Portable microfluidic fluid handling system for the detection of protein biomarkers in whole human blood

The thesis focused on the design and construction of a proof-of-concept polymer based microfluidic Point of Care (POC) device that is portable, requires little user interaction, and is sensitive enough to reliably test for protein biomarkers from a small sample of whole human blood. Specific contributions to the presented system include novel microfluidic channel geometries that support improved fluidic handling, and an improved technique for the fabrication of the poly(dimethylsiloxane) (PDMS) microfluidic chip. Additionally, a commercially available plasma separation membrane was integrated into the microfluidic chip using presented structures and techniques to achieve cellular filtration of whole blood on-chip, yielding a usable volume of plasma to be used as the analyte fluid. A system of valves was used to direct the pressures generated by a new patented syringe-style pump designed for this specific application. The pump was created to more precisely move the collection of fluid volumes through the chip. A previously developed charged couple device (CCD) based vision system was modified and integrated into the presented fluid control system to track the position of the various fluid volumes. Software was developed that used the fluid position sensors data to control the various hardware components of the system. Finally, the above components were combined into a working prototype geared towards ease of use and portability. Efforts were focused on the system\u27s ability to autonomously and reliably control the various microliter sized volumes of fluid within the microfluidic chip. C-reactive protein (CRP) was used as a benchmark protein for biomarker detection because its normal concentration in human blood is at an approximate median to other biomarkers, and because the detection of CRP in a laboratory setting has been well established. A limit of detection (LOD) of 1.87 µg/mL of CRP in buffer was achieved utilizing the proposed stop-flow sequential loading technique. An acceptable volume of plasma was extracted and collected in the microfluidic chip from 50 µL of whole blood using the structures and techniques presented in this work. The CCD based fluid position sensor was capable of sensing a change in the contents of a channel over 97% of the time. Totally autonomous stop-flow fluid handling was accomplished at a similar rate of success utilizing a combination of valves, the custom pump, and the fluid position sensor all working in unison. Results show that protein detection using a previously untested stop-flow procedure still provided an acceptable LOD. The presented portable POC device was able to execute fluid handling in the microfluidic channels at a higher level of precision and reliability than previously possible. The presented prototype gives a viable blueprint for a next-generation protein biomarker detector capable of autonomous complex fluid handling procedures