Characterization and optimization of a real-time, parallel, label-free, polypyrrole-based DNA sensor by surface plasmon resonance imaging

GLAD Based Advanced Nanostructures for Diversified Biosensing Applications: Recent Progress

Glancing angle deposition (GLAD) is a technique for the fabrication of sculpted micro- and nanostructures under the conditions of oblique vapor flux incident and limited adatom diffusion. GLAD-based nanostructures are emerging platforms with broad sensing applications due to their high sensitivity, enhanced optical and catalytic properties, periodicity, and controlled morphology. GLAD-fabricated nanochips and substrates for chemical and biosensing applications are replacing conventionally used nanomaterials due to their broad scope, ease of fabrication, controlled growth parameters, and hence, sensing abilities. This review focuses on recent advances in the diverse nanostructures fabricated via GLAD and their applications in the biomedical field. The effects of morphology and deposition conditions on GLAD structures, their biosensing capability, and the use of these nanostructures for various biosensing applications such as surface plasmon resonance (SPR), fluorescence, surface-enhanced Raman spectroscopy (SERS), and colorimetric- and wettability-based bio-detection will be discussed in detail. GLAD has also found diverse applications in the case of molecular imaging techniques such as fluorescence, super-resolution, and photoacoustic imaging. In addition, some in vivo applications, such as drug delivery, have been discussed. Furthermore, we will also provide an overview of the status of GLAD technology as well as future challenges associated with GLAD-based nanostructures in the mentioned areas.

Nanostructured plasmonic chips employing nanopillar and nanoring hole arrays for enhanced sensitivity of SPR-based biosensing

We present a theoretical analysis of the different nanostructured plasmonic sensor chips-consisting of plasmonic nanostructures present on the surface of plasmonic thin films-interrogated using the Kretschmann configuration for highly sensitive localized sensing, with high tunability from the visible to the infrared regions. Rigorous coupled-wave analysis is performed to analyze all the proposed nanostructured sensor chips and compare their sensing performance. The sensitivity parameters are defined to focus on the detection of a thin layer of biomolecules on the surface of nanostructures. The dimensions of the nanostructures and the incident angle shift the plasmon resonance wavelengths and can be used to tune the operating wavelength. The nanostructured films create local regions of high electric fields, which results in enhanced sensitivity of the proposed structures. The proposed sensors can be used in surface plasmon resonance imaging to detect multiple biomolecules in a single measurement. An extremely high surface sensitivity and figure of merit (FOMS) of 91 nm nm-1 and 0.59 nm-1 has been found, respectively, for one of the proposed nanostructured sensing platforms. Moreover, we demonstrate a very high differential reflectance of 55% per nm thickness of the biolayer.

Electrochemical impedance-based DNA sensor using pyrrolidinyl peptide nucleic acids for tuberculosis detection

A label-free electrochemical DNA sensor based on pyrrolidinyl peptide nucleic acid (acpcPNA)-immobilized on a paper-based analytical device (PAD) was developed. Unlike previous PNA-based electrochemical PAD (ePAD) sensors where the capture element was placed directly on the electrode, acpcPNA was covalently immobilized onto partially oxidized cellulose paper allowing regeneration by simple PAD replacement. As an example application, a sensor probe was designed for Mycobacterium tuberculosis (MTB) detection. The ePAD DNA sensor was used to determine a synthetic 15-base oligonucleotide of MTB by measuring the fractional change in the charge transfer resistance (R_ct) obtained from electrochemical impedance spectroscopy (EIS). The R_ct of [Fe(CN)₆]^3-/4- before and after hybridization with the target DNA could be clearly distinguished. Cyclic voltammetry (CV) was used to verify the EIS results, and showed an increase in peak potential splitting in a similar stepwise manner for each immobilization step. Under optimal conditions, a linear calibration curve in the range of 2-200 nM and the limit of detection 1.24 nM were measured. The acpcPNA probe exhibited very high selectivity for complementary oligonucleotides over single-base-mismatch, two-base-mismatch and non-complementary DNA targets due to the conformationally constrained structure of the acpcPNA. Moreover, the ePAD DNA sensor platform was successfully applied to detect PCR-amplified MTB DNA extracted from clinical samples. The proposed paper-based electrochemical DNA sensor has potential to be an alternative device for low-cost, simple, label-free, sensitive and selective DNA sensor.

Surface plasmon resonance imaging (SPRi) for analysis of DNA aptamer:β-conglutin interactions

Surface plasmon resonance imaging (SPRi) is a label-free detection method that offers a suitable and reliable platform for the real time monitoring of biomolecular interactions. In the work reported here, SPRi was used to evaluate the affinity and specificity of three different aptamers selected against the Lup an 1 anaphylactic allergen β-conglutin (β-conglutin binding aptamers I and II (β-CBA I and β-CBA II)), as well as an 11-mer truncated version of β-CBA I. Thiol modified aptamers were immobilised on a gold substrate through a self-assembling process and the use of different blocking strategies to prevent non-specific binding were evaluated. Dissociation constants of 20, 13 and 1 nM were determined for β-CBA I, β-CBA II and the 11-mer truncated aptamer, respectively. The three aptamers were then studied in various different sandwich formats and the β-CBA I/11-mer and β-CBA II were observed to bind to different aptatopes on the target protein. Each of the aptamers were then used either as surface immobilised aptamer, or as reporter aptamer, and added with the protein target β-conglutin in either a sequential of simultaneous manner, and the changes in SPR signal monitored. The preferred approach for formation of a sandwich aptacomplex was with immobilised β-CBA II, followed by addition of pre-incubated β-conglutin and 11-mer, whilst addition of the 11-mer following addition of the β-conglutin, resulted in displacement of the bound target. The ability to provide parallel qualitative and quantitative detection establishes SPRi as a powerful tool for the study of immobilised aptamer-target interactions.

Microelectrospotting as a new method for electrosynthesis of surface-imprinted polymer microarrays for protein recognition

Here we introduce microelectrospotting as a new approach for preparation of protein-selective molecularly imprinted polymer microarrays on bare gold SPR imaging chips. During electrospotting both the gold chip and the spotting tip are electrically connected to a potentiostat as working and counter electrodes, respectively. The spotting pin encloses the monomer-template protein cocktail that upon contacting the gold surface is in-situ electropolymerized resulting in surface confined polymer spots of ca. 500 µm diameter. By repeating this procedure at preprogrammed locations for various composition monomer-template mixtures microarrays of nanometer-thin surface-imprinted films are generated in a controlled manner. We show that the removal and rebinding kinetics of the template and various potential interferents to such microarrays can be monitored in real-time and multiplexed manner by SPR imaging. The proof of principle for microelectrospotting of electrically insulating surface-imprinted films is made by using scopoletin as monomer and ferritin as protein template. It is shown that microelectrospotting in combination with SPR imaging can offer a versatile platform for label-free and enhanced throughput optimization of the molecularly imprinted polymers for protein recognition and for their analytical application.

Measuring melittin uptake into hydrogel nanoparticles with near-infrared single nanoparticle surface plasmon resonance microscopy

This paper describes how changes in the refractive index of single hydrogel nanoparticles (HNPs) detected with near-infrared surface plasmon resonance microscopy (SPRM) can be used to monitor the uptake of therapeutic compounds for potential drug delivery applications. As a first example, SPRM is used to measure the specific uptake of the bioactive peptide melittin into N-isopropylacrylamide (NIPAm)-based HNPs. Point diffraction patterns in sequential real-time SPRM differential reflectivity images are counted to create digital adsorption binding curves of single 220 nm HNPs from picomolar nanoparticle solutions onto hydrophobic alkanethiol-modified gold surfaces. For each digital adsorption binding curve, the average single nanoparticle SPRM reflectivity response, ⟨Δ%R_NP⟩, was measured. The value of ⟨Δ%R_NP⟩ increased linearly from 1.04 ± 0.04 to 2.10 ± 0.10% when the melittin concentration in the HNP solution varied from zero to 2.5 μM. No change in the average HNP size in the presence of melittin is observed with dynamic light scattering measurements, and no increase in ⟨Δ%R_NP⟩ is observed in the presence of either FLAG octapeptide or bovine serum albumin. Additional bulk fluorescence measurements of melittin uptake into HNPs are used to estimate that a 1% increase in ⟨Δ%R_NP⟩ observed in SPRM corresponds to the incorporation of approximately 65000 molecules into each 220 nm HNP, corresponding to roughly 4% of its volume. The lowest detected amount of melittin loading into the 220 nm HNPs was an increase in ⟨Δ%R_NP⟩ of 0.15%, corresponding to the absorption of 10000 molecules.

Electrochemical DNA hybridization sensors based on conducting polymers

Conducting polymers (CPs) are a group of polymeric materials that have attracted considerable attention because of their unique electronic, chemical, and biochemical properties. This is reflected in their use in a wide range of potential applications, including light-emitting diodes, anti-static coating, electrochromic materials, solar cells, chemical sensors, biosensors, and drug-release systems. Electrochemical DNA sensors based on CPs can be used in numerous areas related to human health. This review summarizes the recent progress made in the development and use of CP-based electrochemical DNA hybridization sensors. We discuss the distinct properties of CPs with respect to their use in the immobilization of probe DNA on electrode surfaces, and we describe the immobilization techniques used for developing DNA hybridization sensors together with the various transduction methods employed. In the concluding part of this review, we present some of the challenges faced in the use of CP-based DNA hybridization sensors, as well as a future perspective.

Diamond nanowires modified with poly[3-(pyrrolyl)carboxylic acid] for the immobilization of histidine-tagged peptides

Coating boron-doped diamond nanowires (BDD NWs) with a conducting polymer, poly[3-(pyrrolyl)carboxylic acid], has been reported. Polymer coating was achieved through electropolymerization of 3-(pyrrolyl)carboxylic acid at the electrode interface by amperometrically biasing the BDD NWs interface until a predefined charge has passed. The poly[3-(pyrrolyl)carboxylic acid] modified BDD NWs (PPA-BDD NWs) were characterized by scanning electron microscopy (SEM) and cyclic voltammetry (CV). Using a deposition charge of 11 mC cm(-2) resulted in a thin polymer film deposition. The availability of the carboxylic groups of the polymer coated BDD NWs electrode was demonstrated through copper ion (Cu(2+)) chelation. The resulting complex was successfully used for the site-specific immobilization of histidine-tagged peptides. The binding process was followed by electrochemical impedance spectroscopy (EIS). The Cu(2+)-chelated PPA-BDD NWs interface showed peptide loading capability comparable to those of commercially available interfaces and can be easily regenerated several times using ethylenediaminetetraacetic acid (EDTA).

Amplified plasmonic detection of DNA hybridization using doxorubicin-capped gold particles

We show in this article that doxorubicin-modified gold nanoparticles (Au NP-DOX) can be used for the post-amplification of the wavelength shift of localized surface plasmon resonance (LSPR) signals after DNA hybridization events. We take advantage of the intercalation properties of DOX with guanine-rich oligonucleotides and the plasmon coupling between surface-linked gold nanostructures and Au NP-DOX in solution to detect in a sensitive manner DNA hybridisation events. Post-treatment of double-stranded DNA with Au NP-DOX resulted in a detection limit of ≈600 pM, several times lower than that without post-incubation (LOD ≈ 40 nM).

Electrochemical transduction of DNA hybridization at modified electrodes by using an electroactive pyridoacridone intercalator

A synthetic redox probe structurally related to natural pyridoacridones was designed and electrochemically characterised. These heterocycles behave as DNA intercalators due to their extended planar structure that promotes stacking in between nucleic acid base pairs. Electrochemical characterization by cyclic voltammetry revealed a quasi-reversible electrochemical behaviour occurring at a mild negative potential in aqueous solution. The study of the mechanism showed that the iminoquinone redox moiety acts similarly to quinone involving a two-electron reduction coupled with proton transfer. The easily accessible potential region with respect to aqueous electro-inactive window makes the pyridoacridone ring suitable for the indirect electrochemical detection of chemically unlabelled DNA. Its usefulness as electrochemical hybridization indicator was assessed on immobilised DNA and compared to doxorubicin. The voltamperometric response of the intercalator acts as an indicator of the presence of double-stranded DNA at the electrode surface and allows the selective transduction of immobilised oligonucleotide hybridization at both macro- and microscale electrodes.

Approach for plasmonic based DNA sensing: amplification of the wavelength shift and simultaneous detection of the plasmon modes of gold nanostructures

In this article, the detection of DNA hybridization taking advantage of the plasmonic properties of gold nanostructures is described. The approach is based on the amplification of the wavelength shift of a multilayered localized surface plasmon resonance (LSPR) sensor interface upon hybridization with gold nanorods and nanostars-labeled DNA. The amplification results in a significant decrease of the limit of detection from ≈40 nM as observed for unlabeled DNA to 0.2 nM for labeled DNA molecules. Furthermore, the plasmonic band, characteristic of the labeled DNA, is different from that of the LSPR interface. Indeed, next to the plasmon band at around 550 nm, being in resonance with the plasmon band of the LSPR interface, additional plasmonic peaks at 439 nm for gold nanostar-labeled DNA and 797 nm for gold nanorod-labeled DNA are observed, which were used as plasmonic signatures for successful hybridization.

Surface plasmon resonance sensing of nucleic acids: a review

Biosensors based on surface plasmon resonance (SPR) have become a central tool for the investigation and quantification of biomolecules and their interactions. Nucleic acids (NAs) play a vital role in numerous biological processes and therefore have been one of the major groups of biomolecules targeted by the SPR biosensors. This paper discusses the advances of NA SPR biosensor technology and reviews its applications both in the research of molecular interactions involving NAs (NA-NA, NA-protein, NA-small molecule), as well as for the field of bioanalytics in the areas of food safety, medical diagnosis and environmental monitoring.

A S-parameters-based detection method for a multilayer SPR biosensor

In this paper, S-parameters investigation of a variable incidence angle multilayer SPR biosensor is presented. Both magnitude and phase of the S-parameters are taken into account in the investigation. The work presented in this paper is the first attempt to apply S-parameters analysis to a multilayer SPR biosensor. The goal is to improve sensitivity through involving S-parameters including their phase values. In addition, further investigation is carried out to understand the relationship between the S-parameters and thickness of biomolecular layer and also the design parameters including the number of graphene layers.

Polypyrrole-oligosaccharide microarray for the measurement of biomolecular interactions by surface plasmon resonance imaging

The polypyrrole approach initially developed for the construction of DNA chips, has been extended to other biochemical compounds such as proteins and more recently oligosaccharides. The copolymerization of a pyrrole monomer with a biomolecule bearing a pyrrole group by an electrochemical process allows a very fast coupling of the biomolecule (probe) to a gold layer used as a working electrode. Fluorescence-based detection is the reference method to detect interactions on biochips; however an alternative label free method, could be more convenient for rapid screening of biointeractions. Surface Plasmon Resonance (SPRi) is a typical label-free method for real time detection of the binding of biological molecules onto functionalized surfaces. This surface sensitive optical method is based upon evanescent wave sensing on a thin metal layer. The SPR approach described herein is performed in an imaging geometry that allows simultaneous monitoring of biorecognition reactions occurring on an array of immobilized probes (chip). In a SPR imaging experiment, local changes in the reflectivity are recorded with a CCD camera and are exploited to monitor up to 100 different biological reactions occurring onto the molecules linked to the polypyrrole matrix. This method will be applied to oligosaccharide recognition.

Plasmonic-based electrochemical impedance spectroscopy: application to molecular binding

Plasmonic-based electrochemical impedance spectroscopy (P-EIS) is developed to investigate molecular binding on surfaces. Its basic principle relies on the sensitive dependence of surface plasmon resonance (SPR) signal on surface charge density, which is modulated by applying an ac potential to a SPR chip surface. The ac component of the SPR response gives the electrochemical impedance, and the dc component provides the conventional SPR detection. The plasmonic-based impedance measured over a range of frequency is in quantitative agreement with the conventional electrochemical impedance. Compared to the conventional SPR detection, P-EIS is sensitive to molecular binding taking place on the chip surface and less sensitive to bulk refractive index changes or nonspecific binding. Moreover, this new approach allows for simultaneous SPR and surface impedance analysis of molecular binding processes.

DNA-directed capture of primary cells from a complex mixture and controlled orthogonal release monitored by SPR imaging

Many biological samples are composed of several cell types. Qualitative and quantitative analysis of these complex mixtures is of major interest for both diagnostic and biomedical applications. Because large amounts of biological material are often challenging to collect, tremendous efforts have been made for a decade to design miniaturized platforms-such as lab-on-a-chip or microarrays-to run sensitive and reliable analysis from tiny quantities of starting material. Although barely explored so far, the release of resolved cellular samples constitutes an exciting strategy for further cell analysis. Herein, we propose a DNA-based biochip suitable for cell-type analysis in a label-free manner. The DNA-array is firstly converted into antibody-array using antibody-DNA conjugates. These protein-DNA hybrid molecules are chemically synthesized by covalent coupling of short oligonucleotides to antibodies directed against cell-type specific markers. We show not only specific capture of primary spleen cells on protein-DNA microarray spots but also their fast and specific orthogonal release according to the antibody-DNA combinations by incorporating restriction sites in DNA. Both molecular and cellular interactions occurring on the biochip are monitored by surface plasmon resonance (SPR) imaging. This optical technique turns out to be a powerful way to monitor, in real-time, biological interactions occurring on the microarrayed features.

Accurate prediction of binding thermodynamics for DNA on surfaces

For DNA mounted on surfaces for microarrays, microbeads, and nanoparticles, the nature of the random attachment of oligonucleotide probes to an amorphous surface gives rise to a locally inhomogeneous probe density. These fluctuations of the probe surface density are inherent to all common surface or bead platforms, regardless of whether they exploit either an attachment of presynthesized probes or probes synthesized in situ on the surface. Here, we demonstrate for the first time the crucial role of the probe surface density fluctuations in the performance of DNA arrays. We account for the density fluctuations with a disordered two-dimensional surface model and derive the corresponding array hybridization isotherm that includes a counterion screened electrostatic repulsion between the assayed DNA and probe array. The calculated melting curves are in excellent agreement with published experimental results for arrays with both presynthesized and in situ synthesized oligonucleotide probes. The approach developed allows one to accurately predict the melting curves of DNA arrays using only the known sequence-dependent hybridization enthalpy and entropy in solution and the experimental macroscopic surface density of probes. This opens the way to high-precision theoretical design and optimization of probes and primers in widely used DNA array-based high-throughput technologies for gene expression, genotyping, next-generation sequencing, and surface polymerase extension.

Isothermal discrimination of single-nucleotide polymorphisms via real-time kinetic desorption and label-free detection of DNA using silicon photonic microring resonator arrays

We report a sensitive, label-free method for detecting single-stranded DNA and discriminating between single nucleotide polymorphisms (SNPs) using arrays of silicon photonic microring resonators. In only a 10 min assay, DNA is detected at subpicomole levels with a dynamic range of 3 orders of magnitude. Following quantitation, sequence discrimination with single nucleotide resolution is achieved isothermally by monitoring the dissociation kinetics of the duplex in real-time using an array of SNP-specific capture probes. By leveraging the capabilities of the microring resonator platform, we successfully generate multiplexed arrays to quickly screen for the presence and identity of SNPs and show the robustness of this methodology by analyzing multiple target sequences of varying GC content. Furthermore, we show that this technique can be used to distinguish both homozygote and heterozygote alleles.

Salt concentration effects on equilibrium melting curves from DNA microarrays

DNA microarrays find applications in an increasing number of domains where more quantitative results are required. DNA being a charged polymer, the repulsive interactions between the surface of the microarray and the targets in solution are increasing upon hybridization. Such electrostatic penalty is generally reduced by increasing the salt concentration. In this article, we present equilibrium-melting curves obtained from dedicated physicochemical experiments on DNA microarrays in order to get a better understanding of the electrostatic penalty incurred during the hybridization reaction at the surface. Various salt concentrations have been considered and deviations from the commonly used Langmuir adsorption model are experimentally quantified for the first time in agreement with theoretical predictions.

On chip real time monitoring of B-cells hybridoma secretion of immunoglobulin

The secretions of molecules by cells are of tremendous interest for both fundamental insights studies and medical purposes. In this study, we propose a new biochip-based approach for the instantaneous monitoring of protein secretions, using antibody production by B lymphocytes cultured in vitro. This was possible thanks to the Surface Plasmon Resonance imaging (SPRi) of a protein biochip where antigen proteins (Hen Egg Lysozyme, HEL) were micro-arrayed along with series of control proteins. B cell hybridomas were cultured on the chip and the secretion of immunoglobulins (antibody) specific to HEL was monitored in real-time and detected within only few minutes rather than after a 30-60 min incubation with standard ELISA experiments. This fast and sensitive detection was possible thanks to the sedimentation of the cells on the biochip sensitive surface, where local antibody concentrations are much higher before dilution in the bulk medium. An other interesting feature of this approach for the secretion monitoring was the independence of the SPR response--after normalization--regarding to the density of the surface-immobilized probes. Such biosensor might thus pave the way to new tools capable of both qualitative and semi-quantitative analysis of proteins secreted by other immune cells.

Surface plasmon resonance on gold and silver films coated with thin layers of amorphous silicon-carbon alloys

The paper reports on a novel surface plasmon resonance (SPR) substrate architecture based on the coating of a gold (Au) or silver (Ag) substrate with 5 nm thin amorphous silicon-carbon alloy films. Ag/a-Si(1-x)C(x):H and Au/a-Si(1-x)C(x):H multilayers are found to provide a significant advantage in terms of sensitivity over both Ag and Au for SPR refractive index sensing. The possibility for the subsequent linking of stable organic monolayers through Si-C bonds is demonstrated. In a proof-of-principle experiment that this structure can be used for real-time biosensing experiments, amine terminated biotin was covalently linked to the acid-terminated SPR surface and the specific streptavidin-biotin interaction recorded.

Surface plasmon resonance imaging for biosensing

Surface plasmon resonance imaging (SPRI) is a useful tool for the study of surface biomolecular interactions allowing for label-free detection and elegant instrumentation. SPRI imaging system is described in this review with an emphasis on recent applications with examples of different biological interactions and high throughput analysis. Signal amplification in SPRI using nanoparticle and waveguide-based optical coupling is introduced. Finally the detection sensitivity of the SPRI system is examined in terms of other competitive methods.

Protein-diazonium adduct direct electrografting onto SPRi-biochip

A direct protein immobilization method for surface plasmon resonance imaging (SPRi) gold chip arraying is exposed. The biomolecule electroaddressing strategy, previously demonstrated by our team on carbon surfaces, is here valuably involved and adapted to create a straightforward and efficient protein immobilization process onto SPRi-biochips. The proteins, modified with an aryl-diazonium adduct, are addressed to the SPRi chip surface through the electroreduction of the aryl-diazonium. The biomolecule deposition was followed through SPRi live measurements during the electrografting process. A specially designed setup enabled us to directly observe the mass increasing at the sensor surface while the proteins were electrografted. A pin electrospotting method, allowing the achievement of distinct sensing layers on gold SPRi-biochips, was used to generate microarray biochips. The integrity of the immobilized proteins and the specificity of the detection, based on antigen/antibody interactions, were demonstrated for the detection of specific antibodies and ovalbumin. The SPRi detection limit of ovalbumin using the electroaddressing of anti-ovalbumin IgG was compared with two other immobilization procedures, cystamine-glutaraldehyde self-assembled monolayer and pyrrole, and was found to be a decade lower than these ones (100 ng/mL, i.e., 2 nM).

Nucleic Acid-based Detection of Bacterial Pathogens Using Integrated Microfluidic Platform Systems

The advent of nucleic acid-based pathogen detection methods offers increased sensitivity and specificity over traditional microbiological techniques, driving the development of portable, integrated biosensors. The miniaturization and automation of integrated detection systems presents a significant advantage for rapid, portable field-based testing. In this review, we highlight current developments and directions in nucleic acid-based micro total analysis systems for the detection of bacterial pathogens. Recent progress in the miniaturization of microfluidic processing steps for cell capture, DNA extraction and purification, polymerase chain reaction, and product detection are detailed. Discussions include strategies and challenges for implementation of an integrated portable platform.

Production of surface plasmon resonance based assay kit for hepatitis diagnosis

Hepatitis B surface antibody (HBsAb) imprinted poly(hydroxyethyl methacrylate-N-methacryloyl-L-tyrosine methyl ester) (PHEMAT) film on the surface plasmon resonance (SPR) sensor chip was prepared for diagnosis of HBsAb in human serum. Gold SPR chip surface was modified with allyl mercaptane and, then, HBsAb-imprinted PHEMAT film was formed on the chip surface. Surface characterization of the non-modified, allyl mercaptane modified and HBsAb-imprinted PHEMAT SPR chips were investigated with contact angle, atomic force microscopy (AFM). Kinetic studies were performed using HBsAb positive human serum. In order to determine the kinetic and binding constants, Scatchard, Langmuir, Freundlich and Langmuir-Freundlich models were applied to experimental data. Scatchard curve shows that HBsAb imprinted SPR chip has some surface heterogeneity, SPR chip obeyed the Langmuir adsorption model. The maximum detection limit was 208.2 mIU/mL. K(A) and K(D) values are 0.015 mIU/mL and 66.0 mL/mIU, respectively. Control experiments of the SPR chip were performed using non-immunized, HBsAb negative serum. The control experiment results show that SPR chip does not give any noticeable response to HBsAb negative serum.

Polypyrrole oligosaccharide array and surface plasmon resonance imaging for the measurement of glycosaminoglycan binding interactions

In order to construct tools able to screen oligosaccharide-protein interactions, we have developed a polypyrrole-based oligosaccharide chip constructed via a copolymerization process of pyrrole and pyrrole-modified oligosaccharide. For our study, GAG (glycosaminoglycans) or GAG fragments, which are involved in many fundamental biological processes, were modified by the pyrrole moiety on their reducing end and then immobilized on the chip. The parallel binding events on the upperside of the surface can be simultaneously monitored and quantified in real time and without labeling by surface plasmon resonance imaging (SPRi). We show that electrocopolymerization of the oligosaccharide-pyrrole above a gold surface enables the covalent immobilization of multiple probes and the subsequent monitoring of their binding capacities using surface plasmon resonance imaging. Moreover, a biological application was made involving different GAG fragments and different proteins, including stromal cell-derived factor-1alpha (SDF-1alpha), interferon-gamma (IFN-gamma), and monoclonal antibody showing different affinity pattern.

Point mutation detection by surface plasmon resonance imaging coupled with a temperature scan method in a model system

The detection of point mutations in genes presents clear biological and medical interest. Various methods have been considered. In this paper, we take advantage of surface plasmon resonance imaging, a technique allowing detection of unlabeled DNA hybridization. Coupled with a temperature scan, this approach allows us to determine the presence of single-point mutations in oligonucleotide samples from the analysis of DNA's melting curves in either the homozygous or heterozygous case. Moreover, these experimental data are confirmed in good agreement with numerical calculations.

Detection of carbohydrate-binding proteins by oligosaccharide-modified polypyrrole interfaces using electrochemical surface plasmon resonance

This paper reports on the use of electrochemical surface plasmon resonance (E-SPR) for the detection of carbohydrate-binding proteins. The generation of an SPR sensor specific to lectins Arachis hypogaea (PNA) and Maackia amurensis (MAA) is based on the electrochemical polymerization of oligosaccharide derivatives functionalized by pyrrole groups. The resulting thin conducting polymer films were characterized using E-SPR and atomic force microscopy (AFM). The specific binding of PNA to polypyrrole-lactosyl and of MAA to polypyrrole-3'-sialyllactosyl films was investigated using SPR. The detection limit was 41 nM for PNA and 83 nM for MAA. Through Scatchard analysis and linear transformation of the SPR sensorgram data, association (k(ass)) and dissociation rate constants (k(diss)) could be determined.

Label-free electrochemical detection of DNA using ferrocene-containing cationic polythiophene and PNA probes on nanogold modified electrodes

A label-free electrochemical method for the detection of DNA-PNA hybridization using a water-soluble, ferrocene-functionalized polythiophene transducer and single-stranded PNA probes on the nanogold modified electrode is investigated. Nanogold modified electrodes can largely increase the immobilization amount of ss-PNA capture probe and lead to an increase of the electrical signal. The ferrocene-containing cationic polythiophene do not interact electrostatically with the PNA probes due to the absence of the anionic phosphate groups on the PNA probes. But after DNA-PNA hybridization, cationic polythiophene is adsorbed on the DNA backbone, giving a clear hybridization detection signal in differential pulse voltammetry (DPV). Very good discrimination against non-complementary DNA and four-base mismatch DNA is observed. These studies show that the proposed method can provide an alternative for expanding the range of detection methods available for DNA hybridization.

Microfluidic systems integrated with two-dimensional surface plasmon resonance phase imaging systems for microarray immunoassay

This study reports a microfluidic chip integrated with an arrayed immunoassay for surface plasmon resonance (SPR) phase imaging of specific bio-samples. The SPR phase imaging system uses a surface-sensitive optical technique to detect two-dimensional (2D) spatial phase variation caused by rabbit immunoglobulin G (IgG) adsorbed on an anti-rabbit IgG film. The microfluidic chip was fabricated by using micro-electro-mechanical-systems (MEMS) technology on glass and polydimethylsiloxane (PDMS) substrates to facilitate well-controlled and reproducible sample delivery and detection. Since SPR detection is very sensitive to temperature variation, a micromachine-based temperature control module comprising micro-heaters and temperature sensors was used to maintain a uniform temperature distribution inside the arrayed detection area with a variation of less than 0.3 degrees C. A self-assembled monolayer (SAM) technique was used to pattern the surface chemistry on a gold layer to immobilize anti-rabbit IgG on the modified substrates. The microfluidic chip is capable of transporting a precise amount of IgG solution by using micropumps/valves to the arrayed detection area such that highly sensitive, highly specific bio-sensing can be achieved. The developed microfluidic chips, which employed SPR phase imaging for immunoassay analysis, could successfully detect the interaction of anti-rabbit IgG and IgG. The interactions between immobilized anti-rabbit IgG and IgG with various concentrations have been measured. The detection limit is experimentally found to be 1 x 10(-4)mg/ml (0.67 nM). The specificity of the arrayed immunoassay was also explored. Experimental data show that only the rabbit IgG can be detected and the porcine IgG cannot be adsorbed. The developed microfluidic system is promising for various applications including medical diagnostics, microarray detection and observing protein-protein interactions.