Novel microfluidics for sustainable chemistry and global diagnostics

Abstract

Microfluidics offers promising advantages which has led to a large influx of microfluidic technologies in global diagnostics and sustainable chemistry. Nevertheless, few studies relate the fundamentals of mass transfer and hydrodynamic limitations to improve their performance. This research uses the Microcapillary Film (MCF) material, a novel microfluidic platform, and analytical dispersion techniques, considering flow regimes and residence time distributions, to address these challenges.

This work captured the transition from convective, segregated flow to plug flow in three tubulars systems (i.d. 363 ± 32.2 – 2400 μm) experimentally and through Computational Fluid Dynamic (CFD) simulations (validated with fluid tracing and continuous flow neutralization and 4th Bourne reactions) which could be linked to time scales of diffusion to convection, tdiff / tconv. Rather than increasing capillary diameter, D, neglecting diffusive effects, splitting the fluid through multiple microcapillaries is a superior scaling up strategy as axial dispersion coefficient values (Dax/uL) remained independent of flow rates (0.0015 ± 0.0005 to 0.0033 ± 0.0006 for 0.5–5.0 mL/min).

The fast fabrication of inexpensive non-linear ‘square’, ‘zigzag’ and ‘wavy’ high performance microreactors was reported using a flexible MCF re-shaped with 3D printed templates. CFD studies validated with RTD breakthrough curves demonstrated a strong link between sharp bends in the square and zigzag and enhanced radial dispersion, supporting increased reaction rates of ~43 and ~46% respectively compared to the straight in an oxidative coupling reaction. Microparticle focusing and controllable positioning, via alignment with velocity streamlines, and predictable flow of E. coli was demonstrated to inform the design of surface-based biosensors.

The automation of a multi-step high performance bioassay simply requiring a fluid handling free mechanical robotic arm and an innovative MCF siphon was presented. Reagent-wash sequential fluid delivery showed no backflow and high reproducibility (colorimetric Dax/uL = 0.049 ± 0.0046) for clinically relevant sensitivity (< 10 ng/ml) and full scalability in a dengue immunoassay. Additionally, a pressure balance study for a membrane siphon evidenced flow is governed by pressure head and frictional resistance forces, rather than capillary action, overcoming flow limitations in lateral flow assays of uneven flow and varying flow resistance which limits assays sensitivity.

Date of Award	25 May 2022
Original language	English
Awarding Institution	University of Bath
Supervisor	Nuno Reis (Supervisor) & Pedro Estrela (Supervisor)