Applications of antibody array platforms

Machine Learning-Assisted Array-Based Detection of Proteins in Serum Using Functionalized MoS2 Nanosheets and Green Fluorescent Protein Conjugates

Abnormal concentrations of a specific protein or the presence of some biomarker proteins may indicate life-threatening diseases. Pattern-based detection of specific analytes using affinity-regulated receptors is one of the potential alternatives to specific antigen-antibody-based detection. In this report, we have schemed a sensor array by using various functionalized two-dimensional (2D)-MoS2 nanosheets and green fluorescent protein (GFP) as the receptor and the signal transducer, respectively. Two-dimensional MoS2 has been used as a promising candidate for recognition of the bioanalytes because of its high surface-to-volume ratio compared to those of other nanomaterials. Easy surface tunability of this material provides additional advantages to analyze the target of interest. The optimized 2D-MoS2-GFP conjugates are able to discriminate 15 different proteins at 50 nM concentration with a detection limit of 1 nM. Moreover, proteins in the binary mixture and in the presence of serum were discriminated successfully. Ten different proteins in serum media at relevant concentrations were classified successfully with 100% jackknifed classification accuracy, which proves the potentiality of the above system. We have also implemented and discussed the implication of using different machine learning models on the pattern recognition problem associated with array-based sensing.

Fabrication of Ag nanorods on micropost array for a metal-enhanced fluorescence substrate with a high signal-to-background ratio

Selective fabrication of metallic nanostructures at the spotting area is required to increase the signal-to-background noise ratio (SBR) of the metal-enhanced fluorescence (MEF) substrate. As a simple and cost-effective fabrication method for MEF substrate with high SBR, a glancing angle deposition (GLAD) process of Ag material on the UV-imprinted micropost array (50 μm in height, 300 μm in diameter, and 600 μm in pitch) was proposed to selectively fabricate Ag nanorods on the top of micropost structure (spotting area). Ag nanorod formation at the bottom of the micropost decreased as the deposition angle in Ag GLAD increased. A deposition angle of 89° and deposition thickness of 500 nm were selected as the optimum GLAD conditions to maximize the SBR. The optimum Ag nanorods on micropost array (AgNMPA) MEF substrate provided 71-fold fluorescence signal enhancement and 25-times higher SBR than the bare glass substrate. It also provided 7-times higher SBR than the Ag nanorod MEF substrate, which has a similar Ag nanorod structure but is not selectively formed. The detection limit of AgNMPA was 16- and 4-times lower than that of the amine-functionalized glass substrate and commercial epoxy slide, respectively. Although the fluorescence signal of AgNMPA was similar to that of Ag nanorod substrate, the detection limit was 2-times lower because of the low signal standard deviation caused by the low background noise and clear spot shape.

PARAFAC study of L-cys@CdTe QDs interaction to BSA, cytochrome c and trypsin: An approach through electrostatic and covalent bonds

Utilizing fluorescence spectroscopy, non-covalent and covalent interactions of L-cys@CdTe quantum dots to bovine serum albumin (BSA), cytochrome c and trypsin were investigated. L-cys@CdTe QDs with the emission maximum at 530 nm and an average diameter of 2.6 nm were synthesized in the aqueous medium. Formaldehyde, N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride (EDC) with N-hydroxysuccinimide (NHS), and glutaraldehyde was applied as cross-linkers. In the case of both electrostatic and covalent strategies PARAFAC, as a powerful multi-way chemometrics technique, was utilized to analyze fluorescence excitation-emission (EEM) spectra. For non-covalent and covalent bonding, two and three significant components composed the PARAFAC models. Resolved EEM shows that in the presence of formaldehyde, a new component with an emission peak similar to BSA was obtained. Using EDC-NHS cross-linker, the fluorescence peak of the newly formed component was in a distinct wavelength with similar emission intensity, compared to L-cys@CdTe QDs and BSA. Employing glutaraldehyde, a distinguished component was easily detected at emission wavelengths higher than that of L-cys@CdTe QDs and proteins. It was concluded that the choice of cross-linker is a critical step to create different emission spectra when dealing with nano-bio-conjugations. This study shows that glutaraldehyde cross-linker leads to increase sensitivity, selectivity, and accuracy of protein analysis.

Protein discrimination based on DNA induced perylene probe self-assembly

The development of a simple and effective method for the highly sensitive and selective discrimination of proteins is a subject of enormous interest. Herein, we report the construction of a novel fluorescence detection method based on a perylene probe for the highly efficient discrimination of multiple proteins. Single-stranded DNA (ssDNA) could induce aggregation of the perylene probe which caused quenching of probe fluorescence. After the addition of a protein, the protein could interact with the ssDNA-probe assembly complex with "turn-on" or further "turn-off" fluorescence response. A sensor array was designed based on the above phenomena which could realize the successful discrimination of proteins with 100% accuracy of cross validation. Nine representative proteins were successfully recognized. Moreover, it was observed that a protein could induce characteristic effect on the DNA-probe assembly with varying pH of assay buffer. Thus, different proteins showed unique fluorescence response towards assay buffers having different pH values. The assay buffer pH was then utilized as a sensing channel. Based on Linear Discriminant Analysis (LDA) nine proteins were successfully discriminated at the nanomolar concentration with 100% accuracy of cross validation. Furthermore, the sensor array also demonstrated differentiation of the nine proteins regardless of their concentration. The developed sensor array could also detect the proteins with great precision in human urine sample at a quite low concentration, which suggests its practical applicability for analysis of biological fluids.

Regioselective SN2-Type Reaction for the Oriented and Irreversible Immobilization of Antibodies to a Glass Surface Assisted by Boronate Formation

Antibodies have exquisite specificities for molecular recognition, which have led to their incorporation into array sensors that are crucial for research, diagnostic, and therapeutic applications. Many of these platforms rely heavily on surface-bound reactive groups to covalently tether antibodies to solid substrates; however, this strategy is hindered by a lack of orientation control over antibody immobilization. Here, we report a mild electrophilic phenylsulfonate (tosylate) ester-containing boronic acid affinity ligand for attaching antibodies to glass slides. A high level of antibody coupling located near the Fc region of the boronated antibody complex could be achieved by the proximal nucleophilic amino acid driven substitution reaction at the phenylsulfonate center. This enabled the full-length antibodies to be permanently tethered onto surfaces in an oriented manner. The advantages of this strategy were demonstrated through the individual and multiplex detection of protein and serum biomarkers. This strategy not only confers stability to the immobilized antibodies but also presents a different direction for the irreversible attachment of antibodies to solid supports in an orientation-controlled way.

Affinity-Bead Assisted Mass Spectrometry (Affi-BAMS): A Multiplexed Microarray Platform for Targeted Proteomics

The ability to quantitatively probe diverse panels of proteins and their post-translational modifications (PTMs) across multiple samples would aid a broad spectrum of biological, biochemical and pharmacological studies. We report a novel, microarray analytical technology that combines immuno-affinity capture with Matrix Assisted Laser Desorption Ionization Mass Spectrometry (MALDI MS), which is capable of supporting highly multiplexed, targeted proteomic assays. Termed "Affinity-Bead Assisted Mass Spectrometry" (Affi-BAMS), this LC-free technology enables development of highly specific and customizable assay panels for simultaneous profiling of multiple proteins and PTMs. While affinity beads have been used previously in combination with MS, the Affi-BAMS workflow uses enrichment on a single bead that contains one type of antibody, generally capturing a single analyte (protein or PTM) while having enough binding capacity to enable quantification within approximately 3 orders of magnitude. The multiplexing capability is achieved by combining Affi-BAMS beads with different protein specificities. To enable screening of bead-captured analytes by MS, we further developed a novel method of performing spatially localized elution of targets from individual beads arrayed on a microscope slide. The resulting arrays of micro spots contain highly concentrated analytes localized within 0.5 mm diameter spots that can be directly measured using MALDI MS. While both intact proteins and protein fragments can be monitored by Affi-BAMS, we initially focused on applying this technology for bottom-up proteomics to enable screening of hundreds of samples per day by combining the robust magnetic bead-based workflow with the high throughput nature of MALDI MS acquisition. To demonstrate the variety of applications and robustness of Affi-BAMS, several studies are presented that focus on the response of 4EBP1, RPS6, ERK1/ERK2, mTOR, Histone H3 and C-MET to stimuli including rapamycin, H2O2, EPO, SU11274, Staurosporine and Vorinostat.

Multichannel DNA Sensor Array Fingerprints Cell States and Identifies Pharmacological Effectors of Catabolic Processes

Cells at disease onset are often associated with subtle changes in the expression level of a single or few molecular components, making traditionally used biomarker-driven clinical diagnosis a challenging task. We demonstrate here the design of a DNA nanosensor array with multichannel output that identifies the normal or pathological state of a cell based on the alteration of its global proteomic signature. Fluorophore-encoded single-stranded DNA (ssDNA) strands were coupled via supramolecular interaction with a surface-functionalized gold nanoparticle quencher to generate this integrated sensor array. In this design, ssDNA sequences exhibit dual roles, where they provide differential affinities with the receptor gold nanoparticle as well as act as transducer elements. The unique interaction mode of the analyte molecules disrupts the noncovalent supramolecular complexation, generating simultaneous multichannel fluorescence output to enable signature-based analyte identification via a linear discriminant analysis-based machine learning algorithm. Different cell types, particularly normal and cancerous cells, were effectively distinguished using their fluorescent fingerprints. Additionally, this DNA sensor array displayed excellent sensitivity to identify cellular alterations associated with chemical modulation of catabolic processes. Importantly, pharmacological effectors, which could modulate autophagic flux, have been effectively distinguished by generating responses from their global protein signatures. Taken together, these studies demonstrate that our multichannel DNA nanosensor is well suited for rapid identification of subtle changes in a complex mixture and thus can be readily expanded for point-of-care clinical diagnosis, high-throughput drug screening, or predicting the therapeutic outcome from a limited sample volume.

---Successful Application of Whole Cell Panning for Isolation of Phage Antibody Fragments Specific to Differentiated Gastric Cancer Cells

Purpose: Generation of antibodies which potentially discriminate between malignant and healthy cells is an important prerequisite for early diagnosis and treatment of gastric cancer (GC). Comparative analysis of cell surface protein landscape will provide an experimental basis for biomarker discovery, which is essential for targeted molecular therapies. This study aimed to isolate phage-displayed antibody fragments recognizing cell surface proteins, which were differently expressed between two closely related GC cell lines, namely AGS and MKN-45.

Methods: We selected and screened a semisynthetic phage-scFv library on AGS, MKN-45, and NIH-3T3 cell lines by utilizing a tailored selection scheme that was designed to isolate phagescFvs that not only recognize the differentiated AGS cells but also distinguish them from NIH3T3 fibroblasts and the poorly differentiated MKN-45 cells.

Results: After four rounds of subtractive whole cell panning, 14 unique clones were identified by ELISA screening and nucleotide sequencing. For further characterization, we focused on four phage-scFvs with strong signals in screening, and their specificity was confirmed by cell-based ELISA. Furthermore, the selected phage-scFvs were able to specifically stain AGS cells with 38.74% (H1), 11.04% (D11), 76.93% (G11), and 69.03% (D1) in flow cytometry analysis which supported the ability of these phage scFvs in distinguishing AGS from MKN-45 and NIH-3T3 cells.

Conclusion: Combined with other proteomic techniques, these phage-scFvs can be applied to membrane proteome analysis and, subsequently, identification of novel tumor-related antigens mediating proliferation and differentiation of cells. Furthermore, such antibody fragments can be exploited for diagnostic purposes as well as targeted drug delivery of GC.

The effects of tether placement on antibody stability on surfaces

Despite their potential benefits, antibody microarrays have fallen short of performing reliably and have not found widespread use outside of the research setting. Experimental techniques have been unable to determine what is occurring on the surface of an atomic level, so molecular simulation has emerged as the primary method of investigating protein/surface interactions. Simulations of small proteins have indicated that the stability of the protein is a function of the residue on the protein where a tether is placed. The purpose of this research is to see whether these findings also apply to antibodies, with their greater size and complexity. To determine this, 24 tethering locations were selected on the antibody Protein Data Bank (PDB) ID: 1IGT. Replica exchange simulations were run on two different surfaces, one hydrophobic and one hydrophilic, to determine the degree to which these tethering sites stabilize or destabilize the antibody. Results showed that antibodies tethered to hydrophobic surfaces were in general less stable than antibodies tethered to hydrophilic surfaces. Moreover, the stability of the antibody was a function of the tether location on hydrophobic surfaces but not hydrophilic surfaces.

New Insights into the Tumor Microenvironment Utilizing Protein Array Technology

The tumor microenvironment (TME) is a considerably heterogeneous niche, which is created by tumor cells, the surrounding tumor stroma, blood vessels, infiltrating immune cells, and a variety of associated stromal cells. Intercellular communication within this niche is driven by soluble proteins synthesized by local tumor and stromal cells and include chemokines, growth factors, interferons, interleukins, and angiogenic factors. The interaction of tumor cells with their microenvironment is essential for tumorigenesis, tumor progression, growth, and metastasis, and resistance to drug therapy. Protein arrays enable the parallel detection of hundreds of proteins in a small amount of biological sample. Recent data have demonstrated that the application of protein arrays may yield valuable information regarding the structure and functional mechanisms of the TME. In this review, we will discuss protein array technologies and their applications in TME analysis to discern pathways involved in promoting the tumorigenic phenotype.

A supramolecular assembly enables discrimination between metalloproteins and non-metalloproteins

A supramolecular assembly yields turn-on fluorescence response for non-metalloproteins and turn-off response for metalloproteins.

Cationic polymer-based plasmonic sensor array that discriminates proteins

Breaking the restrictions of the lock-and-key sensing strategy which relies only on the most dominant interactions between the sensing element and target, here, we develop a colorimetric sensor array with three kinds of cationic polymers (polydiallyl dimethylammonium chloride (PDDA), chitosan (CTS), and cetyltrimethylammonium bromide (CTAB)) as nonspecific receptors.

Targeted quantification of functional enzyme dynamics in environmental samples for microbially mediated biogeochemical processes

Microbial enzymes catalytically drive biogeochemical processes in environments. The dynamic linkage between functional enzymes and biogeochemical species transformation has, however, rarely been investigated for decades because of the challenges to directly quantify enzymes in environmental samples. The diversity of microorganisms, the low amount of available biomass and the complexity of chemical composition in environmental samples represent the main challenges. To address the diversity challenge, we first identify several signature peptides that are conserved in the targeted enzymes with the same functionality across many phylogenetically diverse microorganisms using metagenome-based protein sequence data. Quantification of the signature peptides then allows estimation of the targeted enzyme abundance. To achieve analyses of the requisite sensitivity for complex environmental samples with low available biomass, we adapted a recently developed ultrasensitive targeted quantification technology, termed high-pressure high-resolution separations with intelligent selection and multiplexing (PRISM) by improving peptide separation efficiency and method detection sensitivity. Nitrate reduction dynamics catalyzed by dissimilatory and assimilatory enzymes in a hyporheic zone sediment was used as an example to demonstrate the application of the enzyme quantification approach. Together with the measurements of biogeochemical species, the approach enables investigating the dynamic linkage between functional enzymes and biogeochemical processes.

Precision diagnostics: moving towards protein biomarker signatures of clinical utility in cancer

Interest in precision diagnostics has been fuelled by the concept that early detection of cancer would benefit patients; that is, if detected early, more tumours should be resectable and treatment more efficacious. Serum contains massive amounts of potentially diagnostic information, and affinity proteomics has risen as an accurate approach to decipher this, to generate actionable information that should result in more precise and evidence-based options to manage cancer. To achieve this, we need to move from single to multiplex biomarkers, a so-called signature, that can provide significantly increased diagnostic accuracy. This Opinion article focuses on the progress being made in identifying protein biomarker signatures of clinical utility, using blood-based proteomics.

Low temperature growth of ZnO nanotubes for fluorescence quenching detection of DNA

In this work, large-scale and single-crystalline ZnO nanotubes were fabricated by a simple technique from an aqueous solution at a low temperature of 65 °C. According to detailed morphology, structural and compositional analyses showed that the ZnO nanotubes [diameter ~200 nm (wall thickness ~50 nm); length ~1 µm] have single-crystallite with wurtzite structure. As-prepared ZnO nanotubes showed an effective fluorescence quenching for the detection of calf thymus DNA. In particular, increasing DNA concentrations (5-50 µM) into the fixed concentration of ZnO nanotubes (50 µM) progressively quenched the intrinsic fluorescence of nanotubes, which showed that the nanotubes fluorescence was efficiently quenched upon binding to DNA. At the highest ZnO-DNA molar ratios of 1:1.8, around 50.1 % of fluorescence quenching of DNA was observed. Significance of this study provides simple, cost-effective, and low temperature synthesis of ZnO nanotubes revealed better fluorescence property toward a platform of DNA sensor. ZnO nanotubes with diameter of ~200 nm (wall thickness ~50 nm) and length of about 1 µm prepared at low temperature (65 °C) showed fluorescence was efficiently quenched upon binding to DNA. In particular, around 50.1 % of DNA fluorescence quenching at the highest ZnO-DNA molar ratios of 1:1.8 was observed.

Progress and prospects for the discovery of biomarkers for gastric cancer: a focus on proteomics

INTRODUCTION

Patient outcomes from gastric cancer vary due to the complexity of stomach carcinogenesis. Recent research using proteomic technologies has targeted components of all of these systems in order to develop biomarkers to aid the early diagnosis of gastric cancer and to assist in prognostic stratification. Areas covered: This review is comprised of evidence obtained from literature searches from PubMed. It covers the evidence of diagnostic, prognostic, and predictive biomarkers for gastric cancer using proteomic technologies, and provides up-to-date references. Expert commentary: The proteomic technologies have not only enabled the screening of a large number of samples, but also enabled the identification of diagnostic, prognostic and predictive biomarkers for gastric cancer. While major challenges still remain, to date, proteomic studies in gastric cancer have provided a wealth of information in revealing proteome alterations associated with the disease.

Advancing the global proteome survey platform by using an oriented single chain antibody fragment immobilization approach

Increasing the understanding of a proteome and how its protein composition is affected by for example different diseases, such as cancer, has the potential to improve strategies for early diagnosis and therapeutics. The Global Proteome Survey or GPS is a method that combines mass spectrometry and affinity enrichment with the use of antibodies. The technology enables profiling of complex proteomes in a species independent manner. The sensitivity of GPS, and other methods relying on affinity enrichment, is largely affected by the activity of the exploited affinity reagent. We here present an improvement of the GPS platform by utilizing an antibody immobilization approach which ensures a controlled immobilization process of the antibody to the magnetic bead support. More specifically, we make use of an antibody format that enables site-directed biotinylation and use this in combination with streptavidin coated magnetic beads. The performance of the expanded GPS platform was evaluated by profiling yeast proteome samples. We demonstrate that the oriented antibody immobilization strategy increases the ability of the GPS platform and results in larger fraction of functional antibodies. Additionally, we show that this new antibody format enabled in-solution capture, i.e. immobilization of the antibodies after sample incubation. A workflow has been established that permit the use of an oriented immobilization strategy for the GPS platform.

Multicolor Quantum Dot-Based Chemical Nose for Rapid and Array-Free Differentiation of Multiple Proteins

Nanomaterial-based differential sensors (e.g., chemical nose) have shown great potential for identification of multiple proteins because of their modulatable recognition and transduction capability but with the limitation of array separation, single-channel read-out, and long incubation time. Here, we develop a multicolor quantum dot (QD)-based multichannel sensing platform for rapid identification of multiple proteins in an array-free format within 1 min. A protein-binding dye of bromophenol blue (BPB) is explored as an efficient reversible quencher of QDs, and the mixture of BPB with multicolor QDs may generate the quenched QD-BPB complexes. The addition of proteins will disrupt the QD-BPB complexes as a result of the competitive protein-BPB binding, inducing the separation of BPB from the QDs and the generation of distinct fluorescence patterns. The multicolor patterns may be collected at a single-wavelength excitation and differentiated by a linear discriminant analysis (LDA). This multichannel sensing platform allows for the discrimination of ten proteins and seven cell lines with the fastest response rate reported to date, holding great promise for rapid and high-throughput medical diagnostics.

Antibody Microarray for E. coli O157:H7 and Shiga Toxin in Microtiter Plates

Antibody microarray is a powerful analytical technique because of its inherent ability to simultaneously discriminate and measure numerous analytes, therefore making the technique conducive to both the multiplexed detection and identification of bacterial analytes (i.e., whole cells, as well as associated metabolites and/or toxins). We developed a sandwich fluorescent immunoassay combined with a high-throughput, multiwell plate microarray detection format. Inexpensive polystyrene plates were employed containing passively adsorbed, array-printed capture antibodies. During sample reaction, centrifugation was the only strategy found to significantly improve capture, and hence detection, of bacteria (pathogenic Escherichia coli O157:H7) to planar capture surfaces containing printed antibodies. Whereas several other sample incubation techniques (e.g., static vs. agitation) had minimal effect. Immobilized bacteria were labeled with a red-orange-fluorescent dye (Alexa Fluor 555) conjugated antibody to allow for quantitative detection of the captured bacteria with a laser scanner. Shiga toxin 1 (Stx1) could be simultaneously detected along with the cells, but none of the agitation techniques employed during incubation improved detection of the relatively small biomolecule. Under optimal conditions, the assay had demonstrated limits of detection of ~5.8 × 10⁵ cells/mL and 110 ng/mL for E. coli O157:H7 and Stx1, respectively, in a ~75 min total assay time.

Proteomics in gastric cancer research: Benefits and challenges

Among various cancers, gastric cancer (GC) exhibits relatively high morbidity and mortality rate worldwide. The lack of effective methods in early detection and diagnosis, and immediate therapies makes treating such disease a challenge for both clinicians and oncologists. Proteomics has emerged as a promising technology platform for rationally identifying biomarkers and novel therapeutic targets for GC, as well as discovering underlying mechanisms of carcinogenesis. Its application has greatly benefited mechanistic studies of this disease. This review will demonstrate the applications of proteomic technology in GC research. The advantages and shortcomings of this technology, as reflected by current studies, will also be discussed to improve and expand its application in the field of cancer research.

Antibody microarrays utilizing site-specific antibody-oligonucleotide conjugates

Protein arrays are typically made by random absorption of proteins to the array surface, potentially limiting the amount of properly oriented and functional molecules. We report the development of a DNA encoded antibody microarray utilizing site-specific antibody-oligonucleotide conjugates that can be used for cell immobilization as well as the detection of genes and proteins. This technology allows for the facile generation of antibody microarrays while circumventing many of the drawbacks of conventionally produced antibody arrays. We demonstrate that this method can be used to capture and detect SK-BR-3 cells (Her2+ breast cancer cells) at concentrations as low as 10(2) cells/mL (which is equivalent to 10 cells per 100 μL array) without the use of microfluidics, which is 100- to 10(5)-fold more sensitive than comparable techniques. Additionally, the method was shown to be able to detect cells in a complex mixture, effectively immobilizing and specifically detecting Her2+ cells at a concentration of 10(2) SK-BR-3 cells/mL in 4 × 10(6) white blood cells/mL. Patients with a variety of cancers can have circulating tumor cell counts of between 1 and 10(3) cells/mL in whole blood, well within the range of this technology.

Steric-dependent label-free and washing-free enzyme amplified protein detection with dual-functional synthetic probes

Enzyme-catalyzed signal amplification with an antibody-enzyme conjugate is commonly employed in many bioanalytical methods to increase assay sensitivity. However, covalent labeling of the enzyme to the antibody, laborious operating procedures, and extensive washing steps are necessary for protein recognition and signal amplification. Herein, we describe a novel label-free and washing-free enzyme-amplified protein detection method by using dual-functional synthetic molecules to impose steric effects upon protein binding. In our approach, protein recognition and signal amplification are modulated by a simple dual-functional synthetic probe which consists of a protein ligand and an inhibitor. In the absence of the target protein, the inhibitor from the dual-functional probe would inhibit the enzyme activity. In contrast, binding of the target protein to the ligand perturbs this enzyme-inhibitor affinity due to the generation of steric effects caused by the close proximity between the target protein and the enzyme, thereby activating the enzyme to initiate signal amplification. With this strategy, the fluorescence signal can be amplified to as high as 70-fold. The generality and versatility of this strategy are demonstrated by the rapid, selective, and sensitive detection of four different proteins, avidin, O6-methylguanine DNA methyltransferase (MGMT), SNAP-tag, and lactoferrin, with four different probes.

A theoretical justification for single molecule peptide sequencing

The proteomes of cells, tissues, and organisms reflect active cellular processes and change continuously in response to intracellular and extracellular cues. Deep, quantitative profiling of the proteome, especially if combined with mRNA and metabolite measurements, should provide an unprecedented view of cell state, better revealing functions and interactions of cell components. Molecular diagnostics and biomarker discovery should benefit particularly from the accurate quantification of proteomes, since complex diseases like cancer change protein abundances and modifications. Currently, shotgun mass spectrometry is the primary technology for high-throughput protein identification and quantification; while powerful, it lacks high sensitivity and coverage. We draw parallels with next-generation DNA sequencing and propose a strategy, termed fluorosequencing, for sequencing peptides in a complex protein sample at the level of single molecules. In the proposed approach, millions of individual fluorescently labeled peptides are visualized in parallel, monitoring changing patterns of fluorescence intensity as N-terminal amino acids are sequentially removed, and using the resulting fluorescence signatures (fluorosequences) to uniquely identify individual peptides. We introduce a theoretical foundation for fluorosequencing and, by using Monte Carlo computer simulations, we explore its feasibility, anticipate the most likely experimental errors, quantify their potential impact, and discuss the broad potential utility offered by a high-throughput peptide sequencing technology.

The development of next-generation DNA and RNA sequencing methods has transformed biology, with current platforms generating >1 billion sequencing reads per run. Unfortunately, no method of similar scale and throughput exists to identify and quantify specific proteins in complex mixtures, representing a critical bottleneck in many biochemical and molecular diagnostic assays. What is urgently needed is a massively parallel method, akin to next-gen DNA sequencing, for identifying and quantifying peptides or proteins in a sample. In principle, single-molecule peptide sequencing could achieve this goal, allowing billions of distinct peptides to be sequenced in parallel and thereby identifying proteins composing the sample and digitally quantifying them by direct counting of peptides. Here, we discuss theoretical considerations of single molecule peptide sequencing, suggest one possible experimental strategy, and, using computer simulations, characterize the potential utility and unusual properties of this future proteomics technology.

A CuS-based chemical tongue chip for pattern recognition of proteins and antibiotic-resistant bacteria

A CuS-based sensor array having high stability and selectivity for identifying analytes on a quartz chip.

Distyrylbenzene-aldehydes: identification of proteins in water

Herein we describe the discrimination of different albumins using fluorescence changes in a simple three-compound array and apply this system in the differentiation of protein shake powders.

Array-based sensing of proteins and bacteria by using multiple luminescent nanodots as fluorescent probes

Luminescent nanodots for protein sensing and discrimination of bacteria: Luminescent nanodots are applied as novel fluorescent probes in a sensing array. The sensing strategy uses graphene oxide (GO) for protein recognition, with displacement of fluorescent probes to generate the output. This sensing platform is a powerful tool to detect protein targets and discriminate bacteria.

Fabrication of antibody microarrays by light-induced covalent and oriented immobilization

Antibody microarrays have important applications for the sensitive detection of biologically important target molecules and as biosensors for clinical applications. Microarrays produced by oriented immobilization of antibodies generally have higher antigen-binding capacities than those in which antibodies are immobilized with random orientations. Here, we present a UV photo-cross-linking approach that utilizes boronic acid to achieve oriented immobilization of an antibody on a surface while retaining the antigen-binding activity of the immobilized antibody. A photoactive boronic acid probe was designed and synthesized in which boronic acid provided good affinity and specificity for the recognition of glycan chains on the Fc region of the antibody, enabling covalent tethering to the antibody upon exposure to UV light. Once irradiated with optimal UV exposure (16 mW/cm(2)), significant antibody immobilization on a boronic acid-presenting surface with maximal antigen detection sensitivity in a single step was achieved, thus obviating the necessity of prior antibody modifications. The developed approach is highly modular, as demonstrated by its implementation in sensitive sandwich immunoassays for the protein analytes Ricinus communis agglutinin 120, human prostate-specific antigen, and interleukin-6 with limits of detection of 7.4, 29, and 16 pM, respectively. Furthermore, the present system enabled the detection of multiple analytes in samples without any noticeable cross-reactivities. Antibody coupling via the use of boronic acid and UV light represents a practical, oriented immobilization method with significant implications for the construction of a large array of immunosensors for diagnostic applications.

A universal fluorescence sensing strategy based on biocompatible graphene quantum dots and graphene oxide for the detection of DNA

A novel and efficient fluorescence sensing platform based on biocompatible graphene quantum dots and graphene oxide was established. It showed high selectivity and sensitivity for DNA detection.

Pathophysiology of tobacco smoke exposure: recent insights from comparative and redox proteomics

First-hand and second-hand tobacco smoke are causally linked to a huge number of deaths and are responsible for a broad spectrum of pathologies such as cancer, cardiovascular, respiratory, and eye diseases as well as adverse effects on female reproductive function. Cigarette smoke is a complex mixture of thousands of different chemical species, which exert their negative effects on macromolecules and biochemical pathways, both directly and indirectly. Many compounds can act as oxidants, pro-inflammatory agents, carcinogens, or a combination of these. The redox behavior of cigarette smoke has many implications for smoke related diseases. Reactive oxygen and nitrogen species (both radicals and non-radicals), reactive carbonyl compounds, and other species may induce oxidative damage in almost all the biological macromolecules, compromising their structure and/or function. Different quantitative and redox proteomic approaches have been applied in vitro and in vivo to evaluate, respectively, changes in protein expression and specific oxidative protein modifications induced by exposure to cigarette smoke and are overviewed in this review. Many gel-based and gel-free proteomic techniques have already been used successfully to obtain clues about smoke effects on different proteins in cell cultures, animal models, and humans. The further implementation with other sensitive screening techniques could be useful to integrate the comprehension of cigarette smoke effects on human health. In particular, the redox proteomic approach may also help identify biomarkers of exposure to tobacco smoke useful for preventing these effects or potentially predictive of the onset and/or progression of smoking-induced diseases as well as potential targets for therapeutic strategies.

The Use of Antibodies in Small-Molecule Drug Discovery

Antibodies are powerful research tools that can be used in many areas of biology to probe, measure, and perturb various biological structures. Successful drug discovery is dependent on the correct identification of a target implicated in disease, coupled with the successful selection, optimization, and development of a candidate drug. Because of their specific binding characteristics, with regard to specificity, affinity, and avidity, coupled with their amenability to protein engineering, antibodies have become a key tool in drug discovery, enabling the quantification, localization, and modulation of proteins of interest. This review summarizes the application of antibodies and other protein affinity reagents as specific research tools within the drug discovery process.

Role of proteomics in the investigation of pulmonary fibrosis

Pulmonary fibrosis arises as a consequence of aberrant remodeling and defective repair mechanisms within the lung. This destructive process is the cause of much of the morbidity and mortality in many pulmonary disorders. Unfortunately, therapeutic options are limited. A significant advancement in the management of patients with pulmonary fibrosis would be the identification of biomarkers for diagnosis, prognosis and prediction of patient response to therapy. Bronchoalveolar lavage is an ideal tissue target for the discovery of these potential biomarkers in pulmonary fibrosis. Integrative approaches using both gel- and mass spectrometry-based proteomic workflows will allow full coverage of this complex proteome, thereby unlocking this potential information as a clinical tool to aid diagnosis and guide treatment for individual patients with pulmonary fibrosis.

Promise of multiphoton detection in discovery and diagnostic proteomics

Proteomics has lacked adequate methods for handling the complexity (hundreds of thousands of different proteins) and range of protein concentrations (> or =10(6)) of eukaryotic proteomes. New multiphoton-detection methods for ultrasensitive detection of proteins produce 10,000-fold gains in sensitivity and allow highly quantitative, linear detection of 50 zmol (30,000 molecules) to 500 fmol of proteins in complex samples. The potential of multiphoton detection in top-down proteomics analyses is illustrated with applications in monitoring proteomes in very small numbers of cells, in identifying and monitoring complex functional isoforms of cancer-related proteins, and in super-sensitive immunoassays of serum proteins for high-performance detection of cancer.

High-throughput proteomics using antibody microarrays: an update

Antibody-based microarrays are a rapidly emerging technology that has advanced from the first proof-of-concept studies to demanding serum protein profiling applications during recent years, displaying great promise within disease proteomics. Miniaturized micro- and nanoarrays can be fabricated with an almost infinite number of antibodies carrying the desired specificities. While consuming only minute amounts of reagents, multiplexed and ultrasensitive assays can be performed targeting high- as well as low-abundance analytes in complex nonfractionated proteomes. The microarray images generated can then be converted into protein expression profiles or protein atlases, revealing a detailed composition of the sample. The technology will provide unique opportunities for fields such as disease diagnostics, biomarker discovery, patient stratification, predicting disease recurrence and drug target discovery. This review describes an update of high-throughput proteomics, using antibody-based microarrays, focusing on key technological advances and novel applications that have emerged over the last 3 years.

Antibody array generation and use

Affinity proteomics, represented by antibody arrays, is a multiplex technology for high-throughput protein expression profiling of crude proteomes in a highly specific, sensitive, and miniaturized manner. The antibodies are individually deposited in an ordered pattern, an array, onto a solid support. Next, the sample is added, and any specifically bound proteins are detected and quantified using mainly fluorescence as the mode of detection. The binding pattern is then converted into a relative protein expression map, or protein atlas, delineating the composition of the sample at the molecular level. The technology provides unique opportunities for various applications, such as protein expression profiling, biomarker discovery, disease diagnostics, prognostics, evidence-based therapy selection, and disease monitoring. Here, we describe the generation and use of planar antibody arrays for serum protein profiling.

Recombinant antibody microarray for profiling the serum proteome of SLE

Systemic lupus erythematosus (SLE) is a severe autoimmune connective tissue disease. Our current knowledge about the serum proteome, or serum biomarker panels, reflecting disease and disease status is still very limited. Affinity proteomics, represented by recombinant antibody arrays, is a novel, multiplex technology for high-throughput protein expression profiling of crude serum proteomes in a highly specific, sensitive, and miniaturized manner. The antibodies are deposited one by one in an ordered pattern, an array, onto a solid support. Next, the sample is added, and any specifically bound proteins are detected and quantified. The binding pattern is then converted into a relative protein expression map, or protein map, deciphering the composition of the sample at the molecular level. The methodology provides unique opportunities for delineating serum biomarkers reflecting SLE, thus paving the way for improved diagnosis, classification, and prognosis.

Nanoparticle-GFP "chemical nose" sensor for cancer cell identification

Nanoparticle-based sensor arrays have been used to distinguish a wide range of bio-related molecules through pattern recognition. This "chemical nose" approach uses nanoparticles as receptors to selectively identify the analytes, while a transducer reports the binding through a readable signal (fluorescence). Here we describe a procedure that uses functionalized gold nanoparticles as receptors and green fluorescent protein (GFP) as the transducer to identify and differentiate cell state (normal, cancerous, and metastatic), an important tool in early diagnosis and treatment of tumors.