Bio-Microarray Fabrication Techniques—A Review

Autoimmune profiling with protein microarrays in clinical applications

In recent years, knowledge about immune-related disorders has substantially increased, especially in the field of central nervous system (CNS) disorders. Recent innovations in protein-related microarray technology have enabled the analysis of interactions between numerous samples and up to 20,000 targets. Antibodies directed against ion channels, receptors and other synaptic proteins have been identified, and their causative roles in different disorders have been identified. Knowledge about immunological disorders is likely to expand further as more antibody targets are discovered. Therefore, protein microarrays may become an established tool for routine diagnostic procedures in the future. The identification of relevant target proteins requires the development of new strategies to handle and process vast quantities of data so that these data can be evaluated and correlated with relevant clinical issues, such as disease progression, clinical manifestations and prognostic factors. This review will mainly focus on new protein array technologies, which allow the processing of a large number of samples, and their various applications with a deeper insight into their potential use as diagnostic tools in neurodegenerative diseases and other diseases. This article is part of a Special Issue entitled: Biomarkers: A Proteomic Challenge.

An equipment-free polydimethylsiloxane microfluidic spotter for fabrication of microarrays

This paper presents a low-cost, power-free, and easy-to-use spotter system for fabrication of microarrays. The spotter system uses embedded dispensing microchannels combined with a polydimethylsiloxane (PDMS) membrane containing regular arrays of well-defined thru-holes to produce precise, uniform DNA or protein microarrays for disease diagnosis or drug screening. Powered by pre-evacuation of its PDMS substrate, the spotter system does not require any additional components or external equipment for its operation, which can potentially allow low-cost, high-quality microarray fabrication by minimally trained individuals. Polyvinylpyrrolidone was used to modify the PDMS surface to prevent protein adsorption by the microchannels. Experimental results indicate that the PDMS spotter shows excellent printing performance for immobilizing proteins. The measured coefficient of variation (CV) of the diameter of 48 spots was 2.63% and that of the intensity within one array was 2.87%. Concentration gradient experiments revealed the superiority of the immobilization density of the PDMS spotter over the conventional pin-printing method. Overall, this low-cost, power-free, and easy-to-use spotting system provides an attractive new method to fabricate microarrays.

Microfluidics-based single-cell functional proteomics for fundamental and applied biomedical applications

We review an emerging microfluidics-based toolkit for single-cell functional proteomics. Functional proteins include, but are not limited to, the secreted signaling proteins that can reflect the biological behaviors of immune cells or the intracellular phosphoproteins associated with growth factor-stimulated signaling networks. Advantages of the microfluidics platforms are multiple. First, 20 or more functional proteins may be assayed simultaneously from statistical numbers of single cells. Second, cell behaviors (e.g., motility) may be correlated with protein assays. Third, extensions to quantized cell populations can permit measurements of cell-cell interactions. Fourth, rare cells can be functionally identified and then separated for further analysis or culturing. Finally, certain assay types can provide a conduit between biology and the physicochemical laws. We discuss the history and challenges of the field then review design concepts and uses of the microchip platforms that have been reported, with an eye toward biomedical applications. We then look to the future of the field.

Influence of the relative humidity on the morphology of inkjet printed spots of IgG on a non-porous substrate

During the drying of inkjet printed droplets, the solute particles (IgG-Alexa-635 molecules) in the drop may distribute unevenly on the substrate, resulting in a “coffee-stain” spot morphology.

Large-area molecular patterning with polymer pen lithography

The challenge of constructing surfaces with nanostructured chemical functionality is central to many areas of biology and biotechnology. This protocol describes the steps required for performing molecular printing using polymer pen lithography (PPL), a cantilever-free scanning probe-based technique that can generate sub-100-nm molecular features in a massively parallel fashion. To illustrate how such molecular printing can be used for a variety of biologically relevant applications, we detail the fabrication of the lithographic apparatus and the deposition of two materials, an alkanethiol and a polymer onto a gold and silicon surface, respectively, and show how the present approach can be used to generate nanostructures composed of proteins and metals. Finally, we describe how PPL enables researchers to easily create combinatorial arrays of nanostructures, a powerful approach for high-throughput screening. A typical protocol for fabricating PPL arrays and printing with the arrays takes 48-72 h to complete, including two overnight waiting steps.

Interdigitated multicolored bioink micropatterns by multiplexed polymer pen lithography

Multiplexing, i.e., the application and integration of more than one ink in an interdigitated microscale pattern, is still a challenge for microcontact printing (μCP) and similar techniques. On the other hand there is a strong demand for interdigitated patterns of more than one protein on subcellular to cellular length scales in the lower micrometer range in biological experiments. Here, a new integrative approach is presented for the fabrication of bioactive microarrays and complex multi-ink patterns by polymer pen lithography (PPL). By taking advantage of the strength of microcontact printing (μCP) combined with the spatial control and capability of precise repetition of PPL in an innovative way, a new inking and writing strategy is introduced for PPL that enables true multiplexing within each repetitive subpattern. Furthermore, a specific ink/substrate platform is demonstrated that can be used to immobilize functional proteins and other bioactive compounds over a biotin-streptavidin approach. This patterning strategy aims specifically at application by cell biologists and biochemists addressing a wide range of relevant pattern sizes, easy pattern generation and adjustment, the use of only biofriendly, nontoxic chemicals, and mild processing conditions during the patterning steps. The retained bioactivity of the fabricated cm(2) area filling multiprotein patterns is demonstrated by showing the interaction of fibroblasts and neurons with multiplexed structures of fibronectin and laminin or laminin and ephrin, respectively.

Microfluidic parallel patterning and cellular delivery of molecules with a nanofountain probe

This brief report describes a novel tool for microfluidic patterning of biomolecules and delivery of molecules into cells. The microdevice is based on integration of nanofountain probe (NFP) chips with packaging that creates a closed system and enables operation in liquid. The packaged NFP can be easily coupled to a micro/nano manipulator or atomic force microscope for precise position and force control. We demonstrate here the functionality of the device for continuous direct-write parallel patterning on a surface in air and in liquid. Because of the small volume of the probes (~3 pL), we can achieve flow rates as low as 1 fL/s and have dispensed liquid drops with submicron to 10 µm diameters in a liquid environment. Furthermore, we demonstrate that this microdevice can be used for delivery of molecules into single cells by transient permeabilization of the cell membrane (i.e., electroporation). The significant advantage of NFP-based electroporation compared with bulk electroporation and other transfection techniques is that it allows for precise and targeted delivery while minimizing stress to the cell. We discuss the ongoing development of the tool toward automated operation and its potential as a multifunctional device for microarray applications and time-dependent single-cell studies.

In-situ preparation of metal oxide thin films by inkjet printing acetates solutions

Direct printing of functional oxide thin films could provide a new route to low-cost, efficient and scalable fabrications of electronic devices. One challenge that remains open is to design the inks with long term stability for effective deposition of specific oxide materials of industrial importance. In this paper, we introduce a reliable method of producing stable inks for ‘in-situ’ deposition of oxide thin films by inkjet printing. The inks were prepared from metal-acetates solutions and printed on a variety of substrates. The acetate precursors were decomposed into oxide films during the subsequent calcination process to achieve the ‘in-situ’ deposition of the desired oxide films directly on the substrate. By this procedure we have obtained room temperature contamination free ferromagnetic spintronic materials like Fe doped MgO and ZnO films from their acetate(s) solutions. We find that the origin of magnetism in ZnO, MgO and their Fe-doped films to be intrinsic. For a 28 nm thick film of Fe-doped ZnO we observe an enhanced magnetic moment of 16.0 emu/cm3 while it is 5.5 emu/cm3 for the doped MgO film of single pass printed. The origin of magnetism is attributed to cat-ion vacancies. We have also fabricated highly transparent indium tin oxide films with a transparency >95% both in the visible and IR range which is rather unique compared to films grown by any other technique. The films have a nano-porous structure, an added bonus from inkjetting that makes such films advantageous for a broad range of applications.

Evaporation dynamics of nanodroplets and their anomalous stability on rough substrates

Nanodroplets sitting on substrates in an open system are usually assumed to be thermodynamically unstable, and will eventually either evaporate or grow. However, as a counterpart of nanodroplets, nanobubbles located at the solid-liquid interface were recently demonstrated by numerous experiments to be unexpectedly stable. The accumulated evidence for the existence of stable nanobubbles poses a question of whether nanodroplets are stable. In this work we revisit the stability of nanodroplets upon smooth and rough substrates, concentrating on their evaporation dynamics. On smooth substrates, the droplets evaporate generally in the constant contact angle (CCA) mode, with a contact angle nonmonotonously depending on the fluid-substrate interaction, while on rough substrates, the droplets evaporate in the constant contact line (CCL) mode or the CCL-CCA mixed mode. Our results indeed predict the existence of stable nanodroplets on rough substrates: In situations where the contact line is pinned and the vapor is supersaturated but at a low level of supersaturation, nanodroplets are found to be anomalously stable. The stability of nanodroplets can be interpreted within the framework of the classical nucleation theory.

Scaling advantages and constraints in miniaturized capture assays for single cell protein analysis

Measuring protein expression in single cells is the basis of single cell proteomics. The sensitivity and dynamic range of a single cell immunoassay should ideally be such that proteins that are expressed between 1-10(6) copies per cell can be detected and counted. We have investigated the effect of miniaturizing antibody microarrays by reducing capture spot sizes from 100 μm to 15 μm using dip-pen nanolithography. We demonstrate that protocols developed for printing and passivating antibody capture spots using conventional pin-based contact printing can be directly transferred to dip-pen lithography whilst retaining the capture activity per unit area. Using a simple kinetic model, we highlight how the limit of detection and dynamic range of a sandwich immunoassay, respectively, increase and decrease when spot size is reduced. However, we show that reducing spot size is more effective than increasing assay chamber volume when seeking to multiplex such a microfluidic immunoassay. Although we make particular reference to single cell microfluidic immunoassays, the topics discussed here are applicable to capture assays in general.

On-chip parylene-C microstencil for simple-to-use patterning of proteins and cells on polydimethylsiloxane

Polydimethylsiloxane (PDMS) is widely used as a substrate in miniaturized devices, given its suitability for execution of biological and chemical assays. Here, we present a patterning approach for PDMS, which uses an on-chip Parylene-C microstencil to pattern proteins and cells. To implement the on-chip Parylene-C microstencil, we applied SiOx-like nanoparticle layers using atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) of tetraethyl orthosilicate (TEOS) mixed with oxygen. The complete removal of Parylene-C from PDMS following application of SiOx-like nanoparticle layers was demonstrated by various surface characterization analysis, including optical transparency, surface morphology, chemical composition, and peel-off force. Furthermore, the effects of the number of AP-PECVD treatments were investigated. Our approach overcomes the tendency of Parylene-C to peel off incompletely from PDMS, which has limited its use with PDMS to date. The on-chip Parylene-C microstencil approach that is based on this Parylene-C peel-off process on PDMS can pattern proteins with 2-μm resolution and cells at single-cell resolution with a vacancy ratio as small as 10%. This provides superior user-friendliness and a greater degree of geometrical freedom than previously described approaches that require meticulous care in handling of stencil. Thus, this patterning method could be applied in various research fields to pattern proteins or cells on the flexible PDMS substrate.

Phenotypic MicroRNA Microarrays

Microarray technology has become a very popular approach in cases where multiple experiments need to be conducted repeatedly or done with a variety of samples. In our lab, we are applying our high density spots microarray approach to microscopy visualization of the effects of transiently introduced siRNA or cDNA on cellular morphology or phenotype. In this publication, we are discussing the possibility of using this micro-scale high throughput process to study the role of microRNAs in the biology of selected cellular models. After reverse-transfection of microRNAs and siRNA, the cellular phenotype generated by microRNAs regulated NF-κB expression comparably to the siRNA. The ability to print microRNA molecules for reverse transfection into cells is opening up the wide horizon for the phenotypic high content screening of microRNA libraries using cellular disease models.

A Rapid, Multiplexed, High-Throughput Flow-Through Membrane Immunoassay: A Convenient Alternative to ELISA

This paper describes a rapid, high-throughput flow-through membrane immunoassay (FMIA) platform. A nitrocellulose membrane was spotted in an array format with multiple capture and control reagents for each sample detection area, and assay steps were carried out by sequential aspiration of sample and reagents through each detection area using a 96-well vacuum manifold. The FMIA provides an alternate assay format with several advantages over ELISA. The high surface area of the membrane permits high label concentration using gold labels, and the small pores and vacuum control provide rapid diffusion to reduce total assay time to ~30 min. All reagents used in the FMIA are compatible with dry storage without refrigeration. The results appear as colored spots on the membrane that can be quantified using a flatbed scanner. We demonstrate the platform for detection of IgM specific to lipopolysaccharides (LPS) derived from Salmonella Typhi. The FMIA format provides analytical results comparable to ELISA in less time, provides integrated assay controls, and allows compensation for specimen-to-specimen variability in background, which is a particular challenge for IgM assays.

High-throughput on-chip leukemia diagnosis

Advances in lab-on-a-chip technologies enabled programmable, reconfigurable, and scalable manipulation of a variety of laboratory procedures. Samples, reagents, and fluids can be precisely controlled; buffer temperature, pH, and concentration control systems as well as a variety of detection systems can be integrated on a small chip. These advantages have attracted attention in various fields of clinical application including leukemia diagnosis and research. A lot of research on lab-on-a-chip based diagnosis has been reported and the field is rapidly expanding. This review describes recent developments of lab-on-a-chip technologies as solutions to challenges for high-throughput leukemia diagnosis.

Patterned polymer nanowire arrays as an effective protein immobilizer for biosensing and HIV detection

We report an array of polymeric nanowires for effectively immobilizing biomolecules on biochips owing to the large surface area. The nanowires were fabricated in predesigned patterns using an inductively coupled plasma (ICP) etching process. Microfluidic biochips integrated using the substrates with arrays of nanowires and polydimethylsiloxane channels have been demonstrated to be effective for detecting antigens, and a detection limit of antigens at 0.2 μg mL(-1) has been achieved, which is improved by a factor of 50 compared to that based on flat substrates without the nanowires. In addition, the high sensitivity for clinical detection of human immunodeficiency virus (HIV) antibody has also been demonstrated, showing a 20 times enhancement in fluorescent signal intensity between the samples with positive and negative HIV.

High-resolution epifluorescence and time-of-flight secondary ion mass spectrometry chemical imaging comparisons of single DNA microarray spots

DNA microarray assay performance is commonly compromised by spot-spot probe and signal variations as well as heterogeneity within printed microspots. Accurate metrics for captured DNA target signal rely upon uniform spot distribution of both probe and target DNA to yield reliable hybridized signal. While often presumed, this is neither easily achieved nor often proven experimentally. High-resolution imaging techniques were used to determine spot heterogeneity in identical DNA array microspots comprising varied ratios of unlabeled and dye-labeled DNA probes contact-printed onto commercial arraying surfaces. Epifluorescence imaging data for individual array microspots were correlated with time-of-flight secondary ion mass spectrometry (TOF-SIMS) chemical state imaging of the same spots. Epifluorescence imaging intensity distinguished varying DNA density distributed both within a given spot and from spot to spot. TOF-SIMS chemical analysis confirmed these heterogeneous printed DNA distributions by tracking bound Cy3 dye, DNA base, and phosphate specific ion fragments often correlating to fluorescence patterns within identical spots. TOF-SIMS ion fragments originating from probe DNA and Cy3 dye are enriched in microspot centers, correlating with high fluorescence intensity regions. Both TOF-SIMS and epifluorescence support Marangoni flow effects on spot drying, with high-density DNA-Cy3 located in spot centers and nonhomogeneous DNA distribution within printed spots. Microspot image dimensional analysis results for DNA droplet spreading show differing DNA densities across printed spots. The study directly supports different DNA probe chemical and spatial microenvironments within spots that yield spot-spot signal variations known to affect DNA target hybridization efficiencies and kinetics. These variations critically affect probe-target duplex formation and DNA array signal generation.

Surface plasmon resonance imaging for nucleic acid detection

Surface plasmon resonance imaging (SPRI) is a powerful tool for simple, fast and cheap nucleic acid detection. Great efforts have been made during the last decade with the aim of developing even more sensitive and specific SPRI-based methods to be used for the direct detection of DNA and RNA. Here, after a description of the fundamentals of SPRI, the state of the art of recent platform and assay developments is presented, with special attention given to advances in SPRI signal enhancement procedures.

Print-to-print: a facile multi-object micro-patterning technique

In recent years, micropatterning techniques have gained increasing popularity from a broad range of engineering and biology communities for the promise to establish highly quantitative investigations on miniature biological objects (e.g., cells and bacteria) with spatially defined microenvironments. However, majority of the existing techniques rely on cleanroom-based microfabrication and cannot be easily extended to a regular biological laboratory. In this paper, we present a simple versatile printing-based method, referred to as Print-to-Print (P2P), to form multi-object micropatterns for potential biological applications, along with our recent efforts to deliver out-of-cleanroom microfabrication solutions to the general public (Zhao et al. 2009), (Xing et al. 2011), (Wang et al. 2009), (Pan and Wang 2011), (Zhao et al. 2011). The P2P method employs only a commercially available solid-phase printer and custom-made superhydrophobic films. The entire patterning process does not involve any thermal or chemical treatment. Moreover, the non-contact nature of droplet transferring and printing steps can be highly advantageous for sensitive biological uses. Using the P2P process, a minimal feature resolution of 229 ± 17 μm has been successfully demonstrated. In addition, this approach has been applied to form biological micropatterning on various substrates as well as multi-object co-patterns on the commonly used surfaces. Finally, the reusability of superhydrophobic substrates has also been illustrated.

Infectomics Screening for Novel Antiviral Drug Targets

Preclinical Research

Copyright 2012 Wiley-Liss, Inc., A Wiley Company

Infectomics, a novel way to globally and comprehensively understand the interactions between microbial pathogens and their hosts, has significantly expanded understanding of the microbial infections. The infectomics view of viral–host interactions on the viral perspective principally focuses on gene acquisition, deletion, and point mutation, while traditional antiviral drug discovery concentrates on viral encoding proteins. Recently, high‐throughput technologies, such as mass spectrometry‐based proteomics, activity‐based protein profiling, microarray analysis, yeast two‐hybrid assay, small interfering RNA screening, and micro RNA profiling, have been gradually employed in the research of virus–host interactions. Besides, signaling pathways and cellular processes involved in viral–host interactions provide new insights of infectomics in antiviral drug discovery. In this review, we summarize related infectomics approaches in the studies of virus–host interactions, which shed light on the development of novel antiviral drug targets screening.

Micropatterned surfaces: techniques and applications in cell biology

IMPORTANCE OF THE FIELD

Engineering of cell culture substrates provides a unique opportunity for precise control of the cellular microenvironment with both spatial as well as temporal resolutions. This greatly enhances studies of cell-cell, cell-matrix and cell-factor interaction studies in vitro.

AREAS COVERED IN THIS REVIEW

The technologies used for micropatterning in the biological field over the last decade and new applications in the last few years for dynamic control of surfaces, tissue engineering, drug discovery, cell-cell interactions and stem cell studies are presented.

WHAT THE READER WILL GAIN

The reader will gain knowledge on the state of the art in micropatterning and its wide ranging applications in cell patterning, with new pathways to control the cell environment.

TAKE HOME MESSAGE

Micropatterning of cells has been studied and developed enough to be widely applied ranging from single cell assays to tissue engineering. Techniques have evolved from many-step processes to direct writing of biologically selective patterns.

Superhydrophobic hierarchical honeycomb surfaces

Two-dimensional hexagonally ordered honeycomb surfaces have been created by solvent casting polybutadiene films under controlled humidity. Subsequent CF(4) plasmachemical fluorination introduces cross-linking and surface texturing, leading to hierarchical surfaces with roughness on both the 10 μm (honeycomb) and micrometer (texturing) length scales. For microliter droplets, these display high water contact angle values (>170°) in combination with low contact angle hysteresis (i.e., superhydrophobicity) while displaying bouncing of picoliter water droplets. In the case of picoliter droplets, it is found that surfaces which exhibit similar static contact angles can give rise to different droplet impact dynamics, governed by the underlying surface topography. These studies are of relevance to technological processes such as rapid cooling, delayed freezing, crop spraying, and inkjet printing.

Polymer pen lithography (PPL)-induced site-specific click chemistry for the formation of functional glycan arrays

Polymer pen lithography (PPL) can be combined with the Cu(I) -catalyzed azide-alkyne click reaction to create molecular arrays with control over orientation and sub-1 μm feature sizes over cm(2) areas. The process has been applied to the deposition of carbohydrates to form functional glycochips.

Microarray technology for major chemical contaminants analysis in food: current status and prospects

Chemical contaminants in food have caused serious health issues in both humans and animals. Microarray technology is an advanced technique suitable for the analysis of chemical contaminates. In particular, immuno-microarray approach is one of the most promising methods for chemical contaminants analysis. The use of microarrays for the analysis of chemical contaminants is the subject of this review. Fabrication strategies and detection methods for chemical contaminants are discussed in detail. Application to the analysis of mycotoxins, biotoxins, pesticide residues, and pharmaceutical residues is also described. Finally, future challenges and opportunities are discussed.

Multiplex immunoassay platforms based on shape-coded poly(ethylene glycol) hydrogel microparticles incorporating acrylic acid

A suspension protein microarray was developed using shape-coded poly(ethylene glycol) (PEG) hydrogel microparticles for potential applications in multiplex and high-throughput immunoassays. A simple photopatterning process produced various shapes of hydrogel micropatterns that were weakly bound to poly(dimethylsiloxane) (PDMS)-coated substrates. These micropatterns were easily detached from substrates during the washing process and were collected as non-spherical microparticles. Acrylic acids were incorporated into hydrogels, which could covalently immobilize proteins onto their surfaces due to the presence of carboxyl groups. The amount of immobilized protein increased with the amount of acrylic acid due to more available carboxyl groups. Saturation was reached at 25% v/v of acrylic acid. Immunoassays with IgG and IgM immobilized onto hydrogel microparticles were successfully performed with a linear concentration range from 0 to 500 ng/mL of anti-IgG and anti-IgM, respectively. Finally, a mixture of two different shapes of hydrogel microparticles immobilizing IgG (circle) and IgM (square) was prepared and it was demonstrated that simultaneous detection of two different target proteins was possible without cross-talk using same fluorescence indicator because each immunoassay was easily identified by the shapes of hydrogel microparticles.

Surface plasmon resonance imaging analysis of protein binding to a sialoside-based carbohydrate microarray

Monitoring multiple biological interactions in a multiplexed array format has numerous advantages. However, converting well-developed surface chemistry for spectroscopic measurements to array-based, high-throughput screening is not a trivial process and often proves to be the bottleneck in method development. This chapter reports the fabrication and characterization of a new carbohydrate microarray with synthetic sialosides for surface plasmon resonance imaging analysis of lectin-carbohydrate interactions. Contact printing of functional sialosides on neutravidin-coated surfaces was carried out and the properties of the resulting elements were characterized by fluorescence microscopy. Sambucus nigra agglutinin (SNA) was used for testing on four different carbohydrate-functionalized surfaces and differential binding was analyzed. Multiplexed detection of SNA/biotinylated sialoside interactions on arrays up to 400 elements has been performed with good data correlation, demonstrating the effectiveness of the biotin-neutravidin-based biointerface to control probe orientation for reproducible and efficient protein binding to carbohydrates.

Patterning nanoparticles in a three-dimensional matrix using an electric-field-assisted gel transferring technique

In this paper, we describe an electric-field-assisted gel transferring technique for patterning on two- and three-dimensional media. The transfer process starts with the preparation of a block of agarose gel doped with charged nanoparticles or molecules on top of a screen mask with desired patterns. This gel/mask construct is then brought into contact with the appropriate receiving medium, such as a polymer membrane or a piece of flat hydrogel. An electric field is applied to transfer the doped charged nanoparticles or molecules into the receiving medium with a pattern defined by the screen mask. This printing method is rapid and convenient, the results are reproducible, and the process can be done without using expensive micro/nanofabrication facilities. The capability to pattern structures such as arrays of nanoparticles into three-dimensional hydrogels may find applications for positioning cell signaling molecules to control cell growth and migration.

On-chip sample preparation by controlled release of antibodies for simple CD4 counting

We present a simple system for CD4 and CD8 counting for point-of-care HIV staging in low-resource settings. Automatic sample preparation is achieved through a dried reagent coating inside a thin (26 μm) counting chamber, allowing the delayed release of fluorochrome conjugated monoclonal antibodies after the filling of the chamber with whole blood by capillary flow. A custom-built image cytometer is used to capture fluorescence images representing more than 1 μl of blood. The thin layer of blood in combination with the large image area allows the use of whole blood from a finger prick without the need for dilution, lysis or cell enrichment. Automatic cell counting of CD4(+) and CD8(+) T-lymphocytes correlates well with results obtained by flow cytometry.

Four degree of freedom liquid dispenser for direct write capillary self-assembly with sub-nanoliter precision

Capillary forces provide a ubiquitous means of organizing micro- and nanoscale structures on substrates. In order to investigate the mechanism of capillary self-assembly and to fabricate complex ordered structures, precise control of the meniscus shape is needed. We present a precision instrument that enables deposition of liquid droplets spanning from 2 nl to 300 μl, in concert with mechanical manipulation of the liquid-substrate interface with four degrees of freedom. The substrate has sub-100 nm positioning resolution in three axes of translation, and its temperature is controlled using thermoelectric modules. The capillary tip can rotate about the vertical axis while simultaneously dispensing liquid onto the substrate. Liquid is displaced using a custom bidirectional diaphragm pump, in which an elastic membrane is hydraulically actuated by a stainless steel syringe. The syringe is driven by a piezoelectric actuator, enabling nanoliter volume and rate control. A quantitative model of the liquid dispenser is verified experimentally, and suggests that compressibility in the hydraulic line deamplifies the syringe stroke, enabling sub-nanoliter resolution control of liquid displacement at the capillary tip. We use this system to contact-print water and oil droplets by mechanical manipulation of a liquid bridge between the capillary and the substrate. Finally, we study the effect of droplet volume and substrate temperature on the evaporative self-assembly of monodisperse polymer microspheres from sessile droplets, and demonstrate the formation of 3D chiral assemblies of micro-rods by rotation of the capillary tip during evaporative assembly.

3D thermoplastic elastomer microfluidic devices for biological probe immobilization

Microfluidics has emerged as a valuable tool for the high-resolution patterning of biological probes on solid supports. Yet, its widespread adoption as a universal biological immobilization tool is still limited by several technical challenges, particularly for the patterning of isolated spots using three-dimensional (3D) channel networks. A key limitation arises from the difficulties to adapt the techniques and materials typically used in prototyping to low-cost mass-production. In this paper, we present the fabrication of thin thermoplastic elastomer membranes with microscopic through-holes using a hot-embossing process that is compatible with high-throughput manufacturing. The membranes provide the basis for the fabrication of highly integrated 3D microfluidic devices with a footprint of only 1 × 1 cm(2). When placed on a solid support, the device allows for the immobilization of up to 96 different probes in the form of a 10 × 10 array comprising isolated spots of 50 × 50 μm(2). The design of the channel network is optimized using 3D simulations based on the Lattice-Boltzmann method to promote capillary action as the sole force distributing the liquid in the device. Finally, we demonstrate the patterning of DNA and protein arrays on hard thermoplastic substrates yielding spots of excellent definition that prove to be highly specific in subsequent hybridization experiments.

Impact of picoliter droplets on superhydrophobic surfaces with ultralow spreading ratios

The impact of picoliter-sized water droplets on superhydrophobic CF(4) plasma fluorinated polybutadiene surfaces is investigated with high-speed imaging. Variation of the surface topography by plasmachemical modification enables the dynamics of wetting to be precisely controlled. Final spreading ratios as low as 0.63 can be achieved. A comparison of the maximum spreading ratio and droplet oscillation frequencies to models described in the literature shows that both are found to be much lower than theoretically predicted.

Cell patterning using a template of microstructured organosilane layer fabricated by vacuum ultraviolet light lithography

Micropatterning techniques have become increasingly important in cellular biology. Cell patterning is achieved by various methods. Photolithography is one of the most popular methods, and several light sources (e.g., excimer lasers and mercury lamps) are used for that purpose. Vacuum ultraviolet (VUV) light that can be produced by an excimer lamp is advantageous for fabricating material patterns, since it can decompose organic materials directly and efficiently without photoresist or photosensitive materials. Despite the advantages, applications of VUV light to pattern biological materials are few. We have investigated cell patterning by using a template of a microstructured organosilane layer fabricated by VUV lithography. We first made a template of a microstructured organosilane layer by VUV lithography. Cell adhesive materials (poly(d-lysine) and polyethyleneimine) were chemically immobilized on the organosilane template, producing a cell adhesive material pattern. Primary rat cardiac and neuronal cells were successfully patterned by culturing them on the pattern substrate. Long-term culturing was attained for up to two weeks for cardiac cells and two months for cortex cells. We have discussed the reproducibility of cell patterning and made suggestions to improve it.

Nonvolatile copolymer compositions for fabricating gel element microarrays

By modifying polymer compositions and cross-linking reagents, we have developed a simple yet effective manufacturing strategy for copolymerized three-dimensional gel element arrays. A new gel-forming monomer, 2-(hydroxyethyl) methacrylamide (HEMAA), was used. HEMAA possesses low volatility and improves the stability of copolymerized gel element arrays to on-chip thermal cycling procedures relative to previously used monomers. Probe immobilization efficiency within the new polymer was 55%, equivalent to that obtained with acrylamide (AA) and methacrylamide (MA) monomers. Nonspecific binding of single-stranded targets was equivalent for all monomers. Increasing cross-linker chain length improved hybridization kinetics and end-point signal intensities relative to N,N-methylenebisacrylamide (Bis). The new copolymer formulation was successfully applied to a model orthopox array. Because HEMAA greatly simplifies gel element array manufacture, we expect it (in combination with new cross-linkers described here) to find widespread application in microarray science.