抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

/pdf/self-assembled-monolayers-of-thiolates-on-metals-as-a-form-1neb0hj3k4.pdf

Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

Recent advances in mechanics and materials provide routes to integrated circuits that can offer the electrical properties of conventional, rigid wafer-based technologies but with the ability to be stretched, compressed, twisted, bent, and deformed into arbitrary shapes. Inorganic and organic electronic materials in microstructured and nanostructured forms, intimately integrated with elastomeric substrates, offer particularly attractive characteristics, with realistic pathways to sophisticated embodiments. Here, we review these strategies and describe applications of them in systems ranging from electronic eyeball cameras to deformable light-emitting displays. We conclude with some perspectives on routes to commercialization, new device opportunities, and remaining challenges for research.

http://science.sciencemag.org/content/sci/327/5973/1603.full.pdf

Materials and mechanics for stretchable electronics

基礎講座 電気泳動(Electrophoresis)

Microfluidic paper-based analytical devices (μPADs) are a new class of point-of-care diagnostic devices that are inexpensive, easy to use, and designed specifically for use in developing countries. (To listen to a podcast about this feature, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html.)

http://pubs.acs.org/doi/pdf/10.1021/ac9013989

Diagnostics for the Developing World: Microfluidic Paper-Based Analytical Devices

This paper describes the use of a modified x,y-plotter to generate hydrophilic channels by printing a solution of hydrophobic polymer (pol(dimethylsiloxane; PDMS) dissolved in hexanes onto filter paper. The PDMS penetrates the depth of the paper and forms a hydrophobic wall that aqueous solutions cannot cross. The minimum size of printed features is ∼1 mm; this resolution is adequate for the rapid prototyping of hand-held, visually read, diagnostic assays (and other microfluidic systems) based on paper. After curing the printed PDMS, the paper-based devices can be bent or folded to generate three-dimensional systems of channels. Capillary action pulls aqueous samples into the paper channels. Colorimetric assays for the presence of glucose and protein are demonstrated in the printed devices; spots of Bromothymol Blue distinguished samples with slightly basic pH (8.0) from samples with slightly acidic pH (6.5). The work also describes using printed devices that can be loaded using multipipets and printed fl...

Low-cost printing of poly(dimethylsiloxane) barriers to define microchannels in paper.

This report shows that the direction of polarization of attached mammalian cells determines the direction in which they move. Surfaces micropatterned with appropriately functionalized self-assembled monolayers constrain individual cells to asymmetric geometries (for example, a teardrop); these geometries polarize the morphology of the cell. After electrochemical desorption of the self-assembled monolayers removes these constraints and allows the cells to move across the surface, they move toward their blunt ends.

https://www.pnas.org/content/pnas/102/4/975.full.pdf

Directing cell migration with asymmetric micropatterns

This Communication describes a method of fabricating complex metallic microstructures in 3D by injecting liquid solder into microfluidic channels, and allowing the solder to cool and solidify; after fabrication, the metallic structures can be flexed, bent, or twisted This method of fabrication—which we call microsolidics—takes advantage of the techniques that were developed for fabricating microfluidic channels in poly(dimethylsiloxane) (PDMS) in 2D and 3D, uses surface chemistry to control the interfacial free energy of the metal– PDMS interface, and uses techniques based on microfluidics, but ultimately generates solid metal structures This approach makes it possible to build flexible electronic circuits or connections between circuits, complex embedded or freestanding 3D metal microstructures, 3D electronic components, and hybrid electronic–microfluidic devices There are several techniques for making metal microstructures in 3D Electroplating and electroless deposition are routinely used to construct microstructures with metallic layers several nanometers to several microns thick in 2D or 3D [1–11] To generate solid replicas of 3D objects, several groups have developed a technique, referred to as “microcasting”, to form metals in order to fabricate microparts (eg, posts and gears) with features as small as 10 lm and aspect ratios as high as 10 from steel, zirconia, and alumina [12,13] Techniques based on LIGA (Lithographie, Galvanoformung, und Abformung) produce even more complicated metallic objects by depositing a metal onto a molded polymer template that is subsequently removed to yield an open structure (such as a honeycomb arrangement of cells) [14,15] In principle, these approaches can be used to pattern metals of any thickness to produce features with an aspect ratio that is larger than that produced using electroplating

Microsolidics: Fabrication of Three‐Dimensional Metallic Microstructures in Poly(dimethylsiloxane)

Herein we describe a simple method for fabricating electromagnets with micron-scale dimensions in poly(dimethylsiloxane) (PDMS) in close proximity (ca. 10-mm separation) to microfluidic channels. The method has four steps: 1) fabrication of microchannels, which subsequently form both the microfluidic channels and the templates that become the wires for the electromagnets; 2) silanization of the microchannels destined to become wires with 3-mercaptopropyltrimethoxysilane, to make their surfaces wettable by metals; 3) injection of molten solder into the channels; and 4) cooling the channels to form solid metallic wires. These solder wires can be formed into nonplanar structures (if desired), by remelting, shaping the PDMS template, and recooling the solder. By passing electrical current through the wires, we generated magnetic fields up to 2.8 mT, and magnetic field gradients up to 40 Tm , inside adjacent microfluidic channels. To demonstrate the application of the electromagnets in microfluidic systems, we: 1) modeled the magnetic field and Joule heating of an electromagnet; 2) characterized the capture and release of superparamagnetic beads in a microfluidic channel by turning the electromagnets on and off; and 3) sorted superparamagnetic beads into one of two microfluidic channels by applying an electrical signal to a pair of electromagnets (one on each side of a channel). Magnetic components have the potential to be useful in lab-on-a-chip systems: they form the basis of microfluidic pumps, mixers, and valves, have been integrated into microfluidic systems to trap and move paramagnetic particles, and have been used to guide the self-assembly of particles into structures. There are many biochemical applications of magnetic fields: in immunoassays, they have been used to accelerate the hybridization of DNA and RNA, and for the filtration of biomolecules; in cell biology, magnets have been used to isolate cells from blood, extract DNA from cells, move magnetotactic bacteria, and to measure the mechanical properties of cells. The use of magnetics in microfluidic systems has been reviewed recently. Electromagnets have two advantages over permanent magnets in lab-on-a-chip systems: 1) they can be switched on/ off rapidly using electrical signals, and 2) the strength of their magnetic field can be adjusted. They have the disadvantage that they usually produce weaker magnetic fields than do permanent magnets. Several groups have fabricated electromagnets in microfluidic systems to manipulate superparamagnetic beads magnetically. Ahn et al. fabricated 3D electromagnets surrounding a microfluidic chamber by electroplating copper wires around a nickel–iron core. WirixSpeetjens et al. and Smistrup et al. made electromagnets that produced magnetic fields in channels etched in Si/SiO2. [18,19] Choi et al. fabricated Cu/Ti electrodes in microfluidic channels comprising polyimide, silicon, and glass. Deng and coworkers patterned gold wires with a width of 50–100 mm and thickness of 10–20 mm, and used the wires to produce magnetic fields in PDMS channels. They demonstrated that their wires carried electrical currents as large as 10 A for hours without failure; when the wires were positioned adjacent to a permanent magnet, the wires produced a peak magnetic fields of tens of mT. Lee et al. used lift-off techniques to fabricate gold wires with a width of 1–10 mm and a thickness of approximately 100 nm; an electrical current applied to the wires at a current density < 5 @ 10 Acm 2 produced a magnetic field < 100 mT. Redesigning the wires in a crossbar-array pattern made it possible to trap yeast cells attached to magnetic beads. Suzuki et al. [*] A. C. Siegel, Dr. S. S. Shevkoplyas, Dr. D. B. Weibel, D. A. Bruzewicz, A. W. Martinez, Prof. G. M. Whitesides Department of Chemistry and Chemical Biology Harvard University 12 Oxford Street, Cambridge, MA 02138 (USA) Fax: (+1)617-495-9857 E-mail: gwhitesides@gmwgroup.harvard.edu

Cofabrication of Electromagnets and Microfluidic Systems in Poly(dimethylsiloxane)

Self-assembly is a concept familiar to chemists. In the molecular and nanoscale regimes, it is often used as a strategy in fabricating regular 3D structures—that is, crystals. Self-assembly of components with sizes in the µm-to-mm range is less familiar to chemists; this type of self-assembly may, however, become technologically important in the future. In this size range, self-assembly offers methods to form regular 3D structures from components too small or too numerous to be manipulated by other means, and methods to incorporate function into these structures; it also offers simplicity and economy. This paper focuses on the use of self-assembly to build functional systems of compo- nents with sizes in the range from microns to millimeters. It compares the principles of self- assembly at the molecular and millimeter scales, reviews the possible applications of meso- scale, self-assembled systems, and outlines some of the most important issues in the use of self-assembly to build functional systems.

/pdf/millimeter-scale-self-assembly-and-its-applications-2wi2g1u5og.pdf

Derek A. Bruzewicz

Papers

Low-cost printing of poly(dimethylsiloxane) barriers to define microchannels in paper.

Directing cell migration with asymmetric micropatterns

Microsolidics: Fabrication of Three‐Dimensional Metallic Microstructures in Poly(dimethylsiloxane)

Cofabrication of Electromagnets and Microfluidic Systems in Poly(dimethylsiloxane)

Millimeter-scale self-assembly and its applications