Absorption and related optical dispersion effects on the spectral response of a surface plasmon resonance sensor.

Surface plasmon resonance (SPR) sensing is an optical technique that allows real time detection of small changes in the physical properties, in particular in the refractive index, of a dielectric medium near a metal film surface. One way to increase the SPR signal shift is then to incorporate a substance possessing a strong dispersive refractive index in the range of the plasmon resonance band. In this paper, we investigate the impact of materials possessing a strong dispersive index integrated to the dielectric medium on the SPR reflectivity profile. We present theoretical results based on chromophore absorption spectra and on their associated refractive index obtained from the Lorentz approach and Kramers-Krönig equations. As predicted by the theory, the experimental results show an enhancement of the SPR response, maximized when the chromophore absorption band coincides with the plasmon resonant wavelength. This shows that chromophores labeling can provide a potential way for SPR response enhancement.

Generalization of the Rouard method to an absorbing thin-film stack and application to surface plasmon resonance.

In the context of surface plasmon resonance (SPR) kinetic biochips, it is important to model the SPR phenomenon (i.e., extinction of reflectivity) toward biochip design and optimization. The Rouard approach that models reflectivity off a thin-film stack is shown to be extendable to any number of absorbing layers with no added complexity. Using the generalized Rouard method, the effect of SPR is simulated as a function of the wavelength for various metal thicknesses. Given an optimal metal thickness, the dependence of SPR on the angle of incidence and wavelength is also demonstrated. Such a model constitutes a potential basis for the efficient design and optimization of multidimensional sensors.

Surface plasmon resonance imaging as a multidimensional surface characterization instrument--application to biochip genotyping.

Surface plasmon resonance imaging (SPRI) sensors allow the characterization of a metal/dielectric interface. Providing proper biochemical functionalization and spatial structuration of the functionalized surface, an optical biochip system--label free and real time--can be achieved. We study the impact of the different physical parameters on the quality of the measurements. Such a SPRI system has a great sensitivity to small variations of the physical parameters (layer optical index, thickness, etc.) occurring at the sensor surface. Precision and reliability of the measurements are provided by a multidimensional approach (4D i.e. spatial coordinates x-y, time t, angle of incidence theta) allowing multiple self-calibration procedures. Such apparatus has already been successfully applied in genomics and proteomics, studying DNA:DNA and oligosaccharide:protein interactions. In this article, we illustrate the advantages of the SPRI setup applied to the detection of gene mutations, using as a model the genetic disease Cystic Fibrosis. The results demonstrate that the system is able to monitor and analyse the interaction under investigation, allowing the diagnosis of genetic single nucleotide polymorphisms by exploiting only a part of the multidimensional potential (x, y, t, theta).