Highly sensitive and selective surface plasmon resonance sensor for detection of sub-ppb levels of benzo[a]pyrene by indirect competitive immunoreaction method

A surface plasmon resonance (SPR)-immunosensor for detection of benzo[a]pyrene (BaP) is developed by using a model BaP-hapten compound, BaP-bovine serum albumin conjugate (BaP-BSA), and an anti-BaP-BSA monoclonal antibody. BaP-BSA conjugate is immobilized on a gold thin-film sensor chip by means of simple physical adsorption. The number of BaP-hapten units in BaP-BSA conjugate is estimated to be 28 from the difference in molecular weight (MW) between BaP-BSA conjugate and BSA based on the results of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) measurement. Anti-BaP-BSA antibody on contact with the BaP-BSA conjugate immobilized sensor chip causes an increase in the incident angle of the sensor chip. Binding of anti-BaP-BSA antibody with surface-immobilized BaP-BSA conjugate is inhibited by the presence of BaP in analyte solution, because of the inhibition effect of BaP. The SPR immunosensor for BaP functioning with the indirect competitive immunoreaction of anti-BaP-BSA antibody between the analyte (BaP) in testing solution and the BaP-BSA conjugate immobilized on the sensor chip provides a rapid determination (response time: ca. 15 min) of BaP in the concentration range of 0.01-1000 ppb. The antibody anchored to the sensor chip by antigen-antibody binding is removed on treatment with a pepsin solution (pH 2.0) for few minutes. The SPR sensor chip is found to be reusable for more than 20 times with a little decrease (<7%) in the sensor response. Detection of BaP by direct competitive immunoreactions is also carried out by enzyme-linked immunosorbent assay (ELISA). The concentration of BaP could be determined as low as 0.01 ppb and 2 ppb using the SPR sensor and the ELISA method, respectively. The SPR sensor is found to detect BaP selectively in the presence of 2-hydroxybiphenyl (HBP); the incident angle shift of the SPR sensor for BaP is found to be same irrespective to the presence or the absence of a same concentration (as much as 30 ppb) of HBP together.     

Continuous flow immunosensor for highly selective and real-time detection of sub-ppb levels of 2-hydroxybiphenyl by using surface plasmon resonance imaging

A biosensor based on surface plasmon resonance (SPR) is developed for the detection of 2-hydroxybiphenyl (HBP). A monoclonal antibody against HBP (abbreviated hereafter as HBP-mAb) is developed and used for the detection of HBP by competitive SPR-based immunoassay and enzyme linked immunosorbent assay (ELISA) methods. A novel HBP-hapten compound, HBP-bovine serum albumin conjugate (HBP-BSA), derived by binding several HBP units with BSA by an aliphatic chain spacer is used in the development of antibody and for the functionalization of immunoprobes. HBP-BSA linked to the Au surface of the SPR sensor chip undergoes inhibitive immunoreaction with HBP-mAb in the presence of free HBP. The SPR-based immunoassay provides a rapid determination (response time: approximately 20 min) of the concentration of HBP in the range of 0.1-1000 ppb (ng/ml). Regeneration of the sensor chip is gained by treating the antibody-anchored SPR sensor chip with a pepsin solution (100 ppm (microg/ml); pH 2.0) for few minutes. The SPR sensor chip is reusable for the detection of HBP for more than 20 cycles with average loss of 0.35% reactivity per regeneration step. HBP concentration is determined as low as 0.1 and 3 ppb using the SPR sensor and ELISA measurements, respectively. The developed SPR sensor for HBP is free from interference by coexisting benzo[a]pyrene (BaP), 2,4-dichlorophenoxyacetic acid (2,4-D) and benz[a]anthracene; SPR angle shift obtained to the flow of HBP is almost same irrespective to the presence or absence of a same concentration of these carcinogenic polycyclic aromatic hydrocarbons together. The SPR sensor for HBP is proved to be applicable in simultaneous detection of HBP and BaP in parallel with another SPR sensor for BaP.     

Surface plasmon resonance for monitoring the interaction of Potato virus Y with monoclonal antibodies

Surface plasmon resonance (SPR)-based biosensors have been widely utilized for measuring interactions of a variety of molecules. Fewer examples include higher biological entities such as bacteria and viruses, and even fewer deal with plant viruses. Here, we describe the optimization of an SPR sensor chip for evaluation of the interaction of the economically relevant filamentous Potato virus Y (PVY) with monoclonal antibodies. Different virus isolates were efficiently and stably bound to a previously immobilized polyclonal antibody surface, which remained stable over subsequent injection regeneration steps. The ability of the biosensor to detect and quantify PVY particles was compared with ELISA and RT-qPCR. Stably captured virus surfaces were successfully used to explore kinetic parameters of the interaction of a panel of monoclonal antibodies with two PVY isolates representing the main viral serotypes N and O. In addition, the optimized biosensor proved to be suitable for evaluating whether two given monoclonal antibodies compete for the same epitope within the viral particle surface. The strategy proposed in this work can help to improve existing serologic diagnostic tools that target PVY and will allow investigation of the inherent serological variability of the virus and exploration for new interactions of PVY particles with other proteins.     

A vesicle capture sensor chip for kinetic analysis of interactions with membrane-bound receptors

A novel sensor chip for use in surface plasmon resonance (SPR) biosensors has been developed to capture vesicles which may contain membrane-bound receptors. Sulforhodamine-containing vesicles were shown by fluorescence microscopy to be immobilized intact on the sensor chip. Binding of cholera toxin to captured vesicles containing ganglioside GM(1) was demonstrated using SPR, and the derived kinetic and affinity constants were similar to literature values. Biotinylated vesicles captured on the sensor chip were used to bind streptavidin and then biotinylated ss-DNA. The hybridization of complementary ss-DNA to the immobilized ss-DNA was then analyzed using SPR. The values obtained were similar to those obtained for an identical interaction analyzed using a commercially available streptavidin-containing sensor chip. Binding of vancomycin-group antibiotics to captured vesicles containing a bacterial cell wall mucopeptide analogue was demonstrated. No binding of the bacterial endotoxin Cry1A(c) to captured vesicles containing its cell surface receptor could be demonstrated.     

Real-time monitoring of odorant-induced cellular reactions using surface plasmon resonance

Surface plasmon resonance (SPR) is a powerful technique for measuring molecular interaction in real-time. SPR can be used to detect molecule to cell interactions as well as molecule to molecule interactions. In this study, the SPR-based biosensing technique was applied to real-time monitoring of odorant-induced cellular reactions. An olfactory receptor, OR I7, was fused with a rho-tag import sequence at the N-terminus of OR I7, and expressed on the surface of human embryonic kidney (HEK)-293 cells. These cells were then immobilized on a SPR sensor chip. The intensity of the SPR response was linearly dependent on the amount of injected odorant. Among all the aldehyde containing odorants tested, the SPR response was specifically high for octanal, which is the known cognate odorant for the OR I7. This SPR response is believed to have resulted from intracellular signaling triggered by the binding of odorant molecules to the olfactory receptors expressed on the cell surface. This SPR system combined with olfactory receptor-expressed cells provides a new olfactory biosensor system for selective and quantitative detection of volatile compounds.     

Detection of Fusarium culmorum in wheat by a surface plasmon resonance-based DNA sensor

A surface plasmon resonance (SPR) sensor based on DNA hybridization has been developed for the detection of Fusarium culmorum, a fungal pathogen of cereals. A 0.57 kbp DNA fragment of F. culmorum was amplified by specific primers and a 25-mer oligonucleotide probe was selected within the sequence of the PCR amplicon. After biotinilation, the probe was immobilized on a streptavidin sensor chip and tested for biospecific interaction with PCR products of F. culmorum. The effect of denaturating agents (formamide and urea) and ionic strength (NaCl) on hybridization efficiency of double-stranded PCR products with the immobilized probe and the specificity of the probe were investigated. The SPR biosensor was successfully used for the detection of F. culmorum in culture material of different strains and in naturally infected wheat samples. Tested on fungal cultures, it showed a good selectivity for F. culmorum against other species of either Fusarium or other fungal genera. A background signal was observed in wheat samples strictly depending on the DNA amount of the testing matrix. Testing 30 ng of durum wheat DNA the detection limit was 0.06 pg of F. culmorum DNA. The developed PCR-SPR assay allowed to detect F. culmorum with sensitivity and specificity higher than gel-electrophoresis analysis.     

Highly-sensitive and label-free indium phosphide biosensor for early phytopathogen diagnosis

Basophil activation in response to antigen may represent specificities of type I allergy of individuals and their reactions in the body. We previously demonstrated that surface plasmon resonance (SPR) sensor could detect the activation of human basophils in response to antigens. In this study, we further developed a technique based on SPR imaging (SPRI) system to detect reactions of individual basophils isolated from human blood, and investigated the potential of this sensor as a tool for diagnosis of type I allergy. To detect the change of refractive index (RI) in individual basophils, human basophils were isolated by negative selection with antibodies conjugated with magnetic beads, fixed on a gold film with anti-basophil antibody and stimulated with various antigens under the measurement of SPRI. The sensor could detect the reactions of individual basophils in response to specific antigens as well as non-specific activators. Moreover, the sensor well allocated two spots of basophils on a sensor chip and detected individual reactions to antigen. Thus, the technique developed in this study can visualize the effect of various stimuli or inhibitors on basophils as change of intracellular RI distribution at the single cell level. In combination with a device to rapidly isolate basophils from peripheral blood, this technique may be a useful tool as a high throughput screening system in clinical diagnosis for type I allergy.     

Colloidal Au replacement assay for highly sensitive quantification of low molecular weight analytes by surface plasmon resonance

A novel sensing method based on surface plasmon resonance (SPR) was developed for the highly sensitive quantification of low molecular weight (LMW) analytes (colloidal Au replacement assay). Gold nanoparticles (diameter = 20 nm) functionalized with lactosyl-poly(ethylene glycol) (PEG) were prepared and were specifically adsorbed onto a Ricinus communis agglutinin (RCA120)-immobilized SPR sensor chip surface. Subsequent injection of free d-galactose elicited the elution of the preadsorbed lactosyl-PEGylated gold nanoparticles in a manner proportional to the galactose concentration, achieving a substantial and quantitative analysis over a wide range of galactose concentrations (0.1-50 ppm). This method of d-galactose sensing through the substituted elution of preadsorbed nanoparticles from the sensor chip surface would be applicable for the highly sensitive SPR quantification of various LMW analytes, which are known to be difficult to detect by the conventional SPR sensing regime.     

Replication of simian virus 40 origin-containing DNA during infection with a recombinant Autographa californica multiple nuclear polyhedrosis virus expressing large T antigen.

Autographica californica multiple nuclear polyhedrosis virus (AcMNPV) has been shown to encode many of the enzymes involved in the replication of its own DNA. Although the AcMNPV genome contains multiple sets of reiterated sequences that are thought to function as origins of DNA replication, no initiator protein has yet been identified in the set of viral replication enzymes. In this study, the ability of a heterologous origin initiator system to promote DNA replication in AcMNPV-infected cells was examined. A recombinant AcMNPV that expressed the simian virus 40 (SV40) large T antigen was surprisingly found to induce the efficient replication of a transfected plasmid containing an SV40 origin. This replication was subsequently found to involve three essential components: (i) T antigen, since replication of SV40 origin-containing plasmids was not induced by wild-type AcMNPV which did not express this protein; (ii) an intact SV40 core origin, since deletion of specific functional motifs within the origin resulted in a loss of replicative abilities; and (iii) one or more AcMNPV-encoded proteins, since viral superinfection was required for plasmid amplification. Characterization of the replicated DNA revealed that it existed as a high-molecular-weight concatemer and underwent significant levels of homologous recombination between inverted repeat sequences. These properties were consistent with an AcMNPV-directed mode of DNA synthesis rather than that of SV40 and suggested that T antigen-SV40 origin complexes may be capable of initiating DNA replication reactions that can be completed by AcMNPV-encoded enzymes.     

The fabrication of protein chip based on surface plasmon resonance for detection of pathogens

Protein chip based on surface plasmon resonance (SPR) was developed for detection of pathogens existing in contaminated environment, such as Escherichia coli O157:H7, Salmonella typhimurium, Legionella pneumophila, and Yersinia enterocolitica. Protein G was immobilized to endow the orientation of antibody molecules on the SPR surface. The pathogen binding of the protein chip was investigated by SPR spectroscopy. Consequently, it was found that the four kinds of pathogen could be selectively detected by using SPR-based protein chip.     

A mixed self-assembled monolayer-based surface plasmon immunosensor for detection of E. coli O157:H7

The sensitivity and specificity of a polyethylene glycol terminated alkanethiol mixed self-assembled monolayers (SAM) on surface plasmon resonance (SPR) immunosensor to detect Escherichia coli O157:H7 is demonstrated. Purified monoclonal (Mabs) or polyclonal antibodies (PAbs) against E. coli O157:H7 were immobilized on an activated sensor chip and direct and sandwich assays were carried to detect E. coli O157:H7. Effect of Protein G based detection and effect of concentrations of primary and secondary antibodies in sandwich assay were investigated. The sensor surface was observed under an optical microscope at various stages of the detection process. The sensor could detect as low as 10(3)CFU/ml of E. coli O157:H7 in a sandwich assay, with high specificity against Salmonella Enteritidis. The detection limit using direct assay and Protein G were 10(6)CFU/ml and 10(4)CFU/ml, respectively. Results indicate that an alkanethiol SAM based SPR biosensor has the potential for rapid and specific detection of E. coli O157:H7, using a sandwich assay.     

Self-assembled PEG monolayer based SPR immunosensor for label-free detection of insulin

A simple and rapid continuous-flow immunosensor based on surface plasmon resonance (SPR) has been developed for detection of insulin as low as 1 ng ml-1 (ppb) with a response time of less than 5 min. At first, a heterobifunctional oligo(ethyleneglycol)-dithiocarboxylic acid derivative (OEG-DCA) containing dithiol and carboxyl end groups was used to functionalize the thin Au-film of SPR chip. Insulin was covalently bound to the Au-thiolate monolayer of OEG-DCA for activating the sensor surface to immunoaffinity interactions. An on-line competitive immunosensing principle is examined for detection of insulin, in which the direct affinity binding of anti-insulin antibody to the insulin on sensor surface is examined in the presence and absence of various concentrations of insulin. Immunoreaction of anti-insulin antibody with the sensor surface was optimized with reference to antibody concentration, sample analysis time and flow-rate to provide the desired detection limit and determination range. With the immunosensor developed, the lowest detectable concentration of insulin is 1 ng ml-1 and the determination range covers a wide concentration of 1-300 ng ml-1. The developed OEG-monolayer based sensor chip exhibited high resistance to non-specific adsorption of proteins, and an uninterrupted highly sensitive detection of insulin from insulin-impregnated serum samples has been demonstrated. After an immunoreaction cycle, active sensor surface was regenerated simply by a brief flow of an acidic buffer (glycine.HCl; pH 2.0) for less than 1 min. A same sensor chip was found reusable for more than 25 cycles without an appreciable change in the original sensor activity.     

Development of an immunosensor for human ferritin, a nonspecific tumor marker, based on surface plasmon resonance

A direct human ferritin immunosensor was developed using anti-human ferritin monoclonal antibodies (MAbs) immobilized on the gold surface of a self-assembled surface plasmon resonance (SPR) apparatus. A kind of self-assembled monolayer (SAM) prepared by cystamine-glutaraldehyde method was applied to immobilize the MAbs. The reusability of the sensor chip adopting the SAM was found to be better than the other immobilization methods including adsorption, protein A, concanavalin A method. Ten cycles of measurements could be performed on the same chip regenerated with a 0.1M HCl solution. A linear relationship existed between the angle shifts (millidegrees) and the log values of ferritin concentrations in the range from 0.2 to 200 ng/ml in buffer and human serum. When used for 15 days, the angle shifts were all >95% of those on the response at the first day. A 10 M NaOH solution was used for clearing nonspecific binding in human serum. Correlation coefficient was 0.991 between this SPR method and chemiluminescent immunoassay for determination of ferritin in clinical human serum samples. The SPR sensor offers advantages of simplicity of immobilization, high sensitivity, high specificity, low sample requirement, high reusability, no label and no pretreatment etc.     

Evaluation of two- and three-dimensional streptavidin binding platforms for surface plasmon resonance spectroscopy studies of DNA hybridization and protein-DNA binding

Surface plasmon resonance (SPR) spectroscopy has been used to study DNA assembly, DNA hybridization, and protein-DNA interactions on two streptavidin (SA) sensor chips. On one chip, SA molecules are immobilized on a biotin-exposed surface, forming an ordered two-dimensional (2D) SA monolayer. The other chip, BIAcore's SA chip, contains SA molecules immobilized within a three-dimensional (3D) carboxylated dextran matrix. Compared to the 2D chip, the 3D SA matrix allows for a slower immobilization rate of biotinylated DNA due to diffusion limitation in the dextran matrix, but with twice the amount of the immobilized DNA due to the greater number of reactive sites, which in turn enables a higher sensitivity for DNA hybridization detection. Interestingly, having a greater DNA probe dispersion in the 3D matrix does not induce a higher DNA hybridization efficiency. In a study of protein binding to immobilized DNA (estrogen receptor to estrogen response elements), aiming at assessing the DNA sequence dependent protein binding behavior, the 2D and 3D chips produce different binding characteristics. On the 2D chip, the protein binding exhibits a better selectivity to the specific sequences, regardless of binding stringency (e.g. salt concentration), whereas on the 3D chip, the liquid handling system needs to be optimized in order to minimize transport limitations and to detect small affinity differences. Through this study we demonstrate that the physicochemical structure of SPR chips affects the apparent binding behaviors of biomolecules. When interpreting SPR binding curves and selecting a sensor chip, these effects should be taken into account.     

Surface plasmon resonance detection of interactions between peptide fragments of N-telopeptide and its monoclonal antibodies.

As populations age, osteoporosis is becoming an important public health care problem. Urinary level of the cross-linked N-telopeptide of type I collagen has been reported to be a sensitive marker of bone resorption. Recently, we synthesized and characterized 10 overlapping peptides covering the N-telopeptide of alpha-2 type I collagen and reported their relative binding response to anti-type I collagen cross-linked N-telopeptide (NTX) antibodies determined by a competitive-inhibition enzyme-linked immunosorbent assay (ELISA). In this study, we design an assay based on the surface plasmon resonance (SPR) technology to detect binding interaction of each peptide fragment of NTX with the anti-NTX monoclonal antibodies. Anti-NTX monoclonal antibodies were immobilized on the surface of sensor chip by amine-coupling procedure. Serial dilutions of each peptide were prepared and injected separately onto the antibodies-immobilized sensor chip. The real-time association and dissociation interactions of each peptide were detected and reported as sensorgrams. Binding response of each peptide to the monoclonal antibodies was determined, and the SPR results were compared with the ELISA results. We demonstrate that the trends of binding potency of peptide fragments detected by SPR are in good correlation to the results obtained by ELISA, indicating that our developed SPR-based method can be further applied to detect the NTX fragments in urine and to monitor the bone loss in humans. The potent peptide fragments identified by both assays are promising for further preparation of specific monoclonal antibodies in order to develop bioassays for bone loss in humans.     

Capture molecules preconditioned for kinetic analysis of high-affinity antigen-antibody complex in Biacore A100

Surface plasmon resonance (SPR) is routinely applied on determining association or dissociation constant rates of antigen-antibody complexes. In a SPR system such as Biacore, the capture method is a widely accepted procedure in kinetic analysis for association or dissociation of soluble antigen analytes with antibody ligands initially captured by anti-Fc molecules immobilized on the sensor chip. Appropriate preparations of anti-immunoglobulin G (IgG)-Fc molecules on sensor chips have not been examined yet for stable kinetic analysis of antibodies with several affinities to soluble antigens. Here, we constructed murine monoclonal antibodies (MoAbs) with various affinities to hen egg lysozyme (HEL) and performed kinetic analysis of these MoAbs captured by rat MoAbs against mouse IgG-Fc immobilized on the sensor chip. When capture molecules maximally immobilized on the sensor chip, we observed no apparent dissociation of MoAbs with extremely high affinity to soluble HEL antigens. In contrast, on the limited amount (1000-2000 response units) of capture molecule immobilized on the sensor chip, we could perform stable kinetic analysis of MoAbs with highest affinities to the antigen as well as those with lower or moderate binding affinities. Thus, in some cases, accurate kinetic analysis of high-affinity antibodies can be performed by minimization of capture molecule densities on the sensor chip in SPR.     

Substrate Mode-Integrated SPR Sensor

We present the design, implementation and characterisation of an integrated surface plasmon resonance (SPR) biosensor chip involving diffractive optical coupling elements avoiding the need of prism coupling. The integrated sensor chip uses the angular interrogation principle and includes two diffraction gratings and the SPR sensing zone. The theoretical design is presented as well as the fabrication process. Experimental results (response of a reference water droplet and phosphate-buffered saline/water kinetic) are presented and compared with those obtained with the classical Kretschmann prism coupling setup. We believe that this prism-free architecture is perfectly suitable for low-cost and reproducible SPR biochemical sensor chips since the sensing zone can be functionalised as any other one.     

AcMNPVP35抑制HaSNPV诱导的Tn-Hi5细胞凋亡

苜蓿银纹夜蛾核多角体病毒(Autographa californica multicapsid nuclear polyhedrosis virus,AcMNPV)能够抑制棉铃虫核多角体病毒(Helicoverpa armigera Nucleopoly hedrovirus,HaSNPV)诱导的Tn Hi5 细胞凋亡,并能辅助HaSNPV在Tn Hi5细胞中复制,产生具有感染能力的子代病毒。瞬时表达实验证明,在Tn Hi5细胞中,p35具有明显抑制凋亡的能力,但是不能辅助HaSNPV在Tn Hi5细胞中的复制;进一步构建超表达p35 的重组病毒:vHap35,发现vHap35能够抑制Tn Hi5细胞凋亡,但是不能产生具有感染力的病毒粒子。电镜观察发现感染重组病毒的部分细胞中存在单粒包埋的病毒粒子(ODV)。     

Scanning of guanine-guanine mismatches in DNA by synthetic ligands using surface plasmon resonance

Here we have designed and synthesized ligands that specifically bind with high affinity (K(d) = 53 nM) to the guanine (G)-guanine mismatch, one of four types of single-nucleotide polymorphism (SNP). Detection of the G-G mismatch was performed by a surface plasmon resonance (SPR) assay using a sensor chip carrying the G-G specific ligand on its surface. The accuracy of the G-G mismatch detection by the SPR sensor was demonstrated by a marked SPR response obtained only for the DNA containing the G-G mismatch. DNAs containing G-A and G-T mismatches, as well as a fully matched duplex, produced only a weak response. Furthermore, this assay was found applicable for the detection of SNP existing in PCR amplification products of a 652-nucleotide sequence of the HSP70-2 gene.     

Dimer of 2,7-diamino-1,8-naphthyridine for the detection of mismatches formed by pyrimidine nucleotide bases

Discrimination of base mismatches from normal Watson-Crick base pairs in duplex DNA constitutes a key approach to the detection of single nucleotide polymorphisms (SNPs). We have developed a sensor for a surface plasmon resonance (SPR) assay system to detect G-G, A-A, and C-C mismatch duplexes by employing a surface upon which mismatch-binding ligands (MBLs) are immobilized. We synthesized a new MBL consisting of 2,7-diamino-1,8-naphthyridine (damND) and immobilized it onto a CM5 sensor chip to carry out the SPR assay of DNA duplexes containing a single-base mismatch. The SPR sensor with damND revealed strong responses to all C-C mismatches, and sequence-dependent C-T and T-T mismatches. Compared to ND- and naphthyridine-azaquinolone hybrid (NA)-immobilized sensor surfaces, with affinity to mismatches composed of purine nucleotide bases, the damND-immobilized surface was useful for the detection of the mismatches composed of pyrimidine nucleotide bases.