Quantitative detection of protein arrays

Early Diagnosis of Multiple Sclerosis Based on Optical and Electrochemical Biosensors: Comprehensive Perspective

Background:

Multiple Sclerosis (MS) involves an immune-mediated response in which body’s immune system destructs the protective sheath (myelin). Part of the known MS biomarkers are discovered in cerebrospinal fluid like oligoclonal lgG (OCGB), and also in blood like myelin Oligodendrocyte Glycoprotein (MOG). The conventional MS diagnostic methods often fail to detect the disease in early stages such as Clinically Isolated Syndrome (CIS), which considered as a concerning issue since CIS highlighted as a prognostic factor of MS development in most cases.

Methods:

MS diagnostic techniques include Magnetic Resonance Imaging (MRI) of the brain and spinal cord, lumbar puncture (or spinal tap) that evaluate cerebrospinal fluid, evoked potential testing revealing abnormalities in the brain and spinal cord. These conventional diagnostic methods have some negative points such as extensive processing time as well as restriction in the quantity of samples that can be analyzed concurrently. Scientists have focused on developing the detection methods especially early detection which belongs to ultra-sensitive, non-invasive and needed for the Point of Care (POC) diagnosis because the situation was complicated by false positive or negative results.

Results:

As a result, biosensors are utilized and investigated since they could be ultra-sensitive to specific compounds, cost effective devices, body-friendly and easy to implement. In addition, it has been proved that the biosensors on physiological fluids (blood, serum, urine, saliva, milk etc.) have quick response in a non-invasive rout. In general form, a biosensor system for diagnosis and early detection process usually involves; biomarker (target molecule), bio receptor (recognition element) and compatible bio transducer.

Conclusion:

Studies underlined that early treatment of patients with high possibility of MS can be advantageous by postponing further abnormalities on MRI and subsequent attacks.

:

This Review highlights variable disease diagnosis approaches such as Surface Plasmon Resonance (SPR), electrochemical biosensors, Microarrays and microbeads based Microarrays, which are considered as promising methods for detection and early detection of MS.

Development of an Interaction Assay between Single-Stranded Nucleic Acids Trapped with Silica Particles and Fluorescent Compounds

Biopolymers are easily denatured by heating, a change in pH or chemical substances when they are immobilized on a substrate. To prevent denaturation of biopolymers, we developed a method to trap a polynucleotide on a substrate by hydrogen bonding using silica particles with surfaces modified by aminoalkyl chains ([A-AM silane]/SiO2). [A-AM silane]/SiO2 was synthesized by silane coupling reaction of N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (A-AM silane) with SiO2 particles with a diameter of 5 μm at 100 °C for 20 min. The surface chemical structure of [A-AM silane]/SiO2 was characterized by Fourier transform infrared spectroscopy and molecular orbital calculations. The surface of the silica particles was modified with A-AM silane and primary amine groups were formed. [A-AM silane]/SiO2 was trapped with single-stranded nucleic acids [(Poly-X; X = A (adenine), G (guanine) and C (cytosine)] in PBS solution at 37 °C for 1 h. The single-stranded nucleic acids were trapped on the surface of the [A-AM silane]/SiO2 by hydrogen bonding to form conjugated materials. The resulting complexes were further conjugated by derivatives of acridine orange (AO) as fluorescent labels under the same conditions to form [AO:Poly-X:A-AM silane]/SiO2 complexes. Changes in the fluorescence intensity of these complexes originating from interactions between the single-stranded nucleic acid and aromatic compounds were also evaluated. The change in intensity displayed the order [AO: Poly-G: A-AM silane]/SiO2 > [AO:Poly-A:A-AM silane]/SiO2 >> [AO:Poly-C:A-AM silane]/SiO2. This suggests that the single-stranded nucleic acids conjugated with aminoalkyl chains on the surfaces of SiO2 particles and the change in fluorescence intensity reflected the molecular interaction between AO and the nucleic-acid base in a polynucleotide.

Fluorescence-based multiplex protein detection using optically encoded microbeads

Potential utilization of proteins for early detection and diagnosis of various diseases has drawn considerable interest in the development of protein-based multiplex detection techniques. Among the various techniques for high-throughput protein screening, optically-encoded beads combined with fluorescence-based target monitoring have great advantages over the planar array-based multiplexing assays. This review discusses recent developments of analytical methods of screening protein molecules on microbead-based platforms. These include various strategies such as barcoded microbeads, molecular beacon-based techniques, and surface-enhanced Raman scattering-based techniques. Their applications for label-free protein detection are also addressed. Especially, the optically-encoded beads such as multilayer fluorescence beads and SERS-encoded beads are successful for generating a large number of coding.

Nanoscale labels: nanoparticles and liposomes in the development of high-performance biosensors

Technology for the detection of biological species has generated considerable interest in a variety of fields including healthcare, defense, food and environmental monitoring. In a biosensor, labeled specific binding partners are used to emit a detectable signal. Owing to their unique properties, nanomaterials have been proposed as a novel label category and have led to the development of new assays and new transduction mechanisms. In this article, the role of three major types of nanoscale labels (metallic, semiconductor and liposome nanoparticles) in the development of a new generation of optical, electrochemical or gravimetric biosensors will be presented. The underlying transduction principles will be briefly explained and assay strategies relying on the use of these ‘nanolabels’ will be described. The contribution to increased assay performance and sensitivity will be highlighted. Approaches towards simple, cost efficient and sensitive assays are essential to meet the demands of a growing number of applications.

Diagnostic devices as biomaterials: a review of nucleic acid and protein microarray surface performance issues

This review of current DNA and protein microarray diagnostic and bio-analytical technologies focuses on the different surface chemistries used in these miniaturized surface-capture formats. Description of current strategies in bio-immobilization and coupling to create multiplexed affinity bioassays in micrometer-sized printed spots, problems with current formats and review of some detection methods are included. Recommendations for improving long-standing challenges in DNA- and protein-based arrays are forwarded. The biomaterials community can contribute relevant expertise to these formidable bio-interfacial problems that represent significant barriers to clinical implementation of microarray assays.

Dissecting cancer serum protein profiles using antibody arrays

Antibody arrays represent one of the high-throughput techniques enabling detection of multiple proteins simultaneously. One of the main advantages of the technology over other proteomic approaches resides on that the identities of the measured proteins are known at front of the experimental design or can be readily characterized, facilitating a biological interpretation of the obtained results. This chapter overviews the technical issues of the main antibody array formats as well as various applications using serum specimens in the context of neoplastic diseases. Clinical applications of antibody arrays vary from biomarker discovery for diagnosis, prognosis, and drug response to characterization of s protein pathways and modification changes associated with disease development and progression. As a high-throughput tool addressing protein levels and post-translational modifications, it improves the functional characterization of molecular bases for cancer. Furthermore, the identification and validation of protein expression patterns characteristic of cancer progression and tumor subtypes may enable tailored therapeutic intervention and improvement in the clinical management of cancer patients. Technical requirements such as lower sample volume, antibody concentration, format versatility, and high reproducibility support their increasing impact in cancer research.

Quantitative detection of individual cleaved DNA molecules on surfaces using gold nanoparticles and scanning electron microscope imaging

Single-nucleotide polymorphisms (SNPs) are the most frequent type of human genetic variation. Recent work has shown that it is possible to directly analyze SNPs in unamplified human genomic DNA samples using the surface-invasive cleavage reaction followed by rolling circle amplification (RCA) labeling of the cleavage products. The individual RCA amplicon molecules were counted on the surface using fluorescence microscopy. Two principal limitations of such single-molecule counting are the variability in the amplicon size, which results in a large variation in fluorescence signal intensity from the dye-labeled DNA molecules, and a high level of background fluorescence. It is shown here that an excellent alternative to RCA labeling is tagging with gold nanoparticles followed by imaging with a scanning electron microscope. Gold nanoparticles have a uniform diameter (15 +/- 0.5 nm) and provide excellent contrast against the background of the silicon substrate employed. Individual gold nanoparticles are readily counted using publicly available software. The results demonstrate that the labeling efficiency is improved by as much as approximately 15-fold, and the signal-to-noise ratio is improved by approximately 4-fold. Detection of individual cleaved DNA molecules following surface-invasive cleavage was linear and quantitative over 3 orders of magnitude in amount of target DNA (10(-18)-10(-15) mol).

Carboxyl-terminated dendrimer-coated bioactive interface for protein microarray: high-sensitivity detection of antigen in complex biological samples

Protein microarrays are promising tools that can potentially enable high throughput proteomic screening in areas such as disease diagnosis and drug discovery. A critical aspect in the development of protein microarrays is the optimization of the array's surface chemistry to achieve the high sensitivity required for detection of proteins in cell lysate and other complex biological mixtures. In the present study, a high-density antibody array with minimal nonspecific cellular protein adsorption was prepared using a glass surface coated with a poly(propyleneimine) dendrimer terminated with carboxyl group (PAMAM-COOH). The carboxyl-terminated dendrimer-modified surface has almost similar nonspecific cellular protein adsorption when compared to an inert PEG-modified surface. In addition, the multiple functional sites available for reaction on the dendrimer surface facilitated high-density immobilization of antibodies and efficient capture of bioanalytes. Various molecules were tested for their ability to block or deactivate the reactive carboxyl surface after antibody immobilization to further reduce the nonspecific binding. A short oligoethylene glycol (NH2-d4-PEG-COOH), was found to significantly improve the signal-to-noise ratio of the assay, resulting in higher sensitivity. The properties and functional qualities of the various surfaces were characterized by contact angle and AFM measurements. Nonspecific protein adsorption and protein immobilization as a function of dendrimer generations and sensitivity of antigen capturing from a buffer (1 pM) as well as from the complex cell lysate (10 pM) system were examined. Our detailed experimental studies demonstrated a facile method of preparing surfaces with high protein loading and low nonspecific protein binding for the development of high sensitivity protein microarrays.

Thermosensitive Copolymer Networks Modify Gold Nanoparticles for Nanocomposite Entrapment

The core-shell gold nanoparticles and copolymer of N-isopropylacrylamide (NIPAM) and N,N'-methylenebisacrylamide (MBAA) hybrids (Au@copolymer) were fabricated through surface-initiated atom-transfer radical polymerization (ATRP) on the surface of gold nanoparticles in 2-propanol/water mixed solvents. The surface of citrate-stabilized gold nanoparticles was first modified by a disulfide initiator for ATRP. The slight cross-linking polymerization between NIPAM and MBAA occurred on the gold surface and resulted in the formation of core-shell Au@copolymer nanostructures that were characterized by TEM, and FTIR and UV-visible spectroscopy. Such synthesized Au@copolymer hybrids possess clearly thermosensitive properties and exhibit "inspire" and "expire" water behavior in response to temperature changes in aqueous solution. Because of this property, we enable to trap and encapsulate smaller nanoparticles by using the free space of the copolymer-network scaffold anchored at the gold surface.

Comparison of hydroxylated print additives on antibody microarray performance

Various hydroxylated additives were added to antibody print buffers at different concentrations to stabilize printed antibodies during normal array spot desiccation on commercial polymer-coated microarray slides. Polyvinyl alcohol addition to print buffers produced the most regular spot morphologies, homogeneous intra-spot antibody distribution, uniform fluorescence intensity, and improved analyte capture activity, maintained up to 1 month at 4 degrees C for capturing model analytes, anti-human IL-1beta, IL-4, and TNFalpha, on these microarraying slides.

Highly Sensitive Biomolecule Detection on a Quartz Crystal Microbalance Using Gold Nanoparticles as Signal Amplification Probes

We report here a novel strategy for the high-sensitive detection of target biomolecules with very low concentrations on a quartz crystal microbalance (QCM) device using gold nanoparticles as signal enhancement probes. By employing a streptavidin-biotin interaction as a model system, we could prepare biotin-conjugated gold nanoparticles maintaining good dispersion and long-term stability by controlling the biotin density on the surface of gold nanoparticles that have been investigated by UV-vis spectra and AFM images. These results showed that 10 microM N-(6-[biotinamido]hexyl)-3'-(2'-pyridyldithio)propionamide (biotin-HPDP) was the critical concentration to prevent the nonspecific aggregation of gold nanoparticles in this system. For sensing streptavidin target molecules by QCM, biotinylated BSA was absorbed on the Au surface of the QCM electrode and subsequent coupling of the target streptavidin to the biotin in the sensing interface followed. Amplification of the sensing process was performed by the interaction of the target streptavidin on the sensing surface with gold nanoparticles modified with 10 microM biotin-HPDP. The biotinylated gold nanoparticles were used as signal amplification probes to improve the detection limit, which was 50 ng/ml, of the streptavidin detection system without signal enhancement, and the calibration curve determined for the net frequency changes showed good linearity over a wide range from 1 ng/ml to 10 microg/ml for the quantitative streptavidin target molecule analysis. In addition, the measured dissipation changes suggested that the layer of biotin-BSA adsorbed on the Au electrode and the streptavidin layer assembled on the biotin-BSA surface were highly compact and rigid. On the other hand, the structure formed by the biotinylated gold nanoparticles on the streptavidin layer was flexible and dissipative, being elongated outward from the sensing surface.

Application of electrochemical impedance spectroscopy for monitoring allergen–antibody reactions using gold nanoparticle-based biomolecular immobilization method

Gold nanoparticles were used to enhance the immobilization amount and retain the immunoactivity of recombinant dust mite allergen Der f2 immobilized on a glassy carbon electrode (GCE). The interaction between allergen and antibody was studied by electrochemical impedance spectroscopy (EIS). Self-assembled Au colloid layer (ø=16nm) deposited on (3-mercaptopropyl)trimethoxysilane (MPTS)-modified GCE offered a basis to control the immobilization of allergen Der f2. The impedance measurements were based on the charge transfer kinetics of the [Fe(CN)(6)](3-/4-) redox pair, compared with bare GCE, the immobilization of allergen Der f2 and the allergen-antibody interaction that occurred on the electrode surface altered the interfacial electron transfer resistance and thereby slowed down the charge transfer kinetics by reducing the active area of the electrode or by preventing the redox species in electrolyte solution from approaching the electrode. The interactions of allergen with various concentrations of monoclonal antibody were also monitored through the change of impedance response. The results showed that the electron transfer resistance increased with increasing concentrations of monoclonal antibody.

Antibody Arrays: Technical Considerations and Clinical Applications in Cancer

Antibody arrays represent one of the high-throughput techniques that are able to detect multiple proteins simultaneously. One of the main advantages of this technology over other proteomic approaches is that the identities of the measured proteins are known or can be readily characterized, allowing a biological interpretation of the results. Features such as lower sample volume and antibody concentration requirements, higher format versatility, and reproducibility support the increasing use of antibody arrays in cancer research. Clinical applications include disease marker discovery for diagnosis, prognosis, and drug response, characterization of signaling and protein pathways, and modifications associated with disease development and progression. This report presents an overview of technical issues of the main antibody array formats and various applications in cancer research. Antibody arrays are high-throughput tools that improve the functional characterization of molecular bases for disease. Furthermore, identification and validation of protein expression patterns, characteristic of cancer progression, and tumor subtypes may intervene and improve tailored therapies in the clinical management of cancer patients.

Diagnostic and analytical applications of protein microarrays

DNA microarrays have changed the field of biomedical sciences over the past 10 years. For several reasons, antibody and other protein microarrays have not developed at the same rate. However, protein and antibody arrays have emerged as a powerful tool to complement DNA microarrays during the past 5 years. A genome-scale protein microarray has been demonstrated for identifying protein-protein interactions as well as for rapid identification of protein binding to a particular drug. Furthermore, protein microarrays have been shown as an efficient tool in cancer profiling, detection of bacteria and toxins, identification of allergen reactivity and autoantibodies. They have also demonstrated the ability to measure the absolute concentration of small molecules. Besides their capacity for parallel diagnostics, microarrays can be more sensitive than traditional methods such as enzyme-linked immunosorbent assay, mass spectrometry or high-performance liquid chromatography-based assays. However, for protein and antibody arrays to be successfully introduced into diagnostics, the biochemistry of immunomicroarrays must be better characterized and simplified, they must be validated in a clinical setting and be amenable to automation or integrated into easy-to-use systems, such as micrototal analysis systems or point-of-care devices.

Active bead-linked immunoassay on protein microarrays

Protein microarrays are becoming a powerful tool in proteome, biochemical, and clinical studies. In addition to the quality of arrayed immobilized probe molecules, sensitivity of the microarray-based assay is highly dependent on the detection technique. Here we suggest four simple techniques for rapid detection of analytes bound to protein microarrays. The techniques employ functionalized magnetic and non-magnetic beads moved to, from, or along the array surface by external forces. In contrast to other labeling techniques actively controlled physical labels: (i) make detection extremely fast to allow microarray reading in seconds; (ii) provide a low background due to active removal of weakly bound beads; and (iii) provide a highly sensitive detection, since one antigen-antibody bond is capable of holding bead immobilized on the array surface. In combination with the electrophoretically assisted active immunoassay we described recently such active reading allows to reduce total indirect immunoassay time to 7-10 min while having sensitivity in the femtomolar concentration range. High speed, sensitivity, and specificity make active bead-linked detection an ideal choice in rapid high-throughput screening and in emergency diagnostics.

Investigation on the interaction between colloidal gold and human complement factor 4 at different pH by spectral methods

The interaction between colloidal gold and human complement factor 4 (human C4) at different pH was investigated by spectral methods, including absorption and resonance light-scattering spectrometry. According to the changes of color and absorption spectra of colloidal gold solution in presence of human C4, the interaction between colloidal gold and human C4 was quantitatively investigated using a semi-empirical "flocculation parameter". At the same time, the changes of resonance light-scattering spectra and transmission electron microscopy (TEM) images indicate that the aggregation of colloidal gold happens by electrostatic interaction in presence of human C4 in the pH range 5-6. However, the colloidal gold solution remains stable at pH >6 and pH <5 due to the repulsive electrostatic interaction between colloidal gold and human C4. The flocculation parameter is directly proportional to the concentration of human C4 in the range from 9.7 to 233.0 microgl(-1). In addition, the interactions between the colloidal gold and bovine serum albumin (BSA) as well as human serum albumin (HSA) were also investigated using the same methods. It was found that there was no aggregation of colloidal gold in presence of BSA and HSA in the pH range 5-6. However, when the pH of solution is 4, the aggregation of colloidal gold happens. Because BSA and HSA have different structure, the intensity of aggregation of colloidal gold in presence of BSA is greater than that in presence of HSA at pH 4.

Nanoparticle Conjugation Increases Protein Partitioning in Aqueous Two-Phase Systems

We describe the effect of bioconjugation to colloidal Au nanoparticles on protein partitioning in poly(ethylene glycol) (PEG)/dextran aqueous two-phase systems (ATPS). Horseradish peroxidase (HRP) was conjugated to colloidal Au nanoparticles by direct adsorption. Although HRP alone had very little phase preference, HRP/Au nanoparticle conjugates typically partitioned to the PEG-rich phase, up to a factor of 150:1 for conjugates of 15-nm colloidal Au. Other protein/Au nanoparticle conjugates exhibited partitioning of greater than 2000:1 to the dextran-rich phase, as compared with approximately 5:1 for the free protein. The degree of partitioning was dependent on polymer concentration and molecular weight, nanoparticle diameter, and in some instances, nanoparticle concentration in the ATPS. The substantial improvements in protein partitioning achievable by conjugation to Au nanoparticles appear to result largely from increased surface area of the conjugates and require neither chemical modification of the proteins or polymers with affinity ligands, increased polymer concentrations, nor addition of high concentrations of salts. Adsorption to colloidal particles thus provides an attractive route for increased partitioning of enzymes and other proteins in ATPS. Furthermore, these results point to ATPS partitioning as a powerful means of purification for biomolecule/nanoparticle conjugates, which are increasingly used in diagnostics and materials applications.

Fabrication of high quality microarrays

Fabrication of DNA microarray demands that between ten (diagnostic microarrays) and many hundred thousands of probes (research or screening microarrays) are efficiently immobilised to a glass or plastic surface using a suitable chemistry. DNA microarray performance is measured by parameters like array geometry, spot density, spot characteristics (morphology, probe density and hybridised density), background, specificity and sensitivity. At least 13 factors affect these parameters and factors affecting fabrication of microarrays are used in this review to compare different fabrication methods (spotted microarrays and in situ synthesis of microarrays) and immobilisation chemistries.

Chip devices for miniaturized biotechnology

Chip devices were introduced in chemistry and molecular biology to improve the read-out of information from molecular systems by efficient analytical procedures and to organize automated experiments. Biochips and chip reactor systems are of interest for cellular processes, too, and can be regarded as components in interfaces for the information exchange between living nature and digital electronic systems. In this minireview, different types of chip reactors for biotechnological applications like nanotiterplates, chip thermocyclers and devices for segmented flow operations are discussed. Finally, an outlook is given on the application of chip reactor systems, which are promising tools for automated experiments with highly parallelized screening procedures, for artificial microcompartmentation, cell analogue systems, micro-ecological studies, investigations on modulated morphogenesis, and for a bioanalogue molecular nanotechnology.

Integrated nanoparticle-biomolecule hybrid systems: synthesis, properties, and applications

Nanomaterials, such as metal or semiconductor nanoparticles and nanorods, exhibit similar dimensions to those of biomolecules, such as proteins (enzymes, antigens, antibodies) or DNA. The integration of nanoparticles, which exhibit unique electronic, photonic, and catalytic properties, with biomaterials, which display unique recognition, catalytic, and inhibition properties, yields novel hybrid nanobiomaterials of synergetic properties and functions. This review describes recent advances in the synthesis of biomolecule-nanoparticle/nanorod hybrid systems and the application of such assemblies in the generation of 2D and 3D ordered structures in solutions and on surfaces. Particular emphasis is directed to the use of biomolecule-nanoparticle (metallic or semiconductive) assemblies for bioanalytical applications and for the fabrication of bioelectronic devices.

Development of a nanoparticle-labeled microfluidic immunoassay for detection of pathogenic microorganisms

The light-scattering properties of submicroscopic metal particles ranging from 40 to 120 nm in diameter have recently been investigated. These particles scatter incident white light to generate monochromatic light, which can be seen either by the naked eye or by dark-field microscopy. The nanoparticles are well suited for detection in microchannel-based immunoassays. The goal of the present study was to detect Helicobacter pylori- and Escherichia coli O157:H7-specific antigens with biotinylated polyclonal antibodies. Gold particles (diameter, 80 nm) functionalized with a secondary antibiotin antibody were then used as the readout. A dark-field stereomicroscope was used for particle visualization in poly(dimethylsiloxane) microchannels. A colorimetric quantification scheme was developed for the detection of the visual color changes resulting from immune reactions in the microchannels. The microchannel immunoassays reliably detected H. pylori and E. coli O157:H7 antigens in quantities on the order of 10 ng, which provides a sensitivity of detection comparable to those of conventional dot blot assays. In addition, the nanoparticles within the microchannels can be stored for at least 8 months without a loss of signal intensity. This strategy provides a means for the detection of nanoparticles in microchannels without the use of sophisticated equipment. In addition, the approach has the potential for use for further miniaturization of immunoassays and can be used for long-term archiving of immunoassays.

Surface-enhanced Raman scattering studies on immunoassay

Surface-enhanced Raman scattering (SERS) has recently been a matter of keen interest from the points of both basic science and applications because by using the SERS effect one can obtain Raman signals even from a single molecule. Immunoassay is one of the most promising fields in the applications of SERS, and the purpose of this review paper is to discuss the potential of SERS in immunoassay. This paper consists of four parts work on the indirect and direct methods of immunoassay via SERS. These methods provide the laboratorial attempts on biomedical diagnostic applications of SERS.

Development of a nanoparticle-labeled microfluidic immunoassay for detection of pathogenic microorganisms

The light-scattering properties of submicroscopic metal particles ranging from 40 to 120 nm in diameter have recently been investigated. These particles scatter incident white light to generate monochromatic light, which can be seen either by the naked eye or by dark-field microscopy. The nanoparticles are well suited for detection in microchannel-based immunoassays. The goal of the present study was to detect Helicobacter pylori- and Escherichia coli O157:H7-specific antigens with biotinylated polyclonal antibodies. Gold particles (diameter, 80 nm) functionalized with a secondary antibiotin antibody were then used as the readout. A dark-field stereomicroscope was used for particle visualization in poly(dimethylsiloxane) microchannels. A colorimetric quantification scheme was developed for the detection of the visual color changes resulting from immune reactions in the microchannels. The microchannel immunoassays reliably detected H. pylori and E. coli O157:H7 antigens in quantities on the order of 10 ng, which provides a sensitivity of detection comparable to those of conventional dot blot assays. In addition, the nanoparticles within the microchannels can be stored for at least 8 months without a loss of signal intensity. This strategy provides a means for the detection of nanoparticles in microchannels without the use of sophisticated equipment. In addition, the approach has the potential for use for further miniaturization of immunoassays and can be used for long-term archiving of immunoassays.

Label-Free Reading of Microarray-Based Immunoassays with Surface Plasmon Resonance Imaging

A simple method is presented for patterning of protein antigens at a gold surface for use in surface plasmon resonance (SPR) imaging experiments. Microfluidic devices fabricated from poly(dimethylsiloxane) were used to flow various fluids over a gold substrate in spatially defined channels. This technique was used to pattern the surface chemistry of the gold as well as to adsorb antigens from solution to the modified substrates. The resulting antigen arrays were probed with complementary antibodies in order to demonstrate the effectiveness of the patterning for antibody capture experiments. SPR imaging was used to aid in the optimization of array fabrication and to observe the interactions of unlabeled antibodies with these microarrays. This work presents a means of fabricating microarrays with controlled surface density of antigens. SPR imaging provides both quantitative and qualitative evaluation of antibody binding in a label free format.

Seeing Better through a MIST: Evaluation of Monoclonal Recombinant Antibody Fragments on Microarrays

Automation is the key approach for genomewide and proteomewide screening of function and interaction. Especially for proteomics, antibody microarrays are a useful tool for massive parallel profiling of complex samples. To meet the requirements of antibody microarrays and to obtain a great variety of antibodies, new technologies such as phage display have partly replaced the classical hybridoma method. While the selection process for phage-displayed antibody fragments itself has been automated, the bottleneck was shifted further downstream to the identification of monoclonal binders obtained from the selections. Here, we present a new approach to reduce time, material, and waste to extend automation beyond the selection process by application of conventional microarray machinery. We were able to express recombinant antibody fragments in a single inoculation and expression step and subjected them without purification directly to an automated high-throughput screening procedure based on the multiple spotting technique (MIST). While obtaining comparable sensitivities to enzyme-linked immunosorbent assays, we minimized manual interaction steps and streamlined the technique to be accessible within the automated selection procedure.