Melanys Benitez

This thesis advances the field of Lossy Mode Resonance (LMR) biosensors by transitioning from fiber optic substrates to planar waveguides, emphasizing their simplicity, cost-effectiveness, and versatility. It presents the development of an LMR-based microfluidic platform developed in planar waveguide and its application in detecting critical biomarkers such as anti-IgG, gliadin, antigliadin, VEGF, and IL-6. The performance of the biosensors is assessed when using three nanocoating structures—TiO₂, SiO₂+TiO₂, and Au+TiO₂—selected for their proven utility to generate LMRs and to improve their features. Notably, gold nanoparticles are employed for the first time to enhance signal in LMR sensors, significantly improving the sensitivity. The results obtained demonstrate the versatility and effectiveness of the proposed system, confirming that the microfluidic platform and the planar substrate-based design provide a robust foundation for the development of LMR devices adaptable to a wide range of applications in fields such as medicine, biotechnology, and food industry.

Celiac disease is a chronic autoimmune disorder triggered by gluten consumption which affects between 0.5% and 1% of the global population. Current diagnostic methods still require invasive procedures such as intestinal biopsy. LMR-based sensors hold great potential for the development of reliable and user-friendly devices for diagnosing this condition. In this work, an LMR planar microfluidic system is used to perform the label-free detection of different concentrations of anti-gliadin antibodies, one of the biomarkers of celiac disease, achieving a limit of detection of 1 μg/mL. The specificity of the sensor to the target analyte is also proved, and the validation of the biofunctionalization process is complemented with an AFM analysis

The development of resonance phenomena-based optical biosensors has gained relevance in recent years due to the excellent optical fiber properties and progress in the research on materials and techniques that allow resonance generation. However, for lossy mode resonance (LMR)-based sensors, the optical fiber presents disadvantages, such as the need for splicing the sensor head and the complex polarization control. To avoid these issues, planar waveguides such as coverslips are easier to handle, cost-effective, and more robust structures. In this work, a microfluidic LMR-based planar waveguide platform was proposed, and its use for biosensing applications was evaluated by detecting anti-immunoglobulin G (anti-IgG). In order to generate the wavelength resonance, the sensor surface was coated with a titanium dioxide (TiO₂) thin-film. IgG antibodies were immobilized by covalent binding, and the detection assay was carried out by injecting anti-IgG in PBS buffer solutions from 5 to 20 μg/mL. The LMR wavelength shifted to higher values when increasing the analyte concentration, which means that the proposed system was able to detect the IgG/anti-IgG binding. The calibration curve was built from the experimental data obtained in three repetitions of the assay. In this way, a prototype of an LMR-based biosensing microfluidic platform developed on planar substrates was obtained for the first time.