Preface to Special Topic: Dielectrophoresis

This Special Topic section is on dielectrophoresis, a growing area of widespread interest and relevance to the microfluidics and nanofluidics community.There was a time when the arrival of a telegram from the local post office would foreshadow a step-function change in one’s equilibrium. An internet service provider can now deliver the same effect, as illustrated by an unexpected e-mail from Leslie Yeo inquiring if I would “be interested in guest editing a special issue of Biomicrofluidics on recent advances in dielectrophoresis (DEP).” Flattery directed towards vanity can produce interesting results—which I hope this special issue of Biomicrofluidics demonstrates. The rationale for this special issue is the belief of the journal’s Editors (Dr. Chia Chang and Dr. Leslie Yeo) that dielectrophoresis is a growing area of widespread interest and relevance to the microfluidics and nanofluidics community. Papers, both fundamental and applied, were solicited from the leaders working across this broad interdisciplinary area of research. I was delighted by the positive responses of those whose invited contributions appear in this special issue—efforts certainly not motivated by vanity but through enthusiasm for the subject. Some of those invited to contribute were unable to do so because of other demands on their time. Ongoing advances being made in DEP, especially in its various applications, will surely merit another special issue in the future and hopefully include contributions from those unable to do so now.Two of the papers in this special issue address fundamental aspects of dielectrophoresis (DEP), namely the influences on DEP from electrical double-layers and from particle-particle interactions. Consideration of electrical double layers associated with charged particle surfaces is particularly important for nanoparticles because their effective polarizabilities, associated with field-induced dynamics of the counterions and co-ions in the double layer, can dominate over the intrinsic polarizability of the particle itself. This can influence, for example, to what extent the observation of changes in the DEP crossover frequency (marking the transition between positive and negative DEP) can be relied upon in new immunoassays based on the DEP behavior of functionalized nanoparticles. By considering the electrodynamics of double layers, Basuray et al.¹ propose a theory to predict how the DEP crossover frequency will vary as a function of particle size and the ionic strength of the suspending electrolyte. In their paper, Sancho et al.² derive a theoretical model to describe how particle-particle interactions (e.g., “pearl-chaining”) influence the DEP crossover frequency value. This model also describes well the changes in electrorotation and a newly observed precession effect as particles approach each other under the influence of a rotating field.DEP at the nanoscale is also addressed in contributions from the groups of Ralph Hölzel, Junya Suehiro, and Karan Kaler. Thus, Henning et al.³ describe a new method, based on the measurement of capacitance changes between planar microelectrodes, for the automatic acquisition of the DEP properties of nanoparticles without the need for labeling protocols or visual observations. Suehiro⁴ describes how DEP can be employed as a bottom-up approach for fabricating nanomaterial-based devices such as a carbon nanotube gas sensor and a ZnO nanowire photosensor. Kaler et al.⁵ describe how the DEP manipulation of miniscule amounts of polar aqueous samples, a method known as liquid-DEP, can be used for on-chip bioassays, such as nucleic acid analysis, and through parallel sample processing offer the potential for conducting automated multiplexed assays. The use of DEP to selectively trap and separate cells has been investigated over many years, and contributions from the groups of Hywel Morgan, Ana Valero, Masau Washizu, and Gerard Markx describe the latest advances and applications. Thomas et al.⁶ describe a new automated DEP cell trap design for the isolation, concentration, separation, and recovery of human osteoblast-like cells from a heterogeneous population. Recovery of small populations of human osteoblast-like cells with a purity of 100% is demonstrated. A cell-sorting device, based on the opposition of DEP forces that discriminates between cell types according to such properties as their membrane permittivity and cytoplasm conductivity, is described by Valeroet al.⁷ The versatility of the device is demonstrated by synchronizing a yeast cell culture at a particular phase of the cell cycle. Gel et al.⁸ describe a DEP-assisted cell trapping method for fusing pairs of cells in an array of micro-orifices. This method produces not only a high yield of viable cell fusants, but also allows for subsequent study of postfusion cell development. Zhu et al.⁹ describe a DEP-based microfluidic separation system in which dead and active cells can be collected from a given cell suspension, whilst at the same time eluting dormant cells. In the second paper from Gerard Markx’s group, Zhu et al.¹⁰ demonstrate that the rate-limiting resuscitation of a colony of dormant bacteria is determined by the diffusion of a resuscitation-promoting factor into the colony interior. This study involved the artificial engineering of different sizes and shapes of bacterial aggregates using DEP forces. Finally, in my own contribution,¹¹ I have attempted to summarize the growing output of DEP publications in terms of their contributions to the theory, technology, and applications of DEP.     

Preface to special topic: optofluidics

This Special Topic section of Biomicrofluidics is on optofluidics or micro-optofluidic systems (MOFS), a burgeoning technology that aims to manipulate light and fluid at microscale and exploits their interaction to create highly versatile devices and integrated systems. This special issue puts together various contributed articles focusing on optofluidics or MOFS, which help inspire new research ideas and innovation in the microfluidics and nanofluidics community.     

Preface to the special topic on topological insulators

<正>The most important aspect of condensed mater physics in the last century has been the classiication of quantum states in terms of spontaneous symmetry breaking.In 1980,the quantum Hall state—which is independent of material details and topologically diferent from the previously known states of mater—was discovered in the two-dimensional electron gas under an external magnetic ield.Two years later,the fractional quantum     

Preface to Special Topic: Microfluidics in cell biology and tissue engineering

In this special issue of Biomicrofluidics, a wide variety of applications of microfluidics to tissue engineering and cell biology are presented. The articles illustrate the benefits of using microfluidics for controlling the cellular environment in a precise yet high rate manner using minimum reagents. The topic is very timely and takes a stab at portraying a glimpse of what is to come in this exciting and emerging field of research.     

Preface: mechanical perturbations induced quench: a challenge of superconductor mechanics

<正>Superconducting materials have been gradually applied in many areas including energy,transportation,medical imaging and communication.Among them,superconducting magnets that can generate a strong magnetic field above 10 Tesla with absolute advantages of higher quality,lower energy loss,and smaller volume,have become key to the performance improvement of cutting-edge science and large-scale engineering devices such as high-energy accelerators,thermonuclear fusion reactors,     

Preface to Special Topic: Biological microfluidics in tissue engineering and regenerative medicine

In this special issue of Biomicrofluidics, many manifestations of biological microfluidics have been highlighted that have significance to regenerative biology and medicine. The collated articles demonstrate the applicability of these biological microfluidics for studying a wide range of biomedical problems most useful for understanding and shining light on basic biology to those applications relevant to clinical medicine.     

Preface to Special Topic: Microsystems for manipulation and analysis of living cells

This Preface describes exciting papers contributed to the Special Topic section on manipulation and analysis of cells using microsystems. Brief summaries of each paper are provided and general trends are discussed.     

Preface to Special Topic: Selected Papers from the 5th International Conference on Optofluidics

The 5th International Conference on Optofluidics (Optofluidics 2015) was held in Taipei, Taiwan, July 26–29, 2015. The aim of this conference was to provide a forum to promote scientific exchange and to foster closer networks and collaborative ties between leading international researchers in optics and micro/nanofluidics across various disciplines. The scope of Optofluidics 2015 was deliberately broad and interdisciplinary, encompassing the latest advances and the most innovative developments in micro/nanoscale science and technology. Topics ranged from fundamental research to its applications in chemistry, physics, biology, materials, and medicine.Approximately 300 delegates participated in Optofluidics 2015 from across the globe, including Australia, Canada, China, France, Germany, Hong Kong, India, Japan, Korea, Singapore, Taiwan, UK, and USA. In total, 242 presentations were arranged, including 10 plenary speeches, 27 keynote speeches, 65 invited talks, 33 contributed talks, and 107 poster presentations. This collection of twelve papers on this special topic spans both the fundamentals and the frontier applications of this interdisciplinary research field.Optical measurements of particle or flow and fluidic manipulation for optical applications were presented. Lin and Su¹ reported a novel method to measure the depth position of rapidly moving objects inside a microfluidic channel based on the chromatic aberration effect; the depth positions of label-free particles of diameter as small as 2 μm and erythrocytes of concentration 2 × 10³ cells/μl and velocity 2.78 mm/s were detected within a range ±25 μm in a simple and inexpensive manner. Sun and Huang² demonstrated the use of a microscopic circular polariscope to measure the flow-induced birefringence in a microfluidic device that represents the kinematics of fluid motion optically; CTAB:NaSal, CPyCl:NaSal, and CPyCl:NaSal:NaCl solutions were used to investigate the strain rate and the results were compared with the μPIV diagnosis. He et al.³ studied the fundamentals, especially the thinning and opening of the oil film within each pixel of an electrowetting display; to achieve repeatable oil movement and the resulting pixel performance, a new method to fill each pixel with a controllable oil volume using an oil-droplet emulsion created with a microfluidic device was demonstrated.This special topic includes papers also on particle manipulation. Weng et al.⁴ evaluated the size-dependent crossing frequency of dielectrophoretically driven particles; numerical simulation using a Maxwell stress tensor and a finite element method was reported to assess the size effect. In addition to electric manipulation, magnetic driving of the particles was demonstrated. Ido et al.⁵ examined microswimmers of magnetic particle chains in an oscillating magnetic field experimentally and analyzed numerically with a lattice Boltzmann method, an immersed boundary method, and a discrete particle method based on simplified Stokesian dynamics. Huang et al.⁶ described a technique to manipulate magnetic beads and achieved a great washing efficiency with zero bead loss using an appropriate electrode design and channel height of a digital microfluidic immunoassay; a model immunoassay of human soluble tumor necrosis factor receptor I (sTNF-RI) was performed to offer an improved limit of detection (3.14 pg/ml) with a small number of magnetic beads (25 beads), decreased reagent volumes (200 nl), and decreased duration of analysis (<1 h). Chiu et al.⁷ reported particle separation using cross-flow filtration enhanced with hydrodynamic focusing; label-free separation of particles of diameters 2.7 and 10.6 μm at a sample throughput 10 μl/min was performed; separation of spiked human prostate cancer cell lines (PC3) cells in whole blood was also demonstrated.Chemical sensors and biosensors are covered in this special topic. Cheng et al.⁸ measured the chemical compounds in third-hand smoke on varied clothing fibres with an analytical balance, or nicotine and 3-ethenylpyridine (3-EP) with a surface-acoustic-wave sensor composed of coated oxidized hollow mesoporous carbon nanospheres. Pu et al.⁹ described a continuous glucose monitoring microsystem consisting of a three-electrode electrochemical sensor in which the working electrode (WE) was covered with a single layer of graphene and gold nanoparticles to improve the sensor performance; the results of glucose measurement were linear below concentration 162 mg/dl with a detection limit 1.44 mg/dl. Li et al.¹⁰ implemented a microfluidic device measuring the glucose concentration with integrated fibre-optic surface plasmon resonance sensor and electrode pairs for volume quantification.Implantable devices and microneedles for drug delivery and liquid transport are addressed in this special topic. Zhang et al.¹¹ reported a flexible polyimide device seated under rabbit eyelids to deliver drug by iontophoresis; varied currents to release manganese ions (Mn²⁺) as tracers were investigated; the thermal effect on application of a current was studied. Lee et al.¹² presented a disposable Parylene microneedle array of large aspect ratio that vibrated with a piezoelectric actuator to mimic the vibrating motion of a mosquito''s proboscis and to decrease the insertion force by 40%. Song et al.¹³ demonstrated microinjection into a model organism, Caenorhabditis elegans (C. elegans) on an automated device capable of loading, immobilization, injection, and sorting; with 200 worms studied, injection speed 6.6 worm/min, injection success rate 77.5%, and sorting success rate 100% were obtained.We express our gratitude for the financial support from Ministry of Science and Technology (Taiwan), Bureau of Foreign Trade (Taiwan), National Taiwan University and Research Center for Applied Sciences of Academia Sinica, and for administrative support from Instrument Technology Research Center in making Optofluidics 2015 a successful conference. Our acknowledgements include Leslie Yeo, Frederick Kontur, Christine Urso, and all staff from Biomicrofluidics for their kind assistance during the preparation, and, most importantly, all authors who have contributed their work for this special topic.     

志在四方结善缘——序宇桥长篇叙事散文《紫云英》

<正>认识宇桥先生虽是偶然,也是必然。偶然是在一念之间与其相见;必然是彼此初心相通,多有共识。所谓一念之间,是应家荣兄相邀,欣然而往;果然一见如故,相谈甚欢。宇桥先生为人处世的风格,念念不忘初心,给我留下了深刻的印象。他讲起合肥化工事业,滔滔不绝,如数家珍;论人说事,率性坦言,妙语连珠;谈古论今,博闻强记,诙谐幽默;与人相处,掏心掏肺,平易近人。那次,我现场看到改制重组的中盐红四方新区一派欣欣向荣的景象,后来在采访中才知道,合