| Microdevices employing microfluidics components are attractive for point-of-care testing because of their often-cited advantages in small size, rapid analysis, and low volume requirement for samples and reagents. While there have been many advances in individual components, few lab-on-a-chip procedures are relevant outside of a well-equipped laboratory, and their integration on a single, functioning unit remains a tremendous engineering challenge. Developing diagnostic microdevices is arguably the most challenging for resource-limited settings, where cost and ease-of-use are important constraints.;Also presented in this dissertation are two projects which, while not directly tied to microdevices for global health diagnostics, are nevertheless relevant to global health. The first study was a prioritization of novel protein biomarkers for tuberculosis by comparative analysis of biological properties of validated B-cell antigens. The second study was the development of microfabricated collagen-based scaffolds for artificial skin.;In this dissertation, we explored the development of microdevices performing low-cost and portable immunoassays, which have analytical performance rivaling that of benchtop standards but have the simplicity and speed of a rapid test. Using both computational modeling and experimental testing, we investigated the effects of sample volume and assay time on analyte capture in heterogeneous immunoassays. We identified, for the first time, a new reagent-limited analyte capture regime at small sample volume and sufficiently large flowrate, and gave guidelines on maximizing signal intensity under different operating regimes. As a step towards our long-term goal of deploying novel diagnostic microdevices in resource-limited settings, we developed a multiplexed HIV-syphilis immunoassay by integrating innovations in low-cost fabrication of microfluidic cassettes, valveless delivery of multiple reagents, and signal enhancement with detection by low-cost and robust optics. Evaluations in HIV/syphilis and HIV only test formats at clinics in Rwanda showed analytical performance comparable to that of benchtop ELISA for over hundreds of clinical samples. The test was also capable of processing both sera/plasma and whole blood specimens effectively, using no more than 7 muL per sample and achieving results in less than 20 minutes. In addition to assay development, we developed a handheld, battery-powered instrument which simplifies user operation by integrating, among other components, pre-aligned optics for signal detection, vacuum pump for actuation of pre-loaded reagents, and a satellite and GSM modules for remote data transmission. We found excellent analytical performance of this instrument running HIV tests on whole blood specimens in Rwanda, and were able to transmit results collected on the instrument to a remote electronic health records server currently in use by the Rwandan Ministry of Health. |
