Research On Coupled Plasmon-waveguide Resonance Sensing Method

During the past few years, with the advantages of labeling free and high sensitivity,Surface Plasmon Resonance (SPR) technique has exhibited significant applicationpotential in the field of bio-chemical analysis, clinical diagnosis and food safety.Meanwhile, real-time analysis of bio-interaction process could also be performed onSPR bio-sensors. However, the fast developed biotechnology has put demandingrequirements on modern analysis methods. As conventional SPR sensors exhibitintrinsic limitations in resolution, detection range and throughput, considerableefforts have been devoted to enhance the performance of SPR intrinsically.Among which, Coupled Plasmon-Waveguide Resonance (CPWR) has attractedmore attention as it provides much narrower full width half-maximum of thereflective curves, longer penetration depth and enhanced surfaceelectromagnetic field.In this paper, based on the theoretical research on CPWR curves and theirelectromagnetic field distributions, we firstly propose an optimized symmetricaloptical waveguide structure (MgF2-Au-MgF2) to afford CPWR. Sensingcharacteristics of this symmetrical optical waveguide structure are thenexamined on a two-dimensional CPWR sensor. Experimental results show thatthe MgF2-Au-MgF2structure exhibits higher refractive index resolution(5.22×107refractive index unit) than conventional SPR sensors.Besides its high performance on sensing, CPWR also shows enhancedsurface electromagnetic field which enables the background excitation offluorophore existed in the electric field range more effectively with highersignal-to-noise ratio. Surface fluorescence excitation abilities of theMgF2-Au-MgF2structure are examined in this paper. We also extend ourresearch by finding the optimized parameters of the waveguide structure that aresuitable for simultaneous detection of CPWR sensing and fluorescence analysiswith an excitation wavelength of473nm which has never been reported before.This approach breaks through the limitations on wavelength required byconventional SPR. As more fluorescence indicators exhibit higher quantum efficiency in short wavelengths, fluorophores excited by CPWR under shortwavelength is believed to improve the sensitivity of the fluorescence detection,hence, leading to an improved resolution of CPWR sensing. Combinationsbetween the CPWR sensing and fluorescence technology will make the analysisprocedure more efficient and accurate, it is believed to provide a promisingplatform for the comprehensive understanding of biological interactions.To meet the demands on practical applications, we refer to an effectivemethod to modify the waveguide surface by depositing a film of dopamine as anadhesive layer. Saccharides and platelet derived growth factor existed inaqueous humor are then analyzed to demonstrate the practical applicationpotential of label-free and real-time detection of the SPR waveguide structure.