Zhiyou Wang

Stable and Sensitive Silver Surface Plasmon Resonance Imaging Sensor Using Trilayered Metallic Structures

The silver surface plasmon resonance (SPR) sensor has long been explored due to its intrinsic sensitivity enhancement over the conventional single-layered gold SPR sensor. However, the silver SPR sensor has not been exploited for practical applications because of pronounced instability problems. We propose a novel gold-silver-gold trilayered SPR sensor chip, in which an extra buffer layer of gold is added between the silver and substrate adhesion layer (i.e., chromium) compared to the previously reported silver-gold bilayered SPR sensors. Subjected to prolonged agitation in phosphate-buffered saline (PBS) solution, the new chip exhibited high integrity according to both optical and atomic force microscopy (AFM) analysis. Having undergone repeated cycles of calibration, binding, and regeneration in various chemical solutions, 25 regions of interest (ROIs) over a 14 mm ×14 mm area were chosen and monitored by large detection area SPR microscopy; the new sensor chip exhibited stability comparable to the single gold layered SPR chip. In terms of sensing performances, over 50% increases in sensitivity and signal-to-noise ratio (S/N) than those of the single gold layered SPR chip were determined by SPR microscopy at 660 nm. Protein arrays of protein A and bovine serum albumin (BSA) on both the new chip and single-layered gold SPR chip were fabricated and underwent biomolecular interactions with human IgG, for the purpose of consistency, comparison on kinetics parameters, values from the microarray trilayered chip showed reasonable consistency with those from the single gold layered SPR chip. This study suggests that the new chip is a viable alternative to the conventional single gold layered SPR chip with improved sensing performances.

Competition between band gap and yellow luminescence in undoped GaN grown by MOVPE on sapphire substrate

Undoped GaN epilayer on c-face (0 0 0 1) sapphire substrate has been grown by metalorganic vapor-phase epitaxy (MOVPE) in a horizontal-type low-pressure two-channel reactor. Photoluminescence (PL) as a function of temperature and excitation intensity have been systematically studied, and the competition between near band gap ultraviolet (UV) and defect-related yellow luminescence (YL) has been extensively investigated, It is revealed that the ratio of the UV-to-YL peak intensities depends strongly on the excitation intensity and the measurement temperature. The obtained results have been analyzed in comparison with the theoretical predications based on a bimolecular model

Plain silver surface plasmon resonance for microarray application.

The application scope of surface plasmon resonance (SPR) and SPR imaging (SPRi) is rapidly growing, and tools such as high-performance and low-cost slides could enable more rapid growth of the field. We describe herein a novel silver slide, addressing the inherent instability of plain silver structure by improving adhesion between the glass substrate and the silver layer with a thin buffer layer of gold. Covered by a self-assembled monolayer (SAM) only, SPR characteristics of the slide remain steady for more than 3 months under regular storage. In a bioassay, the slide substantiates the predicted nearly 100% sensitivity improvement over gold slides and exhibits exceptional performance stability as determined by sensitivity and resolution measurements during the extended 40,000 s multicycle experiment. We demonstrate the suitability of this new slide for large-area SPRi, describing analysis results from a 1u202f296-ligand protein microarray. We predict this slide structure will provide a stable, high-sensitivity solution for high-throughput SPRi applications and other surface analysis platforms.

Fabrication and characterization of metal–semiconductor–metal (MSM) ultraviolet photodetectors on undoped GaN/sapphire grown by MBE

Interdigital metal-semiconductor-metal (MSM) ultraviolet photoconductive detectors have been fabricated on undoped GaN films grown by molecular beam epitaxy (MBE), Response dependence on wavelength, applied current, excitation powers and chopper frequency has been extensively investigated. It is shown that the photodetectors spectral response remained nearly constant for wavelengths above the band gap and dropped sharply by almost three orders of magnitude for wavelengths longer than the band gap. It increases linearly with the applied constant current, but very nonlinearly with illuminating power. The photodetectors showed high photoconductor gains resulting from trapping of minority carriers (holes) at acceptor impurities or defects. The results demonstrated the high quality of the GaN crystal used to fabricate these devices

SPRi determination of inter-peptide interaction by using 3D supramolecular co-assembly polyrotaxane film.

Accurate measurement of inter-peptide interactions is beneficial for in-depth understanding disease-related protein folding and peptide aggregation, and further for designing and selecting potential peptide drugs to the target antigen. Herein, we demonstrate a 3D polyrotaxane (PRX) surface for detecting peptides interactions by surface plasmon resonance imaging (SPRi). This surface is supramolecular self-assembly monolayer (SAM) structure fabricated by threading α-cyclodextrans (α-CD) through a linear polyethylene glycol (PEG) chain fixed on gold chip surface to form pseudopolyrotaxane, and further capping the pseudopolyrotaxane with bulky terminated group to form PRX film. The hydroxyl groups of α-CD can provide more active sites to increase molecules immobilization density, and PEG chain has unique protein non-fouling feature. We chose Alzheimers disease marker β-amyloid 40 (Aβ40) as model peptide, and detected the interaction between it and its inhibitors KLVFFK6 by SPRi. As a striking result, the specific adsorption of KLVFFK6 solution at the concentration of 352μM on Aβ40-PRX was 700RU, whereas PEG SAM surface gave no significant binding. Interaction between other lower molecular weight peptides was detected via PRX surface, and the relatively weak interactions (KD=1.73×10(-4)M) between LPFFD (Mw=0.6kDa) and amylin20-29 (Mw=1.0kDa) are successfully detected.

Hybrid differential interrogation method for sensitive surface plasmon resonance measurement enabled by electro-optically tunable SPR sensors.

A novel detection method enabled by electro-optically tunable waveguide-coupled surface plasmon resonance sensors is demonstrated. Both the WCSPR response of sensor and the interrogation light are varied simultaneously in this hybrid scheme. Modulation and demodulation of the sensors response are achieved by applying a high-frequency AC electrical signal and electrically filtering the detected signal. Scanning the incident angle at a lower speed yields an angular dependent response. Theoretical analyses and experimental results show that the angular-dependent signal is closely related to the derivative of the SPR reflectivity with a sharp, linear jump near the minimum of the SPR peak. Thus, simple linear-fitting and zero-finding algorithms can be used to locate the SPR angle, and sophisticated data processing algorithms and electronic hardware can be avoided.

Strong temperature dependence of photoluminescence properties in visible InAlAs quantum dots

Strong temperature dependence of optical properties has been studied in visible InAlAs/AlGaAs quantum dots, by employing photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements. The fast redshift of the exciton emission peak was observed at much lower temperature range compared to that observed in the InAs/GaAs QDs. In TRPL we did not observe the constant decay time even at low temperature. Instead, the observed decay time increases quickly with increasing temperature, showing 2D properties in the transient dynamic process. We attributed our results to the strong lateral coupling effect, which results in the formation of the local minibands or extended states from the discrete energy levels

Effects of interdiffusion on the luminescence of InAs/GaAs quantum dots covered by InGaAs overgrowth layer

We have studied the effects of postgrowth rapid thermal annealing on the optical properties of 3-nm-height InAs/GaAs quantum dots covered by 3-nm-thick InxGa1-xAs (x = 0, 0.1, and 0.2) overgrowth layer. At higher annealing temperature (T greater than or equal to 750 degreesC), the photoluminescence peak of InGaAs layer has been observed at lower-energy side of the InAs quantum-dot peak. In addition, the blueshift in photoluminescence (PL) emission energy is found to he similar for all samples with increasing the annealing temperature from 650 to 850 degreesC. However, the trend of narrowing of photoluminescence linewidth is significantly different for InAs quantum dots with different In mole fractions in InGaAs overgrowth layer. These results suggest that the intermixing in the lateral direction plays an important role in helping to understand the modification of optical properties induced by rapid thermal annealing

Kinetic and high-throughput profiling of epigenetic interactions by 3D-carbene chip-based surface plasmon resonance imaging technology

Significance In the era of functional proteomics, a myriad of new interactions, notably those modification-dependent ones, are widely suggested by advanced proteomic approaches and bioinformatic analysis. Therefore, there exists an urgent need to develop a technology for high-throughput mapping and quantitative characterization of biomolecular binding events. This study achieved the immobilization and kinetic detection of various biomacromolecules (including modified peptides and modified nucleic acids) in high throughput through the 3D-carbene chip-based surface plasmon resonance imaging (SPRi) technology. Modified histone peptides and nucleic acids, which are key epigenetic marks, could be efficiently probed by this platform. We envision that the 3D-carbene SPRi technology described here will have wide appeal in profiling and discovering biological recognitions in and beyond epigenetics. Chemical modifications on histones and DNA/RNA constitute a fundamental mechanism for epigenetic regulation. These modifications often function as docking marks to recruit or stabilize cognate “reader” proteins. So far, a platform for quantitative and high-throughput profiling of the epigenetic interactome is urgently needed but still lacking. Here, we report a 3D-carbene chip-based surface plasmon resonance imaging (SPRi) technology for this purpose. The 3D-carbene chip is suitable for immobilizing versatile biomolecules (e.g., peptides, antibody, DNA/RNA) and features low nonspecific binding, random yet function-retaining immobilization, and robustness for reuses. We systematically profiled binding kinetics of 1,000 histone “reader–mark” pairs on a single 3D-carbene chip and validated two recognition events by calorimetric and structural studies. Notably, a discovery on H3K4me3 recognition by the DNA mismatch repair protein MSH6 in Capsella rubella suggests a mechanism of H3K4me3-mediated DNA damage repair in plant.

Sensitive voltage interrogation method using electro-optically tunable SPR sensors

A novel voltage interrogation method using electro-optically tunable waveguide-coupled surface plasmon resonance sensors is demonstrated. Before measurements, we use a bicell photodetector to detect the reflectance from the sensor and take the differential signal from the photodetector as the resonance condition. For different analytes, by scanning the DC voltage on the waveguide layer of the sensor chip, the resonance condition can be maintained the same. Under this condition, we record the values of this voltage, namely the resonant voltage. Theoretical calculations and experimental results show the resonant voltage has a highly linear and sensitive response to analytes refractive index. This method is simple in configuration, and complicated signal processing algorithms can be avoided.