Enhanced vibrational spectroscopy, intracellular refractive indexing for label-free biosensing and bioimaging by multiband plasmonic-antenna array.

In this study, we report a multiband plasmonic-antenna array that bridges optical biosensing and intracellular bioimaging without requiring a labeling process or coupler. First, a compact plasmonic-antenna array is designed exhibiting a bandwidth of several octaves for use in both multi-band plasmonic resonance-enhanced vibrational spectroscopy and refractive index probing. Second, a single-element plasmonic antenna can be used as a multifunctional sensing pixel that enables mapping the distribution of targets in thin films and biological specimens by enhancing the signals of vibrational signatures and sensing the refractive index contrast. Finally, using the fabricated plasmonic-antenna array yielded reliable intracellular observation was demonstrated from the vibrational signatures and intracellular refractive index contrast requiring neither labeling nor a coupler. These unique features enable the plasmonic-antenna array to function in a label-free manner, facilitating bio-sensing and imaging development.

Ag/Au bi-metallic film based color surface plasmon resonance biosensor with enhanced sensitivity, color contrast and great linearity.

In wavelength surface plasmon resonance (SPR) biosensor, the manipulation of SPR dispersion relation by Ag/Au bi-metallic film was first time implemented. Due to the enhanced resonant wavelength shift and the sharper SPR slope of using Ag/Au bi-metallic film, the illuminated color of reflection shows one order of magnitude greater contrast than conventional SPR biosensors. Such an Ag/Au bi-metallic film based color SPR biosensor (CSPRB) allows the detail bio-interactions, for example 100 nM streptavidin, to be distinguished by directly observing the color change of reflection through naked eyes rather than the analysis of spectrometer. In addition to the enhanced sensitivity and color contrast, this CSPRB also possesses a great linear detection range up to 0.0254 RIU, which leading to the application of point-of-care tests.

Fiber optic biosensor for the detection of C-reactive protein and the study of protein binding kinetics.

Application of a fiber optic biosensor (FOB) to the real-time investigation of the interaction kinetics between FITC-conjugated monoclonal sheep anti-human C-reactive protein (CRP) antibody and CRP isoforms on the surface of optical fiber is described. Recently, both the native pentameric CRP (pCRP), an acute phase protein belonging to pentraxin family, and an isoform of pCRP, modified CRP (mCRP), have been suggested to have proinflammation effects on vascular cells in acute myocardial infarction (AMI). In current studies, we generate mCRP from pCRP, and use several methods including fluorescence spectral properties, circular dichroism, analytical ultracentrifuge, and Western blotting to demonstrate their differences in physical and chemical properties as well as the purity of pCRP and mCRP. In addition, we design and implement an FOB to study the real-time qualitative and quantitative biomolecular recognition of CRP isoforms. Specifically, the association and dissociation rate constants of the reaction between FITC-conjugated monoclonal sheep anti-human CRP antibody and the pCRP and mCRP are determined. The feasibility of our current approach to measure the association and dissociation rate constants of the reaction between tested CRP isoforms was successfully demonstrated.

Localized surface plasmon coupled fluorescence fiber-optic biosensor with gold nanoparticles.

A novel fiber-optic biosensor based on a localized surface plasmon coupled fluorescence (LSPCF) system is proposed and developed. This biosensor consists of a biomolecular complex in a sandwich format of . It is immobilized on the surface of an optical fiber where a complex forms the fluorescence probe and is produced by mixing Cy5-labeled antibody and protein A conjugated gold nanoparticles (Au-PA). The LSPCF is excited by localized surface plasmon on the GNP surface where the evanescent field is applied near the core surface of the optical fiber. At the same time, the fluorescence signal is detected by a photomultiplier tube located beside the unclad optical fiber with high collection efficiency. Experimentally, this novel LSPCF biosensor is able to detect mouse immunoglobulin G (IgG) at a minimum concentration of 1 pg/mL (7 fM) during the biomolecular interaction of the IgG with anti-mouse IgG. The analysis is expanded by a discussion of the amplification of the LSPCF intensity by GNP coupling, and overall, this LSPCF biosensor is confirmed experimentally as a biosensor with very high sensitivity.

Characteristics of a paired surface plasma waves biosensor.

A novel paired surface plasma wave biosensor (PSPWB) is described and setup. By integrating the features of a common-path optical heterodyne interferometer and the amplitude-ratio detection mode, the PSPWB not only produces a high detection sensitivity but also provides a large dynamic measurement range for effective refractive index (Deltan(eff)) based on amplitude-sensitive detection method. Thus, the performance of PSPWB becomes equivalent to shot-noise limited of a conventional SPR biosensor. To our knowledge, this novel PSPWB shows the highest detection sensitivity on (Deltan(eff)) when compared with conventional SPR biosensors using either a non-interferometric or interferometric technique. The experimental results correctly verify the properties of a PSPWB that the detection sensitivity is an order of 10(-7) refractive index unit (RIU) when measuring a 0.001% sucrose-water solution. This result confirms the detection sensitivity up to 10(-9) RIU of the IgG/anti-IgG interaction in real time successfully. Furthermore, a dynamic range of 10(5) using PSPWB was also obtained.

Optical heterodyne surface-plasmon resonance biosensor.

A novel optical heterodyne surface-plasmon resonance (SPR) biosensor with a Zeeman laser is proposed. Two surface plasma waves are excited by two correlated p-polarized waves in a SPR device of the Kretschmann configuration. Two reflected p waves are optically heterodyned such that the magnitude of the heterodyned signal is proportional to the multiplication of two attenuated reflected p waves. Then the detection sensitivity and the dynamic range based on this amplitude-sensitive method are enhanced. In the experiment, the kinetics between mouse immunoglobulin G (IgG) and rabbit antimouse IgG is obtained from sensograms of various concentrations of antimouse IgG. A detection sensitivity of 0.2 nM was achieved. In addition, a concentration of 5 ng/ml of protein G interacting with mouse IgG was measured successfully.

Application of phase-to-amplitude conversion technique to linear birefringence measurements.

A novel technique that measures the linear birefringence of crystal quartz within the configuration of a Soliel-Babinet compensator (SBC) is proposed. A characteristic of this technique is that phase retardation introduced by quartz is amplitude modulation (AM) instead of phase modulation (PM). The linear birefringence is measured regardless of the azimuth angle of the SBC and the orientation of the linear polarization laser beam. Compared with the single-wedge method, the SBC is similar to a parallel plate that allows for a wider range of refracttive index of the test material to be measured. This proposed method uses a conventional amplitude demodulation method in conjunction with an optical heterodyne technique and a bandpass filter to produce a better signal-to-noise ratio. Although the SBC configuration is more complex than a single element, the independence of azimuth angle and the orientation of the linear polarized laser beam can enhance the sensitivity of the linear birefringence measurement.