Development of miniaturized immunoassay: Influence of surface chemistry and comparison with enzyme-linked immunosorbent assay and Western blot

Fabrication of Biosensing Interface with Monolayers

Surface modification is recognized as one of the fundamental techniques to fabricate biosensing interfaces. This review focuses on the surface modification of carbon substrates (GC and HOPG) and silica with a close-packed monolayer, in particular. In the cases of carbon substrates, GC and HOPG, it was demonstrated that surface modification of carbon substrates with diazonium derivatives could create a close-packed monolayer similar to the self-assembled monolayer (SAM) formation with mercapto derivatives. Similarly, the potential of trialkoxysilanes to form a close-packed monolayer was evaluated, and modification with a close-packed monolayer tended to occur under milder conditions when the trialkoxysilanes had a longer alkyl chain. In these studies, we synthesized surface modification materials having ferrocene as a redox active moiety to explore features of the modified surfaces by an electrochemical method using cyclic voltammetry, where surface concentrations of immobilized molecules and blocking effect were studied to obtain insight for density leading to a close-packed layer. Based on those findings, fabrication of a biosensing interface on the silica sensing chip of the waveguide-mode sensor was carried out using triethoxysilane derivatives bearing succinimide ester and oligoethylene glycol moieties to immobilize antibodies and to suppress nonspecific adsorption of proteins, respectively. The results demonstrate that the waveguide-mode sensor powered by the biosensing interface fabricated with those triethoxysilane derivatives and antibody has the potential to detect several tens ng/mL of biomarkers in human serum with unlabeled detection method.

Properties of modified surface for biosensing interface

Properties of modified surface, behavior against salting-out effect, suppressive effect for protein nonspecific adsorption, and wettability were examined using various mercapto compounds bearing methyloligoethylene glycol, oligoethylene glycol, alkyl oligoethylene glycol, alkyl phosphoryl choline, alkyl inverse phosphoryl choline, and alkyl sulfobetaine moieties. The behavior against salting-out effect was examined using gold nanoparticle with PBS and NaCl aqueous solution. The suppressive effect for protein nonspecific adsorption was evaluated by SPR, and the wettability was measured on the SPR chip. The gold nanoparticle modified with 8C3EG, 12C4EG, 12CPC, 6CCP, and 12CCP showed excellent behavior against salting-out effect. The suppression of protein nonspecific adsorption was effective with 6EG, 12C4EG, 12CPC, and 12CS. On the other hand, the modified surface possessed high wettability except for the surface modified with M6EG. The results indicate that incorporation of alkyl group into surface modification materials is effective for the enhancement of behavior against salting-out effect and suppressive effect for protein nonspecific adsorption regardless of wettability. Among the zwitter ionic derivatives, inverse phosphoryl choline derivatives showed intriguing properties, high behavior against salting-out effect with high wettability but low suppressive effect for protein nonspecific adsorption.

Autoantigen Microarray for High-throughput Autoantibody Profiling in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease characterized by the production of autoantibodies to a broad range of self-antigens. Profiling the autoantibody repertoire using array-based technology has emerged as a powerful tool for the identification of biomarkers in SLE and other autoimmune diseases. Proteomic microarray has the capacity to hold large number of self-antigens on a solid surface and serve as a high-throughput screening method for the determination of autoantibody specificities. The autoantigen arrays carrying a wide variety of self-antigens, such as cell nuclear components (nucleic acids and associated proteins), cytoplasmic proteins, phospholipid proteins, cell matrix proteins, mucosal/secreted proteins, glomeruli, and other tissue-specific proteins, have been used for screening of autoantibody specificities associated with different manifestations of SLE. Arrays containing synthetic peptides and molecular modified proteins are also being utilized for identification of autoantibodies targeting to special antigenic epitopes. Different isotypes of autoantibodies, including IgG, IgM, IgA, and IgE, as well as other Ig subtypes, can be detected simultaneously with multi-color labeled secondary antibodies. Serum and plasma are the most common biologic materials for autoantibody detection, but other body fluids such as cerebrospinal fluid, synovial fluid, and saliva can also be a source of autoantibody detection. Proteomic microarray as a multiplexed high-throughput screening platform is playing an increasingly-important role in autoantibody diagnostics. In this article, we highlight the use of autoantigen microarrays for autoantibody exploration in SLE.

Evaluation of optical detection platforms for multiplexed detection of proteins and the need for point-of-care biosensors for clinical use

This review investigates optical sensor platforms for protein multiplexing, the ability to analyze multiple analytes simultaneously. Multiplexing is becoming increasingly important for clinical needs because disease and therapeutic response often involve the interplay between a variety of complex biological networks encompassing multiple, rather than single, proteins. Multiplexing is generally achieved through one of two routes, either through spatial separation on a surface (different wells or spots) or with the use of unique identifiers/labels (such as spectral separation-different colored dyes, or unique beads-size or color). The strengths and weaknesses of conventional platforms such as immunoassays and new platforms involving protein arrays and lab-on-a-chip technology, including commercially-available devices, are discussed. Three major public health concerns are identified whereby detecting medically-relevant markers using Point-of-Care (POC) multiplex assays could potentially allow for a more efficient diagnosis and treatment of diseases.

Realizing the promise of reverse phase protein arrays for clinical, translational, and basic research: a workshop report: the RPPA (Reverse Phase Protein Array) society

Reverse phase protein array (RPPA) technology introduced a miniaturized "antigen-down" or "dot-blot" immunoassay suitable for quantifying the relative, semi-quantitative or quantitative (if a well-accepted reference standard exists) abundance of total protein levels and post-translational modifications across a variety of biological samples including cultured cells, tissues, and body fluids. The recent evolution of RPPA combined with more sophisticated sample handling, optical detection, quality control, and better quality affinity reagents provides exquisite sensitivity and high sample throughput at a reasonable cost per sample. This facilitates large-scale multiplex analysis of multiple post-translational markers across samples from in vitro, preclinical, or clinical samples. The technical power of RPPA is stimulating the application and widespread adoption of RPPA methods within academic, clinical, and industrial research laboratories. Advances in RPPA technology now offer scientists the opportunity to quantify protein analytes with high precision, sensitivity, throughput, and robustness. As a result, adopters of RPPA technology have recognized critical success factors for useful and maximum exploitation of RPPA technologies, including the following: preservation and optimization of pre-analytical sample quality, application of validated high-affinity and specific antibody (or other protein affinity) detection reagents, dedicated informatics solutions to ensure accurate and robust quantification of protein analytes, and quality-assured procedures and data analysis workflows compatible with application within regulated clinical environments. In 2011, 2012, and 2013, the first three Global RPPA workshops were held in the United States, Europe, and Japan, respectively. These workshops provided an opportunity for RPPA laboratories, vendors, and users to share and discuss results, the latest technology platforms, best practices, and future challenges and opportunities. The outcomes of the workshops included a number of key opportunities to advance the RPPA field and provide added benefit to existing and future participants in the RPPA research community. The purpose of this report is to share and disseminate, as a community, current knowledge and future directions of the RPPA technology.

Design and fabrication of biosensing interface for waveguide-mode sensor

In order to develop a biosensing system with waveguide-mode sensor, fabrication of a biosensing interface on the silica surface of the sensing chip was carried out using triethoxysilane derivatives with anti-leptin antibody. Triethoxysilane derivatives bearing succinimide ester and oligoethylene glycol moieties were synthesized to immobilize the antibody and to suppress nonspecific adsorption of proteins, respectively. The chip modified with triethoxysilane derivatives bearing oligoethylene glycol moiety suppressed nonspecific adsorption of proteins derived from human serum effectively by rinse with PBS containing surfactant (0.05% Tween 20). On the other hand, it was confirmed that antibody was immobilized on the chip by immersion into antibody solution to show response of antigen-antibody reaction, where the chip was modified with triethoxysilane derivatives bearing succinimide ester moiety. When the interface was fabricated with antibody and a mixture of triethoxysilane derivatives bearing succinimide ester and oligoethylene glycol moieties, the response of antigen-antibody reaction depended on composition of the mixture and enhanced with the increase of ratio for triethoxysilane derivatives bearing succinimide ester moiety reflecting the antibody concentration immobilized on the chip. While introduction of excess triethoxysilane derivatives bearing succinimide ester moiety induced nonspecific adsorption of proteins derived from human serum, the immobilized antibody on the chip kept its activity after 1-month storage in a refrigerator. Taking into consideration those factors, the biosensing interface was fabricated using triethoxysilane derivatives with anti-leptin antibody to examine performance of the waveguide-mode sensor. It was found that the detection limits for human leptin were 50 ng/mL in PBS and 100 ng/mL in human serum. The results demonstrate that the waveguide-mode sensor powered by the biosensing interface fabricated with those triethoxysilane derivatives and antibody has potential to detect several tens of nanograms per milliliter of biomarkers in human serum with an unlabeled detection method.

Characterization of three amino-functionalized surfaces and evaluation of antibody immobilization for the multiplex detection of tumor markers involved in colorectal cancer

Antibody microarrays are powerful and high-throughput tools for screening and identifying tumor markers from small sample volumes of only a few microliters. Optimization of surface chemistry and spotting conditions are crucial parameters to enhance antibodies' immobilization efficiency and to maintain their biological activity. Here, we report the implementation of an antibody microarray for the detection of tumor markers involved in colorectal cancer. Three-dimensional microstructured glass slides were functionalized with three different aminated molecules ((3-aminopropyl)dimethylethoxysilane (APDMES), Jeffamine, and chitosan) varying in their chain length, their amine density, and their hydrophilic/hydrophobic balance. The physicochemical properties of the resulting surfaces were characterized. Antibody immobilization efficiency through physical interaction was studied as a function of surface properties as well as a function of the immobilization conditions. The results show that surface energy, steric hindrance, and pH of spotting buffer have great effects on protein immobilization. Under optimal conditions, biological activities of four immobilized antitumor marker antibodies were evaluated in multiplex immunoassay for the detection of the corresponding tumor markers. Results indicated that the chitosan functionalized surface displayed the highest binding capacity and allowed to retain maximal biological activity of the four tested antibody/antigen systems. Thus, we successfully demonstrated the application of amino-based surface modification for antibody microarrays to efficiently detect tumor markers.

Improvement of protein immobilization for the elaboration of tumor-associated antigen microarrays: application to the sensitive and specific detection of tumor markers from breast cancer sera

There is an urgent need to identify relevant tumor markers showing high sensitivity and specificity for early diagnosis and prognosis of breast cancer. Protein microarrays have demonstrated to be cost-effective, high through-put and powerful tools for screening and identifying tumor markers with only minute samples. Autoantibodies directed against tumor-associated antigens (TAAs) were shown to be relevant tumor markers. However, due to the variability of immune response from one individual to another and depending on the type of cancer, detection of only one type of anti-TAA autoantibody is not sufficient to give a reliable and precise diagnosis. It is necessary to use a set of several TAAs for determining specific autoimmune profiles. Therefore, combining various TAAs on different surfaces could improve sensitivity and specificity for anti-TAA autoantibody detection. Herein a panel of 10 proteins, including well-known tumor-associated antigens (TAAs) and potential new biomarkers of breast cancer, were immobilized onto microstructured microarray under optimized conditions (spotting pH buffer, surface chemistry, blocking procedure), in order to determine an autoimmune signature of breast cancer. Sera from 29 breast cancer patients and 28 healthy donors were screened in sandwich immunoassays on the miniaturized system to detect the eventual presence of anti-TAAs autoantibodies. Results indicated that the detection level of each anti-TAA autoantibody in a given serum sample was strongly dependant on the surface chemistry. Combining five TAAs (p53, Hsp60, Hsp70, Her2-Fc, NY-ESO-1) on two different surface chemistries (NHS and APDMES) allowed the significant detection of more than 82% breast cancer sera.

Impact of substrates for probe immobilization

Protein chips are becoming a key technology in proteomic research and medical diagnostics. Surface chemistry for immobilization of proteins forms the basis for assay design and determines the properties of protein microarrays. Optimal substrates provide a homogeneous environment for probes, preventing loss of biological activity and unspecific adsorption. Numerous immobilization approaches, based on covalent binding, affinity, or adsorption, have been proposed thus far, and these represent the toolbox for choosing optimized strategies for each individual application.

Reverse phase protein microarrays advance to use in clinical trials

Individualizing cancer therapy for molecular targeted inhibitors requires a new class of molecular profiling technology that can map the functional state of the cancer cell signal pathways containing the drug targets. Reverse phase protein microarrays (RPMA) are a technology platform designed for quantitative, multiplexed analysis of specific phosphorylated, cleaved, or total (phosphorylated and non-phosphorylated) forms of cellular proteins from a limited amount of sample. This class of microarray can be used to interrogate tissue samples, cells, serum, or body fluids. RPMA were previously a research tool; now this technology has graduated to use in research clinical trials with clinical grade sensitivity and precision. In this review we describe the application of RPMA for multiplexed signal pathway analysis in therapeutic monitoring, biomarker discovery, and evaluation of pharmaceutical targets, and conclude with a summary of the technical aspects of RPMA construction and analysis.