Determination of organophosphorous pesticides by a novel biosensor based on localized surface plasmon resonance

Liquid and gas chromatography are commonly used to measure organophosphorus pesticides. However, these methods are relatively time consuming and require a tedious sample pretreatment. Here, we applied the localized surface plasmon resonance (LSPR) of gold nanoparticles covalently coupled with acetylcholinesterase (AChE) to create a biosensor for detecting an example of serial signals responding to paraoxon in the range of 1-100 ppb by an AChE modified LSPR sensor immersing in a 0.05 mM ACh solution. The underlying mechanism is that paraoxon prevents acetylcholine chloride (ACh) reacting with AChE by destroying the OH bond of serine in AChE. We found that the AChE modified LSPR sensors prepared by incubation with 12.5 mU/mL of AChE in phosphate buffer solution at pH 8.5 room temperature for 14 h have the best linear inhibition response with a 0.234 ppb limit of paraoxon detection. A 14% of inhibition on the sensor corresponds to the change of paraoxon concentration from 1 to 100 ppb. The sensor remained 94% of its original activity after six cycles of inhibition with 500 ppb paraoxon followed with reactivation of AChE by 0.5 mM 2-pyriding-aldoxime methoiodide (2-PAM). In addition, the sensor retains activity and gives reproducible results after storage in dry state at 4 degrees C for 60 days. In conclusion, we demonstrated that the AChE modified LSPR sensors can be used to determine the concentration of paraoxon biosensor with high sensitive and stable characteristics.     

Detection of cadmium by a fiber-optic biosensor based on localized surface plasmon resonance

A novel transmission-based localized surface plasmon resonance (LSPR) fiber-optic probe has been developed to determine the heavy metal cadmium ion (Cd(II)) concentration. The LSPR sensor was constructed by immobilizing phytochelatins (PCs), (gammaGlc-Cys)(8)-Gly, onto gold nanoparticle-modified optical fiber (NM(Au)OF). The optimal immobilizing conditions of PCs on to the NM(Au)OF are 71.6mug/ml PCs in pH 7.4 PBS for 2h. The absorbability (change of light absorption) of the PC-functionalized NM(Au)OF sensor increases to 9% upon changing the Cd(II) level from 1 to 8ppb with a sensitivity of 1.24ppb(-1) and a detection limit of 0.16ppb. The sensor retained 85% of its original activity after nine cycles of deactivation and reactivations. In addition, the sensor retains its activity and gives reproducible results after storage in 5% d-(+)-trehalose dehydrate solution at 4 degrees C for 35 days. The dissociation constant (K(d)) of the immobilized PCs with Cd(II) was about 6.77x10(-8)M. In conclusion, the PCs-functionalized NM(Au)OF sensor can be used to determine the concentration of Cd(II) with high sensitivity.     

A surface plasmon resonance array biosensor based on spectroscopic imaging

We have developed a multi-element transduction system which combines conventional SPR spectroscopy with one-dimensional SPR microscopy to create an effective platform for monitoring binding events on macro- or micro-patterned receptor arrays created on disposable sensor chips. This creates an effective platform for monitoring simultaneous binding events on each of the regions patterned with the receptors. This system has been specifically designed with commercially available components to allow relatively easy duplication. Furthermore, this system can use a proven, simple method to compensate for changes in the bulk index of refraction of the solution containing the analytes due to changes in temperature or solute concentration with simple modifications to the sensor chips alone. Preliminary results demonstrate how this system can be used to monitor several independent biospecific binding events simultaneously.     

Characterization of a self-assembled monolayer of thiol on a gold surface and the fabrication of a biosensor chip based on surface plasmon resonance for detecting anti-GAD antibody

A biosensor chip utilizing surface plasmon resonance (SPR) was fabricated for detecting anti-glutamic acid decarboxylase (GAD) antibody, which is an indicator of the presence of type I diabetes mellitus. The sensor surfaces were constructed from various thiol mixtures of different molar ratios of 3-mercaptopropionic acid (3-MPA) to 11-mercaptoundecanoic acid (11-MUA). To determine the surface characteristics of the different alkanethiol monolayers, several quantitative and kinetic measurements were carried out. The extent of immobilization of streptavidin (SA) and biotin-GAD (the anti-GAD receptor) and the immune response of anti-GAD antibody against GAD were measured using the SPR biosensor. The terminal functional group of a thiol has different effects on the adsorption and covalent binding of protein depending on the steric hindrance. The protein chip described herein permits simple, rapid detection of anti-GAD antibody.     

Real-time optical biosensor based on differential phase measurement of surface plasmon resonance

We report a real-time differential phase measurement technique which can be implemented in optical surface plasmon resonance biosensors. The important feature of our design is that sensitivity has been greatly improved by measuring the differential phase change between the s and p-polarizations. Real-time measurement capability is achieved by using a phase extracting routine which continuously monitors the waveforms captured by two photo-detectors. Measurement capability of our setup is demonstrated through real-time monitoring of bovine serum albumin (BSA)/anti-BSA binding reaction. The estimated sensitivity of our current setup is 7.4 ng/ml.     

Monitoring of the refolding process for immobilized firefly luciferase with a biosensor based on surface plasmon resonance

In order to examine the possibility of the use of a surface plasmon resonance (SPR) sensor for real-time monitoring of the process of refolding of immobilized proteins, the refolding of firefly luciferase immobilized on a carboxymethyldextran matrix layer was analyzed. The SPR signal of the immobilized luciferase decreased after unfolding induced by GdnCl and increased gradually in the refolding buffer, while there was no signal change in the reference surface lacking the immobilized protein. The decrease in the SPR signal on unfolding was consistent with the difference between the refractive indices of the native and unfolded protein solutions. The effects of blocking of the excess NHS-groups of the matrix layer on the refolding yield were examined by means of an SPR sensor. The results were consistent with those obtained with the enzymatic activity assay, indicating that the changes in the SPR signal reflected the real-time conformational changes of the immobilized protein. Hence, an SPR biosensor might be used for monitoring of the process of refolding of immobilized proteins and as a novel tool for optimization of the refolding conditions. This is the first demonstration that SPR signal changes reflect the conformational changes of an immobilized protein upon unfolding and refolding.     

Real-time protein biosensor arrays based on surface plasmon resonance differential phase imaging

This paper reports the application of differential phase surface plasmon resonance (SPR) imaging in two-dimensional (2D) protein biosensor arrays. Our phase imaging approach offers a distinct advantage over the conventional angular SPR technique in terms of utilization efficiency of optical sensor elements in the imaging device. In the angular approach, each biosensor site in the biosensor array requires a linear array of optical detector elements to locate the SPR angular dip. The maximum biosensor density that a two-dimensional imaging device can offer is a one-dimensional SPR biosensor array. On the other hand, the phase-sensitive SPR approach captures data in the time domain instead of the spatial domain. It is possible that each pixel in the captured interferogram represents one sensor site, thus offering high-density two-dimensional biosensor arrays. In addition, our differential phase approach improves detection resolution through removing common-mode disturbances. Experimental results demonstrate a system resolution of 8.8 x 10(-7)RIU (refractive index unit). Real-time monitoring of bovine serum albumin (BSA)/anti-BSA binding interactions at various concentration levels was achieved using a biosensor array. The detection limit was 0.77 microg/ml. The reported two-dimensional SPR biosensor array offers a real-time and non-labeling detection tool for high-throughput protein array analysis. It may find promising applications in protein therapeutics, drug screening and clinical diagnostics.     

Analysis of human serum antibody-carbohydrate interaction using biosensor based on surface plasmon resonance

Surface plasmon resonance (SPR) was used to monitor the interaction of alphaGal-antibodies from human blood group O serum with linear blood group B-saccharides, employing Galalpha1-3Galbeta1-4GlcNAc-HSA immobilised on a sensor chip surface. Strong binding of antibodies, as evident from high relative response values exceeding 200 RU, was observed. The interaction was influenced by the nature of the oligosaccharide that was added to the antibody sample prior to measurement. For example, the addition of either of the linear B-saccharides Galalpha1-3Gal and Galalpha1-3Galbeta1-4GlcNAc produced complete inhibition of antibody binding to the sensor surface, whereas the addition of the related but non-specific blood group A saccharide, GalNAcalpha1-3(Fucalpha1-2)Gal, had little effect on binding. The technique was used for the rapid monitoring of the removal of alphaGal-antibodies from human serum by affinity columns, which contained either Galalpha1-3Gal or Galalpha1-3Galbeta1-4GlcNAc as ligand. The above carbohydrates are currently evaluated as inhibitors or as affinity ligands, in the prevention of hyperacute rejection during xenotransplantation.     

Survey of the 1999 surface plasmon resonance biosensor literature

The application of surface plasmon resonance biosensors in life sciences and pharmaceutical research continues to increase. This review provides a comprehensive list of the commercial 1999 SPR biosensor literature and highlights emerging applications that are of general interest to users of the technology. Given the variability in the quality of published biosensor data, we present some general guidelines to help increase confidence in the results reported from biosensor analyses.     

Development of a surface plasmon resonance biosensor for the identification of Campylobacter jejuni

The purpose of this study was to develop a biosensor based on surface plasmon resonance (SPR) for the rapid identification of C. jejuni in broiler samples. We examined the specificity and sensitivity of commercial antibodies against C. jejuni with six Campylobacter strains and six non-Campylobacter bacterial strains. Antigen-antibody interactions were studied using enzyme-linked immunosorbent assay (ELISA) and a commercially available SPR biosensor platform (Spreeta). Campylobacter cells killed with 0.5% formalin had significant lower antibody reactivity when compared to live cells, or cells inactivated with 0.5% thimerosal or heat (70 degrees C for 3 min) using ELISA. The SPR biosensor showed a good sensitivity with commercial antibodies against C. jejuni at 10(3) CFU/ml and a low cross reactivity with Salmonella serotype typhimurium. The sensitivity of the SPR was similar when testing spiked broiler meat samples. However, research is still needed to reduce the high background observed when sampling meat products.     

Wide dynamic range phase-sensitive surface plasmon resonance biosensor based on measuring the modulation harmonics

In this study, a novel phase-sensitive surface plasmon resonance (SPR) setup, based on temporal modulation of a pumping beam by a photoelastic modulator, and subsequent extraction of phase information at the second and the third harmonics of the modulation frequency, has been developed to study biomolecular interactions on SPR-supporting gold. We demonstrated that the design setup provides ultra-high phase sensitivity, together with a wide dynamic range of measurements. In particular, the proposed scheme was used to study real-time interaction of biotin-protein and streptavidin-BSA complexes. We have found that the proposed technique has a detection limit as high as 2.89 x 10(-7) in terms of refractive index units (RIU). In terms of biosensing performance, a detection sensitivity of 1.3 nM from the streptavidin-maleimide/thiolated BSA complex binding reaction has also been demonstrated.     

A 3D localized surface plasmon resonance biosensor for the study of trivalent arsenic binding to the ArsA ATPase

A self-assembled 3D hydrogel-nanoparticle composite integrated surface plasmon resonance (SPR) sensor is reported here. The novel assembled substrate was developed by means of a surface mediated radical co-polymerization process to obtain a highly sensitive hydrogel-based thin film that possesses specific binding sites for target analytes. Initially, amino group modified gold nanoparticles (AuNPs) were covalently linked to acrylic acid monomer. Following this, N-isopropylacrylamide (NIPAAm) and AuNPs linked acrylic acid (AAc) monomers were randomly co-polymerized by the "grafting from" method in the presence of initiator and crosslinker onto the sensing surface. Surface characterization techniques were utilized to evaluate the thickness and composition of the hydrogel-nanoparticle film. The sensing platform was employed to study the binding kinetics and conformational changes of the ArsA ATPase as a consequence of binding trivalent arsenicals under a variety of conditions. ArsA, the catalytic subunit of the ArsAB arsenite (As(III)) translocating ATPase, is one of the five proteins encoded by the arsenical resistance (ars) operon of plasmid R773 in cells of Escherichia coli, that confers resistance to trivalent and pentavalent salts of the metalloid arsenic. SPR measurements indicate that the 3D hydrogel-nanoparticle coated sensors exhibited a higher sensitivity than that of the 2D AuNPs decorated sensors. Binding of As(III) to ArsA is greatly facilitated by the presence of magnesium ion and ATP.     

A novel ultrahigh-resolution surface plasmon resonance biosensor with an Au nanocluster-embedded dielectric film

The detection performance of conventional surface plasmon resonance (SPR) biosensors is limited to a 1 pg/mm(2) surface coverage of biomolecules, and consequently, such sensors struggle to detect the interaction of small molecules in low concentrations. The present study is attempted to propose the use of a novel SPR biosensor with Au nanoclusters embedded in a dielectric film to achieve a 10-fold improvement in the resolution performance. A co-sputtering method utilizing a multi-target sputtering system is used to fabricate the present dielectric films (SiO(2)) with embedded Au nanoclusters. It is shown that the sensitivity of the developed SPR biosensor can be improved by adjusting the size and volume fraction of the embedded Au nanoclusters in order to control the surface plasmon effect. The present gas detection and DNA hybridization experimental results confirm that the proposed Au nanocluster-enhanced SPR biosensor provides the potential to achieve an ultrahigh-resolution detection performance of approximately 0.1 pg/mm(2) surface coverage of biomolecules.     

Enhanced performance of a surface plasmon resonance immunosensor for detecting Ab-GAD antibody based on the modified self-assembled monolayers

To enhance the feasibility of surface plasmon resonance (SPR) immunosensor as a tool for diagnosing type I diabetes, we enhanced the sensitivity of immunoresponse for detecting the monoclonal anti-glutamic acid decarboxylase (GAD) antibody by modification of mixed self-assembled monolayers (SAMs). The effects of the different mixed SAMs were evaluated with respect to the degree of streptavidin immobilization, the degree of biotin-GAD immobilization, and the immunoresponse sensitivity. Consequently, the sensitivity of the immunoresponse for the detection of anti-GAD antibody was enhanced as a result of the reduction in steric hindrance brought about by using SAMs of heterogeneous lengths. The immunoresponse for detecting the monoclonal anti-GAD antibody was also enhanced with the reduction of the excess immobilization of biotin-GAD and the minimization of non-specific binding that resulted from the simple substitution of the spacer from a carboxylic-terminated SAM for the hydroxyl-terminated SAM.     

Immobilizing topoisomerase I on a surface plasmon resonance biosensor chip to screen for inhibitors

Background  

The topoisomerase I (TopI) reaction intermediate consists of an enzyme covalently linked to a nicked DNA molecule, known as a TopI-DNA complex, that can be trapped by inhibitors and results in failure of re-ligation. Attempts at new derivative designs for TopI inhibition are enthusiastically being pursued, and TopI inhibitors were developed for a variety of applications. Surface plasmon resonance (SPR) was recently used in TopI-inhibition studies. However, most such immobilized small molecules or short-sequence nucleotides are used as ligands onto sensor chips, and TopI was used as the analyte that flowed through the sensor chip.     

Estrogen receptor binding assay of chemicals with a surface plasmon resonance biosensor

We have developed a simple assay method for the evaluation of estrogen receptor (ER) binding capacity of chemicals without the use of radio- or fluorescence-labeled compounds. We used the solution competition assay by the BIACORE biosensor, a surface plasmon resonance biosensor, with estradiol as a ligand, human recombinant ER(alpha) (hrER(alpha)) as a high molecular weight (hmw) interactant and test chemicals as analytes. For the ligand, aminated estradiol with a spacer molecule (E2-17PeNH) was synthesized and immobilized on a carboxymethyl dextran-coated sensor chip by the amine coupling method. The injection of the hmw interactant hrER(alpha) to the biosensor raised the sensorgram, indicating its binding to the ligand E2-17PeNH. The binding of test chemicals to hrERalpha was determined as a reduction in the hrER(alpha) binding to E2-17PeNH. The dissociation constant for the binding to hrER(alpha) was calculated for estrone (4.29 x 10(-9)M), estradiol (4.04 x 10(-10)M), estriol (8.35 x 10(-10)M), tamoxifen (2.16 x 10(-8)M), diethylstilbestrol (1.46 x 10(-10)M), bisphenol A (1.35 x 10(-6)M) and 4-nonylphenol (7.49 x 10(-6)M), by plotting the data according to an equation based on mass action law. This method can also be used as a high throughput screening method.     

Sensitivity enhancement of surface plasmon resonance biosensor with colloidal gold

We enhanced the sensitivity of surface plasmon resonance biosensor by the conversion of the real-time direct binding immunoassay into the sandwich immunoassay, in which colloidal gold particles coated with anti-mouse IgG was used. By the immobilization of anti-mouse IgG onto the carboxymethyl dextran surface of thin gold film, the direct binding of analyte (mouse IgG) onto the sensor chip, and the injection of colloidal gold particles coated with antimouse IgG, about 100 times of sensitivity enhancement was obtained. This result suggests that nanoparticles, which has a high refractive index, homogeneous ultrafine structure and capability of size control, would be applicable for the detection of very small quantity of biomaterial.     

Sensitivity-enhancement of wavelength-modulation surface plasmon resonance biosensor for human complement factor 4

Sandwich and colloidal Au techniques for enhancing the sensitivity of a wavelength-modulation surface plasmon resonance (SPR) immunosensor are demonstrated by the detection of human complement factor 4 (C4). The design of the wavelength-modulation SPR biosensor is based on fixing the incident angle of light and measuring the reflected intensity of light in the wavelength range spanning 500-900 nm simultaneously. The human C4 had good response in the concentration range 2-20 microg/mL in the direct assay. However, in the sandwich assay, the human C4 had good response in the concentration range 0.2-20 microg/mL and the lowest concentration is 10-fold lower than that obtained by the direct assay. With human C4-Au colloidal conjugate, the human C4 had good response in the concentration range 0.1-20 microg/mL and the lowest concentration is 20-fold lower than that obtained by the direct assay. In the colloidal-Au-enhanced sandwich assay, the human C4 had good response in the concentration range 0.05-5 microg/mL and the lowest concentration is 40-fold lower than that obtained by the direct assay. Under selected experimental conditions, the reproducibility, sensitivity, and reversibility of the enhanced SPR immunoassay are very satisfactory. The results represent potentially significant advantages in the sensitivity of SPR biosensors.