Common-path interferometric sensing with resonant dielectric nanostructures

Photonic sensors have the potential to enable highly sensitive point-of-care diagnostic technology and become an essential element of the global health system. To maximise its benefits, the technology needs to provide affordability in addition to accuracy, which is a challenge that is reflected in the currently available diagnostic technologies. For example, the gold standard diagnostic technology, enzyme-linked immunosorbent assay, requires trained personnel and a well-equipped laboratory. In contrast, the low-cost lateral flow devices offer limited sensitivity. New technologies are emerging, such as label-free photonic biosensors that are intrinsically simple, as they can directly monitor the presence of a target biomarker without requiring additional processing steps. However, when high sensitivity is required, they typically rely on expensive components.

Circumventing the connection between high cost and high performance in photonic biosensing and demonstrating a viable alternative requires a novel approach and is the primary aim of my thesis. To this end, I have developed a common-path interferometric sensor based on guided-mode resonances to combine high performance with inherent stability. The concept of spatially superimposing two beams carrying the phase information of two orthogonally polarised resonant modes and interferometrically measuring the relative phase difference between them is here introduced and experimentally realised. To validate the developed technology, the sensor is applied to bulk refractive index sensing as well as the proof-of-principle detection of procalcitonin.

The results of this thesis reveal the interesting physics involved in an interferometric probing of resonances in dielectric nanostructures and indicate the potential of the developed sensor for high-performance diagnostics based on photonics.