Microfluidic technology allows the miniaturisation and automation of chemical and biological
processes. Specific advantages include the ease of process automation and integration,
high analytical throughput, reduced sample and power consumption, increased
speed and efficiency of reactions and system portability. Droplet-based microfluidics can be broadly categorised into 'conventional' channel devices or digital microfluidic (DMF) devices. The latter are also known as electrowetting-on-dielectric (EWOD)
devices. Both platforms have distinct characteristics, with specific advantages and disadvantages
when applied to chemical or biological analysis. High-throughput droplet
manipulation is easily achieved with channel microfluidic devices, but it is hard to access
individual droplets in this format. On the other hand, DM devices are designed
for the manipulation of individual droplets in low-throughput.
The bulk of the work in this thesis focuses on developing a complete platform for
droplet manipulation using digital microfluidics. Extensive experimentation was undertaken
to determine all relevant components of the device, including the composition
of the dielectric layer, electrodes and hydrophobic layer. Once the optimum device had
been constructed and tested, full automation of device function and droplet manipulation
was achieved. Characterisation of on-chip droplet operations was subsequently
performed. Special attention was given to droplet 'dispensing' and 'splitting'.
Once the fabricated DMF devices had been fully characterised, three proof of principle
experiments were developed to investigate the capabilities of DMF devices. To this
aim, first a
fluorescent dilution series was performed and characterised on-chip, second a
peptide bond formation experiment was performed, and finally, iron oxide nanoparticle
synthesis was performed on-chip. The integration of DMF devices with a miniaturised
spectrometer was used to provide an on-line detection system.
Channel microfluidic devices were also investigated with respect to the high-through-put
creation of droplet interface bilayers (DIBs). Aqueous droplets containing lipids
were formed in an oil carrier medium. As droplets were brought together a lipid bilayer
was formed at the interface, creating an artificial membrane. This approach can be
used as a platform technology to study trans-membrane proteins and drug-membrane interactions. Although there has been a lot of interest in this area, previous work has
focused on the low-throughput formation of DIBs. The method developed here enables
the formation of DIBs at rates in excess of 1 DIB per second.