Characterization of dispersions in microdroplets through an optomicrofluidic lab-on-a-chip in lithium niobate

Lab-on-a-chips integrating microfluidics and optics set a new frontier in sample processing, merging miniaturization of the devices with real-time content analysis. The dramatic reduction of the liquid sample required for the analysis, as well as the possibility to exploit optical analysis and manipulation tools in multi-stage platforms, can have many fields of application such as micro-analytical chemistry and biomedical analysis. This PhD thesis reports concept, fabrication, modelling and testing of an optomicrofluidic lab-on-a-chip in lithium niobate. The integration is achieved herein by integrating together on the same substrate surface two crossed micrometric channels and an array of parallel waveguides in a crossed configuration. Such configuration allows to bring and collect light in the channel through the waveguides, enabling an optical interaction with flowing microdroplets that generates a time signal linked to the droplet shape and content. The presented work focuses both on the mathematical description of the detection process and on the experimental test of its sensing performance. While several contributes are responsible for the optical interaction, the proposed model correctly predicts the signal outcomes under simple assumptions, coherently with the system symmetry and geometry. Furthermore, this research validates the extrapolation of the content information by comparing the droplet signals from the solutions of interest with the droplet signals of an appropriate baseline, once the shape of the compared droplets is fixed. Investigations have been conducted by integrating in the device the well-known Bradford protein assay for the protein concentration determination of a solution, as well as by encapsulating in the microdroplets dispersions with gold nanoparticles at different concentrations and diameters. The obtained results verified in both the cases a sensitivity increase in comparison with the one expected in a direct transmission configuration, thus requiring to include in the modelling of the light interaction internal cycles of the light rays inside the droplet. This unique light interaction proposed in the presented device offers then an effective detection strategy for content analyses, paving the way for further future applications.