Surface Plasmon Resonance Imaging Detection Research Articles

Unraveling the binding microprocess of individual Streptococcus mutans cells via sucrose-dependent adhesion based on surface plasmon resonance imaging

ABSTRACT The initial microprocess of a major cariogenic bacterium Streptococcus mutans forming biofilm at a single-cell level via sucrose-dependent adhesion has not been observed because the cells’ high moisture content caused measurement challenges. To develop a high-sensitivity biosensor chip and a real-time, label-free method to observe bioactive molecule interactions with single cells from oral biofilms. We made the chips of immobilized bacteria by micronano-processing. A surface plasmon resonance imaging (SPRI) system was used to detect and record the association and dissociation microprocess of S. mutans with sucrose/dextran solutions of various concentrations, and the calculus model was adopted to treat the data. At the location of S. mutans, a unique ‘comet-tail’ SPRI signal was observed. The binding patterns of S. mutans differed between individual cells exposed to the same solution as well as between sucrose and dextran. The different cells exhibited different affinities with dissociation constants for sucrose being 5.697 × 10−3 to 3.689 M and for dextran 1.235 × 10−3 to 1.282 M, indicating cell-to-cell heterogeneity. Our SPRI detection method is effective in investigating microbial binding, initial biofilm formation, and oral microecology. It offers new possibilities for studying oral microorganism characteristics and development of oral diseases.

Resonance plasmonic gold microwell arrays for high-performance surface plasmon resonance imaging based on polarization contrast modulation

The throughput and label-free multianalyte interrogation ability provided by surface plasmon resonance imaging (SPRi) sensors has gained considerable interest in biochemical analysis. Here, we report an optical platform based on polarization contrast modulation, in which a three-dimensional plasmonic microwell array is used as a sensing chip to eliminate background resonance and greatly enhance the electromagnetic field response in the microwell structure by confining the SPR. In addition, the sensor can provide an extremely high contrast and signal-to-noise ratio and can achieve a very high sensitivity response (1.52 × 105 pixel / RIU). Additionally, the signal-to-background ratio is improved to 40. The low-concentration limit of detection can reach 5.38 × 10 − 7 RIU, which is 1 order of magnitude improvement. In biomolecular interaction analysis, the sensor can detect a 5.12 × 104-fold diluted bovine serum albumin antibody solution. The special chip architecture and high image quality introduce an array screening method using SPRi detection.

Single-layer graphene-coated gold chip for enhanced SPR imaging immunoassay

Surface plasmon resonance imaging (SPRi) is a powerful tool for label-free, real-time and high-throughput immunoassay, but its sensitivity needs essential improvement. It has been recently reported that the sensitivity of angular-interrogation surface plasmon resonance (SPR) could be efficiently enhanced on single-layer graphene-coated gold chip. The usefulness of this method however remains unclear for reflectivity-based SPRi platform. Herein for the first time we demonstrate that the graphene coating-enabled intrinsic sensitivity enhancement is applicable to high-throughput SPRi and the enhancement factor is further quantitatively evaluated. High-quality single-layer graphene is transferred in a site-controllable manner to cover half of spots on the SPRi gold array chip. With anti-zearalenone (ZEN) antibody as a model target and polydopamine (PDA) thin film as a reactive layer for probe immobilization, the SPRi detection signals on two types of sensing spots are quantitatively compared on a single chip and the enhancement factor is evaluated. It is unambiguously disclosed that on the reflectivity-based SPRi platform, single-layer graphene coating results in a ca. 40% enhancement on the detection signal (reflectivity increase, ΔR). This work unveils the compelling SPRi sensitivity enhancement of graphene coating and may facilitate its broad practical applications.

<inline-formula> <tex-math notation="LaTeX">$\text{MoS}_2$</tex-math> </inline-formula>-Based Highly Sensitive Near-Infrared Surface Plasmon Resonance Refractive Index Sensor

A surface plasmon resonance imaging biosensor based on $\text{MoS}_2$ deposited on Aluminium substrate is designed for high imaging sensitivity and detection accuracy. The proposed biosensor exhibits better performance than graphene-based biosensor in the near-infrared regime. A high imaging sensitivity of more than 970 $\text{RIU}^{-1}$ is obtained at the wavelength of 1540 nm. The effect of aluminium thickness, number of $\text{MoS}_2$ layers and the refractive index of sensing layer are investigated to obtain an optimized design for high sensor performance. In addition, the sensor performance comparison of $\text{MoS}_2$ and other two-dimensional transition metal dichalcogenide materials based biosensor in the near-infrared regime are also presented. The designed $\text{MoS}_2$ mediated surface plasmon resonance imaging biosensor could provide potential applications in surface plasmon resonance imaging detection of multiple biomolecular interactions simultaneously.

Surface Plasmon Resonance Imaging Detection of Sub-femtomolar MicroRNA.

MicroRNA (miRNA) is a promising new type of biomarkers but at a low fM level and hard to be analyzed. Herein proposed is an innovated surface plasmon resonance imaging (SPRi) method merged with a novel in-plane and vertical signal amplification strategy, that is, orthogonal signal amplification to enable a direct determination of sub-fM miRNA-15a (a multiple tumor diagnostic biomarker). The core idea is to add more mass on a target sample spot first along the surficial direction, then upward from the surface. In detection of miRNA, this was realized by coupling a miRNA-initiated surficial cyclic DNA-DNA hybridization reaction with a DNA-initiated upward cyclic polymerization reaction. A perfect SPRi sensing chip with isolated gold islands bordered by hydrophobic CYTOP was fabricated and used to obtain high-quality chip with low fabrication difficulty. As a result, SPRi contrast largely increases, able to reach a limit of detection and limit of quantification down to 0.56 and 5fM for miRNA-15a, about 107-fold improvement of sensitivity compared with a common SPRi detection. The method could quantify standard miRNA-15a spiked in human serum with an ideal recovery ranging from 98.6% to 104.9% and was validated to be applicable to the direct determination of miRNA-15a in healthy and cancer human serums. The orderly and controllable in situ sensitizing strategy is powerful and readily extendable to detection of other miRNAs.

Ultrasensitive Detection of Staphylococcus aureus and Listeria monocytogenes Genomic DNA by Nanoparticle‐Enhanced Surface Plasmon Resonance Imaging

AbstractThe rapid, sensitive and specific detection of pathogenic bacteria is key to the prevention of a variety of foodborne illnesses representing a significant threat to public health. Conventional methods for the detection and identification of pathogens may take up to a few days to yield an answer, and for this reason, efforts have been made to develop new biosensing platforms for the efficient detection of foodborne pathogens. Here we report the use of a nanoparticle‐enhanced surface plasmon resonance (SPR) imaging biosensor for the rapid and femtomolar‐attomolar detection of Staphylococcus aureus and Listeria monocytogenes genomic DNAs. We performed the nanoparticle enhanced SPR imaging detection of pathogen genomic DNAs with no need for the polymerase chain reaction (PCR) pre‐amplification of the sequences to be detected. Here we show that peptide nucleic acid (PNA) probes can discriminate between two pathogenic genomic DNAs. We tested the selectivity of the detection method against control probe sequences or contaminating bovine genomic DNA and demonstrated, for the first time, the attomolar detection of Staphylococcus aureus genomic DNA in the presence of a 10‐fold higher concentration of bovine genomic DNA.

Chemical Strategy to Stepwise Amplification of Signals in Surface Plasmon Resonance Imaging Detection of Saccharides and Glycoconjugates.

A stepwise strategy was proposed to controllably amplify surface plasmon resonance imaging (SPRi) signals and used to establish a method for sensitive detection of small saccharides and large glycoconjugates. The key is to enlarge the target analytes step by step through a cyclic recognition reaction of concanavalin A (ConA) with dextran, which can easily be integrated into SPRi detection. The reaction is theoretically expected to proceed with infinite cycles by addition of ConA and dextran one after another, and in practice, it allows for performing signal amplification for up to 20 steps, which nearly reaches the limit of the propagation depth of surface plasmon waves. Because of the nonspecific adsorption effect, the maximum signals of small sugars were measured at steps 5-7 by the use of small molecules like ethanol amine to block the nonspecific adsorption. The real applicability of the method was validated by SPRi determination of either immobilized saccharides and glycoproteins or captured carcinoembryonic antigen (CEA) from patient samples with a limit of detection down to 2.5 μM glucose or 50 pg/mL of CEA. A wide extendibility of the method was confirmed by detecting other ConA-recognizable analytes like human IgG, ovalbumin, α-fetoprotein, and analytes convertible to ConA- or dextran-recognizable forms. Notably, other cyclic reactions specific to saccharides or other analytes are in theory exploitable, which will further widen the applicability of the method and strategy.

SPR and SPR Imaging: Recent Trends in Developing Nanodevices for Detection and Real-Time Monitoring of Biomolecular Events.

In this paper we review the underlying principles of the surface plasmon resonance (SPR) technique, particularly emphasizing its advantages along with its limitations regarding the ability to discriminate between the specific binding response and the interfering effects from biological samples. While SPR sensors were developed almost three decades, SPR detection is not yet able to reduce the time-consuming steps of the analysis, and is hardly amenable for miniaturized, portable platforms required in point-of-care (POC) testing. Recent advances in near-field optics have emerged, resulting in the development of SPR imaging (SPRi) as a powerful optical, label-free monitoring tool for multiplexed detection and monitoring of biomolecular events. The microarrays design of the SPRi chips incorporating various metallic nanostructures make these optofluidic devices more suitable for diagnosis and near-patient testing than the traditional SPR sensors. The latest developments indicate SPRi detection as being the most promising surface plasmon-based technique fulfilling the demands for implementation in lab-on-a-chip (LOC) technologies.

Comparative Analysis of Human Growth Hormone in Serum Using SPRi, Nano-SPRi and ELISA Assays

Sensitive and selective methods for the detection of human growth hormone (hGH) over a wide range of concentrations (high levels of 50-100 ng ml−1 and minimum levels of 0.03 ng ml−1) in circulating blood are essential as variable levels may indicate altered physiology. For example, growth disorders occurring in childhood can be diagnosed by measuring levels of hGH in blood. Also, the misuse of recombinant hGH in sports not only poses an ethical issue it also presents serious health threats to the abuser. One popular strategy for measuring hGH misuse, relies on the detection of the ratio of 22 kDa hGH to total hGH, as non-22 kDa endogenous levels drop after exogenous recombinant hGH (rhGH) administration. Surface plasmon resonance imaging (SPRi) is an analytical tool that allows direct (label-free) monitoring and visualization of biomolecular interactions by recording changes of the refractive index adjacent to the sensor surface in real time. In contrast, the most frequently used colorimetric method, enzyme-linked immunosorbent assay (ELISA) uses enzyme labeled detection antibodies to indirectly measure analyte concentration after the addition of a substrate that induces a color change. To increase detection sensitivity, amplified SPRi uses a sandwich assay format and near infrared quantum dots (QDs) to increase signal strength. After direct SPRi detection of recombinant rhGH in spiked human serum, the SPRi signal is amplified by the sequential injection of detection antibody coated with near-infrared QDs (Nano-SPRi). In this study, the diagnostic potential of direct and amplified SPRi was assessed for measuring rhGH spiked in human serum and compared directly with the capabilities of a commercially available ELISA kit.

Real-time toxicity testing of silver nanoparticles to Salmonella Enteritidis using surface plasmon resonance imaging: A proof of concept

In this paper we report for the first time on the suitability of surface plasmon resonance imaging (SPRi) for performing ecotoxicity testing of nanoparticles (NPs). Specifically, the impact of silver NPs (using Ag NM-300K) and ions (using AgNO3 salt) on Salmonella Enteritidis growth was assessed in Luria Bertani medium using the culture-capture-measure (CCM) based SPRi method. Clear effects were observed at 10mgL−1 Ag NPs characterised by shifted SPRi detection times (TD) by ca. 2.6h compared to the control. Comparable results were obtained using 1mgL−1 Ag ions. No clear effects were observed at 1mgL−1 Ag NPs and 0.1mgL−1 Ag ions. Overall results match the current trend in nanoecotoxicology using bacteria (e.g. impact of Ag NPs between 1 and 10mgL−1 and higher toxicity of Ag ions compared to Ag NPs). The dose dependent patterns of toxicity were coherent with those obtained using a standard plating method; however, the SPRi approach was faster (i.e. results within a few hours) and generated kinetic data (i.e. real-time monitoring). In addition, SPRi presents many valuable intrinsic advantages (e.g. label-free, multiplex, bespoke and robust) over current approaches. Consequently, a plethora of opportunities for future developments and applications of SPRi in NP testing is associated with the proof of concept reported herein.

Rapid and specific SPRi detection of L. pneumophila in complex environmental water samples.

Legionellosis is a very devastating disease worldwide mainly due to unpredictable outbreaks in man-made water systems. Developing a highly specific and sensitive rapid detection system that detects only metabolically active bacteria is a main priority for water quality assessment. We previously developed a versatile technique for sensitive and specific detection of synthetic RNA. In the present work, we further investigated the performance of the developed biosensor for detection of Legionella pneumophila in complex environmental samples, particularly those containing protozoa. The specificity and sensitivity of the detection system were verified using total RNA extracted from L. pneumophila in spiked water co-cultured with amoebae. We demonstrated that the expression level of ribosomal RNA (rRNA) is extremely dependent on the environmental conditions. The presence of amoebae with L. pneumophila, especially in nutrition-deprived samples, increased the amount of L. pneumophila 15-fold after 1week as measured through the expression of 16s rRNA. Using the developed surface plasmon resonance imaging (SPRi) detection method, we were also able to successfully detect L. pneumophila within 3h, both in the presence and absence of amoebae in the complex environmental samples obtained from a cooling water tower. These findings suggest that the developed biosensing system is a viable method for rapid, real-time and effective detection not only for L. pneumophila in environmental samples but also to assess the risk associated with the use of water contaminated with other pathogens.

Gold Nanoparticles Surface Plasmon Resonance Enhanced Signal for the Detection of Small Molecules on Split-Aptamer Microarrays (Small Molecules Detection from Split-Aptamers).

The detection of small molecules by biosensors remains a challenge for diagnostics in many areas like pharmacology, environment or homeland security. The main difficulty comes from both the low molecular weight and low concentrations of most targets, which generally requires an indirect detection with an amplification or a sandwich procedure. In this study, we combine both strategies as the amplification of Surface Plasmon Resonance imaging (SPRi) signal is obtained by the use of gold nanoparticles and the sequence engineering of split-aptamers, short oligonucleotides strands with strong affinity towards small targets, allows for a sandwich structure. Combining those two strategies, we obtained state-of-the-art results in the limit of detection (LOD = 50 nM) with the model target adenosine. Furthermore, the SPRi detection led on aptamer microarrays paves the way for potential multi-target detections thanks to the multi-probe imaging approach.

Polydopamine-Functionalization of Graphene Oxide to Enable Dual Signal Amplification for Sensitive Surface Plasmon Resonance Imaging Detection of Biomarker

Surface plasmon resonance imaging (SPRi) is one of the powerful tools for immunoassays with advantages of label-free, real-time, and high-throughput; however, it often suffers from limited sensitivity. Herein we report a dual signal amplification strategy utilizing polydopamine (PDA) functionalization of reduced graphene oxide (PDA-rGO) nanosheets for sensitive SPRi immunoassay in serum. The PDA-rGO nanosheet is synthesized by oxidative polymerization of dopamine in a gentle alkaline solution in the presence of graphene oxide (GO) sheets and then is antibody-conjugated via a spontaneous reaction between the protein and the PDA component. In the dual amplification mode, the first signal comes from capture of the antibody-conjugated PDA-rGO to form sandwiched immunocomplexes on the SPRi chip, followed by a PDA-induced spontaneous gold reductive deposition on PDA-rGO to further enhance the SPRi signal. The detection limit as low as 500 pg mL(-1) is achieved on a nonfouling SPRi chip with high specificity and a wide dynamic range for a model biomarker, carcinoembryonic antigen (CEA) in 10% human serum.

Surface Plasmon Resonance imaging: A method to measure the affinity of the antibodies in allergy diagnosis

AimThe biological diagnosis of type I hypersensitivity reactions is based on the quantification of specific IgEs. However, the IgE titer is not always strongly related to the clinical symptoms or predictive of the evolution of the disease. The specificity and affinity of antibodies of other isotypes may contribute to the allergic status of the patients. The aim of the present work was to develop a method that simultaneously detects the complex antibody response to various allergens and measures the avidity of the antibodies directed to each allergen. MethodsA chip based on a covalent binding of 3 major milk allergens on a gold-activated surface was developed. The binding of specific antibodies to α-lactalbumin, β-lactoglobulin or caseins was monitored using Surface Plasmon Resonance imaging (SPRi). The sensitivity and specificity of the method were compared to those obtained by ELISA, the reference method. ResultsThe specificity of the antibodies characterized by SPRi was identical to the one obtained by ELISA. The intensity of the signal was proportional to the quantity of antibodies bound to each allergen. The sensitivity of the SPRi detection was about 8–10 times lower than for ELISA but the SPRi is faster and the analysis of association/dissociation kinetics allowed the determination of the avidity of the antibody response. ConclusionThe present study shows that SPRi allows a multiplex monitoring of the complex antibody response to the major allergens of an allergenic source. This label-free method constitutes a new tool that may be added to IgE detection to improve allergy diagnosis.

Visualization of high-throughput and label-free antibody-polypeptide binding for drug screening based on microarrays and surface plasmon resonance imaging

This work presents a visualization method for the high-throughput monitoring of antibody-polypeptide binding by integrating a microarray chip with surface plasmon resonance imaging (SPRi). A prism-coupled SPRi system with smart images processing software and a 5 × 5 polypeptide microarray was developed. The modeling analysis was performed to optimize the system and the materials of prism and chip, looking for the optimal incident wavelength and angle of incidence for dynamic SPRi detection in solution. The system can dynamically monitor 25 tunnels of biomolecule interactions in solution without secondary tag reactants. In addition, this system can determine the specific profile of antibody-polypeptide binding in each tunnel and yield a visual three-dimensional histogram of dynamic combinations in all microarray tunnels. Furthermore, the detection limit of the label-free antibody-polypeptide binding reached 1 pg/μL in a one-step binding test, and an ultrasensitive detection of 10 fg/μL was obtained using three-step cascade binding. Using the peptide microarray, the amount of sample and reagents used was reduced to 80 nL per tunnel, and 20 × 20 tunnels of biomolecule interactions could be analyzed in parallel in a 7 mm × 7 mm microreaction cells. This device and method offer a potential platform for high-throughput and label-free dynamic monitoring multiple biomolecule interactions for drug discovery and basic biomedical research.

Etched glass microarrays with differential resonance for enhanced contrast and sensitivity of surface plasmon resonance imaging analysis.

We report the fabrication and characterization of gold-coated etched glass array substrates for surface plasmon resonance imaging (SPRi) analysis with significantly enhanced performance, in particular image contrast and sensitivity. The etching of the glass substrate induces a variation in the resonance condition and thus in the resonance angle between the etched wells and the surrounding area, leading to the isolation of the array spot resonance with a significant reduction of the background signal. FDTD simulations show arrays with large spots and minimal spot-to-spot spacing yield ideal differential resonance conditions, which are verified by experimental results. Simulations also indicate the etched well structure exhibits enhanced SPR electric field intensity by 3-fold as compared to standard planar gold chips. Changes in the bulk sensitivity of the etched arrays have been obtained at the 10(-4) RIU level based on image intensity difference. The strong image contrast allows for improved microarray imaging analysis with easily distinguished signals from background resonance. The etched array chips are demonstrated for SPRi detection of bacterial toxins through the coating of an ultrathin SiO(2) film for direct vesicle fusion that establishes a supported membrane-based biosensing interface. Protein detection with cholera toxin (CT) at 5 nM is obtained, making this chip one of the most sensitive SPR imaging substrates ever reported without a postbinding amplification scheme. Furthermore, the surface can be regenerated by Triton X-100 for repeated cycles of membrane formation, protein binding, and biomolecular removal. The reusability and enhanced performance of the etched glass array chips should find a broad range of applications, opening up new avenues for high-throughput SPR imaging detection with convenience and marked surface sensitivity.

Designed Biointerface Using Near-Infrared Quantum Dots for Ultrasensitive Surface Plasmon Resonance Imaging Biosensors

The surface plasmon resonance imaging chip biointerface is fully designed using near-infrared (NIR) quantum dots (QDs) for the enhancement of surface plasmon resonance imaging (SPRi) signals in order to extend their application for medical diagnostics. The measured SPRi detection signal following the QD binding to the surface was amplified 25-fold for a 1 nM concentration of single-stranded DNA (ssDNA) and 50-fold for a 1 μg/mL concentration of prostate-specific antigen (PSA), a cancer biomarker, thus substantiating their wide potential to study interactions of a diverse set of small biomolecules. This significant enhancement is attributed to the QD's mass-loading effect and spontaneous emission coupling with propagating surface plasmons, which allowed the SPRi limit of detection to be reduced to 100 fM and 100 pg/mL for ssDNA and PSA, respectively. Furthermore, this study illustrates the potential of SPRi to be easily integrated with fluorescent imaging for advanced correlative surface-interaction analysis.

Investigation on an application of silver substrates for sensitive surface plasmon resonance imaging detection

A surface plasmon resonance (SPR) imaging biosensor based on silver substrates was investigated to demonstrate that silver could be used as a substrate material for sensitive detection of biomolecular interactions, despite its poor chemical stability. The calculation results showed that oxidation of silver film may lead to a decrease in the sensitivity due to a variation in SPR characteristics such as a broader curve width and shallower minimum reflectance at resonance. The effect of a change in the refractive index of target analytes on the sensitivity was also explored. In particular, it is noteworthy that Ag/Au bimetallic substrates with a thin gold protection layer to prevent oxidation of a silver film can provide a significant amplification of SPR imaging signals in comparison with conventional gold substrates.

Nanostructured digital microfluidics for enhanced surface plasmon resonance imaging

The advances in genomics and proteomics have unveiled an exhaustive catalogue of biomarkers that can potentially be used as diagnostic and prognostic indicators of genetic and infectious diseases. Current thrust in biosensor development is towards rapid, real-time, label-free and highly sensitive detection of the indicative biomarkers. While surface plasmon resonance imaging (SPRi) biosensors could potentially be the best suited candidate for biomarker-based diagnosis, important milestones need to be reached. Commercially available SPRi instrumentation is currently limited by the flow-cell technology to serial-sample processing and has limited sensitivity for the detection of markers present at low concentration. In this paper, we have implemented an approach to enhance sample handling and increase the sensitivity of the SPRi detection technique. We have developed a digital microfluidic platform with an integrated nanostructured biosensor interface that allows for rapid, ultra-low volume, sensitive, and automated on-chip SPRi detection of DNA hybridization reactions. Through the exploitation of electromagnetic properties of nanofabricated periodic gold nanoposts, SPRi signal was increased by 200% with the estimated limit of detection of 500 pM (90 attomoles). Using the versatile fluidic manipulation provided by the digital microfluidics, rapid and parallel target identification was achieved on multiple array elements within 1 min using 180 nL sample volume. By delivering multiple target analytes in individually addressable low volume droplets, without external pumps and fluidic interconnects, the overall assay time, cost and complexity was reduced. The proposed platform allows extreme versatility in the manipulation of precious low volume samples which makes this technology very suitable for diagnostic applications.

Aryl Diazonium for Biomolecules Immobilization onto SPRi Chips

A method for the immobilization of proteins at the surface of surface plasmon resonance imaging (SPRi) chips is presented. The technology, based on the electro-deposition of a 4-carboxymethyl aryl diazonium (CMA) monolayer is compared to a classical thioctic acid self-assembled monolayer. SPRi live recording experiments followed by the quantification of the diazonium surface coverage demonstrate the presence of a monolayer of electro-deposited molecules (11*10(12) molecules mm(-2)). This monolayer, when activated through a classical carbodiimide route, generates a surface suitable for the protein immobilization. In the present study, protein A and BSA are immobilized as specific and control spots (150 microm id), respectively. The AFM characterization of the spots deposited onto CMA or thioctic acid modified chips prove the presence of 4.7 nm protein monolayers. Finally, the SPRi detection capabilities of the two surface chemistries are compared according to specific signal, non-specific interaction and regeneration possibilities. Advantages are given to the CMA surface modification since no measurable non-specific signal is obtained while reaching a higher specific signal.