UC Irvine

Life-saving treatment starts with proper diagnosis. This thesis therefore discusses two central aspects: detection methods and integration of fluidic steps onto fully automated diagnostic platforms. To investigate performance of different common commercial detection methods with regard to detection characteristics, such as limit of detection (LOD), sensitivity, and dynamic range (DR), horseradish peroxidase (HRP) was chosen as label and detection was conducted via absorbance, chemiluminescence, and amperometry. While these performance parameters vary for different substrates and depend on specific procedure for each technique, the importance of choosing the proper detection method for a given application is conspicuous. Integration of a colorimetric, HRP-based enzyme-linked immunosorbent assay (ELISA) for detection of malaria is demonstrated on a rapid prototyped platform (3D printed microfluidic structure) and electrochemical detection is integrated on a compact disc (CD) microfluidic device. The latter is most commonly produced via injection molding and thus compatible with mass manufacturing. While CD microfluidics excels in simplicity of pumping principle based on centrifugal force from a single motor and elegance of instrumentation-free, passive valving based on changing capillary forces at cross-section changes (burst valves), this type of valving often shows unreliable. Burst valves are therefore analytically modelled and experimentally analyzed and evaluated. While instrumentation-free principle incites their application, control of burst pressure underlies effects of surface imperfections and dimensional control is critical. While pumping on CD microfluidic platforms inherently enables fluid motion towards the outer perimeter of the disc, reversed flow is demonstrated on material jetted CD-inserts.

Integration of electrochemical detection on the CD, allows for signal amplification via enhanced mass transport. The effect of flow onto electrochemical measurements is investigated in cyclic voltammetry experiments on Interdigitated Electrode Arrays (IDAs) on the CD. While flow generally increases mass transport to the electrode surface, redox amplification suffers. Nevertheless, dual mode cyclic voltammetry during flow results in lowest LOD.