Lusheng Song

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.

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.

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.