Microfluidic bioassays mediated by chip-integrated luminescence-based temperature and pH sensors

Abstract

Significant advantages of microfluidics such as lower sample consumption and shorter reaction time make it become popular in chemical and biological analysis. Luminescence sensors are attractive to measure these parameters as they provide high sensitivity, non-invasive detection, and fast response. In this dissertation, luminescence sensors were integrated with different microfluidic systems to monitor the temperature or pH value during the analytical process. These systems were designed, proposed, and extensively discussed. Several integration methods have been explored that combines sensor probes and microfluidics as a detection scheme, which simplified the fabrication process and reduced the cost. The methods for temperature sensing, poly(styrene-co-acrylonitrile) and temperature probe tris(1,10-phenanthroline)ruthenium(II) was generated by blade coating on a glass substrate. This sensing layer was directly bound to PDMS with microfluidic channels which led to a microfluidic system that was feasible for temperature detection in the microchannel by imaging. In DNA melting curve analysis, the chips could be employed to generate and measure thermal gradients in the resolution of 0.13 ℃. Analysis of the fluorescence intensity of stained DNA through multispectral optical imaging illuminated by LED was done, giving the results for screening of the BRCA 2 breast cancer gene that enabled to discriminate two double-strand DNA even in 0.7 ºC difference. For pH sensing, the fluorescent pH probe fluorescein isothiocyanate was conjugated to fluorinated silica nanoparticles, which formed the droplets by Pickering emulsion. This conjugation led to stabilization of the emulsified droplets as well as capability of detecting the pH in the droplets. This pH sensor innovatively used in the microdroplet system could measure the pH of the extracellular microenvironment (pH_e) of single-cell and provided support for the growth of cells in the droplets. The pH_e showed 6.84 ± 0.04 and 6.81 ± 0.04 for cancer cells (MCF-7 and A549, respectively) and 7.36 ± 0.03 for healthy cells (HUVEC), which can be potentially applied in circulating tumor cells distinguishing. Such coupling leads to better accuracies and sensitivities in the assays, making the microsystems more convenient to use in temperature or pH detection.

Date of Award	2021
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Stefan NAGL (Supervisor)