Quantification of immobilized protein in pharmaceutical production by bio-assisted potentiometric multisensor system

Quantification of proteins is a key biochemical assay in molecular biology, biotechnology, medicine and pharmacology. Protein quantification protocols can be based on spectrophotometry, enzyme-linked immunosorbent assay, mass spectrometry or quantitative immunoblotting depending on analyte. In case of immobilized protein these methods require suitable sample preparation. Thus, sophisticated analysis becomes even more complex, expensive and time-consuming. Such drawbacks are highly undesirable in industry. In this study we propose a new approach for evaluation of immobilized protein concentration based on application of bio-assisted potentiometric multisensor system. Surface-immobilized recombinant protein A from Staphylococcus aureus (SpA, expressed in Escherichia coli), which is commonly used as affinity ligand immobilized to stationary phase (сhromatography media) for monoclonal antibody purification was employed as the model object. Chromatography media samples containing different amounts of immobilized SpA were analyzed. Proteinase K from Tritirachium album was employed as a bio-transducer. We demonstrated that the suggested approach provides information about immobilized SpA concentration with 0.8mg/ml accuracy in the range 1-6.7mg/ml and within just 16min. Moreover, the proposed procedure requires no expensive materials and equipment and no bio-transducer immobilization. This method has potential of application for fast monitoring of other immobilized proteins in different tasks.

Optimized Specific Isolation of Placenta-Derived Exosomes from Maternal Circulation

Exosomes are small (~100 nm) vesicles that carry a wide range of molecules including proteins, RNAs, and DNA. Exosomes are secreted from a wide range of cells including placental cells. Interestingly, exosomes secreted from placental cells have been identified in maternal circulation as early as in 6 weeks of gestation, and their concentration increases with the gestational age. While there is growing interest in elucidating the role of exosomes during normal and complicated pregnancies (such as preeclampsia), progress in the field has been delayed because of the inability to isolate placental exosomes from maternal circulation. Therefore, here we describe a workflow to isolate placental exosomes from maternal circulation.

Development of An Impedimetric Aptasensor for the Detection of Staphylococcus aureus

In combination with electrochemical impedance spectroscopy, aptamer-based biosensors are a powerful tool for fast analytical devices. Herein, we present an impedimetric aptasensor for the detection of the human pathogen Staphylococcus aureus. The used aptamer targets protein A, a surface bound virulence factor of S. aureus. The thiol-modified protein A-binding aptamer was co-immobilized with 6-mercapto-1-hexanol onto gold electrodes by self-assembly. Optimization of the ratio of aptamer to 6-mercapto-1-hexanol resulted in an average density of 1.01 ± 0.44 × 10¹³ aptamer molecules per cm². As shown with quartz crystal microbalance experiments, the immobilized aptamer retained its functionality to bind recombinant protein A. Our impedimetric biosensor is based on the principle that binding of target molecules to the immobilized aptamer decreases the electron transfer between electrode and ferri-/ferrocyanide in solution, which is measured as an increase of impedance. Microscale thermophoresis measurements showed that addition of the redox probe ferri-/ferrocyanide has no influence on the binding of aptamer and its target. We demonstrated that upon incubation with various concentrations of S. aureus, the charge-transfer resistance increased proportionally. The developed biosensor showed a limit of detection of 10 CFU·mL^-1 and results were available within 10 minutes. The biosensor is highly selective, distinguishing non-target bacteria such as Escherichia coli and Staphylococcus epidermidis. This work highlights the immense potential of impedimetric aptasensors for future biosensing applications.

Using PyMOL to Explore the Effects of pH on Noncovalent Interactions between Immunoglobulin G and Protein A: A Guided-Inquiry Biochemistry Activity

Students' understandings of foundational concepts such as noncovalent interactions, pH and pK_a are crucial for success in undergraduate biochemistry courses. We developed a guided-inquiry activity to aid students in making connections between noncovalent interactions and pH/pK_a . Students explore these concepts by examining the primary and tertiary structures of immunoglobulin G (IgG) and Protein A. Students use PyMOL, an open source molecular visualization application, to (1) identify hydrogen bonds and salt bridges between and within the proteins at physiological pH and (2) apply their knowledge of pH/pK_a to association rate constant data for these proteins at pH 4 and pH 11. The laboratory activity was implemented within a one semester biochemistry laboratory for students majoring in allied health disciplines, engineering, and biological sciences. Several extensions for more advanced students are discussed. Students' overall performance highlighted their ability to successfully complete tasks such as labeling and identifying noncovalent interactions and revealed difficulties with analyzing noncovalent interactions under varying pH/pK_a conditions. Students' evaluations after completing the activity indicated they felt challenged but also recognized the potential of the activity to help them gain meaningful understanding of the connections between noncovalent interactions, pH, pK_a , and protein structure. © 2017 by The International Union of Biochemistry and Molecular Biology, 45(6):528-536, 2017.

3-2-1: Structural insights from stepwise shrinkage of a three-helix Fc-binding domain to a single helix

The well-studied B-domain from Staphylococcal protein A is a 59 amino acid three-helix bundle that binds the Fc portion of IgG with a dissociation constant of ~35 nM. The B-domain variant bearing a Gly to Ala mutation (=Z-domain) has been the subject of efforts to minimize a domain's size while retaining its function. We report X-ray crystallographic characterization of three steps in such a process using complexes with Fc: the full three-helix Z-domain, a 34 amino acid two-helix version called Z34C and a 13 amino acid single helix stabilized with an exo-helix tether, called LH1.

Chimeric Flock House virus protein A with endoplasmic reticulum-targeting domain enhances viral replication and virus-like particle trans-encapsidation in plants

Flock House virus (FHV) RNA can be trans-encapsidated, entirely in planta, by tobacco mosaic virus coat protein to form virus-like particles (VLPs). Vaccination with these VLPs leads to strong antigen expression in mice and immune-activation. We hypothesize that creating an additional cellular site for replication and/or trans-encapsidation might significantly improve the final output of trans-encapsidated product. FHV protein A was engineered to target the endoplasmic reticulum (ER) via a heterologous tobacco etch virus ER-targeting domain, and was expressed in cis or in trans relative to the replicating FHV RNA1. A strong increase in marker gene expression in plants was noted when ER-targeted protein A was supplied in trans. RNA fluorescence in situ hybridization revealed RNA1 replication in both the mitochondria and ER, and total RNA1 accumulation was increased. In support of our hypothesis, VLP yield was increased significantly by the addition of this single genetic component to the inoculum.

Site-selective orientated immobilization of antibodies and conjugates for immunodiagnostics development

Immobilized antibody systems are the key to develop efficient diagnostics and separations tools. In the last decade, developments in the field of biomolecular engineering and crosslinker chemistry have greatly influenced the development of this field. With all these new approaches at our disposal, several new immobilization methods have been created to address the main challenges associated with immobilized antibodies. Few of these challenges that we have discussed in this review are mainly associated to the site-specific immobilization, appropriate orientation, and activity retention. We have discussed the effect of antibody immobilization approaches on the parameters on the performance of an immunoassay.

Excitation Energy Transfer by Coherent and Incoherent Mechanisms in the Peridinin-Chlorophyll a Protein

Excitation energy transfer from peridinin to chlorophyll (Chl) a is unusually efficient in the peridinin-chlorophyll a protein (PCP) from dinoflagellates. This enhanced performance is derived from the long intrinsic lifetime of 4.4 ps for the S₂ (1¹B_u⁺) state of peridinin in PCP, which arises from the electron-withdrawing properties of its carbonyl substituent. Results from heterodyne transient grating spectroscopy indicate that S₂ serves as the donor for two channels of energy transfer: a 30 fs process involving quantum coherence and delocalized peridinin-Chl states and an incoherent, 2.5 ps process initiated by dynamic exciton localization, which accompanies the formation of a conformationally distorted intermediate in 45 fs. The lifetime of the S₂ state is lengthened in PCP by its intramolecular charge-transfer character, which increases the system-bath coupling and slows the torsional motions that promote nonradiative decay to the S₁ (2¹A_g^-) state.

Purification of Antibodies Using Affinity Chromatography

Affinity chromatography permits the isolation of a target analyte from a complex mixture and can be utilized to purify proteins, carbohydrates, drugs, haptens, or any analyte of interest once an affinity pair is available. It involves the exploitation of specific interactions between a binding affinity pair, such as those between an antibody and its associated antigen, or between any ligand and its associated binding receptor/protein. With the discovery of protein A in 1970, and, subsequently protein G and L, immuno-affinity chromatography has grown in popularity and is now the standard methodology for the purification of antibodies which may be implemented for a selection of different applications such as immunodiagnostics. This chapter is designed to inform the researcher about the basic techniques involved in the affinity chromatography-based purification of monoclonal, polyclonal, and recombinant antibodies. Examples are provided for the use of protein A and G. In addition, tables are provided that allow the reader to select the most appropriate protein for use in the isolation of their antibody.

Direct electrical control of IgG conformation and functional activity at surfaces

We have devised a supramolecular edifice involving His-tagged protein A and antibodies to yield surface immobilized, uniformly oriented, IgG-type, antibody layers with Fab fragments exposed off an electrode surface. We demonstrate here that we can affect the conformation of IgGs, likely pushing/pulling electrostatically Fab fragments towards/from the electrode surface. A potential difference between electrode and solution acts on IgGs' charged aminoacids modulating the accessibility of the specific recognition regions of Fab fragments by antigens in solution. Consequently, antibody-antigen affinity is affected by the sign of the applied potential: a positive potential enables an effective capture of antigens; a negative one pulls the fragments towards the electrode, where steric hindrance caused by neighboring molecules largely hampers the capture of antigens. Different experimental techniques (electrochemical quartz crystal microbalance, electrochemical impedance spectroscopy, fluorescence confocal microscopy and electrochemical atomic force spectroscopy) were used to evaluate binding kinetics, surface coverage, effect of the applied electric field on IgGs, and role of charged residues on the phenomenon described. These findings expand the concept of electrical control of biological reactions and can be used to gate electrically specific recognition reactions with impact in biosensors, bioactuators, smart biodevices, nanomedicine, and fundamental studies related to chemical reaction kinetics.

Bio-functional surfaces for the immunocapture of AGO2-bound microRNAs

MicroRNAs (miRNAs) are endogenous, small (18-24nt), non-coding RNAs that regulate gene expression. Among miRNAs, those bound to the AGO2 protein are the functionally active fraction which mediates the cell regulatory processes and regulate messages exchanged by cells. Several methods have been developed to purify this fraction of microRNAs, such as immunoprecipitation and immunoprecipitation-derived techniques. However, all these techniques are generally recognized as technically complicated and time consuming. Here, a new bio-functional surface for the specific capture of AGO2-bound microRNAs is proposed. Starting from a silicon oxide surface, a protein A layer was covalently bound via epoxy chemistry to orient specific anti-AGO2 antibodies on the surface. The anti-AGO2 antibodies captured the AGO2 protein present in cell lysate and in human plasma. The AGO2-bound microRNAs were then released by enzymatic digestion and detected via RT-qPCR. Control surfaces were also prepared and tested. Every step in the preparation of the bio-functional surfaces was fully characterized from the chemical, morphological and functional point of view. The resulting bio-functional surface is able to specifically capture the AGO2-bound miRNAs from biologically-relevant samples, such as cell lysate and human plasma. These samples contain different proportions of AGO2-bound microRNAs, as reliably detected with the immunocapture method here proposed. This work opens new perspectives for a simple and faster method to isolate not only AGO2-bound microRNAs, but also the multiprotein complex containing AGO2 and miRNAs.

[SURFACE PLASMON RESONANCE: APPROACHES AND PERSPECTIVES OF APPLICATION FOR VIRUS-SPECIFIC INTERACTIONS INVESTIGATIONS]

In the review the published data on the use of surface plasmon resonance methods for the study of individual viral proteins as well as intact viruses are reviewed. . The principles of the method, its benefits and peculiarities of its use to study viruses are introduced. Particular attention is paid to the requirements to the sensor surface and the methods of its modification, including the formation self assembled monolayers of amphiphilic organic molecules containing functional groups to connect to the surface, creating of the intermediate protective thiocyanate layer between protein and metal, forming of the favorable microenvironment using dextran hydrogels around biomolecules, immobilization of proteins on the surface of the sensor using streptavidin-biotin system, use of protein A Staphylococcus aureus as an sensitive element of the sensory system structure. The approaches to enhance the signal used in virological studies, including the use of labeled antibodies, using competitive analysis for the detection of small molecules, the formation of a complex directly on the sensor surface, and immobilization on the surface of the sensor previously obtained complex receptor-analyte are considered. The conclusion is that the SPR method contains many potential opportunities to study various aspects of the interaction of viruses with specific agents, and changes in the structure of viruses caused by various external factors.

Molecular dynamics of protein A and a WW domain with a united-residue model including hydrodynamic interaction

The folding of the N-terminal part of the B-domain of staphylococcal protein A (PDB ID: 1BDD, a 46-residue three-α-helix bundle) and the formin-binding protein 28 WW domain (PDB ID: 1E0L, a 37-residue three-stranded anti-parallel β protein) was studied by means of Langevin dynamics with the coarse-grained UNRES force field to assess the influence of hydrodynamic interactions on protein-folding pathways and kinetics. The unfolded, intermediate, and native-like structures were identified by cluster analysis, and multi-exponential functions were fitted to the time dependence of the fractions of native and intermediate structures, respectively, to determine bulk kinetics. It was found that introducing hydrodynamic interactions slows down both the formation of an intermediate state and the transition from the collapsed structures to the final native-like structures by creating multiple kinetic traps. Therefore, introducing hydrodynamic interactions considerably slows the folding, as opposed to the results obtained from earlier studies with the use of Gō-like models.

Control of Protein Affinity of Bioactive Nanocellulose and Passivation Using Engineered Block and Random Copolymers

We passivated TEMPO-oxidized cellulose nanofibrils (TOCNF) toward human immunoglobulin G (hIgG) by modification with block and random copolymers of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA). The block copolymers reversibly adsorbed on TOCNF and were highly effective in preventing nonspecific interactions with hIgG, especially if short PDMAEMA blocks were used. In such cases, total protein rejection was achieved. This is in contrast to typical blocking agents, which performed poorly. When an anti-human IgG biointerface was installed onto the passivated TOCNF, remarkably high affinity antibody-antigen interactions were observed (0.90 ± 0.09 mg/m(2)). This is in contrast to the nonpassivated biointerface, which resulted in a significant false response. In addition, regeneration of the biointerface was possible by low pH aqueous wash. Protein A from Staphylococcus aureus was also utilized to successfully increase the sensitivity for human IgG recognition (1.28 ± 0.11 mg/m(2)). Overall, the developed system based on TOCNF modified with multifunctional polymers can be easily deployed as bioactive material with minimum fouling and excellent selectivity.

Routes to improve binding capacities of affinity resins demonstrated for Protein A chromatography

Protein A chromatography is a well-established platform in downstream purification of monoclonal antibodies. Dynamic binding capacities are continuously increasing with almost every newly launched Protein A resin. Nevertheless, binding capacities of affinity chromatography resins cannot compete with binding capacities obtained with modern ion exchange media. Capacities of affinity resins are roughly 50% lower. High binding capacities of ion exchange media are supported by spacer technologies. In this article, we review existing spacer technologies of affinity chromatography resins. A yet known effective approach to increase the dynamic binding capacity of Protein A resins is oligomerization of the particular Protein A motifs. This resembles the tentacle technology used in ion exchange chromatography. Dynamic binding capacities of a hexameric ligand are roughly twice as high compared to capacities obtained with a tetrameric ligand. Further capacity increases up to 130mg/ml can be realized with the hexamer ligand, if the sodium phosphate buffer concentration is increased from 20 to 100mM. Equilibrium isotherms revealed a BET shape for the hexamer ligand at monoclonal antibody liquid phase concentrations higher than 9mg/ml. The apparent multilayer formation may be due to hydrophobic forces. Other quality attributes such as recovery, aggregate content, and overall purity of the captured monoclonal antibody are not affected.

Preparation of Colloidal Gold Particles and Conjugation to Protein A/G/L, IgG, F(ab')2, and Streptavidin

Colloidal gold probes, including protein A/G/L, IgG, F(ab')2, and streptavidin labeled with gold particles, are useful tools to localize antigens in cells and tissues by immunoelectron microscopy (IEM). This chapter describes different methods for the preparation of colloidal gold and conjugation of colloidal gold to protein A/G/L, IgG, and streptavidin.

Characterization of Field Effect Transistor Biosensors Fabricated Using Layer-by-Layer Nanoassembly Process

In order to avoid the fabrication complexity involved with a single carbon nanotube (CNT) based immunosensor, herein we report an FET based biosensor, in which the channel is made out of Carbon Nanotube Thin Film (CNTF). The CNTF channel between the source and drain electrodes is assembled using a combination of photolithography and electrostatic layer-by-layer self-assembly (LbL). The fabricated device behaves like a p-type transistor. The bio-affinity interaction between Protein A and rabbit Immunoglobulin G (IgG) is used to model the immunosensing, and our initial results show the device is capable of detecting IgG concentrations as low as 1 pg/mL.

Cleaning-in-place of immunoaffinity resins monitored by in situ ATR-FTIR spectroscopy

In the next 10 years, the pharmaceutical industry anticipates that revenue from biotherapeutics will overtake those generated from small drug molecules. Despite effectively treating a range of chronic and life-threatening diseases, the high cost of biotherapeutics limits their use. For biotherapeutic monoclonal antibodies (mAbs), an important production cost is the affinity resin used for protein capture. Cleaning-in-place (CIP) protocols aim to optimise the lifespan of the resin by slowing binding capacity decay. Binding assays can determine resin capacity from the mobile phase, but do not reveal the underlying causes of Protein A ligand degradation. The focus needs to be on the stationary phase to examine the effect of CIP on the resin. To directly determine both the local Protein A ligand concentration and conformation on two Protein A resins, we developed a method based on attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy. ATR-FTIR spectroscopic imaging revealed that applying a carefully controlled load to agarose beads produces an even and reproducible contact with the internal reflection element. This allowed detection and quantification of the binding capacity of the stationary phase. ATR-FTIR spectroscopy also showed that Protein A proteolysis does not seem to occur under typical CIP conditions (below 1 M NaOH). However, our data revealed that concentrations of NaOH above 0.1 M cause significant changes in Protein A conformation. The addition of >0.4 M trehalose during CIP significantly reduced NaOH-induced ligand unfolding observed for one of the two Protein A resins tested. Such insights could help to optimise CIP protocols in order to extend resin lifetime and reduce mAb production costs.

Post-Translational Modification of Bionanoparticles as a Modular Platform for Biosensor Assembly

Context driven biosensor assembly with modular targeting and detection moieties is gaining significant attentions. Although protein-based nanoparticles have emerged as an excellent platform for biosensor assembly, current strategies of decorating bionanoparticles with targeting and detection moieties often suffer from unfavorable spacing and orientation as well as bionanoparticle aggregation. Herein, we report a highly modular post-translational modification approach for biosensor assembly based on sortase A-mediated ligation. This approach enables the simultaneous modifications of the Bacillus stearothermophilus E2 nanoparticles with different functional moieties for antibody, enzyme, DNA aptamer, and dye decoration. The resulting easy-purification platform offers a high degree of targeting and detection modularity with signal amplification. This flexibility is demonstrated for the detection of both immobilized antigens and cancer cells.

Bacteria-mimicking nanoparticle surface functionalization with targeting motifs

In recent years, surface modification of nanocarriers with targeting motifs has been explored to modulate delivery of various diagnostic, sensing and therapeutic molecular cargo to desired sites of interest in in vitro bioengineering platforms and in vivo pathologic tissue. However, most surface functionalization approaches are often plagued by complex chemical modifications and effortful purifications. To resolve such challenges, this study demonstrates a unique method to immobilize antibodies that can act as targeting motifs on the surfaces of nanocarriers, inspired by a process that bacteria use for immobilization of the host's antibodies. We hypothesized that alkylated Staphylococcus aureus protein A (SpA) would self-assemble with micelles and subsequently induce stable coupling of antibodies to the micelles. We examined this hypothesis by using poly(2-hydroxyethyl-co-octadecyl aspartamide) (PHEA-g-C18) as a model polymer to form micelles. The self-assembly between the micelles and alkylated SpA became more thermodynamically favorable by increasing the degree of substitution of octadecyl chains to PHEA-g-C18, due to a positive entropy change. Lastly, the mixing of SpA-PA-coupled micelles with antibodies resulted in the coating of micelles with antibodies, as confirmed with a fluorescence resonance energy transfer (FRET) assay. The micelles coated with antibodies to VCAM-1 or integrin αv displayed a higher binding affinity to substrates coated with VCAM-1 and integrin αvβ3, respectively, than other controls, as evaluated with surface plasmon resonance (SPR) spectroscopy and a circulation-simulating flow chamber. We envisage that this bacteria-inspired protein immobilization approach will be useful to improve the quality of targeted delivery of nanoparticles, and can be extended to modify the surface of a wide array of nanocarriers.

NMR assignment of the amylase-binding protein A from Streptococcus parasanguinis

Streptococcus parasanguinis is a primary colonizer of tooth surfaces in the oral cavity. Amylase-binding protein A (AbpA) from S. parasanguinis is responsible for the recruitment of salivary amylase to bacterial surface, which plays an important role in the development of oral biofilms. Here, we describe the essentially complete NMR assignments for AbpA.

Surface enhanced Raman spectroscopy detection of biomolecules using EBL fabricated nanostructured substrates

Fabrication and characterization of conjugate nano-biological systems interfacing metallic nanostructures on solid supports with immobilized biomolecules is reported. The entire sequence of relevant experimental steps is described, involving the fabrication of nanostructured substrates using electron beam lithography, immobilization of biomolecules on the substrates, and their characterization utilizing surface-enhanced Raman spectroscopy (SERS). Three different designs of nano-biological systems are employed, including protein A, glucose binding protein, and a dopamine binding DNA aptamer. In the latter two cases, the binding of respective ligands, D-glucose and dopamine, is also included. The three kinds of biomolecules are immobilized on nanostructured substrates by different methods, and the results of SERS imaging are reported. The capabilities of SERS to detect vibrational modes from surface-immobilized proteins, as well as to capture the protein-ligand and aptamer-ligand binding are demonstrated. The results also illustrate the influence of the surface nanostructure geometry, biomolecules immobilization strategy, Raman activity of the molecules and presence or absence of the ligand binding on the SERS spectra acquired.

Nano-magnetic immunosensor based on staphylococcus protein a and the amplification effect of HRP-conjugated phage antibody

In this research, super-paramagnetic Fe3O4 nanoparticles (magnetic particles) were coated with Staphylococcus protein A (SPA) and coupled with polyclonal antibody (pcAb) to construct magnetic capturing probes, and HRP-conjugated phage antibody was then used as specific detecting probe to design a labeled immunosensor for trace detection of Staphylococcus aureus enterotoxin B (SEB). The linear detection range of the sensor was 0.008~125 µg/L, the regression equation was Y = 0.487X + 1.2 (R = 0.996, N = 15, p < 0.0001), the limit of detection (LOD) was 0.008 µg/L, and the limit of quantification (LOQ) was 0.008 µg/L. HRP-conjugated phage antibody, SPA and magnetic particles can enhance the sensitivity 4-fold, 3-fold and 2.6-fold higher, respectively. Compared with conventional double-antibody sandwich ELISA, the detection sensitivity of the sensor was 31-fold higher resulting from the integrated amplifying effect. The immunosensor integrates the unique advantages of SPA-oriented antibody as magnetic capturing probe, HRP-conjugated phage antibody as detecting probe, magnetic separation immunoassay technique, and several other advanced techniques, so it achieves high sensitivity, specificity and interference-resistance. It is proven to be well suited for analysis of trace SEB in various environmental samples with high recovery rate and reproducibility.

The Biochemical Properties of Antibodies and Their Fragments

Immunoglobulins (Ig) or antibodies are powerful molecular recognition tools that can be used to identify minute quantities of a given target analyte. Their antigen-binding properties define both the sensitivity and selectivity of an immunoassay. Understanding the biochemical properties of this class of protein will provide users with the knowledge necessary to select the appropriate antibody composition to maximize immunoassay results. Here we define the general biochemical properties of antibodies and their similarities and differences, explain how these properties influence their functional relationship to an antigen target, and describe a method for the enzymatic fragmentation of antibodies into smaller functional parts.

Flow-Through Assay for Detection of Antibodies Using Protein-A Colloidal Gold Conjugate as a Probe

Flow-through assay (FTA) is a rapid, simple-to-perform, cost-effective, and user-friendly diagnostic test for monitoring infections in non-laboratory settings. It is mostly applied for antibody detection. FTA employing protein-A colloidal gold conjugate to detect antibodies against porcine cysticerci using cyst fluid and whole cyst antigens of Taenia solium metacestode is described here. Antibodies in the serum are captured by an antigen spotted onto a nitrocellulose membrane mounted on a flow-through device that serves as the antigen capture matrix. The bound antibodies are visualized by the addition of protein-A colloidal gold conjugate, which imparts a pink color. The test can be completed within 3 min at room temperature without any instrumentation. The sensitivity and specificity of the FTA are in agreement with ELISA.