Surface plasmon-coupled emission for applications in biomedical diagnostics
Trnavsky, Michal (2009) Surface plasmon-coupled emission for applications in biomedical diagnostics. PhD thesis, Dublin City University.
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Surface plasmon-coupled emission (SPCE) is a phenomenon whereby the light emitted from a fluorescent molecule can couple into the surface plasmon of an adjacent metal layer
resulting in highly directional emission in the region of the surface plasmon resonance (SPR) angle. As well as the high directionality of emission, SPCE has the added advantage of surface selectivity in that the coupling depends on the distance from the surface. This effect can be exploited in bioassays whereby a fluorescing background from the sample can be suppressed.
This thesis reports, both theoretically and experimentally, the SPCE effect for a fluorophorespacersilver layer system. Both the angular dependence and the dependence of SPCE
emission intensity on fluorophore-metal separation were investigated. It is demonstrated that SPCE leads to lower total fluorescence signal than that obtained in the absence of a metal layer (e.g. when a supercritical angle fluorescence approach is adopted). The experimental results are in good agreement with the theoretical model and with recently published work. Despite the lower overall intensities achievable with SPCE, the advantages
of highly directional emission and surface selectivity make it a useful tool for development of high performance fluorescence-based biosensors.
The SPCE principles were exploited to achieve an enhanced optical bioassay using a novel, disposable parabolic biochip. This biochip is designed to capture the light generated near the interface with high efficiency. The plasmonic structure is integrated into the chip by
depositing a thin metal film on top of the recognition area and by carrying out appropriate surface modification. An optical reader was designed and validated by raytracing simulations and aspects of illumination and polarisation were broadly discussed. The use of various materials was assessed in terms of both their chemical stability and compatibility with the biochip design. The proof-of-concept has been demonstrated by performing a model human
Immunoglobulin G sandwich immunoassay and a limit of detection below 5ng/ml of the analyte was achieved. Real time antibody-antigen binding was also demonstrated.
This works shows the potential of SPCE to become a useful analytical technique which has a high degree of surface sensitivity and the inherent capability to reject background
luminescence. Among the additional advantages are compatibility with the electrochemiluminescence
(ECL) technique and multiwavelength discrimination.
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