Enhancing extraction of light from metal composite structures for plasmonic emitters using light-coupling effect.

This work demonstrates the efficiency and directionality of a method of extracting light from thin-film emissive devices by near-field evanescent waves in plasmonic emitters used in metal composite grating structures. A near-field evanescent wave can induce a surface plasmon wave on the surface of a metal under resonant conditions. Enhancing the near-field evanescent wave generates strong far-field nonlinear optical effects. This effect is highly efficient in some plasmonic emitter structures. Theoretical and experimental results demonstrate that such a metal composite grating structure exhibits good performance, a high coupling ratio, a small coupling angle, enhanced light extraction and a small FWHM. It also improves luminous efficiency, emitter angle, and directivity.

Real-time and stepwise deoxidization processes to tune the photoluminescence properties of graphene oxide using EC-SPR spectroscopy.

The development of a stepwise deoxidized process and real-time monitoring of the large-scale mass production of electrochemically reduced graphene oxide (ErGO) sheets are important issues. In this study, we have shown that graphene oxide (GO) sheets can be quantitatively monitored in real-time and controlled in a stepwise manner using electrochemical-surface plasmon resonance (EC-SPR), due to the fact that the oxygen functional groups can be tuned through a deoxidization procedure. The SPR signal can then be detected quantitatively in real-time by changes in the dielectric constant of the GO film during the EC stepwise removal of oxygen functional groups. This is because the refractive index of the GO sheets is affected by the oxygen-containing groups, so that monitoring the SPR angle shift provides a real-time measure of changes in the concentration of the residual oxygen functional groups of the GO sheets. In this study, we demonstrated GO and 100 CV cycles of ErGO at X-ray photoelectron spectroscopy carbon-to-oxygen ratios of 4.1 and 31.57 respectively, and Raman spectra of the D/G intensity ratio of 0.85 and 1.89, respectively. The 100 CV cycles of ErGO at SPR angle shifts were -227.13 mdeg for GO at a concentration of 0.275 mg ml-1, and -263.47 mdeg for GO at a concentration of 1 mg ml-1. The photoluminescence emission bands of the GO and the CV 100 cycles of ErGO were 615 to 470 nm. These results may be beneficial for future studies on GO fluorescence characteristics in the field of optoelectronic and biosensor applications.

Enhanced Plasmonic Biosensors of Hybrid Gold Nanoparticle-Graphene Oxide-Based Label-Free Immunoassay.

In this study, we propose a modified gold nanoparticle-graphene oxide sheet (AuNP-GO) nanocomposite to detect two different interactions between proteins and hybrid nanocomposites for use in biomedical applications. GO sheets have high bioaffinity, which facilitates the attachment of biomolecules to carboxyl groups and has led to its use in the development of sensing mechanisms. When GO sheets are decorated with AuNPs, they introduce localized surface plasmon resonance (LSPR) in the resonance energy transfer of spectral changes. Our results suggest a promising future for AuNP-GO-based label-free immunoassays to detect disease biomarkers and rapidly diagnose infectious diseases. The results showed the detection of antiBSA in 10 ng/ml of hCG non-specific interfering protein with dynamic responses ranging from 1.45 nM to 145 fM, and a LOD of 145 fM. Considering the wide range of potential applications of GO sheets as a host material for a variety of nanoparticles, the approach developed here may be beneficial for the future integration of nanoparticles with GO nanosheets for blood sensing. The excellent anti-interference characteristics allow for the use of the biosensor in clinical analysis and point-of-care testing (POCT) diagnostics of rapid immunoassay products, and it may also be a potential tool for the measurement of biomarkers in human serum.

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.