看法。我想对你讲我观察的一些细节。     

属于别离的四个词语

认识小信是在大二的夏天。那时候广院门口有个叫“西街”的小市场,破破烂烂的,生意却特别火暴。我记得街口有个卖青菜肉丝炒饭的,连店面都没有,生意却火暴得不行。小信就是这家卖炒饭的旁边的一个西瓜摊主。我们初次见她都有些惊讶,对于一个瘦瘦小小的女生独自出来卖西瓜颇有怀疑,可事实证明小信的生意是那个夏天里西街上最好的。