Multichannel Surface Plasmon Resonance Research Articles

Multiplex ready flow cytometric immunoassay for total insulin like growth factor 1 in serum of cattle

The European Union has banned the use of recombinant bovine somatotropins (rbST, growth hormones) to increase milk yield in dairy cattle. As direct detection of rbST in serum is problematic, methods based on the detection of changes in multiple rbST-dependent biomarkers have high potential for monitoring rbST abuse. In this study immunoassays were developed for total insulin-like growth factor 1 (IGF-1) in cow sera. Ultimately aiming at combination with other rbST-dependent biomarker assays two multiplex formats were studied and compared critically, a multi-channel surface plasmon resonance (SPR)-based biosensor and flow cytometry combined with color encoded microbeads. Moreover, a new dedicated sample pretreatment was developed for the dissociation of complexed IGF-1 in serum, while keeping other biomarkers in solution. Compared to the SPR biosensor immunoassay, the flow cytometric immunoassay (FCIA) was more sensitive, less antibody-consuming and less vulnerable to necessary but interfering reagents from the sample treatment. In an initial in-house validation study the developed FCIA showed to be fast, specific, robust, and a high repeatability and reliability, and generated realistic IGF-1 values for bovine serum, without compromising the potential for simultaneous detection of other biomarkers. Due to the xMAP technology, in which 100 different bead sets can be measured simultaneously, the total IGF-1 assay can easily be extended with other immunoassays for candidate biomarkers. Preliminary results about a FCIA for IGF-1 multiplexing with insulin-like growth factor binding protein 2 (IGFBP2) are presented which strongly supported both the FCIA multiplex format as well as the generic nature of the developed sample pretreatment.

Two-dimensional droplet-based surface plasmon resonance imaging using electrowetting-on-dielectric microfluidics

This article presents a multichannel droplet-based surface plasmon resonance platform. The platform comprises a digital electrowetting-on-dielectric (EWOD) microfluidic device coupled to surface plasmon resonance imaging (SPRi). SPRi is now a well-established detection technique that enables in-situ monitoring of multiple reactions occurring at the surface of the chip without the use of labels. Currently, the limiting factor in the application of SPRi for high-throughput applications is the flow-cell technology which relies on sequential sample processing within the continuous fluid flow. An original solution compared to the continuous flow-cell technology is proposed to increase the capability of existing SPRi technology. A parallel SPRi detection of different samples on the surface is achieved using the array-based digital microfluidic device.

SPR Sensor Chips with Polymer Nanogratings

This paper presents low-cost, multi-channel, nano-grating SPR (Surface Plasmon Resonance) sensor chips for applications to disposable biomolecule detection. The present SPR sensor chip consists of two fluidic channels, including a sample channel and a reference channel, each having 833 nm-pitch PDMS gratings. The SPR signals from each channel are coupled by an external mirror and the SPR dip shift in the coupled signals is detected by a single spectrometer. Compared to the previous multi-channel SPR sensors using fiber-optic switches or special prisms, the present SPR sensor chips with PDMS nanogratings result in more compact and less expensive SPR detectors. We have designed and fabricated the SPR sensor chips with two channel gratings having the refractive index sensitivity of 321.78 nm/RI and 514.26 nm/RI, respectively. From the fabricated SPR sensor chips, we measure the SPR dip shift of 1.13±0.16 nm for the target biomolecules of 0.5 μM streptavidin binded on a 10% biotinylated surface. The real-time binding reaction rates of m-antibiotin has been monitored for the fixed concentration of 0.2 μM streptavidin as well as for the varying concentration range of 2-50 nM; thus obtaining the results for the fixed and varying concentration in good agreement with those obtained from a commercialized SPR sensor. It is demonstrated that the polymer nanograting SPR sensor chips offer simple and disposable biomolecule detection methods for point-of-care applications. [DOI: 10.1380/ejssnt.2009.750]

Novel concept of multi-channel fiber optic surface plasmon resonance sensor

A novel multi-channel fiber optic surface plasmon resonance (SPR) sensor is reported. The sensing structure consists of a single-mode optical fiber, covered with a thin gold layer, which supports a surface plasmon (SP), and a Bragg grating. The Bragg grating induces coupling between the forward-propagating fundamental core mode and the back-propagating SP-cladding mode. As the SP-cladding modes are highly sensitive to changes in the refractive index of the surrounding medium, the changes can be accurately measured by spectroscopy of these hybrid modes. Multichannel capability is achieved by employing a sequence of Bragg gratings of different periods and their reading via the wavelength division multiplexing. Theoretical analysis and optimization based on the coupled-mode theory (CMT) is carried out and performance characteristics of the sensor are determined.

Surface plasmon resonance biosensors for detection of Alzheimer disease biomarker

This paper describes direct label-free detection of 17beta-hydroxysteroid dehydrogenase type 10 (17β-HSD10) using a surface plasmon resonance (SPR) biosensor. This multifunctional mitochondrial enzyme is involved in pathogenesis of Alzheimer disease (AD) and represents a potential target for AD diagnostics. A multichannel SPR sensor with spectral modulation is functionalized with amyloid beta or polyclonal antibody against 17β-HSD10 peptide using a self-assembled monolayer of alkylthiolates and amino coupling chemistry. Detection of a synthetic peptide of 14 amino acids from the 17β-HSD10 molecule (residues 133–146aa) and whole enzyme 17β-HSD10 is performed. Detection of 17β-HSD10 enzyme in artificial cerebrospinal fluid (ACSF) buffer is also carried out. It is demonstrated that the reported SPR biosensor is capable of detecting 17β-HSD10 enzyme at ng/ml levels.

Effect of the immobilisation of DNA aptamers on the detection of thrombin by means of surface plasmon resonance

We report a multichannel surface plasmon resonance (SPR) sensor for detection of thrombin via DNA aptamers immobilized on the SPR sensor surface. A detailed investigation of the effect of the immobilisation method on the interaction between thrombin and DNA aptamers is presented. Three basic approaches to the immobilisation of aptamers on the surface of the SPR sensor are examined: (i) immobilisation based on chemisorption of aptamers modified with SH groups, (ii) immobilisation of biotin-tagged aptamers via previously immobilized avidin, neutravidin or streptavidin molecular linkers, and (iii) immobilisation employing dendrimers as a support layer for subsequent immobilisation of aptamers. A level of nonspecific binding of thrombin to immobilized human serum albumin (HSA) for each of the immobilisation methods is determined. Immobilisation of aptamers by means of the streptavidin-biotin system yields the best results both in terms of sensor specificity and sensitivity.

다파장 광원을 이용한 폴리머 광도파로형 SPR 센서

In this paper, we fabricated the polymer waveguide type surface plasmon resonance (SPR) sensor using a white light source and optical spectrum analyzer (OSA). Fabricated sensor uses the principle of phase matching between evanescent wave and surface plasmon wave. According to the measuring result, the shift of resonance wavelength conducts the change of the refractive index. The proposed SPR sensor is expected to apply the integrated multichannel SPR sensor and the realtime monitoring system.

Multichannel SPR biosensor for detection of endocrine-disrupting compounds

A surface plasmon resonance (SPR) biosensor for simultaneous detection of multiple organic pollutants exhibiting endocrine-disrupting activity, namely atrazine, benzo[a]pyrene, 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-nonylphenol, is reported. The biosensor utilizes a multichannel SPR sensor based on wavelength modulation of SPR and wavelength division multiplexing (WDM) of sensing channels, antibodies as biorecognition element and a competitive immunoassay detection format. An analysis time of 45 min (including 30-min incubation of the sample with antibodies) and limits of detection as low as 0.05, 0.07, 0.16 and 0.26 ng mL(-1) are demonstrated for benzo[a]pyrene, atrazine, 2,4-D and 4-nonylphenol, respectively. The biosensor is also shown to be regenerable and suitable for repeated use.

Dual biosensor immunoassay-directed identification of fluoroquinolones in chicken muscle by liquid chromatography electrospray time-of-flight mass spectrometry

Fluoroquinolones (FQs) are synthetic antibiotics of broad-spectrum antibacterial activity widely used to treat infections in farmed fish, turkeys, pigs, calves and poultry. Monitoring these substances residues is therefore regulated by law.For the detection of FQs, we studied the feasibility of coupling the simultaneous screening of several FQs, using a dual surface plasmon resonance (SPR) biosensor immunoassay (BIA), in parallel, with an analytical chemical methodology for their identification.Six FQs were simultaneously screened at or below their maximum residue level (MRL) in chicken muscle using a multi-FQ BIA for norfloxacin, ciprofloxacin, enrofloxacin, difloxacin and sarafloxacin, and a specific BIA for flumequine. The two BIAs were serially coupled in a multi-channel SPR biosensor featuring a dual BIA in a competitive inhibition format.The samples non-compliant during the screening with the dual BIA were further concentrated and fractionated with gradient liquid chromatography (LC). The effluent was splitted toward two 96-well fraction collectors resulting in two identical 96-well plates. One was re-screened with the dual BIA to identify the immunoactive fractions and direct the identification efforts toward the relevant fractions in the second well-plate with high resolution LC-electrospray time-of-flight mass spectrometry (ESI-TOFMS). The system not only allows the possibility to screen and identify known FQs, but also to discover unknown chemicals of similar structure which show activity in the dual BIA.

Quantitative and simultaneous detection of four foodborne bacterial pathogens with a multi-channel SPR sensor

We report the quantitative and simultaneous detection of four species of bacteria, Escherichia coli O157:H7, Salmonella choleraesuis serotype typhimurium, Listeria monocytogenes, and Campylobacter jejuni, using an eight-channel surface plasmon resonance (SPR) sensor based on wavelength division multiplexing. Detection curves showing SPR response versus analyte concentration were established for each species of bacteria in buffer at pH 7.4, apple juice at native pH 3.7, and apple juice at an adjusted pH of 7.4, as well as for a mixture containing all four species of bacteria in buffer. Control experiments were performed to show the non-fouling characteristics of the sensor surface as well as the specificity of the amplification antibodies used in this study. The limit of detection (LOD) for each of the four species of bacteria in the tested matrices ranges from 3.4 x 10(3) to 1.2 x 10(5) cfu/ml. Detection curves in buffer of an individual species of bacteria in a mixture of all four species of bacteria correlated well with detection curves of the individual species of bacteria alone. SPR responses were higher for bacteria in apple juice at pH 7.4 than in apple juice at pH 3.7. This difference in sensor response could be partly attributed to the pH dependence of antibody-antigen binding.

Surface plasmon resonance detection of metal ions: layer-by-layer assembly of polyelectrolyte sensing layers on a multichannel chip

A single-chip multichannel surface plasmon resonance sensor (SPR) has been used to detect metal ions in aqueous solutions. The equipment was designed around a commercial light-emitting diode and a CCD camera and incorporated no moving parts. The sensing materials were based on molecular architectures of polyelectrolyte films, deposited by the layer-by-layer self-assembly technique. Two bilayer architectures, poly(ethyleneimine) (PEI)/poly(ethylenealt-maleic acid) and PEI/poly(styrenesulfonate), were shown to produce different responses to solutions containing copper, nickel, and iron. The SPR equipment was able to measure concentrations of these metals down to levels of at least 2/spl times/10/sup -5/ M.

Multi-analyte surface plasmon resonance biosensing

Surface plasmon resonance (SPR) biosensors are affinity sensing devices exploiting a special mode of electromagnetic field—surface plasmon-polariton—to detect the binding of analyte molecules from a liquid sample to biomolecular recognition elements immobilized on the surface of the sensor. In this paper, we review advances of SPR biosensor technology towards detection systems for the simultaneous detection of multiple analytes (multi-analyte detection). In addition, we report application of a recently developed multichannel SPR sensor based on spectroscopy of surface plasmons and wavelength division multiplexing of sensing channels to multi-analyte detection.

Modular multichannel surface plasmon spectrometer

We have developed a modular multichannel surface plasmon resonance (SPR) spectrometer on the basis of a commercially available hybrid sensor chip. Due to its modularity this inexpensive and easy to use setup can readily be adapted to different experimental environments. High temperature stability is achieved through efficient thermal coupling of individual SPR units. With standard systems the performance of the multichannel instrument was evaluated. The absorption kinetics of a cysteamine monolayer, as well as the concentration dependence of the specific receptor-ligand interaction between biotin and streptavidin was measured.

Multichannel surface plasmon resonance biosensor with wavelength division multiplexing

A novel multichannel surface plasmon resonance (SPR) biosensor with spectral interrogation and wavelength division multiplexing of sensing channels is presented. A special design of SPR prism element is used to enable wavelength division multiplexing of serial sensing channels. In addition to increasing the number of sensing channels, this approach allows discrimination of the sensor response due to analyte–receptor binding from interfering background refractive index fluctuations. A novel eight-channel SPR sensor combining the wavelength division multiplexing of serial sensing channels with the conventional parallel channel architecture is described. Application of this multichannel SPR sensor for simultaneous detection of multiple analytes is described.

Multichannel Surface Plasmon Resonance Imaging and Analysis of Micropatterned Self-Assembled Monolayers and Protein Affinity Interactions

Multichannel images of 11-mercaptoundecanoic acid and 11-mercapto-1-undecanol self-assembled monolayers together with a biospecific interferon-gamma (IFN-gamma)/anti-IFN-gamma antibody immunoaffinity interaction were observed by the two-dimensional surface plasmon resonance (2D-SPR) imaging system. With the fabricated 2D-SPR imaging system, adopting a white light source in combination with a narrow band-pass filter, sharp images were resolved, minimizing the diffraction patterns on the resulting images. Micropatterning of self-assembled monolayers was acheived by exploiting the UV photolysis of thiol bonding, instead of conventional photolithography. The line profile calibration of the image contrast with ellipsometric analysis enabled us to discriminate the change in monolayer thickness within a sub-nanometer scale. For the protein interactions on the surface, the biospecific affinity recognition reaction of IFN-gamma antigen with surface-immobilized antibody was analyzed. Through the signal amplification strategy based on the enzyme-catalyzed precipitation reaction in a sandwich-type immunoassay, biospecific antigen binding was found detectable down to a concentration of 1 ng/mL.

A single chip multi-channel surface plasmon resonance imaging system

A single chip, multi-channel surface plasmon resonance (SPR) imaging system has been developed. The equipment has no moving parts and uses a single sensor chip on which multiple channels can be incorporated. A light emitting diode is used as a photon source while a CCD camera forms the detector. The optical configuration has been designed to achieve a uniform illumination of the sample over a fixed area with a range of incident angles. A calibration test using sucrose solutions shows that the sensitivity of the equipment is 4.3×10 −4 refractive index units per pixel line-pair. The use of the system for simultaneous interrogation of different polyelectrolyte thin films, formed by the electrostatic layer-by-layer deposition method, is demonstrated. A reversible pH-dependent response for these organic layers is also reported.

On-line detection of sulfamethazine and sulfadiazine in porcine bile using a multi-channel high-throughput SPR biosensor

The performance of a prototype multi-channel optical biosensor in both the laboratory and on site at an abattoir was evaluated. The high-throughput surface plasmon resonance (SPR) instrument allows either simultaneous analysis of eight samples for a single analyte or multi-analyte analysis. In conjunction with an automated sample pipetting station, direct analysis of up to 650 bile samples for sulfamethazine (SMZ) and sulfadiazine (SDZ) per day was possible. Instrument performance was assessed in a laboratory based trial by comparing results of the prototype assay method with the routine Biacore 1000 procedure used in the laboratory. During the assay of 1751 samples, false positive rates were calculated as 0.86% for SMZ and 1.48% for SDZ using the prototype biosensor as compared to 0.63% (SMZ) and 0.69% (SDZ) when using the Biacore 1000 instrument. During a 2-month on-site study at an abattoir, a total of 6069 bile samples were analysed. No false negative results were recorded while extremely low false positive rates (0.13% for SMZ and 0.74% for SDZ) were found. The present study clearly demonstrates the potential of high-speed SPR biosensor technology for high-throughput veterinary drug detection.

A novel multichannel surface plasmon resonance biosensor

We report a novel multichannel surface plasmon resonance (SPR) sensor based on the combination of parallel sensing channel architecture and the method of spectral discrimination of sensing channels. This sensor configuration provides multichannel performance and, through probing surface processes (e.g. binding of immobilized antibody and antigen in solution) with surface plasmons with different field distributions, it allows distinguishing sensor response to surface and bulk effects, enabling more accurate quantification of biomolecular interaction events. The potential of this mixed-architecture sensor is illustrated in a model biosensing experiment in which the detection of monoclonal anti-dinitrophenyl antibody (a-DNP) is compensated for non-specific adsorption and background refractive index interferences.

Surface Plasmon Resonance Multisensing

We have demonstrated the feasibility of surface plasmon resonance (SPR) multisensing by monitoring four separate immunoreactions simultaneously in real time using a multichannel SPR instrument. A plasmon carrying gold layer, onto which a four-channel flow cell was pressed, was imaged at a fixed angle of incidence. First, the four-channels were coated with antibodies and then the flow cell was turned by 90° such that the flow channels overlapped the areas coated in the first step. In that geometry, antigens were applied to the different antibodies on the surface. Thus, all antibody−antigen combinations can be measured in a two-dimensional array of sensor surfaces in real time. Our results do correlate with expected immunologic specificity. The emphasis will be on presenting this method to obtain data on immunosystems and not as much on the assessment of biological activity.