DESIGN PRINCIPLES FOR LAB-IN-A-PHOTONIC-CRYSTAL BIOSENSORS

A new class of photonic crystal biosensors, geared towards rapid biomedical diagnostics at the point-of-care, is proposed. These Lab-in-a-Photonic-Crystal devices employ cascaded transmission of light through a photonic band-gap material by leveraging the interaction of surface modes at entry and exit termini with waveguide modes in centrally-embedded line-defects. A rich spectral signature, composed of conventional resonance-shifts complemented by transmission-level modulation, enables these devices to discriminate between combinations of various bio-markers, attached as thin layers to the surface and line-defect artifacts. An initial two-dimensional conceptual paradigm is proposed, and then developed into a full-fledged, fabrication-feasible, three-dimensional design. The final design consists of a high-index nano-pillar array forming a two-dimensional, fluid-infiltrated photonic crystal with two surface gratings and a central waveguide, whose optical modes are trapped by index-guiding in the third dimension. The nano-pillars are housed in a glass trough, while being open to fluid at the top, allowing easy addition of bio-fluid samples onto the device, and helping prevent clogs due to macroscopic suspended impurities. The design is further optimized, both optically and structurally, by the introduction of a thin-layer of high-index backing material between the nano-pillars and the glass trough substrate, reducing nano-pillar height by half of the unbacked-design height. The system is capable of detecting all eight possible combinations of up to three distinct bio-markers, with the possibility to increase the number of sensed bio-markers through the use of multi-mode waveguides (and potentially, multi-mode surfaces). Using index-guided bulk modes of the three-dimensional structure, a mechanism for calibrating the device under impurity-induced variations in fluid refractive index is proposed. The Lab-in-a-Photonic-Crystal device is suitable for the detection of multiple diseases, or multiple stages of a given disease, in a single optical measurement. Its functionality, as well as robustness to imperfect fabrication, has been validated using Finite-Difference Time-Domain solutions to Maxwell’s Equations.Ph.D