Nan Fu Chiu

High-sensitivity detection of carbohydrate antigen 15-3 using a gold/zinc oxide thin film surface plasmon resonance-based biosensor

We report that gold/zinc oxide (Au/ZnO) nanocomposite films were effectively employed to enhance the performance of surface plasmon resonance (SPR) for the detection of tumor markers. Carbohydrate antigen 15.3 (CA15-3), a tumor marker for breast cancer, was chosen as a model analyte. We analyzed intensity response to the samples at various concentrations (0.0125 U/mL to 160 U/mL) in pleural fluid to evaluate the detection capability of the SPR biosensor based on Au/ZnO thin films. The linear range extended from 1 to 40 U/mL with a correlation coefficient of R(2) = 0.991 and a limit of detection reaching 0.025 U/mL at a signal-to-noise ratio of 3:1. Compared with the degree of the shift in SPR intensity induced by the specific binding event between antibody and antigen, the change of intensity on the Au/ZnO layers was increased by at least 2 fold over that on the gold/chromium (Au/Cr) layers. In addition, we determined that the Au/ZnO layers allowed for a detection limit 4 times lower than the Au/Cr layers, which are in widespread use as the sensing interfaces in current SPR-based detectors. In conclusion, the use of Au/ZnO films greatly enhanced the SPR signal yield for this bimolecular interaction and showed high sensitivity.

Enhanced luminescence of organic/metal nanostructure for grating coupler active long-range surface plasmonic device

This letter is intended to demonstrate the effect of coupled active long-range surface plasmon polaritons (SPPs) on the plasmonics response of a lamellar grating nanostructure with organic material on the surface. The phenomenon of nano-optics gives rise to a selective spectral response and a local field enhancement. The authors’ fabricated device consists of coupled organic/metal nanostructure with specific width and symmetric dielectric structure. The interaction between organic/metal interface SPPs can allow specific directional emission rather than isotropic emission. The authors present recent experimental results and discuss potential applications of such an active plasmonic biosensor with enhanced resonance energy emission due to interactions on the organic/metal nanograting.

Enhancement and tunability of active plasmonic by multilayer grating coupled emission

The effect of coupled mode surface plasmon polaritons (SPPs) on the active emission of a nanostructure grating with organic semiconductor material, Alq(3), on the surface was investigated in this study. We report surface plasmon grating coupled emission (SPGCE) from excited organic layer on metal grating in both organic/metal (2-Layer) and organic/metal/organic/metal (4-Layer) structures. The dispersion relation was obtained from angle-resolved photoluminescence measurement. The resultant emission intensity can have up to 6 times enhancement on the 4- Layer device and the Full-Width Half-Maximum (FWHM) is less than 50 nm. The combination of SPPs on organic/metal interface allows specific directional emission and color appearance of Alq(3) fluorophores. Potential applications of such an active plasmonics with enhanced resonant energy emission due to interactions on the organic/metal nano-grating as biosensor were presented and discussed.

Carboxyl-functionalized graphene oxide composites as SPR biosensors with enhanced sensitivity for immunoaffinity detection

This work demonstrates the excellent potential of carboxyl-functionalized graphene oxide (GO-COOH) composites to form biocompatible surfaces on sensing films for use in surface plasmon resonance (SPR)-based immunoaffinity biosensors. Carboxyl-functionalization of graphene carbon can modulate its visible spectrum, and can therefore be used to improve and control the plasmonic coupling mechanism. The binding properties of the molecules between a sensing film and a protein were elucidated at various flow rates of those molecules. The bio-specific binding interaction among the molecules was investigated by performing an antigen and antibody affinity immunoassay. The results thus obtained revealed that the overall affinity binding value, KA, of the Au/GO-COOH chip can be significantly enhanced by up to ∼5.15 times that of the Au/GO chip. With respect to the shifts of the SPR angles of the chips, the affinity immunoassay interaction at a BSA concentration of 1μg/ml for an Au/GO-COOH chip, an Au/GO chip and a traditional SPR chip are 35.5m°, 9.128m° and 8.816m°, respectively. The enhancement of the antigen-antibody interaction of the Au/GO-COOH chip cause this chip to become four times as sensitive to the SPR angle shift and to have the lowest antibody detection limit of 0.01pg/ml. These results indicate the potential of the chip in detecting specific proteins, and the development of real-time in vivo blood analysis and diagnosis based on cancer tumor markers.

Directional photoluminescence enhancement of organic emitters via surface plasmon coupling

In this paper, we had quantitatively investigated the photoluminescence of organic emitter on a Si substrate with periodically corrugated metal thin film experimentally and theoretically. Due to the plasmonic coupling by the metal gratings, 4.3 times and 1.7 times enhancements in optical intensities were observed at specified and full viewing angles at certain wavelengths, respectively. Good agreement of angular-frequency versus in-plane wavevector (ω-k) curves between experiments and calculations were obtained when varying organic materials, metal materials, and grating pitches. Two different metal materials were used, which show slight shift in ω-k curves due to the high sensitivity of the surface plasmon to the relative permittivity.

Enhanced Sensitivity of Anti-Symmetrically Structured Surface Plasmon Resonance Sensors with Zinc Oxide Intermediate Layers

We report a novel design wherein high-refractive-index zinc oxide (ZnO) intermediary layers are used in anti-symmetrically structured surface plasmon resonance (SPR) devices to enhance signal quality and improve the full width at half maximum (FWHM) of the SPR reflectivity curve. The surface plasmon (SP) modes of the ZnO intermediary layer were excited by irradiating both sides of the Au film, thus inducing a high electric field at the Au/ZnO interface. We demonstrated that an improvement in the ZnO (002) crystal orientation led to a decrease in the FWHM of the SPR reflectivity curves. We optimized the design of ZnO thin films using different parameters and performed analytical comparisons of the ZnO with conventional chromium (Cr) and indium tin oxide (ITO) intermediary layers. The present study is based on application of the Fresnel equation, which provides an explanation and verification for the observed narrow SPR reflectivity curve and optical transmittance spectra exhibited by (ZnO/Au), (Cr/Au), and (ITO/Au) devices. On exposure to ethanol, the anti-symmetrically structured showed a huge electric field at the Au/ZnO interface and a 2-fold decrease in the FWHM value and a 1.3-fold larger shift in angle interrogation and a 4.5-fold high-sensitivity shift in intensity interrogation. The anti-symmetrically structured of ZnO intermediate layers exhibited a wider linearity range and much higher sensitivity. It also exhibited a good linear relationship between the incident angle and ethanol concentration in the tested range. Thus, we demonstrated a novel and simple method for fabricating high-sensitivity, high-resolution SPR biosensors that provide high accuracy and precision over relevant ranges of analyte measurement.

Graphene Oxide Based Surface Plasmon Resonance Biosensors

Graphene oxide (GO), an amorphous insulatormaterial, has consists of a hexagonal ring based carbon network having both sp2-hybridized carbon atoms and sp3-hybridizedcarbons bearing hydroxyl andepoxide functional groups on either side of the sheet, whereas the sheet edges are mostly decorated by carboxyl and carbonyl groups [1-6]. These unique properties hold great promise for potential applications in many technological aspects such as nanoelectronics [7-10], nanophotonics [11-16], and bio-sensors [9, 17-21], and nanocomposites [22, 23].

Ultra-high sensitivity of the non-immunological affinity of graphene oxide-peptide-based surface plasmon resonance biosensors to detect human chorionic gonadotropin

Specific peptide aptamers can be used in place of expensive antibody proteins, and they are gaining increasing importance as sensing probes due to their potential in the development of non-immunological assays with high sensitivity, affinity and specificity for human chorionic gonadotropin (hCG) protein. We combined graphene oxide (GO) sheets with a specific peptide aptamer to create a novel, simple and label-free tool to detect abnormalities at an early stage of pregnancy, a GO-peptide-based surface plasmon resonance (SPR) biosensor. This is the first binding interface experiment to successfully demonstrate binding specificity in kinetic analysis biomechanics in peptide aptamers and GO sheets. In addition to the improved affinity offered by the high compatibility with the target hCG protein, the major advantage of GO-peptide-based SPR sensors was their reduced nonspecific adsorption and enhanced sensitivity. The calculation of total electric field intensity (ΔE) in the GO-based sensing interfaces was significantly enhanced by up to 1.2 times that of a conventional SPR chip. The GO-peptide-based chip (1mM) had a high affinity (KA) of 6.37×1012M-1, limit of detection of 0.065nM and ultra-high sensitivity of 16 times that of a conventional SPR chip. The sensitivity of the slope ratio of the low concentration hCG protein assay in linear regression analysis was GO-peptide (1mM): GO-peptide (0.1mM): conventional chip (8-mercaptooctanoic acid)-peptide (0.1mM)=8.6: 3.3: 1. In summary, the excellent binding affinity, low detection limit, high sensitivity, good stability and specificity suggest the potential of this GO-peptide-based SPR chip detection method in clinical application. The development of real-time whole blood analytic and diagnostic tools to detect abnormalities at an early stage of pregnancy is a promising technique for future clinical application.

Constructing a Novel Asymmetric Dielectric Structure Toward the Realization of High-Performance Surface Plasmon Resonance Biosensors

This paper is intended to demonstrate the effect of the high refractive index of an intermediary zinc oxide (ZnO) layer to improving the full width at half maximum (FWHM) of the surface plasmon resonance (SPR) reflectance curve. This case is an asymmetric dielectric structure (ADS) of low-loss surface plasmon resonance (LLSPR). The ADS-LLSPR chip is particularly interesting for two surface plasmons (SPs) mode of external and internal on a gold (Au) interface. These SPs have different energy fields, which enables separation of the surface and bulk refractive index changes. We optimize ZnO and Au thin films thicknesses through analytical comparisons with conventional SPR structures. Upon exposure to ethanol, the ADS-LLSPR chip showed a 2-times decrease in the FWHM and a 4.5-times larger shift in intensity interrogation. The ADS-LLSPR chip exhibits a widely linearity range, high accuracy and high sensitivity. This characteristic of the ADS-LLSPR chip is the basis for early diagnosis crucial in DNA-based viruses.

Surface plasmon resonance biochip based on ZnO thin film for nitric oxide sensing

In this study, the design of a novel optical sensor that comprises surface plasmon resonance sensing chip and zinc oxide nano-film was proposed for the detection of nitric oxide gas. The electrical and optical properties of zinc oxide film vary in the presence of nitric oxide. This effect was utilized to prepare biochemical sensors with transduction based on surface plasmon resonance. Due to the refractive index of the transparent zinc oxide film that was deposited on the gold film, however, changes will be observed in the surface plasmon resonance spectra. For this reason, the thickness of zinc oxide film will be investigated and determined in this study. The interaction of nitric oxide with a 20 nm zinc oxide layer on gold leads to the shift of the resonance angle. The analysis on the reflectance intensity of light demonstrates that such effect is caused by the variation of conductivity and permittivity of zinc oxide film. Finally, a shift in surface plasmon resonance angle was measured in 25 ppm nitric oxide at 180C and a calibration curve of nitride oxide concentration versus response intensity was successfully obtained in the range of 250 to 1000 ppm nitric oxide at lower temperature of 150C. Moreover, these effects are quasi-reversible.In this study, the design of a novel optical sensor that comprises surface plasmon resonance sensing chip and zinc oxide nano-film was proposed for the detection of nitric oxide gas. The electrical and optical properties of zinc oxide film vary in the presence of nitric oxide. This effect was utilized to prepare biochemical sensors with transduction based on surface plasmon resonance. Due to the refractive index of the transparent zinc oxide film that was deposited on the gold film, however, changes will be observed in the surface plasmon resonance spectra. For this reason, the thickness of zinc oxide film will be investigated and determined in this study. The interaction of nitric oxide with a 20 nm zinc oxide layer on gold leads to the shift of the resonance angle. The analysis on the reflectance intensity of light demonstrates that such effect is caused by the variation of conductivity and permittivity of zinc oxide film. Finally, a shift in surface plasmon resonance angle was measured in 25 ppm nitric oxide at 180C and a calibration curve of nitride oxide concentration versus response intensity was successfully obtained in the range of 250 to 1000 ppm nitric oxide at lower temperature of 150C. Moreover, these effects are quasi-reversible.