Showing papers by "George M. Whitesides published in 2009"

Understanding wax printing: a simple micropatterning process for paper-based microfluidics.

Abstract: This technical note describes a detailed study on wax printing, a simple and inexpensive method for fabricating microfluidic devices in paper using a commercially available printer and hot plate. The printer prints patterns of solid wax on the surface of the paper, and the hot plate melts the wax so that it penetrates the full thickness of the paper. This process creates complete hydrophobic barriers in paper that define hydrophilic channels, fluid reservoirs, and reaction zones. The design of each device was based on a simple equation that accounts for the spreading of molten wax in paper.

Preparation of monodisperse biodegradable polymer microparticles using a microfluidic flow-focusing device for controlled drug delivery.

Abstract: Degradable microparticles have broad utility as vehicles for drug delivery and form the basis of several therapies approved by the US Food and Drug Administration. Conventional emulsion-based methods of manufacturing produce particles with a wide range of diameters (and thus kinetics of release) in each batch. This paper describes the fabrication of monodisperse, drug-loaded microparticles from biodegradable polymers using the microfluidic flow-focusing (FF) devices and the drug-delivery properties of those particles. Particles are engineered with defined sizes, ranging from 10 microm to 50 microm. These particles are nearly monodisperse (polydispersity index = 3.9%). A model amphiphilic drug (bupivacaine) is incorporated within the biodegradable matrix of the particles. Kinetic analysis shows that the release of the drug from these monodisperse particles is slower than that from conventional methods of the same average size but a broader distribution of sizes and, most importantly, exhibit a significantly lower initial burst than that observed with conventional particles. The difference in the initial kinetics of drug release is attributed to the uniform distribution of the drug inside the particles generated using the microfluidic methods. These results demonstrate the utility of microfluidic FF for the generation of homogenous systems of particles for the delivery of drugs.

Paper-supported 3D cell culture for tissue-based bioassays

Abstract: Fundamental investigations of human biology, and the development of therapeutics, commonly rely on 2D cell-culture systems that do not accurately recapitulate the structure, function, or physiology of living tissues. Systems for 3D cultures exist but do not replicate the spatial distributions of oxygen, metabolites, and signaling molecules found in tissues. Microfabrication can create architecturally complex scaffolds for 3D cell cultures that circumvent some of these limitations; unfortunately, these approaches require instrumentation not commonly available in biology laboratories. Here we report that stacking and destacking layers of paper impregnated with suspensions of cells in extracellular matrix hydrogel makes it possible to control oxygen and nutrient gradients in 3D and to analyze molecular and genetic responses. Stacking assembles the “tissue”, whereas destacking disassembles it, and allows its analysis. Breast cancer cells cultured within stacks of layered paper recapitulate behaviors observed both in 3D tumor spheroids in vitro and in tumors in vivo: Proliferating cells in the stacks localize in an outer layer a few hundreds of microns thick, and growth-arrested, apoptotic, and necrotic cells concentrate in the hypoxic core where hypoxia-sensitive genes are overexpressed. Altering gas permeability at the ends of stacks controlled the gradient in the concentration of the O2 and was sufficient by itself to determine the distribution of viable cells in 3D. Cell cultures in stacked, paper-supported gels offer a uniquely flexible approach to study cell responses to 3D molecular gradients and to mimic tissue- and organ-level functions.

Quantifying Colorimetric Assays in Paper-Based Microfluidic Devices by Measuring the Transmission of Light through Paper

Abstract: This article describes a point-of-care (POC) system—comprising a microfluidic, paper-based analytical device (μ-PAD) and a hand-held optical colorimeter—for quantifying the concentration of analytes in biological fluids. The μ-PAD runs colorimetric assays, and consists of paper that has been (i) patterned to expose isolated regions of hydrophilic zones and (ii) wet with an index-matching fluid (e.g., vegetable oil) that is applied using a disposable, plastic sleeve encasement. Measuring transmittance through paper represents a new method of quantitative detection that expands the potential functionality of μ-PADs. This prototype transmittance colorimeter is inexpensive, rugged, and fully self-contained, and thus potentially attractive for use in resource-limited environments and developing countries.

Paper Microzone Plates

Abstract: This paper describes 96- and 384-microzone plates fabricated in paper as alternatives to conventional multiwell plates fabricated in molded polymers. Paper-based plates are functionally related to plastic well plates, but they offer new capabilities. For example, paper-microzone plates are thin (∼180 μm), require small volumes of sample (5 μL per zone), and can be manufactured from inexpensive materials ($0.05 per plate). The paper-based plates are fabricated by patterning sheets of paper, using photolithography, into hydrophilic zones surrounded by hydrophobic polymeric barriers. This photolithography used an inexpensive formulation photoresist that allows rapid (∼15 min) prototyping of paper-based plates. These plates are compatible with conventional microplate readers for quantitative absorbance and fluorescence measurements. The limit of detection per zone loaded for fluorescence was 125 fmol for fluorescein isothiocyanate-labeled bovine serum albumin, and this level corresponds to 0.02 the quantity o...

Molecular Rectification in Metal−SAM−Metal Oxide−Metal Junctions

Abstract: This Article compares the ability of self-assembled monolayers (SAMs) of alkanethiolates with ferrocene (Fc) head groups (SC11Fc), and SAMs of alkanethiolates lacking the Fc moiety (SC10CH3 and SC14CH3), to conduct charge. Ultraflat surfaces of template-stripped silver (AgTS) supported these SAMs, and a eutectic alloy of gallium and indium (EGaIn), covered with a skin of gallium oxide (presumably Ga2O3), formed electrical top-contacts with them. EGaIn is a liquid at room temperature, but its spontaneously formed surface oxide skin gives it apparent non-Newtonian properties and allows it to be molded into conically shaped tips; these tips formed soft electrical contacts with SAMs and formed stable SAM-based tunneling junctions in high (70−90%) yields. Measurements of current density, J, versus applied voltage, V, showed that tunneling junctions composed of SAMs of SC11Fc rectify current with a rectification ratio R ≈ 1.0 × 102 (R = |J(−V)|/|J(V)| at ±1 V and with a log-standard deviation of 3.0). In contra...

Optical antenna arrays on a fiber facet for in situ surface-enhanced Raman scattering detection

Abstract: This paper reports a bidirectional fiber optic probe for the detection of surface-enhanced Raman scattering (SERS). One facet of the probe features an array of gold optical antennas designed to enhance Raman signals, while the other facet of the fiber is used for the input and collection of light. Simultaneous detection of benzenethiol and 2-[(E)-2-pyridin-4-ylethenyl]pyridine is demonstrated through a 35 cm long fiber. The array of nanoscale optical antennas was first defined by electron-beam lithography on a silicon wafer. The array was subsequently stripped from the wafer and then transferred to the facet of a fiber. Lithographic definition of the antennas provides a method for producing two-dimensional arrays with well-defined geometry, which allows (i) the optical response of the probe to be tuned and (ii) the density of “hot spots” generating the enhanced Raman signal to be controlled. It is difficult to determine the Raman signal enhancement factor (EF) of most fiber optic Raman sensors featuring h...

A multi-color fast-switching microfluidic droplet dye laser.

Abstract: We describe a multi-color microfluidic dye laser operating in whispering gallery mode based on a train of alternating droplets containing solutions of different dyes; this laser is capable of switching the wavelength of its emission between 580 nm and 680 nm at frequencies up to 3.6 kHz-the fastest among all dye lasers reported; it has potential applications in on-chip spectroscopy and flow cytometry.

Thin, lightweight, foldable thermochromic displays on paper

Abstract: This article describes an electronic display that is fabricated by patterning electrically conductive wires (heaters) with micron-scale dimensions on one side of a sheet of paper, and thermochromic ink on the opposite side. Passing electrical current through the wires heats the paper and changes the thermochromic ink from colored (black, green, or other colors) to transparent; this change in property reveals the paper underneath the ink—exposing any messages printed on the paper—and serves as the basis for a two-state “shutter” display. This type of display is thin (100 µm), flat, lightweight (the display weighs <20 mg/cm2), can be folded, rolled, twisted, and creased while maintaining function, and ultimately can (if required) be disposed of by incineration. The display is appropriate for applications where information must be presented clearly (usually only once) for little cost (each display costs <$0.10/m2 in materials) and where limited electrical power is available.

Measuring Densities of Solids and Liquids Using Magnetic Levitation: Fundamentals

Abstract: This paper describes an analytical system that uses magnetic levitation to measure densities of solids and water-immiscible organic liquids with accuracies ranging from ±0.0002 to ±0.02 g/cm3, depe...

A microfluidic apparatus for the study of ice nucleation in supercooled water drops

Abstract: This paper describes a microfluidic instrument that produces drops of supercooled water suspended in a moving stream of liquid fluorocarbon, and measures the temperatures at which ice nucleates in the drops. A microfluidic chip containing a monodisperse drop generator and a straight channel with 38 embedded resistance thermometers was placed in contact with a seven-zone temperature-control plate and imaged under a microscope with a high-speed camera. This instrument can record the freezing temperatures of tens of thousands of drops within minutes, with an accuracy of 0.4 degrees C. The ice-nucleation temperatures in approximately 80-microm drops were reported for the freezing of 37 061 drops of pure water, and of 8898 drops of water seeded with silver iodide. Nucleation of ice in pure water was homogenous and occurred at temperatures between -36 and -37.8 degrees C, while water containing silver iodide froze between -10 and -19 degrees C. The instrument recorded the largest sets of individual freezing temperatures (37 061), had the fastest data acquisition rate (75 measurements/s), and the best optical (3 microm) and temporal (70 micros) resolutions among instruments designed to study nucleation of ice. The dendritic growth of ice in 150-microm drops of supercooled water at -35 degrees C was observed and imaged at a rate of 16 000 frames/s.

A technique to transfer metallic nanoscale patterns to small and non-planar surfaces.

Abstract: Conventional lithographic methods (e.g., electron-beam lithography, photolithography) are capable of producing high-resolution structures over large areas but are generally limited to large (>1 cm2) planar substrates. Incorporation of these features on unconventional substrates (i.e., small (<1 mm2) and/or non-planar substrates) would open possibilities for many applications, including remote fiber-based sensing, nanoscale optical lithography, three-dimensional fabrication, and integration of compact optical elements on fiber and semiconductor lasers. Here we introduce a simple method in which a thin thiol-ene film strips arbitrary nanoscale metallic features from one substrate and is then transferred, along with the attached features, to a substrate that would be difficult or impossible to pattern with conventional lithographic techniques. An oxygen plasma removes the sacrificial film, leaving behind the metallic features. The transfer of dense and sparse patterns of isolated and connected gold features ...

Viscoelastic properties of oxide-coated liquid metals

Abstract: Many liquid metals exposed to air develop an oxide film on their outer surface. This film is sufficiently solid-like to provide mechanical stability to small liquid metal droplets, yet weak enough to allow the droplets to be malleable. These properties are useful in both micro-electronics and microfluidics; however, little is known about how to characterize them. Here we probe the elastic, yielding, and relaxation properties of oxide-coated gallium and eutectic gallium indium using a rheometer equipped with a parallel-plate geometry. By using parallel plates of different size, we show that surface stresses dominate bulk stresses. These experiments also demonstrate that the apparent elastic properties of the oxide film are highly sensitive to its strain history. Moreover, the apparent elasticity is sensitive to the stresses stored in the oxide skin. We probe these stresses and their time-dependence, with both torque and normal force measurements. We also characterize the time-dependence of the elasticity b...

Independent control of drop size and velocity in microfluidic flow-focusing generators using variable temperature and flow rate

Abstract: This paper describes a method to control the volume and the velocity of drops generated in a flow-focusing device dynamically and independently. This method involves simultaneous tuning of the temperature of the nozzle of the device and of the flow rate of the continuous phase; the method requires a continuous phase liquid that has a viscosity that varies steeply with temperature. Increasing the temperature of the flow-focusing nozzle from 0 to 80 °C increased the volume of the drops by almost 2 orders of magnitude. Tuning both the temperature and the flow rate controlled the drop volume and the drop velocity independently; this feature is not possible in a basic flow-focusing device. This paper also demonstrates a procedure for identifying the range of possible drop volumes and drop velocities for a given flow-focusing device and shows how to generate drops with a specified volume and velocity within this range. This method is easy to implement in on-chip applications where thermal management is already ...

Incorporation of prefabricated screw, pneumatic, and solenoid valves into microfluidic devices

Abstract: This paper describes a method for prefabricating screw, pneumatic, and solenoid valves and embedding them in microfluidic devices. This method of prefabrication and embedding is simple, requires no advanced fabrication, and is compatible with soft lithography. Because prefabrication allows many identical valves to be made at one time, the performance across different valves made in the same manner is reproducible. In addition, the performance of a single valve is reproducible over many cycles of opening and closing: an embedded solenoid valve opened and closed a microfluidic channel more than 100,000 times with no apparent deterioration in its function. It was possible to combine all three types of prefabricated valves in a single microfluidic device to control chemical gradients in a microfluidic channel temporally and spatially.

Lateral Flow and Flow-through Bioassay Devices Based on Patterned Porous Media, Methods of Making Same, and Methods of Using Same

Abstract: Embodiments of the invention provide lateral flow and flow-through bioassay devices based on patterned porous media, methods of making same, and methods of using same. Under one aspect, an assay device includes a porous, hydrophilic medium; a fluid impervious barrier comprising polymerized photoresist, the barrier substantially permeating the thickness of the porous, hydrophilic medium and defining a boundary of an assay region within the porous, hydrophilic medium; and an assay reagent in the assay region.

Propulsion of flexible polymer structures in a rotating magnetic field

Abstract: We demonstrate a new concept for the propulsions of abiological structures at low Reynolds numbers. The approach is based on the design of flexible, planar polymer structures with a permanent magnetic moment. In the presence of an external, uniform, rotating magnetic field these structures deform into three-dimensional shapes that have helical symmetry and translate linearly through fluids at Re between 10 −1 and 10. The mechanism for the motility of these structures involves reversible deformation that breaks their planar symmetry and generates propulsion. These elastic propellers resemble microorganisms that use rotational mechanisms based on flagella and cilia for their motility in fluids at low Re. M This article features online multimedia enhancements (Some figures in this article are in colour only in the electronic version)

Three-dimensional microfluidic devices

Abstract: Three-dimensional microfluidic devices including by a plurality of patterned porous, hydrophilic layers and a fluid-impermeable layer disposed between every two adjacent patterned porous, hydrophilic layers are described. Each patterned porous, hydrophilic layer has a fluid-impermeable barrier which substantially permeates the thickness of the porous, hydrophilic layer and defines boundaries of one or more hydrophilic regions within the patterned porous, hydrophilic layer. The fluid-impermeable layer has openings which are aligned with at least part of the hydrophilic region within at least one adjacent patterned porous, hydrophilic layer. Microfluidic assay device, microfluidic mixer, microfluidic flow control device are also described.

Using self-assembled monolayers to pattern ECM proteins and cells on substrates.

Abstract: We present a method that uses microcontact printing of alkanethiols on gold to generate patterned substrates presenting "islands" of extracellular matrix (ECM) surrounded by nonadhesive regions such that single cells attach and spread only on the adhesive regions. We have used this micropatterning technology to demonstrate that mammalian cells can be switched between growth and apoptosis programs in the presence of saturating concentrations of growth factors by either promoting or preventing cell spreading (Science 276:1425-1428, 1997). From the perspective of fundamental cell biology, these results suggested that the local differentials in growth and viability that are critical for the formation of complex tissue patterns may be generated by local changes in cell-ECM interactions. In the context of cell culture technologies, such as bioreactors and cellular engineering applications, the regulation of cell function by cell shape indicates that the adhesive microenvironment around cells can be carefully optimized by patterning a substrate in addition to using soluble factors (Biotech. Prog. 14:356-363, 1998). Micropatterning technology is playing a central role both in our understanding how ECM and cell shape regulate cell physiology and in facilitating the development of cellular biosensor and tissue engineering applications (Science 264:696-698, 1994; J. Neurosci. Res. 13:213-20, 1985; Biotech. Bioeng. 43:792-800, 1994).

Paper-based microfluidic systems

Abstract: The invention features an assay device, a microfluidic device, and a method of detecting the presence of high electrolyte concentration in a fluid sample. The assay device comprises a porous, hydrophilic substrate; a fluid-impermeable barrier defining a boundary of an assay region and a boundary of a main channel region, the main channel region fluidically connected to the assay region; and a strip of conductive material disposed on the porous, hydrophilic substrate. The microfluidic device comprises a porous, hydrophilic substrate; a fluid-impermeable barrier, the barrier permeating the thickness of the porous, hydrophilic substrate and defining within the porous, hydrophilic substrate a boundary of an open-ended channel having first and second lateral walls; and an electrically conductive pathway disposed on the porous, hydrophilic substrate, the electrically conductive pathway comprising (i) a strip of conductive material forming an open circuit in the absence of an electrically conductive material bridging the first and second lateral walls; and (ii) a battery, an electrically-responsive indicator, and a resistor electrically connected to the strip of conductive material.

Soft nanotechnology: "structure" vs. "function".

Abstract: This paper offers a perspective on “soft nanotechnology”; that is, the branch of nanotechnology concerned with the synthesis and properties of organic and organometallic nanostructures, and with nanofabrication using techniques in which soft components play key roles. It begins with a brief history of soft nanotechnology. This history has followed a path involving a gradual shift from the promise of revolutionary electronics, nanorobotics, and other futuristic concepts, to the realization of evolutionary improvements in the technology for current challenges in information technology, medicine, and sustainability. Soft nanoscience is an area that is occupied principally by chemists, and is in many ways indistinguishable from “nanochemistry”. The paper identifies the natural tendency of its practitioners—exemplified by the speakers at this Faraday Discussion—to focus on synthesis and structure, rather than on function and application, of nanostructures. Soft nanotechnology has the potential to apply to a wide variety of large-scale applied (information technology, healthcare cost reduction, sustainability, energy) and fundamental (molecular biochemistry, cell biology, charge transport in organic matter) problems.

Shaped Films of Ionotropic Hydrogels Fabricated Using Templates of Patterned Paper

Abstract: This article describes the use of paper—patterned either by hand or with a color laser printer—to fabricate films of ionotropic hydrogels structured into regular shapes with lateral dimensions from 2mm to several centimeters, and with thicknesses from 0.2 to 1.3mm. Water-soluble polymers such as alginic acid (AA) and carboxymethyl cellulose (CMC) form hydrogel films with defined shapes when solutions of these polymers are brought into contact with patterned templates of paper wetted with aqueous solutions of multivalent cations. The hydrogel films have sufficient mechanical strength to be handled with tweezers, and they retain their shapes when stored in water for weeks. When multivalent cations of high magnetic susceptibility (x) cross-link the polymers (as in holmiumor gadolinium-cross-linked AA, Ho3þ–AA and Gd3þ–AA), the films can be manipulated using rare-earth bar magnets. This procedure provides a new method for the fabrication of hydrogel films into structures that cannot be achieved (easily, or at all) using other methods. It renders possible the production of topographically and topologically complex three-dimensional shapes (e.g., interlocking rings and Mobius strips), and overcomes the difficulty presented in adding solutions of crosslinking ions to millimeter-sized layers of uncured polymer without deforming the shapes of the resulting hydrogel films. For certain patterns, our procedure provides a manufacturing method, since the patterned paper templates can be reused. Ionotropic hydrogels are hydrated gel matrices that form when metal ions cross-link water-soluble linear polymers. Polymers that form hydrogels in the presence ofmultivalent cations include AA, CMC, i-carrageenan (CG), poly(galacturonic acid) (PG), and poly[bis(4-carboxyphenoxy)-phosphazene]. Ionotropic hydrogels shaped in three dimensions with controlled compositions are an important class of biomaterials, with applications in the fields of controlled (drug) delivery, cellular immobilization, and biomimicry. Ionotropic hydrogels can serve as delivery devices for drugs and proteins when the polymers are biocompatible and degrade slowly relative to conventional sustained/slow-release systems. Ionotropic hydrogels (especially Ca2þ–AA) have been investigated as cellular scaffolds, but usually as spherical beads because other 3D structures are more difficult to fabricate. Lim and Sun demonstrated that alginate gels are suitable materials for cell encapsulation, although cells will usually not attach directly to unmodified alginate. Ionotropic hydrogels modified to present ligands for cell receptors have been used to mimic extracellular matrices (ECMs) that provide structural support to cells in tissue. Biomimetic materials are synthetic materials that have physical properties and biological functions similar to materials found in nature. Hydrogels have attracted interest as biomimetic materials due to their pliability, extent of hydration, low toxicity, and biocompatibility. For instance, Aizenberg and coworkers used hydrogels to mimic the microlens arrays of brittle stars (Ophiocoma wendii). Hydrogels can also be used to study creatures that creep, crawl, inch, and slither. Mahadevan et al. agitated cylindrical rods of hydrogels to simulate the muscular contractions of a snail. Yeghiazarian et al. heated rods of thermosensitive hydrogels confined to glass capillaries to mimic the movement of earthworms. Other uses for ionotropic hydrogels include as binding agents in food products, as sorbents for toxic metals, and as wound dressings. AA cross-linked with radioactive Ho3þ has been used in anti-tumor therapy that can be monitored by MRI. On sub-micrometer scales, Lahav et al. used microfluidic channels to pattern thin films of poly(acrylic acid) (PAA) crosslinked by metallic ions (e.g., Pb2þ, Ba2þ, Zn2þ, Pd2þ, Cu2þ, La3þ, Ho3þ).[14] Winkleman et al. used photolithography to create patterns of thin films of PAA cross-linked bymetal ions to assist in theproductionof low-kdielectricmaterials.Whileourgroupand others have fabricated sub-micrometer-thick layers of metal cross-linked polymers such as PAA, films of ionotropic hydrogels with millimeter thicknesses are more challenging to construct, because of the difficulty of introducing the multivalent cations across the entire surface of the film without disturbing the uniformity of the uncured layer of polymer. Techniques used to construct ionotropic gels on this scale include that of Chang et al., who produced synthetic facial implants in the shapes of chins, cheeks, and nasal septa out of hydrogels by injecting mixtures of chondrocytes, alginate, and CaSO4 into Silastic molds. [16] Cohen et al. developed a robotic system to fabricate arbitrary 3D hydrogel structuresby sequentially printing2D layers ofCa2þ–AApatterned with 1.2mmwide and 0.8mm tall threads of a solution of alginate for which cross-linking with CaSO4 was initiated prior to deposition. Liu and coworkers fabricated microscale spheres, rods, plugs, disks, and threads of alginate hydrogels using a flow-focusingmicrofluidic device. In their process, droplets of a solution of sodium alginate collided with droplets of a solution of CaCl2 inside microchannels and formed hydrogels. Solutions of sodium alginate gelled into membranes when cast onto porous media—including paper—wetted with solutions of multivalent cations. Cheng and coworkers controlled the porosity of these

Heterogeneous Films of Ionotropic Hydrogels Fabricated From Delivery Templates of Patterned Paper

Abstract: The use of delivery templates makes it possible to fabricate shaped, millimeter-thick heterogeneously patterned films of ionotropic hydrogels. These structures include two-dimensional (2-D) pattern...

Microcontact Transfer Printing of Zeolite Monolayers

Abstract: 2009 WILEY-VCH Verlag Gmb Zeolites are aluminosilicates that are used in a broad field of applications. Because of their ion-exchange capabilities, presence of well-defined rigid cavities, and transparency in the UV–vis/NIR region, zeolites can act as water softeners, catalysts, and host systems for a variety of photoactive guests. In particular, zeolite L, which possesses unidirectional channels, has been shown to be a suitable material for supramolecular organization of different kinds of molecules. The size (30 nm to several micrometers) and aspect ratio of L-type zeolite can be controlled synthetically. Furthermore, it has been shown recently that they can be organized in monolayers on a silica substrate by chemical functionalization. Interestingly, the orientation of the channels is perpendicular to the surface so that they can be filled after their immobilization. However, reports on the formation of well-orderedmonolayers on other (conductive) substrates have been very limited and so far it has not yet been possible to transfer them from one surface to another without disruption of the monolayer. However, the preparation of an oriented monolayer of zeolite L crystals on certain substrates (silicon wafers, ITO, gold) represents an important prerequisite for achieving a controlled architecture of such microsized building blocks for possible optoelectronic applications. Many authors have reported several methods for pursuing this goal by chemical treatment of target surfaces via different kinds of molecular linkers, and in some cases perfect monolayers were achieved, especially for zeolite A. We report a strategy based on the microcontact printing technique (MCP) to obtain well-ordered and uniformly oriented zeolite L monolayers on conductive surfaces without any chemical modification of the zeolite or the substrate. MCP, which has been employed by many authors, represents an inexpensive tool for the formation of a wide variety of molecular assemblies, ranging from quantum dots and silicon particles to carbon nanotubes and nanowires, and it has been also applied to pattern materials allowing new applications in device fabrication. [21–26] We have successfully applied this technique to create particular patterns with L-type zeolites that were filled with fluorescent dyes. We have also demonstrated that it is possible not only to apply the method to cylindrical objects by transferring them and maintaining their orientation, but also to use the anisotropy of the systems to control the different color emissions of zeolites filled with two different dyes by exciting the materials with polarized light.

Infochemistry and infofuses for the chemical storage and transmission of coded information

Abstract: This article describes a self-powered system that uses chemical reactions—the thermal excitation of alkali metals—to transmit coded alphanumeric information. The transmitter (an “infofuse”) is a strip of the flammable polymer nitrocellulose patterned with alkali metal ions; this pattern encodes the information. The wavelengths of 2 consecutive pulses of light represent each alphanumeric character. While burning, infofuses transmit a sequence of pulses (at 5–20 Hz) of atomic emission that correspond to the sequence of metallic salts (and therefore to the encoded information). This system combines information technology and chemical reactions into a new area—“infochemistry”—that is the first step toward systems that combine sensing and transduction of chemical signals with multicolor transmission of alphanumeric information.

A Non-Chromatographic Method for the Purification of a Bivalently Active Monoclonal IgG Antibody from Biological Fluids

Abstract: This paper describes a method for the purification of monoclonal antibodies (rat anti-2,4-dinitrophenyl IgG: IgG(DNP); and mouse antidigoxin IgG: IgG(Dgn)) from ascites fluid This procedure (for IgG(DNP)) has three steps: (i) precipitation of proteins heavier than immunoglobulins with ammonium sulfate; (ii) formation of cyclic complexes of IgG(DNP) by causing it to bind to synthetic multivalent haptens containing multiple DNP groups; (iii) selective precipitation of these dimers, trimers, and higher oligomers of the target antibody, followed by regeneration of the free antibody This procedure separates the targeted antibody from a mixture of antibodies, as well as from other proteins and globulins in a biological fluid This method is applicable to antibodies with a wide range of monovalent binding constants (01 microM to 01 nM) The multivalent ligands we used (derivatives of DNP and digoxin) isolated IgG(DNP) and IgG(Dgn) from ascites fluid in yields of >80% and with >95% purity This technique has two advantages over conventional chromatographic methods for purifying antibodies: (i) it is selective for antibodies with two active Fab binding sites (both sites are required to form the cyclic complexes) over antibodies with one or zero active Fab binding sites; (ii) it does not require chromatographic separation It has the disadvantage that the structure of the hapten must be compatible with the synthesis of bi- and/or trivalent analogues

Controlling the Kinetics of Contact Electrification with Patterned Surfaces

Abstract: This communication describes a new approach for controlling static charging (contact electrification), and resulting electrical discharging, that occurs when two contacting materials separate. The prevention of contact electrification is an important problem; unwanted adhesion between oppositely charged materials, spark-initiated explosions, and damage to microelectronic circuitry are some of the deleterious effects of static charging. Current strategies for controlling contact electrification rely upon dissipating an accumulated charge by making contacting surfaces conductive and, therefore, can be difficult to implement with electrically insulating materials. Specifically, using our understanding of the ion-transfer mechanism of contact electrification, we patterned glass slides with negatively charging areas (clean glass) and positively charging areas (glass silanized with a cationic siloxane terminated with a quaternary ammonium group). The rate of charge separation due to a steel sphere rolling on th...

Infochemistry: encoding information as optical pulses using droplets in a microfluidic device.

Abstract: This article describes a new procedure for generating and transmitting a message--a sequence of optical pulses--by aligning a mask (an opaque sheet containing transparent "windows") below a microfluidic channel in which flows an opaque continuous fluid containing transparent droplets. The optical mask encodes the message as a unique sequence of windows that can transmit or block light; the flow of transparent droplets in the channel converts this message into a sequence of optical pulses. The properties of the windows on the mask (e.g., their size, wavelength of transmittance, orientation of polarization) determine the information carried in these optical pulses (e.g., intensity, color, polarization). The structure of a transmitted signal depends on the number and spacing of droplets in the channel. Fourier transformation can deconvolve superimposed signals created by the flow of multiple droplets into the message that a single droplet would transmit. The research described in this contribution explores a new field at the intersection of chemistry, materials science, and information technology: infochemistry.

Integrated Fabrication and Magnetic Positioning of Metallic and Polymeric Nanowires Embedded in Thin Epoxy Slabs

Abstract: This paper describes a process for the fabrication and positioning of nanowires (of Au, Pd, and conjugated polymers) embedded in thin epoxy slabs. The procedure has four steps: (i) coembedding a thinfilm of metal or conducting polymer with a thin film of nickel metal (Ni) in epoxy; (ii) sectioning the embedded structures into nanowires with an ultramicrotome ("nanoskiving"); (iii)floating the epoxy sections on a pool of water; and (iv) positioning the sections with an external magnet to a desired location ("magnetic mooring"). As the water evaporates, capillary interactions cause the sections to adhere to the substrate. Both the Ni and epoxy canbeetchedtogeneratefree-standingmetallicnanowires.Theaveragetranslationaldeviationinthepositioning of two nanowires with respect to each other is 16 13 m, and the average angular deviation is 3 2°. Successive depositions of nanowires yield the following structures of interest for electronic and photonic applications: electrically continuous junctions of two Au nanowires, two Au nanowires spanned by a poly(3- hexylthiophene) (P3HT) nanowire; single-crystalline Au nanowires that cross; crossbar arrays of Au nanowires; crossbar arrays of Au and Pd nanowires; and a 5050 array of poly(benzimidazobenzophenanthroline ladder) (BBL) nanowires. Single-crystalline Au nanowires can be placed on glass woolfibers or on microfabricated polymeric waveguides, with which the nanowire can be addressed optically.