Simplified Chemical Analysis Using Microfluidics and Surface Sampling Mass Spectrometry

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Authors

Hillen, Phillip

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thesis

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eng

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Digital Microfluidics , Surface Energy Traps , Mass Spectrometry , Surface Sampling Probe , Droplets

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Abstract

Microfluidics studies fluids on a femtoliter to milliliter scale. There are several ways to investigate fluids at this scale, from continuous flows through capillaries to individual droplets, which has created a range of subcategories in microfluidics. One of these subcategories, digital microfluidics, has been expanding and growing in importance recently. Digital microfluidics is the study of platforms that enable a number of droplet manipulations and functions. Apart from microfluidics, mass spectrometry is an important tool in analytical chemistry and beyond. Mass spectrometry is able to provide compositional information by analysing the ions produced by a sample. This thesis seeks to bring these concepts together in a novel way. Herein, digital microfluidic devices are coupled with mass spectrometry through a liquid micro-junction surface sampling probe (LMJ-SSP). First, a study is carried out on the LMJ-SSP and a method is developed to use the probe to directly sample ink and paint samples that are potentially of forensic interest. Next, an investigation involving the fabrication of the microfluidic chips using commercial omniphobic coatings is done, and improvements to the fabrication method are made that allow for the creation of structures with higher spatial resolution. On these microfluidic chips, patterns are created that can spontaneously generate droplets, by using the differential wetting energies of hydrophilic and hydrophobic surfaces, called surface energy traps (SETs). A wide range of SET patterns are created and observed, to gain insight about their influence on droplet behaviour as they dry down on top the SETs. One of these patterns, composed of concentric circles, is investigated for its ability to concentrate salt solutions. These investigations culminate in the presentation of a digital microfluidic device capable of evaporatively splitting a droplet in half and pre-concentrating the analytes to two targeting spots on a SET, the surface of which is then sampled by an LMJ-SSP and analyzed using mass spectrometry.

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