Design and microfabrication of a droplet-based microfluidic probe for sampling and delivery

Conventional needles (or similar probes) cannot deliver sequences of different drugs in one insertion. Neither can they transport a rapidly changing chemical signal from the insertion point to an analytical instrument. Both of these limitations are caused by the phenomenon known as Taylor dispersion. Delivery of sequences of drugs (multi-drug delivery) requires multiple injection lines/tubes, each carrying different drugs. Measurement of rapidly changing chemical signals requires that we bring the instrument directly to the sampling point (expensive and impractical). In a droplet-based microfluidic system, water-based liquids are carried by an immiscible oil (continuous phase) in a hydrophobic channel. If we discretise the fluid into droplets (delivery or sampling), each droplet is isolated and does not mix with neighbouring droplets. This overcomes the signal distortion caused by Taylor dispersion in continuous flow for both sampling and delivery of chemical signals. If the droplet-based microfluidic device is to be used as a needle, the oil phase cannot be injected into the tissue. However, the oil must be provided at the injection site to partition the sampled liquid. This thesis is focused on developing new droplet-based microfluidic probes with the flow barrier at the tip. We have successfully developed two kinds of droplet-based microfluidic probes, one for silicon-based microfluidic probes, another for membrane-based microfluidic probes. Each system incorporates a Laplace pressure flow barrier that prevents oil from exiting into the tissue but allows easy passage of water. This new version of an ancient medical device may allow research into rapidly changing chemical signals such as neurotransmitters. With further development, it may also find applications in disease and trauma diagnostics and treatments.