Detection of ozone gas using gold nanoislands and surface plasmon resonance

Gold nanoislands interact with gaseous ozone to produce a surface plasmon resonance shift, similarly to the interaction of ozone and gold nanoparticles in water. Gold nanoislands are produced by sputtering, which significantly simplifies the synthesis and produces controlled size for the gold nanoislands. The shift of surface plasmon resonance peak was monitored while gold nanoislands were exposed to variable concentration of gaseous ozone. The shift was then correlated with ozone concentration. Our current results indicate sensing gaseous ozone at concentration of as low as 20 μg/L is achievable. Gold nanoislands were reversed to their original wavelength and were able to cycle between the wavelengths as ozone was introduced and removed. Potentially, this system can be useful as a sensor that identifies the presence of ozone at low part-per-billion concentrations of ozone in gaseous media.     

Electrochemical enzyme immunoassay using immobilized antibody on gold film with monitoring of surface plasmon resonance signal

Sandwich immunoassay was conducted on a thin gold film set in a surface plasmon resonance (SPR) cell. Monochronal antibody (anti-IgG) was immobilized onto the gold film via 4,4′-dithiodibutyric acid (DDA) and avidin-biotin bonding. Next, IgG sample and alkaline phosphatase-conjugated anti-IgG (ALP anti-IgG) were introduced into the cell successively. Finally, p-aminophenyl phosphate (PAPP) was injected as an enzyme substrate, and the produced p-aminophenol (PAP) was electrochemically measured. Flow did not need to be stopped for incubation for the enzyme reaction, because of the thinness of the cell. In these processes, all the antigen-antibody reactions took place on the gold film. Therefore, the immobilization was performed quickly, and each process could be confirmed by SPR signal. This system had the advantage that the middle of the complicated process could be monitored. For example, the amount of antibody immobilized, which affected on the final electrochemical signal, could be confirmed in the course of immobilization. It was also convenient to investigate process conditions, such as removal of used antigens and labeled antibodies. Good correlation was obtained between the electrochemical current and the SPR signals due to the adsorption of IgG and ALP anti-IgG, and the sensitivity of the electrochemical measurement was much higher than the SPR’s.     

Recent advances in surface plasmon resonance based techniques for bioanalysis

Surface plasmon resonance (SPR) is a powerful and versatile spectroscopic method for biomolecular interaction analysis (BIA) and has been well reviewed in previous years. This updated 2006 review of SPR, SPR spectroscopy, and SPR imaging explores cutting-edge technology with a focus on material, method, and instrument development. A number of recent SPR developments and interesting applications for bioanalysis are provided. Three focus topics are discussed in more detail to exemplify recent progress. They include surface plasmon fluorescence spectroscopy, nanoscale glassification of SPR substrates, and enzymatic amplification in SPR imaging. Through these examples it is clear to us that the development of SPR-based methods continues to grow, while the applications continue to diversify. Major trends appear to be present in the development of combined techniques, use of new materials, and development of new methodologies. Together, these works constitute a major thrust that could eventually make SPR a common tool for surface interaction analysis and biosensing. The future outlook for SPR and SPR-associated BIA studies, in our opinion, is very bright. Surface plasmon resonance (SPR) is a powerful and versatile spectroscopic method for biomolecular interaction analysis (BIA) and has been well reviewed in previous years. This updated 2006 review of SPR, SPR spectroscopy, and SPR imaging explores cutting-edge technology with a focus on material, method, and instrument development. A number of recent SPR developments and interesting applications for bioanalysis are provided. Three focus topics are discussed in more detail to exemplify recent progress. They include surface plasmon fluorescence spectroscopy, nanoscale glassification of SPR substrates, and enzymatic amplification in SPR imaging. Through these examples it is clear to us that the development of SPR-based methods continues to grow, while the applications continue to diversify. Major trends appear to be present in the development of combined techniques, use of new materials, and development of new methodologies. Together, these works constitute a major thrust that could eventually make SPR a common tool for surface interaction analysis and biosensing. The future outlook for SPR and SPR-associated BIA studies, in our opinion, is very bright.      

The preparation and characterization of poly(o-phenylenediamine)/gold nanoparticles interface for immunoassay by surface plasmon resonance and electrochemistry

The poly-o-phenylenediamine (PoPD) nonconducting film and gold nanoparticles (AuNPs) were combined to fabricate AuNPs/PoPD film, which is used as a novel biocompatible interface for the immobilization of antibody and develop a simple and sensitive label-free immunoassay for the detection of the related antigen (human immunoglobulin G (IgG)). Surface plasmon resonance (SPR) and electrochemical methods were used to provide the real-time information about the polymer film growth, assembling of various sizes of gold nanoparticles, anti-human IgG antibody (anti-hIgG) immobilization and the antigen–antibody interaction. The microstructures of the PoPD and AuNPs/PoPD films were characterized by atomic force microscopy (AFM). These results demonstrated that AuNPs were uniformly dispersed on the porous surface of PoPD film, which formed a nano-structure biocompatible AuNPs/PoPD interface. The use of gold nanoparticles and PoPD film could enhance the immunoassay sensitivity and anti-nonspecific property of the resulting immunoassay electrode. Additionally, the reproducibility and preliminary application of anti-hIgG/AuNPs/PoPD/Au electrode for SPR detection of hIgG was also evaluated.     

Highly sensitive detection of human cardiac myoglobin using a reverse sandwich immunoassay with a gold nanoparticle-enhanced surface plasmon resonance biosensor

A highly sensitive reverse sandwich immunoassay for the detection of human cardiac myoglobin (cMb) in serum was designed utilizing a gold nanoparticle (AuNP)-enhanced surface plasmon resonance (SPR) biosensor. First, a monoclonal anti-cMb antibody (Mab1) was covalently immobilized on the sensor surface. AuNPs were covalently conjugated to the second monoclonal anti-cMb antibody (Mab2) to form an immuno-gold reagent (Mab2-AuNP). The reverse sandwich immunoassay consists of two steps: (1) mixing the serum sample with Mab2-AuNP and incubation for the formation of cMb/Mab2-AuNP complexes and (2) sample injection over the sensor surface and evaluation of the Mab1/cMb/Mab2-AuNP complex formation, with the subsequent calculation of the cMb concentration in the serum. The biosensor signal was amplified approximately 30-fold compared with the direct reaction of cMb with Mab1 on the sensor surface. The limit of detection of cMb in a human blood serum sample was found to be as low as 10 pM (approx. 0.18 ng mL⁻¹), and the inter-assay coefficient of variation was less than 3%. Thus, the developed SPR-based reverse sandwich immunoassay has a sensitivity that is sufficient to measure cMb across a wide range of normal and pathological concentrations, allowing an adequate estimation of the disease severity and the monitoring of treatment.     

A gold nanoparticle labeling strategy for the sensitive kinetic assay of the carbamate-acetylcholinesterase interaction by surface plasmon resonance

The article presents a novel strategy for a sensitive investigation of the interaction between acetylcholinesterase (AChE) and its small molecular carbamate inhibitors. Two carbamate inhibitors with different ether linkages and the terminal lipoate were synthesized and labeled with gold nanoparticles (AuNPs). With the signal amplification of AuNPs, the specific interactions between the AuNPs labeled carbamate inhibitors (ALC1 and ALC2) and the immobilized AChE on sensor chip surface were readily examined. The detection sensitivities of ALC1 and ALC2 were 176 and 121 m°/nM, respectively, with the detection limits of 7.0 and 12 pM at a signal-to-noise ratio of 3. The association/dissociation constants for the binding interaction between carbamate inhibitors and AChE were reported for the first time. The affinity constants were estimated to be 3.13 × 10⁶ and 6.39 × 10⁵ M⁻¹ for ALC1 and ALC2 respectively. This AuNPs labeling strategy is versatile and may be applicable for the direct or competitive SPR kinetic assay of the interaction between small molecule inhibitors and their target proteins with a high sensitivity.     

Gold nanoparticle-enhanced surface plasmon resonance measurement with a highly sensitive quantification for human tissue inhibitor of metalloproteinases-2

Two different methods for the quantification of human tissue inhibitor of metalloproteinases-2 (TIMP-2) were developed using surface plasmon resonance (SPR) and gold nanoparticles for signal enhancement. The first method, a competitive assay, used TIMP-2 immobilized to the sensor surface and the inactive form of matrix metalloproteinase-2 (proMMP-2) (EC 3.4.24.24) adsorbed to gold nanoparticles. The sensor signals resulting from the interaction of MMP-2-gold nanoparticles with immobilized TIMP-2 were inversely proportional to the amounts of TIMP-2 of the sample. The measuring range for TIMP-2 was about 15–180 pM. The second method, a one-step sandwich assay, used proMMP-2 immobilized to the sensor surface and an anti-TIMP-2 monoclonal antibody coupled to gold nanoparticles. The lower detection limit of this assay format was 0.5 pM of TIMP-2. The binding signals were highly reproducible up to 100 pM of the inhibitor. The improvements obtained in TIMP-2 quantification over already existing tests could contribute to a better understanding and diagnosis of diseases like cancer.     

Modeling protein binding and elution over a chromatographic surface probed by surface plasmon resonance

Surface plasmon resonance (SPR) spectroscopy is used as a scaled-down, analytical, pseudo-chromatography tool for analyzing protein binding and elution over an ion-exchange surface under cyclic sorption conditions. A micrometric-scale adsorption surface was produced by immobilizing a typical ion exchange ligand – diethylaminoethyl (DEAE) – onto commercially available planar gold sensor chip surfaces pre-derivatized with a self-assembled monolayer of 11-mercaptoundecanoic acid with known density. An explicit mathematical formulation is provided for the deconvolution and interpretation of the SPR sensorgrams. An adsorption rate model is proposed to describe the SPR sensorgrams for bovine serum albumin, used here as model protein, when the DEAE surface is subjected to a cyclic series of binding and elution steps. Overall, we demonstrate that the adsorption rate model is capable of quantitatively describing BSA binding and elution for protein titers from dilute conditions up to overloaded conditions and a broad range of salt concentrations.     

High-sensitivity biosensors fabricated by tailoring the localized surface plasmon resonance property of core-shell gold nanorods

An enhanced sensitive biosensor has been developed to detect biological targets by tailoring the localized surface plasmon resonance property of core–shell gold nanorods. In this new concept, a shell layer is produced on gold nanorods by generating a layer of chalcogenide on the gold nanorod surface after attachment of the recognition reagent, namely, goat IgG and antigen of schistosomiasis japonica. The bioactivity of these attached biomolecules is retained and the sensitivity of this biosensor is thus enhanced significantly. The plasmonic properties of the gold nanorods attached with the biomolecules can be adjusted and the plasmon resonance wavelength can be red-shifted up to several hundred nanometers in the visible or near infrared (NIR) region, which is extremely important to biosensing applications. This leads to a lager red-shift in the localized surface plasmon resonance absorption compared to the original gold nanorod-based sensor and hence offers greatly enhanced sensitivity in the detection of schistosomiasis japonica. The human serum infected with schistosomiasis japonica diluted to 1:50,000 (volume ratio, serum/buffer solution) can be detected readily. The technique offers enhanced sensitivity and can be easily extended to other sensing applications based on not only immuno-recognition but also other types of specific reactions.     

High sensitivity detection of 16s rRNA using peptide nucleic acid probes and a surface plasmon resonance biosensor

A signal enhancing method allowing highly sensitive detection of E. coli 16s rRNA was developed using peptide nucleic acid (PNA) as a capture probe and a surface plasmon resonance (SPR) sensor as a detector. 16s rRNA has been used as a genetic marker for identification of organisms, and can be analyzed directly without PCR amplification due to the relatively high number of copies. PNA has a neutral backbone structure, therefore hybridization with 16s rRNA results in the ionic condition being changed from neutral to negative. A cationic Au nanoparticle was synthesized and used for signal amplification by ionic interaction with 16s rRNA hybridized on the PNA probe-immobilized SPR sensor chip. This method resulted in a detection limit of E. coli rRNA of 58.2 ± 1.37 pg mL⁻¹. Using this analytical method, Staphylococcus aureus was detected without purification of rRNA.     

Enhanced surface plasmon resonance immunoassay for human complement factor 4

Using an enhanced surface plasmon resonance (SPR) immunosensor, we have determined the concentration of human complement factor 4 (C4). Antibody protein was concentrated into a carboxymethyldextran-modified gold surface by electrostatic attraction force and a simultaneous covalent immobilization of antibody based on amine coupling reaction took place. The sandwich method was applied to enhance the response signal and the specificity of antigen binding assay. The antibody immobilized surface had good response to C4 in the range of 0.02-20 μg/ml by this enhanced immunoassay. The regeneration effect by pH 2 glycine-HCl buffer was also investigated. The same antibody immobilized surface could be used more than 80 cycles of C4 binding and regeneration. In addition, the ability to determinate C4 directly from serum sample without any purification was investigated. The sensitivity, specificity and reproducibility of the enhanced immunoassay are satisfactory. The results clearly demonstrate the advantages of the enhanced SPR technique for C4 immunoassay.     

Gold nanostar-enhanced surface plasmon resonance biosensor based on carboxyl-functionalized graphene oxide

A new high-sensitivity surface plasmon resonance (SPR) biosensor based on biofunctional gold nanostars (AuNSs) and carboxyl-functionalized graphene oxide (cGO) sheets was described. Compared with spherical gold nanoparticles (AuNPs), the anisotropic structure of AuNSs, which concentrates the electric charge density on its sharp tips, could enhance the local electromagnetic field and the electronic coupling effect significantly. cGO was obtained by a diazonium reaction of graphene oxide (GO) with 4-aminobenzoic acid. Compared with GO, cGO could immobilize more antibodies due to the abundant carboxylic groups on its surface. Testing results show that there are fairly large improvements in the analytical performance of the SPR biosensor using cGO/AuNSs-antigen conjugate, and the detection limit of the proposed biosensor is 0.0375 μg mL⁻¹, which is 32 times lower than that of graphene oxide-based biosensor.     

A surface plasmon resonance probe without optical fibers as a portable sensing device

A surface plasmon resonance (SPR) sensor integrating a small sensor probe, a laser emission diode, a photo detector, and a polarizer was developed as a portable sensing device. The sensor probe was made with a glass cylinder, 50 mm long and 1.5 mm in diameter, that was connected directly to a beam splitter without optical fibers. The SPR spectrum obtained with this probe system showed a 10% reflectivity minimum at 690 nm. Shifts of the SPR spectrum induced by refractive index (RI) changes in the sample were measured by detecting the reflection light intensity at 670 nm. When the sensitivity was compared using a BIAcore™ SPR instrument, the lowest sensor response of 1 mV observed with the SPR probe system coincided with 1.4 × 10⁻⁶ of the RI changes. The RI resolution of the SPR probe was estimated with experimentally evaluated noise on the signal, and, consequently, it was concluded that the RI resolution was 1.2 × 10⁻⁵. Moreover, immunoreaction was demonstrated with adsorbed bovine serum albumin (BSA) and anti-BSA antibody as an analyte. As a result, 50 ng mL⁻¹ of the lower detection limit was estimated.     

Detection of parathion methyl using a surface plasmon resonance sensor combined with molecularly imprinted films

An ultra-sensitive and highly selective parathion methyl(PM) detection method by surface plasmon resonance(SPR) combined with molecularly imprinted films(MIF) was developed. The PM-imprinted film was prepared by thermo initiated polymerization on the bare Au surface of an SPR sensor chip.Template PM molecules were quickly removed by an organic solution of acetonitrile/acetic acid(9:1,v/v), causing a shift of 0.58 in SPR angle. In the concentrations range of 10à13–10à10mol/L, the refractive index showed a gradual increase with higher concentrations of template PM and the changes of SPR angles were linear with the negative logarithm of PM concentrations. In the experiment, the minimum detectable concentration was 10à13mol/L. The selectivity of the thin PM-imprinted film against diuron,tetrachlorvinphose and fenitrothion was examined, but no observable binding was detected. The results in the experiment suggested that the MIF had the advantages of high sensitivity and selectivity.     

Real-time immunoassay of ferritin using surface plasmon resonance biosensor

A surface plasmon resonance (SPR) biosensor was used for the first time to determine the concentration of ferritin in both HBS-EP buffer and serum. The monoclonal antibody was immobilized on the carboxymethyl dextran-modified gold surface by an amine coupling method. The interaction of antibody with antigen was monitored in real-time. The signal was enhanced by sandwich amplification strategy to improve the sensitivity and specificity of the immunoassay, especially in serum. The linear range of the assay in serum is over 30-200 ng ml⁻¹ with the detection limit of 28 ng ml⁻¹. The sensitivity, specificity, and reproducibility of the assay are satisfactory. The analyte and enhancement antibody-binding surface could be regenerated by pH 2.0 glycine-HCl buffer and the same antibody-immobilized surface could be used for more than 50 cycles of ferritin binding and regeneration.     

An optical immunosensor based on surface plasmon resonance for determination of bFGF

An optical immunosensor based on surface plasmon resonance (SPR) has been developed for immunosensing. The sensor is designed on the basis of fixing incident angle of light and measuring the reflected intensities in the wavelength range of 400-800 nm simultaneously. The SPR spectrum was shown in terms of reflected light intensities versus wavelengths of incident light. The intensity of the reflected light reaches the minimum at the resonant wavelength. Molecular self-assembling in solution is used to form the sensing membrane on gold substrate. The kinetic processes of sensing monolayer formation were studied. The basic fibroblast growth factor, a kind of basic polypeptide, was determined in the concentration range of 0.24-9.6 μg/ml. Under optimum experimental conditions, the sensor has a good repeatability, reversibility and selectivity.     

Measurement of antibody binding to protein immobilized on gold nanoparticles by localized surface plasmon spectroscopy

Antibody binding to bovine serum albumin (BSA) and human serum albumin (HSA) immobilized onto gold nanoparticles was studied by means of localized surface plasmon resonance (LSPR) spectroscopy. Amine-modified glass was prepared by self-assembly of amine-terminated silane on substrate, and gold (Au) nanoparticles were deposited on the amine-modified glass substrate. Au nanoparticles deposited on the glass surface were functionalized by BSA and HSA. BSA immobilization was confirmed by LSPR spectroscopy in conjunction with surface-enhanced Raman scattering spectroscopy. Then, LSPR response attributable to the binding of anti-BSA and anti-HSA to BSA- and HSA-functionalized Au nanoparticles, respectively, was examined. Anti-HSA at levels larger than ∼10 nM could be detected by HSA-immobilized chips with LSPR optical response, which was saturated at concentrations greater than ∼650 nM of anti-HSA. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible to authorized users.     

A self-assembled fusion protein-based surface plasmon resonance biosensor for rapid diagnosis of severe acute respiratory syndrome

A surface plasmon resonance (SPR)-based biosensor was developed for simple diagnosis of severe acute respiratory syndrome (SARS) using a protein created by genetically fusing gold binding polypeptides (GBPs) to a SARS coronaviral surface antigen (SCVme). The GBP domain of the fusion protein serves as an anchoring component onto the gold surface, exploiting the gold binding affinity of the domain, whereas the SCVme domain is a recognition element for anti-SCVme antibody, the target analyte in this study. SPR analysis indicated the fusion protein simply and strongly self-immobilized onto the gold surface, through GBP, without surface chemical modification, offering a stable and specific sensing platform for anti-SCVme detection. AFM and SPR imaging analyses demonstrated that anti-SCVme specifically bound to the fusion protein immobilized onto the gold-micropatterned chip, implying that appropriate orientation of bound fusion protein by GBP resulted in optimal exposure of the SCVme domain to the assay solution, resulting in efficient capture of anti-SCVme antibody. The best packing density of the fusion protein onto the SPR chip was achieved at the concentration of 10 μg mL⁻¹; this density showed the highest detection response (906 RU) for anti-SCVme. The fusion protein-coated SPR chip at the best packing density had a lower limit of detection of 200 ng mL⁻¹ anti-SCVme within 10 min and also allowed selective detection of anti-SCVme with significantly low responses for non-specific mouse IgG at all tested concentrations. The fusion protein provides a simple and effective method for construction of SPR sensing platforms permitting sensitive and selective detection of anti-SCVme antibody.     

Rapid detection of nivalenol and deoxynivalenol in wheat using surface plasmon resonance immunoassay

A surface plasmon resonance (SPR) immunoassay using a monoclonal antibody was developed to measure nivalenol (NIV) and deoxynivalenol (DON) contamination in wheat. A highly sensitive and stable DON-immobilized sensor chip was prepared, and an SPR detection procedure was developed. The competitive inhibition assay used a monoclonal antibody that cross-reacts with NIV and DON. The half maximal inhibitory concentration (IC₅₀) values of the SPR assay were 28.8 and 14.9 ng mL⁻¹ for NIV and DON, respectively. The combined responses of NIV and DON in wheat were obtained using a simultaneous detection assay in a one-step cleanup procedure. NIV and DON were separated using a commercial DON-specific immunoaffinity column (IAC) and their responses were obtained using an independent detection assay. Spiked tests using these toxins revealed that recoveries were in the range 91.5-107% with good relative standard deviations (RSDs) (0.40-4.1%) and that detection limits were 0.1 and 0.05 mg kg⁻¹ for NIV and DON, respectively. The independent detection using IAC showed detection limits of 0.2 and 0.1 mg kg⁻¹ for NIV and DON, respectively. SPR analysis results were correlated with those obtained using a conventional LC/MS/MS method for wheat co-contaminated with NIV and DON. These results suggested that the developed SPR assay is a practical method to rapidly screen the NIV and DON co-contamination of wheat and one of a very few immunoassays to detect NIV directly.