Carrier, Dominic – MSc.

Accessibility to advanced analysis techniques is often problematic when establishing diagnostics by medical personel. Classical techniques often require considerable infrastructures or needs large and hard-to-obtain instruments.

To solve this problem, the usage of a technological platform composed of the partial integration of a biosensor upon a self-emitting structure is an interesting starting point. This platform address directly the technology accessibility problem by reducing the size and price of the technology. The usage of a structure compatible with microfabrication techniques widely used in microelectronics industry leaves the way to the possibility of upscaling production easily and with minimal costs.

On the other hand, non-integrated systems are usually more flexible regarding the possible detection processes but are also more sensitive, using extensive and complex optical systems. The integration of an interferometric system and its linkage to the existing technological platform allows the implementation of a novel measurement technique, presenting both a phase shift measurement scheme and the conventional SPR shift measurement, leading to an increase in measurement accuracy and therefore sensitivity.

Using the Electromagnetic Theory of Coupled Modes within laminar structures to create the theoretical background and FEM (Finite element method) modelization to provide preliminary demonstrations, the objective of this project is to study the characteristics of a SPR (surface plasmon resonance) biosensor where the surficial refractive index change is measured with an interferometric approach. To do so, a microstructure is added to the biosensor surface in order to couple incident light to the plasmon surface modes.

Those surface modes are resulting from the interaction and interference of the diffracted surface plasmons by the different microstructure components. In the case of a simple microstructure (e.g. a pair of finite adjacent gratings), the detailed analysis of the diffracted plasmons’ interaction is possible and demonstrated. This interaction is then linked to the inherent resonance shape of the microstructure and compared to other simple cases, like the classical SPR structure.

This transformation of the sensor’s resonance shape increases the global precision achievable by the biosensor without greatly increasing its complexity. The interferometric method proposed here promise very interesting results under certain conditions, also defined and highlighted.