Paper-based diagnostic biosensors for protein and DNA detection

My thesis research work focuses on the integration of potential functionality into microfluidic paper-based analytical devices (μPADs) for a variety of practical applications. The current academic efforts on μPADs are dedicated to seeking to investigate potential incorporating functionality, including i) detection and readout, ii) programming and timing, iii) multi-step processing, and iv) surface chemistry from laboratory-scale research to commercialization.In the research, we first developed an all-in-one μPAD to improve the functionality of μPADs on detection and readout to diagnose cardiac biomarkers in real human blood. By introducing high surface-to-volume ratio and superior electron-transferring properties, zinc oxide nanowires (ZnO NWs) were used to amplify electrochemical signal outputs on μPADs. The ZnO-NW-decorated μPADs were employed in biosensing for ultrasensitive measurements that were demonstrated equivalent to commercial enzyme-linked immunosorbent assay (ELISA) kits. The all-in-one μPAD enables a portable, utility, and user-friendly detection in a highly integrated paper-based device as the promising detection and readout integration for μPADs. To investigate and incorporate functionality of programming and timing, and multi-step processing on μPADs, we established an autonomous platform to turn on and off heat-responsive shame-memory-polymer (SMP) actuators to connect and disconnect paper channels on a μPAD by manipulating paper cantilever arms. The developed platform is capable of realizing sample-in-answer-out (SIAO) detections in fully-automated behaviors for multi-step assays such as ELISAs. We demonstrated its practical feasibility of on-site testing for rat and human samples by running automated ELISAs. The platform can be further tuned for DNA sensing that is suitable to improve its sensing ability from protein-level to nucleic-acid-level. We also carried out a systematic investigation of comparing five single-step biofunctionalization methods for μPADs to explore surface chemistry functionality. The chemically-modified μPADs provided more active binding sites on paper surface for covalent binding of proteins. The modification methods were compared and the potassium periodate (KIO4)-based biofunctionalization route was then utilized with superior surface chemistry performance in experimental sections of automated ELISAs on the autonomous platform