Surface Plasmon Resonance Detection Research Articles

Mucin modified SPR interfaces for studying the effect of flow on pathogen binding to Atlantic salmon mucins

Knowledge on host-pathogen interactions contributes to the development of approaches to alleviate infectious disease. In this work, we developed a surface plasmon resonance (SPR) based method for investigating bacteria/mucins interactions. Furthermore, we investigated adhesion of three pathogens, Aeromonas salmonicida, Aeromonas hydrophila and Vibrio harveyi, to Atlantic salmon mucins isolated from different epithelial sites, using SPR and microtiter-based binding assays. We demonstrated that performing bacterial binding assays to mucins using SPR is feasible and has advantages over microtiter-based binding assays, especially under flow conditions. The fluid flow in the SPR is linear and continuous and SPR enables real-time reading of mucin-bacterial bonds, which provides an in vivo-like setup for analysis of bacterial binding to mucins. The variation between technical replicates was smaller using SPR detection compared to the adenosine 5′-triphosphate (ATP) bioluminescence assay in microtiter plates. Furthermore, we demonstrated that the effect of flow on pathogen-mucin interaction is significant and that bacterial adhesion differ non-linearly with flow rates and depend on the epithelial source of the mucin.

A highly sensitive tetracycline sensor based on a combination of magnetic molecularly imprinted polymer nanoparticles and surface plasmon resonance detection.

A method is reported for in-situ detection of the antibiotic tetracycline (TC). It is based on a combination of extraction of TC by magnetic molecularly imprinted polymers nanoparticles (MMIPs NPs) and detection by surface plasmon resonance (SPR). The TC-captured MMIPs NPs were flowed over the surface of the SPR chip that was modified with mercaptoethylamine. The SPR signal undergoes a strong increase through the use of MMIPs NPs. It increases linearly in the 5.0-100pg·mL-1 TC concentration range, and the detection limit is as low as 1.0pg·mL-1 (at S/N = 3). This method shows selectivity to TC compared with structurally analogues. In order to demonstrate the power of the method, it was applied to the analysis of milk spiked with TC. These results were validated by comparing them to those of an enzyme-linked immunoassay. The average recovery is in the range of 95.7-104.6%. Graphical abstract Schematic representation of a surface plasmon resonance assay for the sensitive determination of tetracycline in milk using the magnetic molecularly imprinted polymers nanoparticles that can extract tetracycline and amplify the SPR signal.

Development and Application of an Optical Biosensor Immunoassay for Aflatoxin M1 in Bovine Milk

An automated optical biosensor-based immunoassay exploiting surface plasmon resonance detection for the quantitation of aflatoxin M1 (AFM1) in milk and milk powders is described. A monoclonal antibody and an immobilized protein–AFM1 conjugate are utilized in a simple inhibition format following aqueous extraction and immunoaffinity clean-up of the sample, thereby avoiding the need for signal amplification techniques. The sensor surface is stable over multiple regeneration cycles, and the technique yields a method detection limit of 0.1 ng g−1, which is five times lower than the European Commission maximum residue limit. The described antibody-based biosensor technique provides the advantages of quantitative data, automation, and real-time and non-labeled detection of AFM1. The method therefore facilitates routine quantitative threshold-level screening for the identification of potential non-compliance of AFM1 content prior to confirmatory analysis by reference chromatographic methods and may be considered to complement the enzyme-linked immunosorbent assay technique.

Ion-specific quantitative measurement scheme using transit-time surface plasmon resonance

A sensitive, ion-specific measurement scheme is proposed and analysed theoretically. It is based on transit-time surface plasmon resonance (SPR) sensing in an electrolytic conductivity cell comprising an electrode supporting surface plasmons (SPs). The transit-time SPR response involves dynamics of ion transport in the electrolytic conductivity cell and a highly sensitive SPR response from the electrode supporting SPs. This is modelled by solving the modified-Poisson–Nernst–Planck equations and the Fresnel equations. It is shown that the magnitude of the transit-time SPR detection signal scales with the square root of ion concentration (), whilst bulk SPR detection scales linearly with ion concentration (). Transit-time SPR is, therefore, a superior detection scheme at low ion concentrations. Analyses by Tikhonov regularization show that transit-time SPR response enables specific ion detection through differences in ion mobility and charge. The proposed method is purely physical, not requiring chemical affinity layers or chemical reduction-oxidation processes at the electrodes. It is based on a differential measurement scheme with and without voltage applied. Compared to conductivity sensors, the method adds specificity, while compared to bulk SPR sensors, it improves the resolution at low concentration levels and enables specificity without use of surface chemistry or biochemistry.

Development of a Surface Plasmon Resonance and Fluorescence Imaging System for Biochemical Sensing.

Surface plasmon resonance (SPR) biosensors are an extremely sensitive optical technique used to detect the changes in refractive index occurring at the sensor interface. Fluorescence involves the emission of light by a substance that has absorbed light or other electromagnetic radiation, and the parameters of the absorbed and emitted radiation are used to identify the presence and the amount of specific molecules in a specimen. SPR biosensors and fluorescence analysis are both effective methods for real-time detection. The combination of these technologies would improve the quantitative detection sensitivity of fluorescence analysis and the specificity of SPR detection. We designed and developed an SPR and fluorescence synchronous detection system. The SPR module was based on two kinds of modulation methods, and the fluorescence module was capable of switching between four wavelengths. The fluorescence microspheres and A549 cells of different concentration were both detected by the SPR and fluorescence method synchronously in real time. The fluorescent signal and the optical signal of the SPR were shown to correlate. The correlation coefficient for fluorescent microspheres detection reached up to 0.9866. The system could be used in cell analysis and molecule diagnosis in the future.

A gold/Fe3O4 nanocomposite for use in a surface plasmon resonance immunosensor for carbendazim.

A surface plasmon resonance (SPR) biosensor for the pesticide carbendazim is described that has enhanced performance due to the use of a Au/Fe3O4 nanocomposite as an amplifying label on the surface the carboxymethyldextran-coated gold layer of the sensor. The surface was further modified with monoclonal antibody to obtain a sensor for real-time detection of carbendazim. Binding of carbendazim results in a change in refractive index. SPR detection in the absence of Au/Fe3O4 nanocomposite and by UPLC-MS analysis demonstrated the improved performance to be due to the use of the Au/Fe3O4 nanocomposite. Response is linear in the 0.05 to 150ng·mL-1 carbendazim concentration range, and the limit of detection is 0.44ng·mL-1. This is more than 1 order of magnitude lower than that of the conventional SPR assay. The recoveries from spiked medlar are between 102.4 and 115.0%. The selectivity was tested by using the pesticides benzimidazole, 2-mercaptobenzimidazole, 2-benzimidazole propionic acid, and 2-(2-aminoethyl) benzimidazole as potential interferents. Conceivably, this Au/Fe3O4 nanocomposite-based method has a large potential for the detection of other small analytes at trace concentrations. Graphical abstract Schematic presentation of the SPR sensor for the detection of the fungicide carbendazim (methyl 2-benzimidazole carbamate; MBC) based on the use of a gold/Fe3O4 nanocomposites.

Highly parallel remote SPR detection of DNA hybridization by micropillar optical arrays.

Remote detection by surface plasmon resonance (SPR) is demonstrated through microstructured optical arrays of conical nanotips or micropillars. Both geometries were fabricated by controlled wet chemical etching of bundles comprising several thousands of individual optical fibers. Their surface was coated by a thin gold layer in order to confer SPR properties. The sensitivity and resolution of both shapes were evaluated as a function of global optical index changes in remote detection mode performed by imaging through the etched optical fiber bundle itself. With optimized geometry of micropillar arrays, resolution was increased up to 10-4 refractive index units. The gold-coated micropillar arrays were functionalized with DNA and were able to monitor remotely the kinetics of DNA hybridization with complementary strands. We demonstrate for the first time highly parallel remote SPR detection of DNA via microstructured optical arrays. The obtained SPR sensitivity combined with the remote intrinsic properties of the optical fiber bundles should find promising applications in biosensing, remote SPR imaging, a lab-on-fiber platform dedicated to biomolecular analysis, and in vivo endoscopic diagnosis. Graphical abstract We present a single fabrication step to structure simultaneously all the individual cores of an optical fiber bundle composed of thousands of fibers. The resulting sensor is optimized for reflection mode (compatible with in vivo applications) and is used to perform for the first time highly parallel remote SPR detection of DNA via several thousands of individual optical fiber SPR sensors paving the way for multiplexed biological detection.

A potential peptide derived from cytokine receptors can bind proinflammatory cytokines as a therapeutic strategy for anti-inflammation

Chronic inflammation is a pivotal event in the pathogenesis of cardiovascular diseases, including atherosclerosis, restenosis, and coronary artery disease. The efficacy of current treatment or preventive strategies for such inflammation is still inadequate. Thus, new anti-inflammatory strategies are needed. In this study, based on molecular docking and structural analysis, a potential peptide KCF18 with amphiphilic properties (positively charged and hydrophobic residues) derived from the receptors of proinflammatory cytokines was designed to inhibit cytokine-induced inflammatory response. Simulations suggested that KCF18 could bind to cytokines simultaneously, and electrostatic interactions were dominant. Surface plasmon resonance detection showed that KCF18 bound to both tumor necrosis factor-α (TNF-α) and interleukin-6, which is consistent with MM/PBSA binding free energy calculations. The cell experiments showed that KCF18 significantly reduced the binding of proinflammatory cytokines to their cognate receptors, suppressed TNF-α mRNA expression and monocyte binding and transmigration, and alleviated the infiltration of white blood cells in a peritonitis mouse model. The designed peptide KCF18 could remarkably diminish the risk of vascular inflammation by decreasing plasma cytokines release and by directly acting on the vascular endothelium. This study demonstrated that a combination of structure-based in silico design calculations, together with experimental measurements can be used to develop potential anti-inflammatory agents.

Synthesis of Fe₃C@C from Pyrolysis of Fe₃O₄-Lignin Clusters and Its Application for Quick and Sensitive Detection of PrPSc through a Sandwich SPR Detection Assay.

The prion protein (PrPSc) has drawn widespread attention due to its pathological potential to cause prion diseases. Herein, we successfully synthesized Fe3C@C by carbonizing Fe3O4-lignin clusters, which were prepared through a facile hydrogen bonding interaction between ≡Fe-OH and hydroxyl groups of lignin. Our in-depth investigation confirmed that the composites were Fe3C@C core/shell particles. We constructed a novel sandwich surface plasmon resonance (SPR) detection assay for sensitive PrPSc detection, utilizing bare gold surface and aptamer-modified Fe3C@C (Fe3C@C-aptamer). Due to the highly specific affinity of Fe3C@C-aptamer towards PrPSc, the sandwich type SPR sensor exhibited excellent analytical performance towards the discrimination and quantitation of PrPSc. A good linear relationship was obtained between the SPR responses and the logarithm of PrPSc concentrations over a range of 0.1–200 ng/mL. The detection sensitivity for PrPSc was improved by ~10 fold compared with the SPR direct detection format. The required detection time was only 20 min. The specificity of the present biosensor was also confirmed by PrPC and other reagents as controls. This proposed approach could also be used to isolate and detect other highly pathogenic biomolecules with similar structural characteristics by altering the corresponding aptamer in the Fe3C@C conjugates.

Improving nanoparticle-enhanced surface plasmon resonance detection of small molecules by reducing steric hindrance via molecular linkers

Ultrasensitive Surface Plasmon Resonance (SPR) detection of small molecules can be achieved using nanoparticles to both enhance the SPR signals and pre-concentrate low levels of target analytes in the sample. However, the short effective penetration depth of the SPR evanescent field, and steric hindrance of binding when immobilizing small molecules on surfaces, limits the applicability of using relatively large nanoparticles (≥100 nm) for SPR detection. To overcome the issues of steric hindrance, this paper investigates the role of the molecular linkers to tether both the antibodies to the magnetic nanoparticles, and to bind the small molecules to the surface of the SPR chips. By extending the distance of the small molecule (progesterone) away from the SPR chip surface and improving the antibody orientation on the large magnetic nanoparticles, a sensitive SPR detection for progesterone was achieved in buffer (0.013 ng mL−1). The results of the SPR assay for progesterone in milk were in good correlation with ELISA results, and could be used to verify the onset of estrus in cows.

Effective optical properties of nanoparticle-mediated surface plasmon resonance sensors.

We investigate effective medium properties of nanoparticles (NPs) in surface plasmon (SP) resonance detection. Attention was paid to the effective medium characteristics with respect to the particle distribution in equally spaced, aggregated, and intermediate models, although effects of other parameters such as size, material, and concentration were also explored. The results suggest that the distribution may cause significant measurement deviation by as much as 20% for gold NPs and less than 5% for silica. Particle concentration showed complicated dependence in the effective medium. Different mechanisms were observed to govern effective medium properties of dielectric and metal NPs, SP mode transition and multiple scattering for silica NPs. In contrast, metal damping dominated resonance characteristics for gold NPs. The results are expected to provide fresh insights on how to apply an effective medium and interpret measured data in SP resonance sensors and beyond.

Covalent affixation of histidine-tagged proteins tethered onto Ni-nitrilotriacetic acid sensors for enhanced surface plasmon resonance detection of small molecule drugs and kinetic studies of antibody/antigen interactions.

The Ni2+-histidine (His) chelation yields a more uniform and predicable orientation of immobilized protein molecules than an amine-coupling reaction in surface plasmon resonance (SPR) analyses. However, the gradual dissociation of His-tagged proteins leads to a long and sloped baseline, which adversely affects kinetic studies. Furthermore, as shown in this work for the first time, the strong binding affinity between the histidine-rich Fc domain of immunoglobulin-type antibodies and Ni-nitrilotriacetic acid (NTA) interferes with the kinetic studies of these antibodies and their His-tagged antigens. By performing an amine-coupling reaction immediately after the Ni2+-His chelation, essentially all of the Ni2+-tethered protein molecules can be covalently linked to the carboxyl groups on the underlying carboxymethylated dextran surface. The sequential injections of pH 8.6 phosphate-buffered saline provided additional time to ensure a higher amine coupling efficiency and reverted NHS esters on the protein molecules to carboxyl groups. The application of our method to antibody/antigen interactions is demonstrated with the kinetic analysis of His-tagged t-DARPP protein/anti-t-DARPP interactions. In a separate experiment, the highly efficient immobilization method resulted in a higher immobilization density of His-tagged human carbonic anhydrase (HCA) II, affording accurate kinetic measurements for the binding of 4-carboxybenzenesulfonamide. In addition, the higher HCA II density enhanced the SPR sensitivity, allowing 4-carboxybenzenesulfonamide to be determined with a remarkable detection limit (14 nM).

Recent progress in the studies of electrochemical interfaces by surface plasmon resonance spectroscopy and microscopy

Surface plasmon resonance (SPR) is a label-free spectroscopic technique that is highly sensitive to various surface reactions. Incorporating SPR into electrochemical measurements has emerged as a powerful method to study both faradaic and non-faradaic processes. SPR microscopy (SPRM) integrates an optical microscope into SPR detection, which further offers high throughput detection and spatially resolved information at an electrode surface and thus, has attracted attention especially in single entity electrochemical studies. In this review, the progress in the studies of electrochemical interfaces by SPR and SPRM during the past two years will be discussed.

Selective Plasmonic Sensing and Highly Ordered Metallodielectrics via Encapsulation of Plasmonic Metal Nanoparticles with Metal Oxides

Novel materials for sensing and metallodielectric arrays have been prepared by encapsulation of gold-protected shape-selected silver nanoparticles with a diverse range of shells including iron, manganese, and iridium oxides using a versatile deposition procedure. These shells of varying thickness, porosity, and smoothness encapsulating metal nanoparticles advantageously combine functionalities of plasmonic cores and oxide shells into resulting functional materials. In particular, the size-uniform metal oxide encapsulated metal nanoparticles (MO-MNPs) assemble into well-ordered metallodielectric arrays for plasmonic applications. The shape and the localized surface plasmon resonance (LSPR) of the metal cores are well preserved, while the chemical and colloidal stability are enhanced by the formation of oxide shells. Metal oxide shells impart the selectivity of detection in surface-enhanced Raman spectroscopy (SERS) and surface plasmon resonance (SPR) sensing. Notably, selective sub-millimolar SPR detection...

Sensitive surface plasmon resonance detection of methyltransferase activity and screening of its inhibitors amplified by p53 protein bound to methylation-specific ds-DNA consensus sites

Abnormal DNA methylation is closely related to cancer initiation and progression, and strategies to assay methyltransferase activity and screen its inhibitors are essential for cancer diagnosis and therapy. In this work, surface plasmon resonance (SPR)-based assay for real-time and sensitive monitoring of DNA methyltransferase activity and screening of its inhibitors was conducted via methylation of double-stranded (ds)-DNA consensus sites and the follow-up p53 protein recognition. The consensus ds-DNA possesses a specific sequence of 5′-CCGG-3′ in which the second C base can be methylated by M.SssI methyltransferase (M.SssI MTase) and the methylation process impedes the recognition and cleavage of the ds-DNA by HpaII endonuclease, thus, the attachment of p53 protein leads to remarkable SPR signals. In contrast, inhibition of M.SssI MTase activity by a potent inhibitor leaves the consensus ds-DNA unmethylated, and the cleavage of the ds-DNA by HpaII prevents p53 protein from adsorbing onto the chip surface, leading to tiny SPR signals. The binding affinity (KD) between p53 protein and the methylated consensus ds-DNA was deduced to be 3.04 nM, evidencing the strong binding capability. Two nucleoside inhibitors of 5-Azacytidine (5-Aza) and 5-aza-2′-deoxycytidine (5-Aza-dC), and a non-nucleoside inhibitor of procaine were examined, and their half-maximal inhibiting concentration (IC50) values were highly comparable with those by other methods. The sensing protocol has been successfully utilized for the assay of M.SssI MTase activity in normal and cancer cell lysates. The proof-of-concept experiments demonstrate that SPR serves as a viable means for sensitive detection of methyltransferase activity and screening of its inhibitors using p53 protein bound to methylation-specific ds-DNA consensus sites.

Dual Sensing Arrays for Surface Plasmon Resonance (SPR) and Surface‐Enhanced Raman Scattering (SERS) Based on Nanowire/Nanorod Hybrid Nanostructures

AbstractA multifunctional sensing array with gold nanowire–nanorod hybrid nanostructures for dual detection of surface plasmon resonance (SPR) and surface‐enhanced Raman scattering (SERS) is presented. The cost‐effective and arrayed nanostructures are made simply onto plastic films using hot‐embossing nanoimprint lithography. Five different hybrid nanostructures are studied and compared by measuring SERS enhancement factor and SPR thickness sensitivity. The combination of nanowire and nanorod structures in specific arrangement and quantities of nanorods can not only enhance the SERS effect but also further increase the SPR thickness sensitivity. The area percentage of nanorods of 16.51% can achieve the highest SPR thickness sensitivity and 106 SERS enhancement. On comparison of the nanowire structure, the SERS signal and SPR thickness sensitivity of nanowire/nanorod hybrid nanostructure are increased up to 6 times and 2 times simultaneously. The estimated SERS enhancement factor and SPR thickness sensitivity are 2.82 × 106 and 0.74 (nm/nm), respectively. The enhanced sensitivity is attributed to the increased nanorods contributing to dense hot spots and the reduced SPR evanescent length caused by the localized surface plasmons. These results are verified by finite‐difference time‐domain (FDTD) calculations. Such low‐cost SPR–SERS chips for multifunctional chemical analysis can increase the reliability of biological detection and broaden sensing applications.

Quantitative Cross-Platform Performance Comparison between Different Detection Mechanisms in Surface Plasmon Sensors for Voltage Sensing

Surface plasmon Resonance (SPR) has recently been of interest for label-free voltage sensing. Several SPR structures have been proposed. However, making a quantitative cross-platform comparison for these structures is not straightforward due to (1) different SPR measurement mechanisms; (2) different electrolytic solution and concentration in the measurement; and (3) different levels of external applied potential. Here, we propose a quantitative approach to make a direct quantitative comparison across different SPR structures, different electrolytic solutions and different SPR measurement mechanisms. There are two structures employed as example in this theoretical study including uniform plasmonic gold sensor and bimetallic layered structure consisting of uniform silver layer (Ag) coated by uniform gold layer (Ag). The cross-platform comparison was carried by several performance parameters including sensitivity (S), full width half maximum (FWHM) and figure of merit (FoM). We also discuss how the SPR measurement mechanisms enhance the performance parameters and how the bimetallic layer can be employed to enhance the FoM by a factor of 1.34 to 25 depending on the SPR detection mechanism.

The role of the central metal ion of ethane-bridged bis-porphyrins in histidine sensing

Ethane-bridged bis-porphyrin derivatives are reported for the selective detection of various analytes in sensing applications. The central metal ion is able to rule specific molecular arrangements upon analyte binding. Three bis-porphyrin compounds: a free base (metal free), Ni complex, and Cu complex, have been tested for histidine detection in aqueous media. Histidine is involved in various biological processes, including such deadly disease as lung cancer. The conformational changes of bis-porphyrins, induced by histidine binding, can be detected by monitoring the Soret band position. The spectroscopic characterization, at the air-water subphase interface, indicates that, in the presence of histidine, the Ni and Cu metallated derivatives undergo conformational changes. This behaviour was confirmed when these two derivatives were deposited onto the solid support by Langmuir-Schaefer (LS) technique. A prototypal Surface Plasmon Resonance (SPR) detection system for histidine based on these two porphyrin LS films was developed. The Cu substituted compound based SPR system allows the histidine sensing down to nanomolar concentration. Furthermore, a SPR response of the Ni bis-porphyrin shows a semilogarithmic dependence on the histidine concentration up to 10−6 M proposing the use of these two porphyrins in a sensor array for the monitoring of histidine levels in plasma.

Ultrasensitive Detection of Bacterial Protein Toxins on Patterned Microarray via Surface Plasmon Resonance Imaging with Signal Amplification by Conjugate Nanoparticle Clusters.

Sensitive detection and monitoring of biological interactions in a high throughput, multiplexed array format has numerous advantages. We report here a method to enhance detection sensitivity in surface plasmon resonance (SPR) spectroscopy and SPR imaging via the effect of accumulation of conjugated nanoparticles of varying sizes. Bacterial cholera toxin (CT) was chosen for the demonstration of enhanced immunoassay by SPR. After immobilization of CT on a gold surface, specific recognition is achieved by biotinylated anti-CT. The signal is amplified by the attachment of biotinylated 20 nm AuNP via streptavidin bridge, followed by attachment of 5 nm streptavidin-functionalized Fe3O4NP to the AuNP-biotin surface. The continuous surface binding of two differently sized conjugated nanoparticles effectively increases their packing density on surface and significantly improves SPR detection sensitivity, allowing quantitative measurement of CT at very low concentration. The dense packing of conjugated nanoparticles on the surface was confirmed by atomic force microscopy characterization. SPR imaging of the immunoassay for high-throughput analysis utilized an Au-well microarray that attenuated the background resonance interference on the resulting images. A calibration curve of conjugated nanoparticle binding signal amplification for CT detection based on surface coverage has been obtained that shows a correlation in a range from 6.31 × 10-16 to 2.51 × 10-13 mol/cm2 with the limit of detection of 5.01 × 10-16 mol/cm2. The absolute quantity of detection limit using SPR imaging was 0.25 fmol. The versatile nanoparticles and biotin-streptavidin interaction used here should allow adaptation of this enhancement method to many other systems that include DNA, RNA, peptides, and carbohydrates, opening new avenues for ultrasensitive analysis of biomolecules.

Label-free, spatially multiplexed SPR detection of immunoassays on a highly integrated centrifugal Lab-on-a-Disc platform

As a direct, label-free method, Surface Plasmon Resonance (SPR) detection significantly reduces the needs for liquid handling and reagent storage compared to common enzyme-linked immunosorbent assays (ELISAs), thus enabling comprehensive multiplexing of bioassays on microfluidic sample-to-answer systems. This paper describes a highly integrated centrifugal Lab-on-a-Disc (LoaD) platform for automating the full process chain extending between plasma extraction and subsequent aliquoting to five parallelized reaction channels for quantitative SPR detection by an inexpensive smartphone camera. The entire, multi-step / multi-reagent operation completes within less than 1 h. While the emphasis of this work is on the fluidic automation and parallelization by previously introduced, very robust event-triggered valving and buoyancy-driven centripetal pumping schemes, we successfully implement an immunoglobulin G (IgG) assay; by specific functionalization of the detection surfaces, the same disc layout can readily be customised for immunoassays panels from whole blood.