Rapid determination of the concentrations of molecules related to diseases can provide timely information for treatment options. However, most biomarker quantitation methods require costly and complex equipment. On the other hand, point-of-care systems have less complex instrumentation needs than laboratory-based equipment, but often provide less information; for example, biomarker presence or absence instead of concentration. A complete analysis setup addressing key limitations of both laboratory-based and portable systems is highly desirable. I developed microfluidic devices with visual inspection readout of a target’s concentration from microliter volumes of solution flowed into a microchannel. Microchannels are formed within polydimethylsiloxane (PDMS), and the surfaces are coated with receptors. Capillary flow of target solution in the channel crosslinks the top and bottom surfaces, which constricts the channel and stops flow. The flow distance of the target solution in the channel before flow stops indicates the target’s concentration, enabling simple visual inspection readout without complex detection instrumentation. Because of its easy readout and portability, my system has great potential for use in point-of-care diagnostics. I initially demonstrated a proof-of-concept assay using biotin-streptavidin. Solution capillary flow distances scaled linearly with the negative logarithm of streptavidin concentration over a 100,000-fold range. I measured streptavidin concentrations as low as 1 ng/mL using these microsystems, demonstrating low detection limits. I also characterized the mechanism wherein time-dependent channel constriction in the first few millimeters leads to concentration-dependent flow distances. I demonstrated the visual detection and quantification capability of my system to determine an antigen target, thymidine kinase 1 (TK1). I developed surface modification methods for carrying out flow assays and verified receptor attachment on channel surfaces using fluorescence imaging. I obtained a 1 ng/mL TK1 detection limit in flow assays. I also demonstrated nucleic acid quantitation in my flow devices. I detected specific DNA targets in buffer and synthetic urine at 10 pg/mL levels. A dynamic range of 106 was obtained with single-base mismatch specificity. DNA analogues of two miRNA biomarkers were measured near clinically significant levels, showing great promise for future medical application. The promising results demonstrate that this diagnostic tool offers a simple route to analyte quantitation in microliter volumes, with excellent potential for point-of-care application.



College and Department

Physical and Mathematical Sciences; Chemistry and Biochemistry



Date Submitted


Document Type





Analysis system, biomarkers, detectorless, microfluidics, point-of-care, quantitation