Reusable and highly sensitive SERS immunoassay utilizing gold nanostars and a cellulose hydrogel-based platform.

The development of robust and sensitive point-of-care testing platforms is necessary to improve patient care and outcomes. Surface-enhanced Raman scattering (SERS)-based immunosensors are especially suited for this purpose. Here, we present a highly sensitive and selective SERS immunoassay, demonstrating for example the detection of horseradish peroxidase (HRP), in a sandwich format. The strength of our biosensor lies in merging: (i) SERS-immunotags based on gold nanostars, allowing exceptional intense SERS from attached Raman probes, covalent attachment of anti-HRP antibodies by a simple chemical method providing exceptional antigen binding activity; (ii) the ease of preparation of the capture platform from a regenerated cellulose-based hydrogel, a transparent material, ideal for microfluidics applications, with low background fluorescence and Raman signal, particularly suited for preserving high activity of the covalently bound anti-HRP antibodies. The sandwich complexes formed were characterised by atomic force microscopy, and by scanning electron microscopy coupled with electron diffraction spectroscopy; and (iii) the robustness of the simple Classical Least Squares method for SERS data analysis, resulting in superior discrimination of SERS signals from the background and much better data fitting, compared to the commonly used peak integral method. Our SERS immunoassay greatly improves the detection limits of traditional enzyme-linked immunosorbent assay approaches, and its performance is better or comparable to those of existing SERS-based immunosensors. Our approach successfully overcomes the main challenges of application at point-of-care, including increasing reproducibility, sensitivity, and specificity, associated with an environmentally friendly and robust design. Also, the proposed design withstands several cycles of regeneration, a feature absent in paper-SERS immunoassays and this opens the way for sensitive multiplexing applications on a microfluidic platform.

High-Affinity Points of Interaction on Antibody Allow Synthesis of Stable and Highly Functional Antibody-Gold Nanoparticle Conjugates.

Many emerging nanobiotechnologies rely on the proper function of proteins immobilized on gold nanoparticles. Often, the surface chemistry of the AuNP is engineered to control the orientation, surface coverage, and structure of the adsorbed protein to maximize conjugate function. Here, we chemically modified antibody to investigate the effect of protein surface chemistries on adsorption to AuNPs. A monoclonal anti-horseradish peroxidase IgG antibody (anti-HRP) was reacted with N-succinimidyl acrylate (NSA) or reduced dithiobissuccinimidyl propionate (DSP) to modify lysine residues. Zeta potential measurements confirmed that both chemical modifications reduced the localized regions of positive charge on the protein surface, while the DSP modification incorporated additional free thiols. Dynamic light scattering confirmed that native and chemically modified antibodies adsorbed onto AuNPs to form bioconjugates; however, adsorption kinetics revealed that the NSA-modified antibody required significantly more time to allow for the formation of a hard corona. Moreover, conjugates formed with the NSA-modified antibody lost antigen-binding function, whereas unmodified and DSP-modified antibodies adsorbed onto AuNPs to form functional conjugates. These results indicate that high-affinity functional groups are required to prevent protein unfolding and loss of function when adsorbed on the AuNP surface. The reduced protein charge and high-affinity thiol groups on the DSP-modified antibody enabled pH-dependent control of protein orientation and the formation of highly active conjugates at solution pHs (<7.5) that are inaccessible with unmodified antibody due to conjugate aggregation. This study establishes parameters for protein modification to facilitate the formation of highly functional and stable protein-AuNP conjugates.

Oriented immobilization of antibodies through different surface regions containing amino groups: Selective immobilization through the bottom of the Fc region.

Amino groups on the antibody surface (amino terminus and Lys) are very interesting conjugation targets due to their substantial quantities and selectivity toward various reactive groups. Oriented immobilization of antibodies via amino moieties on the Fc region instead of the antigen-binding fragment (Fab) is highly appreciated to conserve antigen-binding capacity. In this paper, targeting amino moieties on distinct regions, three antibody immobilization strategies were compared with the recognition ability of corresponding adsorbents. Our results demonstrate that oriented immobilization of antibodies onto heterofunctional chelate-epoxy support selectively involving Lys residues placed at the bottom of the Fc region, thus preserved the highest antigen recognition capacity (over 75% functionality). For homofunctional aldehyde support, immobilization at pH 10 demonstrates 50% remaining functionality due to the random orientation of tethered antibodies; while only 10% functionality remained when N-terminus were specifically conjugated at pH 8.5. With the rationalization of moieties density onto heterofunctional support, 2-fold recognition capacity was exhibited over randomly immobilization for antigens with higher size (ß-galactosidase, 425 kDa vs. horseradish peroxidase, 40 kDa). Meanwhile, at least 97% of antigens with a varied concentration in diluted human serum were efficiently captured by the optimized chelate-epoxy support. Therefore, our antibody immobilization protocol proved the potential to be utilized as a promising candidate to capture voluminous antigens (large proteins and cells) in real samples.

A nanobody-horseradish peroxidase fusion protein-based competitive ELISA for rapid detection of antibodies against porcine circovirus type 2.

BACKGROUND: The widespread popularity of porcine circovirus type 2(PCV2) has seriously affected the healthy development of the pig industry and caused huge economic losses worldwide. A rapid and reliable method is required for epidemiological investigation and evaluating the effect of immunization. However, the current methods for PCV2 antibody detection are time-consuming or very expensive and rarely meet the requirements for clinical application. we have constructed the platform for expressing the nanobody(Nb)­horseradish peroxidase(HRP) fusion protein as an ultrasensitive probe to detect antibodies against the Newcastle disease virus(NDV), previously. In the present work, an Nb-HRP fusion protein-based competitive ELISA(cELISA) for rapid and simple detection antibodies against PCV2 was developed using this platform to detect anti-PCV2 antibodies in clinical porcine serum. RESULTS: Using phage display technology, 19 anti-PCV2-Cap protein nanobodies were screened from a PCV2-Cap protein immunized Bactrian camel. With the platform, the PCV2-Nb15­HRP fusion protein was then produced and used as a sensitive reagent for developing a cELISA to detect anti­PCV2 antibodies. The cut­off value of the cELISA is 20.72 %. Three hundreds and sixty porcine serum samples were tested by both newly developed cELISA and commercial kits. The sensitivity and specificity were 99.68 % and 95.92 %, respectively. The coincidence rate of the two methods was 99.17 %. When detecting 620 clinical porcine serum samples, a good consistent (kappa value = 0.954) was found between the results of the cELISA and those of commercial kits. CONCLUSIONS: In brief, the newly developed cELISA based PCV2-Nb15­HRP fusion protein is a rapid, low-cost, reliable and useful nanobody-based tool for the serological evaluation of current PCV2 vaccine efficacy and the indirect diagnosis of PCV2 infection.

Horseradish-peroxidase-conjugated anti-erythropoietin antibodies for direct recombinant human erythropoietin detection: Proof of concept.

Antidoping testing for recombinant human erythropoietin (EPO) is routinely performed by gel electrophoresis followed by western blot analysis with primary and secondary antibodies. The two antibody steps add more than 24 h to the testing time of a purified sample. The aim of this study was to test the concept of using directly horseradish-peroxidase (HRP)-conjugated anti-EPO primary antibody, without the need for a secondary antibody, to reduce the analysis time and eliminate non-specific cross-reactivity with secondary antibodies. An in-house, periodate coupling (R&D systems, clone AE7A5) and three commercially available anti-human EPO-HRP conjugates from Genetex, Novus Biologicals and Santa Cruz were evaluated for specificity and sensitivity, using recombinant human EPO standards, negative human urine samples and urine samples from an EPO excretion study. The in-house anti-EPO-HRP conjugate was performed as well as the current two-step application of unconjugated primary and secondary antibodies used in routine analysis, with comparable specificity and sensitivity. The analysis time was markedly reduced for purified samples from 25 h with the routine method down to 7 h with the in-house HRP conjugate. Of the three commercially available conjugates tested, only the Santa Cruz anti-EPO-HRP conjugate showed comparable specificity but had lower sensitivity to both the in-house and the antibody combination currently applied routinely. The other two commercially available conjugates (Genetex and Novus Biologicals) did not show any visible bands with the EPO standards. The results clearly demonstrate the potential utility of a directly HRP-conjugated anti-EPO antibody to reduce analysis time for EPO in doping control.

Conjugation of Antibodies to Horseradish Peroxidase.

Antibodies conjugated with horseradish peroxidase (HRP) are one of the most widely used bioreagents in the biological sciences. This protocol is a basic method for adding HRP to a thiolated antibody and can be adapted for use with different cross-linkers. Conjugation methods usually focus on linking through the lysines on HRP because there are only six of them and their modification does not adversely affect enzyme activity.

Photochemistry on the Space Station-Antibody Resistance to Space Conditions after Exposure Outside the International Space Station.

Antibody-based analytical instruments are under development to detect signatures of life on planetary bodies. Antibodies are molecular recognition reagents able to detect their target at sub-nanomolar concentrations, with high affinity and specificity. Studying antibody binding performances under space conditions is mandatory to convince space agencies of the adequacy of this promising tool for planetary exploration. To complement previous ground-based experiments on antibody resistance to simulated irradiation, we evaluate in this paper the effects of antibody exposure to real space conditions during the EXPOSE-R2 mission outside the International Space Station. The absorbed dose of ionizing radiation recorded during the 588 days of this mission (220 mGy) corresponded to the absorbed dose expected during a mission to Mars. Moreover, samples faced, at the same time as irradiation, thermal cycles, launch constraints, and long-term storage. A model biochip was used in this study with antibodies in freeze-dried form and under two formats: free or covalently grafted to a solid surface. We found that antibody-binding performances were not significantly affected by cosmic radiation, and more than 40% of the exposed antibody, independent of its format, was still functional during all this experiment. We conclude that antibody-based instruments are well suited for in situ analysis on planetary bodies.

Peroxidase-immobilized porous silica particles for in situ formation of peroxidase-free hydrogels with attenuated immune responses.

Enzymatic crosslinking chemistry using horseradish peroxidase (HRP) has been widely utilized as an effective approach to fabricating injectable hydrogels with high efficiency under mild reaction conditions. However, their clinical applications are limited by the immunogenicity of the plant-derived enzyme. Herein we report the design, synthesis and characterization of HRP-immobilized porous silica particles (HRP-particles) and their use for in situ formation of HRP-free hydrogels. HRP was immobilized on aminopropyl-modified porous silica particles of 70-140 µm in diameter via poly(ethylene glycol) spacers of different molecular weights by reductive amination reaction. Two different HRP-free hydrogels based on dextran-tyramine and gelatin-hydroxyphenylpropionic acid (GHPA) conjugates were produced by passing a solution containing the conjugates and H2O2 through a syringe packed with HRP-particles. The storage modulus and gelation rate of both hydrogels were tunable by varying the contact time between the polymer solution and HRP-particles. Our in vitro study revealed that HRP-free GHPA hydrogel was less stimulatory to activated mouse macrophages than HRP-containing GHPA hydrogel with the same stiffness. Furthermore, HRP-free GHPA hydrogel exhibited remarkably lower levels of local and systemic inflammation than HRP-containing one upon subcutaneous injection in immunocompetent C57BL/6J mice. The attenuated immunogenicity of HRP-free GHPA hydrogels makes them an attractive platform for tissue engineering applications. STATEMENT OF SIGNIFICANCE: The immunogenicity of HRP is a significant issue for clinical application of HRP-catalyzed in situ forming hydrogels. HRP-particles are developed to overcome the safety concerns by fabricating HRP-free hydrogels. The porosity of silica particles and molecular weight of poly(ethylene glycol) spacers are discovered as important factors determining the catalytic ability of HRP-particles to induce the in situ crosslinking of polymer-phenol conjugates. Although several articles speculate the potential of HRP to trigger immune responses when administered as a part of hydrogel formulation, no literature has attempted to investigate the immunogenicity of HRP-containing hydrogels in comparison with HRP-free hydrogels. Our findings suggest that the immunogenicity issue should be carefully considered before clinical translation of HRP-containing hydrogels.

Development of a Sensitive Enzyme-Linked Immunosorbent Assay and Rapid Gold Nanoparticle Immunochromatographic Strip for Detecting Citrinin in Monascus Fermented Food.

Antibodies against citrinin (CTN) were generated from rabbits, which were injected with CTN-keyhole limpet hemocyanin (KLH). This work involved the development of a sensitive competitive direct enzyme-linked immunosorbent assay (cdELISA) and a rapid gold nanoparticle immunochromatographic strip (immunostrip) method for analyzing CTN in Monascus-fermented food. CTN at a concentration of 5.0 ng/mL caused 50% inhibition (IC50) of CTN-horseradish peroxidase (CTN-HRP) binding to the antibodies in the cdELISA. The capable on-site detection of CTN was accomplished by a rapid antibody-gold nanoparticle immunostrip with a detection limit of 20 ng/mL and that was completed within 15 min. A close inspection of 19 Monascus-fermented foods by cdELISA confirmed that 14 were contaminated with citrinin at levels from 28.6⁻9454 ng/g. Further analysis with the immunostrip is consistent with those results obtained using cdELISA. Both means are sensitive enough for the rapid examination of CTN in Monascus-fermented food products.

Development of a Magnetic Nanoparticles-Based Screen-Printed Electrodes (MNPs-SPEs) Biosensor for the Quantification of Ochratoxin A in Cereal and Feed Samples.

A rapid and sensitive electrochemical biosensor based on magnetic nanoparticles and screen-printed electrodes (MNPs-SPEs sensor) was developed for the detection of ochratoxin A (OTA) in cereal and feed samples. Different types of magnetic nanoparticles-based ELISA (MNPs-ELISA) were optimized, and the signal detection, as well as sensitivity, was enhanced by the combined use of screen-printed electrodes (SPEs). Under the optimized conditions, the calibration curve of the MNPs-SPEs sensor was y = 0.3372x + 0.8324 (R² = 0.9805). The linear range of detection and the detection limit were 0.01⁻0.82 ng/mL and 0.007 ng/mL, respectively. In addition, 50% inhibition (IC50) was detectable at 0.10 ng/mL. The limit of detection (LOD) of this MNPs-SPEs sensor in cereal and feed samples was 0.28 µg/kg. The recovery rates in spiked samples were between 78.7% and 113.5%, and the relative standard deviations (RSDs) were 3.6⁻9.8%, with the coefficient of variation lower than 15%. Parallel analysis of commercial samples (corn, wheat, and feedstuff) showed a good correlation between MNPs-SPEs sensor and liquid chromatography tandem mass spectrometry (LC/MS-MS). This new method provides a rapid, highly sensitive, and less time-consuming method to determine levels of ochratoxin A in cereal and feedstuff samples.

A diagnostic curiosity of isolated androstenedione elevation due to autoantibodies against horseradish peroxidase label of the immunoassay.

Two sisters with hirsutism presented with mild hirsutism and isolated, grossly elevated (>34.9nmol/L) serum concentrations of androstenedione measured by competitive, homogeneous immunoassay. The clinically discordant laboratory results prompted us to look for assay interference. In this immunoassay, horseradish peroxidase (HRP)-conjugated androstenedione competes with endogenous androstenedione for binding with the solid-phase polyclonal rabbit IgG antibodies. After a wash step, the amount of signal generated by the bound HRP conjugate is inversely proportional to the androstenedione concentration. Alternative analysis by tandem mass spectrometry (a good first line option for troubleshooting) and repeating the competitive immunoassay after polyethylene glycol treatment returned androstenedione concentrations within reference limits. These findings suggested that the original result was spuriously elevated due to assay interference. Additionally, the patient samples were pre-incubated with heterophile blocking reagents, normal rabbit IgG antibodies and HRP-conjugated normal goat IgG antibodies, followed by repeat measurement using the immunoassay. Only samples pre-incubated with HRP-conjugate returned significantly lower androstenedione (9.5 and 12.5nmol/L, respectively), implying neutralisation of the interfering antibodies. Androstenedione remained grossly elevated in the other experiments. This deductive exercise showed that the interference is due to autoantibodies against the HRP label used in the immunoassay. Another immunoassay using HRP label (5α-dihydrotestosterone) also produced gross elevation that was normal by tandem mass spectrometry analysis. Assay interferences, though not uncommon, are frequently overlooked. Laboratory results discordant with clinical features should prompt consideration of assay interference to avoid unnecessary investigations and treatment. This is the first report of autoantibodies against the HRP label used in immunoassay.

Comparison of two indirect ELISA coating antigens for the detection of dairy cow antibodies against Pasteurella multocida.

The ELISA is recognized as an efficient diagnostic tool for antibody detection, but there is no standard ELISA assay for detection of antibodies against hemorrhagic septicemia (HS) in cattle. The present study reports on an indirect ELISA assay for antibody detection of HS in dairy cows, and evaluates the sensitivity (Se) and specificity (Sp) of the method using a Bayesian approach. An indirect ELISA was developed with two types of heat extract antigens, Pasteurella multocida strains P-1256 and M-1404, as coating antigens. A checkerboard titration was employed using dairy cow sera immunized with P. multocida bacterin and colostrum-deprived calf sera. The concentrations of heat extract antigen (160µg/mL), sample serum (1:100) and goat anti-bovine immunoglobulin G labeled with horseradish peroxidase (1:2000) were optimal for the assay. The cut-off values were 0.147 and 0.128 for P-1256 and M-1404 coating antigens, and there were no differences in the results of tests with positive and negative sera (p<0.05). The characteristics of three diagnostic tests were evaluated using a one-population Bayesian model, assuming conditional dependence between two types of coating antigen-based ELISAs and indirect hemagglutination assay (IHA). A total of 415 sera samples from dairy cows without HS vaccination and no history of disease were tested. The Se and Sp of the P-1256 and M-1404 ELISAs were higher than those of the IHA. The Se and Sp of the P-1256 ELISA were 90.3% and 90.1%, while the Se and Sp of the M-1404 ELISA were 92.1% and 71.9%. The median values of Se and Sp from the IHA were 36.0% and 58.2%.

One-step direct immunoassay with horseradish peroxidase as antigen for studying the functionality of antibody surfaces.

Antibody-coated surfaces (Ab surfaces) play a key role in bioanalytical tools developed for biosensors and diagnostics. Therefore, a high and well-defined functional activity of the Ab surface is required. The functional activity of the Ab surface depends on its available binding sites i.e. "the active sites" that are able to capture antigen (Ag). The number of active binding sites strongly depends on the immobilization strategy used to fix the Ab on the solid surface. Determination of layer thickness or surface topology are often used to characterize the Ab surfaces but there is no gold standard method for the study of the functionality of the Ab surfaces. For that purpose, we aim at developing an assay allowing to determine the performances of Ab surfaces. In the present study, anti-horseradish peroxidase antibody (anti-HRP Ab) is used as capture Ab covalently bound to the surface and enzyme HRP as Ag. This direct assay permits, in one-step, to generate a signal utilizing the catalytic properties of HRP. The signal is directly proportional to the amount of HRP bound on the Ab surface, and therefore to the active binding sites of immobilized Ab. The HRP/anti-HRP Ab interactions may be a useful indicator to construct accurate and reproducible active Ab surfaces and also to improve their performances in term of stability and sensitivity. Optimization of the assay parameters and quality of the results are presented. A good repeatability and an acceptable inter-day precision (RSD < 10%) are reported.

A detergent-based procedure for the preparation of IgG-like bispecific antibodies in high yield.

Bispecific antibodies (BsAbs), with the ability to recognize two different epitopes simultaneously, offer remarkable advantages in bioassays, cancer therapy, biosensors, and enzyme electrodes. Preparation and purification of BsAbs in adequate quantities remains a major hurdle in their use in various applications. Poor yield is also the principal limitation in the preparation of BsAbs by the redox procedure. IgG with reduced inter-heavy chain disulfides do not dissociate into half molecules at neutral pH. In this study, we report that the dissociation occurs in presence of sodium dodecyl sulphate (SDS) and inclusion of the detergent during the redox procedure results in remarkable increase in the formation of the BsAbs. Exposure of antibodies to 0.1% (w/v) SDS causes only minor loss in secondary/tertiary structure and the ability to bind the antigen. The BsAbs prepared using the modified redox procedure that recognize the antigens HRP and α-LA were prepared and successfully employed for detecting α-LA in milk/dairy products by ELISA and dot blot techniques. BsAbs were also prepared from partially purified immunoglobulin gamma (IgG). This work shows for the first time that SDS, by dissociating IgG with reduced inter-heavy chain disulfides into half molecules, markedly enhances the formation of BsAbs by the redox procedure.

The fucomic potential of mosquitoes: Fucosylated N-glycan epitopes and their cognate fucosyltransferases.

Fucoconjugates are key mediators of protein-glycan interactions in prokaryotes and eukaryotes. As examples, N-glycans modified with the non-mammalian core α1,3-linked fucose have been detected in various organisms ranging from plants to insects and are immunogenic in mammals. The rabbit polyclonal antibody raised against plant horseradish peroxidase (anti-HRP) is able to recognize the α1,3-linked fucose epitope and is also known to specifically stain neural tissues in the fruit fly Drosophila melanogaster. In this study, we have detected and localized the anti-HRP cross-reactivity in another insect species, the malaria mosquito vector Anopheles gambiae. We were able to identify and structurally elucidate fucosylated N-glycans including core mono- and difucosylated structures (responsible for anti-HRP cross reactivity) as well as a Lewis-type antennal modification on mosquito anionic N-glycans by applying enzymatic and chemical treatments. The three mosquito fucosyltransferase open reading frames (FucT6, FucTA and FucTC) required for the in vivo biosynthesis of the fucosylated N-glycan epitopes were identified in the Anopheles gambiae genome, cloned and recombinantly expressed in Pichia pastoris. Using a robust MALDI-TOF MS approach, we characterised the activity of the three recombinant fucosyltransferases in vitro and demonstrate that they share similar enzymatic properties as compared to their homologues from D. melanogaster and Apis mellifera. Thus, not only do we confirm the neural reactivity of anti-HRP in a mosquito species, but also demonstrate enzymatic activity for all its α1,3- and α1,6-fucosyltransferase homologues, whose specificity matches the results of glycomic analyses.

Quantification of Sorafenib in Human Serum by Competitive Enzyme-Linked Immunosorbent Assay.

The multikinase inhibitor sorafenib has been used in the treatment of hepatocellular carcinoma, renal cell carcinoma, and differentiated thyroid carcinoma. Here we have demonstrated the production of the first specific antibody against sorafenib. Anti-sorafenib serum was obtained by immunizing mice with an antigen conjugated with bovine serum albumin and carboxylic modified 4-(4-aminophenoxy)-N-methyl-2-pyridinecarboxamide (AMPC) using the N-succinimidyl ester method. Enzyme labeling of sorafenib with horseradish peroxidase was similarly performed using carboxylic modified AMPC. A simple competitive enzyme-linked immunosorbent assay (ELISA) for sorafenib was developed using the principle of direct competition between sorafenib and the enzyme marker for anti-sorafenib antibody, which had been adsorbed by the plastic surface of a microtiter plate. Serum sorafenib concentrations lower than 0.04 µg/mL were reproducibly measurable using the ELISA. This ELISA was specific to sorafenib and showed very slight cross-reactivity (2.5%) with a major metabolite, sorafenib N-oxide. The values of serum sorafenib levels from 32 patients measured by this ELISA were comparable with those measured by HPLC, and there was a strong correlation between the values determined by the two methods (Y=1.016X-0.137, r=0.979). The specificity and sensitivity of the ELISA for sorafenib should provide a valuable new tool for use in therapeutic drug monitoring and pharmacokinetic studies of sorafenib.

Binding of actin to thioglycolic acid modified superparamagnetic nanoparticles for antibody conjugation.

Thioglycolic acid modified superparamagnetic iron oxide nanoparticles (TG-APTS-SPION) were synthesized by using (3-aminopropyl) triethoxysilane (APTS) and thioglycolic acid (TG). Actin was immobilized on the nanoparticle surfaces. Binding amount of the actin (Act) on TG-APTS-SPIONs was determined by using a calibration curve equation that was drawn using fluorescence spectra at 280 and 342 nm of excitation and emission wavelengths. Anti-Actin (anti-Act) was interacted with the actin immobilized TG-APTS-SPIONs as primary antibody. Horse radish peroxidase (HRP) was also interacted with antibody conjugated nanoparticles as secondary antibody. The binding capacity of primary and secondary antibodies was also estimated by fluorescence spectroscopy. Scanning electron microscopy (SEM), Infrared spectroscopy (FTIR) and energy dispersive X-ray (EDX) analysis were also clarified binding of the protein and antibodies to the nanoparticles' surfaces. Western blot analysis was also done for actin conjunction with anti Act antibody to confirm binding of the antibody to the protein.

Development of monoclonal antibody-based sandwich ELISA for detection of dextran.

Dextran as anti-nutritional factor is usually a result of bacteria activity and has associated serial problems during the process stream in the sugar industry and in medical therapy. A sensitive method is expected to detect dextran quantitatively. Here we generated four monoclonal antibodies (MAbs) against dextran using dextran T40 conjugated with bovine serum albumin (BSA) as immunogen in our lab following hybridoma protocol. Through pairwise, an MAb named D24 was determined to be conjugated with horseradish peroxidase (HRP) and was used in the establishment of a sensitive sandwich enzyme-linked immunosorbent assay (ELISA) method for determination of dextran, in which MAb D9 was chosen as a capture antibody. The detection limit and working scope of the developed sandwich ELISA method were 3.9 ng/mL and 7.8-500 ng/mL with a correlation coefficient of 0.9909. In addition, the cross-reaction assay demonstrated that the method possessed high specificity with no significant cross-reaction with dextran-related substances, and the recovery rate ranged from 96.35 to 102.00%, with coefficient of variation ranging from 1.58 to 6.94%. These results indicated that we developed a detection system of MAb-based sandwich ELISA to measure dextran and this system should be a potential tool to determine dextran levels.

Tips for the functionalization of nanoparticles with antibodies.

Multiple antibody immobilization methodologies have been developed for several applications including affinity chromatography, immunosensing, and drug delivery. Most of them have been carried out without considering the orientation of the antigen binding site of the antibody, or after the chemical modification of the antibody. An efficient immobilization to improve the biological activity of the antibody is one of the key fundamental issues to pursue. A simple and effective methodology for well-oriented covalently immobilization of antibodies on nanoparticles is reported in this chapter.

Enzyme-linked Fab' fragment based competitive immunoassay for ovalbumin in hot-processed food.

A hen's egg is one of the most common causes of food allergy. The allergen quantitation in hot-processed food is always a difficult task, because the protein in these samples will be denatured, insoluble, and degraded. This article presents a competitive enzyme linked immunosorbent assay (ELISA) for the quantitation of ovalbumin in hot-processed food. Its recovery was improved nearly two times by the assay method as compared with previous sandwich ELISA. The heat and DL-Dithiothreitol treated ovalbumin was used as antigen for monoclonal antibody preparation. A smaller labeled antibody molecule, horseradish peroxidase (HRP) labeled Fab' fragment, was used to replace IgG in ELISA for improving sensitivity and analytical speed of the method. A binding site protection procedure was developed for Fab' fragment labeling with HRP, which prevented damage to the Fab' binding site. The combination and separation steps were efficiently completed in an affinity spin column. Based on the optimized ELISA condition, the IC50 was 1.2 µg/mL and the coefficients of variation were less than 10%.