Liquid-core Waveguide TCSPC Fluorescence Lifetime Detection Microsystem for DNA Biosensing

Abstract

Demand for accurate, rapid, and low-cost medical diagnostics is rising on a global scale. Design techniques for advanced devices for medical diagnostics are undergoing intense attention for a variety of applications from viral and pathogenic screening to genetic and cancer studies. At the core of many diagnostics methods is the detection of biomolecules such as deoxyribonucleic acid (DNA) and protein. Time-resolved fluorescence is a widely adopted technique for DNA detection due to its high sensitivity and selectivity. However, due to stringent requirements on optics and electronics, instrumentation with time-resolved capability is traditionally bulky and expensive, prohibiting their use in portable and point-of-care applications. This thesis presents the design of a fully-integrated DNA detection microsystem based on liquid-core waveguide (LCW) optics and time-correlated single-photon counting (TCSPC) electronics, achieving a performance level comparable to current commercial devices, but at a fraction of their size and cost.

First, a model for the TCSPC fluorescence lifetime analysis system using Monte Carlo methods is proposed and experimentally verified. The model describes the relationship between various key design parameters, including both optics and electronics, and the performance of the TCSPC system. Simulation results based on the proposed model and experimental results obtained from a commercial TCSPC lifetime instrument show good agreement.

Second, a compact liquid-core waveguide time-correlated single-photon counting (LCW-TCSPC) microsystem for fluorescence lifetime measurement (FLM) is presented. The propagation of excitation within the LCW is analyzed both analytically and in simulations, enabling the LCW to deliver superior performance in excitation rejection and low temporal dispersion. The proposed prototype achieves high-accuracy fluorescence lifetime measurement, demonstrating a detection limit of 5 nM for Coumarin 6 in dimethyl sulfoxide with a lifetime error below 3%.

Third, the LCW-TCSPC microsystem combined with a custom bioassay for DNA detection, delivering near the sample-to-answer level of integration, is presented. Lifetime, rather than intensity, is exploited as the analytical signal from the synthesized turn-on fluorescent probe, V-carbazole. Detection of DNA down to 15 base pairs at a low detection limit of 1.38 nM demonstrates the high applicability of the proposed microsystem for compact, application-specific, and low-cost diagnostics devices.

Date of Award	5 Sept 2019
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Derek HO (Supervisor)