Characterization of antibody–antigen interactions: Comparison between surface plasmon resonance measurements and high-mass matrix-assisted laser desorption/ionization mass spectrometry

Hemin/G-quadruplex and AuNPs-MoS2 based novel dual signal amplification strategy for ultrasensitively sandwich-type electrochemical thrombin aptasensor

In this work, a novel sandwich-type electrochemical aptasensor based on the dual signal amplification strategy of hemin/G-quadruplex and AuNPs-MoS2 was designed and constructed, which realized the highly sensitive and specific detection of thrombin (TB). In this aptasensor, the 15-mer TB-binding aptamer (TBA-1) modified with thiol group was immobilized on the surface of AuNPs modified glassy carbon electrode (AuNPs/GCE) as capturing elements. Another thiol-modified 29-mer TB-binding aptamer (TBA-2) sequence containing G-quadruplex structure for hemin immobilization was designed. The formed hemin/G-quadruplex/TBA-2 sequence was further combined to the AuNPs decorated flower-like molybdenum disulfide (AuNPs-MoS2) composite surface via Au-S bonds, acting the role of reporter probe. In presence of the target TB, the sandwich-type electrochemical aptamer detection system could be formed properly. With the assistance of the dual signal amplification of AuNPs-MoS2 and hemin/G-quadruplex toward H2O2 reduction, the sandwich-type electrochemical aptasensor was successfully constructed for sensitive detection of TB. The results demonstrate that the fabricated aptasensor displays a wide linear range of 1.0 × 10-6 ∼ 10.0 nM with a low detection limit of 0.34 fM. This proposed aptasensor shows potential application in the detection of TB content in real biological samples with high sensitivity, selectivity, and reliability.

An Insight Into the Physicochemical Properties of Gold Nanoparticles in Relation to Their Clinical and Diagnostic Applications

The ease of formulation and surface modification of gold nanoparticles (AuNPs) by ligands, greater biocompatibility, non-cytotoxicity, and excellent optical properties are the characteristics that necessitate their application in clinical and genomic research. Not only that, but the extensive synthetic chemistry of AuNPs also offers precise control over physicochemical and optical properties owing to the inert, biocompatible, and non-toxic nature of the inner gold core. Another important property of AuNPs involves their incorporation into larger structures, including liposomes or polymeric materials, thereby increasing their capability of drug delivery in concurrent therapy and imaging labels for enhanced diagnostic applications. AuNPs are endowed with physical properties that suggest their use as adjuvants for radiotherapy and bio-imaging and in computed tomography (CT) scans, diagnostic systems, and therapy. Thus, these features strongly endorse the AuNPs in thrust areas of biomedical fields. The diverse properties of gold nanoparticles (AuNPs) have made them promising candidates in biomedical fields, including in the development of theranostics, which encompasses using these gold nanoparticles for both diagnosis and therapy simultaneously. To appreciate these and related applications, a need arises to review the basic principles and multifunctional attributes of AuNPs in relation to their advances in imaging, therapy, and diagnostics.

High-Mass Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry for Absolute Quantitation of Noncovalent Protein-Protein Binding Interactions

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a robust and powerful tool for studying biomacromolecules and their interactions. However, quantitative detection of high-mass analytes (kDa to MDa range) remains challenging for MALDI-MS. Herein, we successfully used commercially available purified proteins (β-galactosidase and BSA) as internal standards for high-mass MALDI-MS analysis and achieved absolute quantification of several high-mass analytes. We systematically evaluated four sample deposition methods, and using the sandwich deposition method with saturated sinapinic acid as the top layer, we performed a robust quantitative analysis by high-mass MALDI-MS. Combined with chemical cross-linking, this quantitative strategy was further used to evaluate the affinity of protein-protein interactions (PPIs), specifically of two soluble protein receptors (interleukin 1 receptor and interleukin 2 receptor) and two membrane protein receptors (rhodopsin and angiotensin 2 receptor 1) with their interaction partners. The measured dissociation constants of the protein complexes formed were between 10 nM and 5 μM. We expect this high-throughput, rapid method, which does not require labeling or immobilization of any of the interaction partners, to become a viable alternative to traditional biophysical methods for studying PPIs.

Conjugating immunoassays to mass spectrometry: Solutions to contemporary challenges in clinical diagnostics

Developments in immunoassays and mass spectrometry have independently influenced diagnostic technology. However, both techniques possess unique strengths and limitations, which define their ability to meet evolving requirements for faster, more affordable and more accurate clinical tests. In response, hybrid techniques, which combine the accessibility and ease-of-use of immunoassays with the sensitivity, high throughput and multiplexing capabilities of mass spectrometry are continually being explored. Developments in antibody conjugation methodology have expanded the role of these biomolecules to applications outside of conventional colorimetric assays and histology. Furthermore, the range of different mass spectrometry ionisation and analysis technologies has enabled its successful adaptation as a detection method for numerous clinically relevant immunological assays. Several recent examples of combined mass spectrometry-immunoassay techniques demonstrate the potential of these methods as improved diagnostic tests for several important human diseases. The present challenges are to continue technological advancements in mass spectrometry instrumentation and develop improved bioconjugation methods, which can overcome their existing limitations and demonstrate the clinical significance of these hybrid approaches.

Characterization of Mega-Dalton-Sized Nanoparticles by Superconducting Tunnel Junction Cryodetection Mass Spectrometry

The characterization of nanomaterials is critical to understand the size/structure-dependent properties of these particles. In this report, a form of heavy ion mass spectrometry, namely, superconducting tunnel junction (STJ) cryodetection mass spectrometry (MS) is used to characterize quantum dot semiconductor nanocrystals and gold nanoparticles. The nanoparticles studied ranged in mass from 200 kDa to >1.5 MDa and included lead sulfide quantum dots, various cadmium selenide and/or telluride-based core-shell quantum dots coated with different ligands, and gold nanoparticles. Nanoparticles were ionized by both matrix-assisted laser desorption ionization (MALDI) and laser desorption ionization (LDI), shot with an aimed ion gun into a flight tube, mass separated by time-of-flight (TOF), and detected by an energy-sensitive STJ cryodetector. STJ cryodetection MS can be used to analyze intact heterogeneous nanoparticles, allowing determination of average particle mass, dispersity, and ligand loading. Some nanoparticles, however, do undergo fragmentation during the MALDI or LDI-TOF mass analyses. The measurement of the energy deposited into the detector was found to be different for different types of particles. Metastable fragments from these nanoparticles were observed at lower energies. The lower energies deposited for metastable fragments can provide insight into the stability and surface compositions of these materials. Cadmium selenide core-shell quantum dots (655 nm emission) conjugated to biomacromolecules, such as cholera toxin B and human serum transferrin, were also analyzed. When compared to unconjugated particles by mass, it was determined that ∼96 cholera toxin B and ∼14 transferrin proteins were attached to the surface of these nanoparticles.

TREM-1 multimerization is essential for its activation on monocytes and neutrophils

The triggering receptor expressed on myeloid cells-1 (TREM-1) is a receptor expressed on innate immune cells. By promoting the amplification of inflammatory signals that are initially triggered by Toll-like receptors (TLRs), TREM-1 has been characterized as a major player in the pathophysiology of acute and chronic inflammatory diseases, such as septic shock, myocardial infarction, atherosclerosis, and inflammatory bowel diseases. However, the molecular events leading to the activation of TREM-1 in innate immune cells remain unknown. Here, we show that TREM-1 is activated by multimerization and that the levels of intracellular Ca²⁺ release, reactive oxygen species, and cytokine production correlate with the degree of TREM-1 aggregation. TREM-1 activation on primary human monocytes by LPS required a two-step process consisting of upregulation followed by clustering of TREM-1 at the cell surface, in contrast to primary human neutrophils, where LPS induced a rapid cell membrane reorganization of TREM-1, which confirmed that TREM-1 is regulated differently in primary human neutrophils and monocytes. In addition, we show that the ectodomain of TREM-1 is able to homooligomerize in a concentration-dependent manner, which suggests that the clustering of TREM-1 on the membrane promotes its oligomerization. We further show that the adapter protein DAP12 stabilizes TREM-1 surface expression and multimerization. TREM-1 multimerization at the cell surface is also mediated by its endogenous ligand, a conclusion supported by the ability of the TREM-1 inhibitor LR12 to limit TREM-1 multimerization. These results provide evidence for ligand-induced, receptor-mediated dimerization of TREM-1. Collectively, our findings uncover the mechanisms necessary for TREM-1 activation in monocytes and neutrophils.

Applying mass spectrometry to study non-covalent biomolecule complexes

Non-covalent interactions are essential for the structural organization of biomacromolecules and play an important role in molecular recognition processes, such as the interactions between proteins, glycans, lipids, DNA, and RNA. Mass spectrometry (MS) is a powerful tool for studying of non-covalent interactions, due to the low sample consumption, high sensitivity, and label-free nature. Nowadays, native-ESI MS is heavily used in studies of non-covalent interactions and to understand the architecture of biomolecular complexes. However, MALDI-MS is also becoming increasingly useful. It is challenging to detect the intact complex without fragmentation when analyzing non-covalent interactions with MALDI-MS. There are two methodological approaches to do so. In the first approach, different experimental and instrumental parameters are fine-tuned in order to find conditions under which the complex is stable, such as applying non-acidic matrices and collecting first-shot spectra. In the second approach, the interacting species are "artificially" stabilized by chemical crosslinking. Both approaches are capable of studying non-covalently bound biomolecules even in quite challenging systems, such as membrane protein complexes. Herein, we review and compare native-ESI and MALDI MS for the study of non-covalent interactions.

Analytical methods for kinetic studies of biological interactions: A review

The rates at which biological interactions occur can provide important information concerning the mechanism and behavior of these processes in living systems. This review discusses several analytical methods that can be used to examine the kinetics of biological interactions. These techniques include common or traditional methods such as stopped-flow analysis and surface plasmon resonance spectroscopy, as well as alternative methods based on affinity chromatography and capillary electrophoresis. The general principles and theory behind these approaches are examined, and it is shown how each technique can be utilized to provide information on the kinetics of biological interactions. Examples of applications are also given for each method. In addition, a discussion is provided on the relative advantages or potential limitations of each technique regarding its use in kinetic studies.

Noncovalent mass spectrometry for the characterization of antibody/antigen complexes

Monoclonal antibodies (mAbs) have taken on an increasing importance for the treatment of various diseases including cancers, immunological disorders, and other pathologies. These large biomolecules display specific structural features, which affect their efficiency and need therefore to be extensively characterized using sensitive and orthogonal analytical techniques. Among them, mass spectrometry (MS) has become the method of choice to study mAb amino acid sequences as well as their posttranslational modifications with the aim of reducing their chemistry, manufacturing, and control liabilities. This chapter will provide the reader with a description of the general approach allowing antibody/antigen systems to be characterized by noncovalent MS. In the present chapter, we describe how recent noncovalent MS technologies are used to characterize immune complexes involving both murine and humanized mAb 6F4 directed against human JAM-A, a newly identified antigenic protein (Ag) over-expressed in tumor cells. We will detail experimental conditions (sample preparation, optimization of instrumental parameters, etc.) required for the detection of noncovalent antibody/antigen complexes by MS. We will then focus on the type and the reliability of the information that we get from noncovalent MS data, with emphasis on the determination of the stoichiometry of antibody/antigen systems. Noncovalent MS appears as an additional supporting technique for therapeutic mAbs lead characterization and development.

Mapping of antigenic determinants on a SAT2 foot-and-mouth disease virus using chicken single-chain antibody fragments

Recombinant single-chain variable fragments (scFvs) of antibodies make it possible to localize antigenic and immunogenic determinants, identify protective epitopes and can be exploited for the design of improved diagnostic tests and vaccines. A neutralizing epitope, as well as other potential antigenic sites of a SAT2 foot-and-mouth disease virus (FMDV) were identified using phage-displayed scFvs. Three unique ZIM/7/83-specific scFvs, designated scFv1, scFv2 and scFv3, were isolated. Further characterization of these scFvs revealed that only scFv2 was capable of neutralizing the ZIM/7/83 virus and was used to generate neutralization-resistant virus variants. Sequence analysis of the P1 region of virus escaping neutralization revealed a residue change from His to Arg at position 159 of the VP1 protein. Residue 159 is not only surface exposed but is also located at the C-terminal base of the G-H loop, a known immunogenic region of FMDV. A synthetic peptide, of which the sequence corresponded to the predicted antigenic site of the VP1 G-H loop of ZIM/7/83, inhibited binding of scFv2 to ZIM/7/83 in a concentration-dependent manner. This region can therefore be considered in the design of SAT2 vaccine seed viruses for the regional control of FMD in Africa.

MALDI-ToF mass spectrometry for studying noncovalent complexes of biomolecules

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been demonstrated to be a valuable tool to investigate noncovalent interactions of biomolecules. The direct detection of noncovalent assemblies is often more troublesome than with electrospray ionization. Using dedicated sample preparation techniques and carefully optimized instrumental parameters, a number of biomolecule assemblies were successfully analyzed. For complexes dissociating under MALDI conditions, covalent stabilization with chemical cross-linking is a suitable alternative. Indirect methods allow the detection of noncovalent assemblies by monitoring the fading of binding partners or altered H/D exchange patterns.

Monitoring ligand modulation of protein-protein interactions by chemical cross-linking and High-Mass MALDI mass spectrometry

Analyzing the effect of ligands on protein-protein interactions is important to better understand the cellular processes. In vitro characterization of these modulations remains challenging because of the drawbacks associated with the analysis of noncovalent interactions. To facilitate the analysis, stabilization of the protein complex by chemical cross-linking followed by High-Mass MALDI mass spectrometry is a recently developed method offering several advantages: No need for immobilization or special tags, the analysis is possible directly on wild-type protein complexes, no need for buffer exchange, large applicability range for any type of protein complex from 0 to 1,500 kDa. Using this method, we analyzed the effect of the inhibitors Nutlin-3a and Nutlin-3b on the protein complex MDM2-p53. Using this fast and sensitive method, the IC(50) values of these inhibitors have been determined.

Biophysical characterization of the molecular orientation of an antibody-immobilized layer using secondary ion mass spectrometry

The molecular orientation of antibody layers formed on separate solid matrices (e.g., gold-coated glass substrate) was characterized by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS) in static mode. For comparison, three different antibody species, IgG, F(ab')(2), and Fab, were prepared, biotinylated in random and site-directed fashions, and immobilized on distinct streptavidin-coated surfaces. ToF-SIMS analyses of each antibody layer revealed that the secondary ion intensity peaks measured at the mass-to-charge (m/z) ratio 253, 325, and 647 were unique to the site-directly immobilized antibodies. The ions in the three peaks were detected neither from the streptavidin layer nor from the randomly prepared antibody, indicating that the insolubilized antibody layers constructed in the two different manners had distinct molecular arrangements. The antibody preparations were further tested for their binding characteristics in sandwich-type immunoassays, which showed that the site-directed antibodies consistently enhanced the detection capability comparing to those randomly prepared. Based on the analytical results of both the ToF-SIMS analysis and sandwich-type immunoassays, the site-directed antibody species were immobilized on the surfaces in a more orientated manner, with their antigen binding sites exposed to the bulk solution, than when random immobilization was used.

Does chemical cross-linking with NHS esters reflect the chemical equilibrium of protein-protein noncovalent interactions in solution?

Chemical cross-linking in combination with mass spectrometry has emerged as a powerful tool to study noncovalent protein complexes. Nevertheless, there are still many questions to answer. Does the amount of detected cross-linked complex correlate with the amount of protein complex in solution? In which concentration and affinity range is specific cross-linking possible? To answer these questions, we performed systematic cross-linking studies with two complexes, using the N-hydroxysuccinimidyl ester disuccinimidyl suberate (DSS): (1) NCoA-1 and mutants of the interacting peptide STAT6Y, covering a K(D) range of 30 nM to >25 μM, and (2) α-thrombin and basic pancreatic trypsin inhibitor (BPTI), a system that shows a buffer-dependent K(D) value between 100 and 320 μM. Samples were analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). For NCoA-1•STAT6Y, a good correlation between the amount of cross-linked species and the calculated fraction of complex present in solution was observed. Thus, chemical cross-linking in combination with MALDI-MS can be used to rank binding affinities. For the mid-affinity range up to about K(D) ≈ 25 μM, experiments with a nonbinding peptide and studies of the concentration dependence showed that only specific complexes undergo cross-linking with DSS. To study in which affinity range specific cross-linking can be applied, the weak α-thrombin•BPTI complex was investigated. We found that the detected complex is a nonspecifically cross-linked species. Consequently, based on the experimental approach used in this study, chemical cross-linking is not suitable for studying low-affinity complexes with K(D) >> 25 μM.

MALDI linear TOF mass spectrometry of PEGylated (glyco)proteins

PEGylation of proteins is a fast growing field in biotechnology and pharmaceutical sciences owing to its ability to prolong the serum half-life time of recombinant proteins. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS) has been shown to be a powerful tool in the analysis of several PEGylated small proteins. Here we present data obtained with a standard secondary electron multiplier (SEM) and a high mass (HM) detector combined with a MALDI linear TOF MS system for the detection of PEGylated (glyco)proteins in the range of 60-600 kDa. Examples of MALDI TOF MS of small (interferon alpha2a), middle (human serum albumin (HSA)) and high molecular mass proteins (coagulation factor VIII and von Willebrand factor (vWF), both heavily glycosylated proteins) are presented. The particular challenge for the analysis was the heterogeneity of the (glyco)proteins in the high molecular weight range in combination with additional PEGylation, which even introduced more heterogeneity and was more challenging for interpretation. Nevertheless, the performance of MALDI linear TOF MS with both detector systems in terms molecular weight and heterogeneity determination depending on the m/z range was superior to the other methods. Although the SEM was able to obtain information about protein PEGylation in the mass range up to 100 kDa (e.g. PEGylated HSA), the HM system was crucial for detection of HM ions (e.g. PEGylated recombinant vWF), which was impossible with the standard SEM.

Detection of nucleic acid-nuclear hormone receptor complexes with mass spectrometry

Nuclear receptors, such as the retinoic acid receptor (RAR) or the 9-cis retinoic acid receptor (RXR), interact not only with their ligands but also with other types of receptors and with DNA. Here, two complementary mass spectrometry (MS) methods were used to study the interactions between retinoic receptors (RXR/RAR) and DNA: non-denaturing nano-electrospray (nanoESI MS), and high-mass matrix-assisted laser desorption ionization (MALDI MS) combined with chemical cross-linking. The RAR x RXR heterodimer was studied in the presence of a specific DNA sequence (DR5), and a specific RAR x RXR x DNA complex was detected with both MS techniques. RAR by itself showed no significant homodimerization. A complex between RAR and the double stranded DR5 was detected with nanoESI. After cross-linking, high-mass MALDI mass spectra showed that the RAR binds the single stranded DR5, and the RAR dimer binds both single and double stranded DR5. Moreover, the MALDI mass spectrum shows a larger RAR dimer signal in the presence of DNA. These results suggest that a gene-regulatory site on DNA can induce quaternary structural changes in a transcription factor such as RAR.

Reactivity and applications of new amine reactive cross-linkers for mass spectrometric detection of protein-protein complexes

Chemical cross-linking of proteins permits the stabilization of noncovalent complexes through introduction of covalent bonds. A crucial challenge is to find the fastest and most efficient cross-linkers in order to minimize reaction times and to handle delicate complexes. New cross-linkers were synthesized by introducing N-hydroxyphthalimide, hydroxybenzotriazole, and 1-hydroxy-7-azabenzotriazole as leaving groups instead of the commonly used N-hydroxysuccimidyl moiety. With the use of matrix-assisted laser desorption ionization (MALDI) mass spectrometry, these new cross-linkers were then compared with the commercially available disuccinimidyl suberate (DSS) for covalent stabilization of the gluthatione-S-transferase (GST) dimer and of an antibody-antigen complex. They showed a better efficiency, generated about 30% more cross-linked complex, and reacted about 10 times faster than DSS. The reaction with the GST dimer was utilized to get information about their reaction efficiency and kinetics. Their ability to stabilize only specific protein complexes was verified by incubating them with a mixture of the proteins GST and ubiquitin. Finally, the cross-linkers were incubated with synthetic peptides to study the selectivity of the binding with various amino acid side chains. Not only lysine but also tyrosine was found to react with the newly synthesized cross-linker containing 1-hydroxy-7-azabenzotriazole as the reactive group.

Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'

Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.

The reaction of hydrogen peroxide with hemoglobin induces extensive alpha-globin crosslinking and impairs the interaction of hemoglobin with endogenous scavenger pathways

Cell-free hemoglobin (Hb) enhances the oxidation-related toxicity associated with inflammation, ischemia, and hemolytic disorders. Hb is highly vulnerable to oxidative damage, and irreversible structural changes involving iron/heme oxidation, heme-adduct products, and amino acid oxidation have been reported. Specific structural features of Hb, such as unconstrained alpha-chains and molecular size, determine the efficiency of interactions between the endogenous Hb scavengers haptoglobin (Hp) and CD163. Using HPLC, mass spectrometry, and Western blotting, we show that H(2)O(2)-mediated Hb oxidation results in the formation of covalently stabilized globin multimers, with prominent intramolecular crosslinking between alpha-globin chains. These structural alterations are associated with reduced Hp binding, reduced CD163 interaction, and severely impaired endocytosis of oxidized Hb by the Hp-CD163 pathway. As a result, when exposed to oxidized Hb, CD163-positive HEK293 cells and human macrophages do not increase hemeoxygenase-1 (HO-1) expression, the physiological anti-oxidative macrophage response to Hb exposure. Failed Hb clearance, inadequate HO-1 expression, and the subsequent accumulation of oxidatively damaged Hb species might thus contribute to pathologies related to oxidative stress.

Construction of recB-recD genetic fusion and functional analysis of RecBDC fusion enzyme in Escherichia coli

Background

recD, located between recB and argA, encodes the smallest polypeptide (60 kDa) of the heterotrimeric enzyme RecBCD in Escherichia coli. RecD is a 5'-3' helicase and is required for the nuclease activity of RecBCD and for tight binding to dsDNA ends. Here, we have tested the hypothesis that RecD regulates the structure and activities of RecBCD, including RecA loading.

Results

To characterize its regulatory functions, recD was genetically fused to recB through deletion and substitution mutations. The recB-recD fusion led to a decreased amount of the heterotrimer. Both fusion mutants proved to be recombination proficient, viable and resistant to DNA damaging agents, and to have DNA unwinding, ATP-dependent dsDNA exonuclease and Chi genetic activities.

Conclusion

Our findings suggest that the recB-recD fusion may form a RecBD fusion protein and therefore affect RecD assembly, but this does not change the three-dimensional structure of the heterotrimer.

A triad of lys12, lys41, arg78 spatial domain, a novel identified heparin binding site on tat protein, facilitates tat-driven cell adhesion

Tat protein, released by HIV-infected cells, has a battery of important biological effects leading to distinct AIDS-associated pathologies. Cell surface heparan sulfate protoglycans (HSPGs) have been accepted as endogenous Tat receptors, and the Tat basic domain has been identified as the heparin binding site. However, findings that deletion or substitution of the basic domain inhibits but does not completely eliminate Tat–heparin interactions suggest that the basic domain is not the sole Tat heparin binding site. In the current study, an approach integrating computational modeling, mutagenesis, biophysical and cell-based assays was used to elucidate a novel, high affinity heparin-binding site: a Lys12, Lys41, Arg78 (KKR) spatial domain. This domain was also found to facilitate Tat-driven β1 integrin activation, producing subsequent SLK cell adhesion in an HSPG-dependent manner, but was not involved in Tat internalization. The identification of this new heparin binding site may foster further insight into the nature of Tat-heparin interactions and subsequent biological functions, facilitating the rational design of new therapeutics against Tat-mediated pathological events.

Au-nanoparticles as an electrochemical sensing platform for aptamer-thrombin interaction

A novel electrochemical method for the detection of bioaffinity interactions based on a gold-nanoparticles sensing platform and on the usage of stripping voltammetry technique was developed. The oxidation of gold surface (resulted in gold oxide formation) upon polarization served as a basis for analytical response. As a model, thrombin-thrombin binding aptamer couple was chosen. The aptamer was immobilized on a screen-printed electrode modified with gold-nanoparticles by avidin-biotin technology. Cathodic peak area was found proportional to thrombin quantity specifically adsorbed onto electrode surface. Sigmoid calibration curve as is typical for immunoassay was obtained, with thrombin detection limit of 10(-9)M. Linear range corresponds from 10(-8) to 10(-5)M thrombin concentration or 2 x 10(-14) to 2 x 10(-11)mol/electrode (R=0.996). Binding of thrombin to an aptamer has also been detected using the ferricyanide/ferrocyanide redox couple as electrochemical indicator.