Distance-based microfluidic paper analytical devices for portable, low-cost, and rapid analyses

The work presented in this thesis describes research towards design, and novel means of fabrication of distance-based microfluidic paper-based analytical devices (μPADs), and development of selected applications for (bio)chemical point-of-care analysis. Chapter 1 provides insights into the principles and evolution of μPADs, particularly those based on the distance-based detection method. Chapter 2 introduces a new facile fabrication technique for (distance-based) μPADs using a low-cost desktop electronic craft plotter/cutter. This simple approach enabled rapid prototyping of μPADs by coupling a wax printer with a plotter/cutter, enabling the desired cutting and reagent deposition steps being performed in a fully integrated and geometrically aligned manner along with the wax-printing step. Chapter 3 extends the development of this fabrication method and further investigates the deposition characteristics and performance of this novel approach, demonstrating its capability for deposition of in-house formulated reagents upon μPADs with various designs, while the deposition volume could be precisely quantified gravimetrically. Chapter 4 demonstrates the effect of the μPAD device geometry on the distance signal obtained from the fabricated distance-based μPADs. It is shown that implementation of asymmetrical geometry microfluidic paper channels (varying width instead of the typical rectangular channels) improved analytical parameters significantly. This is demonstrated with the instrumentation-free determination of chloride via trapezoidal distance-based μPADs from as little as 5 μL sample volume, a key requirement for analysis of chloride in sweat as a basis of diagnosis of cystic fibrosis. In chapter 5, the stable immobilization of chromogenic reagents upon paper, being a significant issue in regard to distance-based detection, is addressed. Herein, anion exchange filter paper is introduced as a new substrate for fabrication of μPADs, providing immobilization of water-soluble anionic reagents upon the paper surface and consequently allowing the development of distance-based assays without being compromised by the sample fluid washing away effect, otherwise limiting the choice of reagents to only water-insoluble ones. This extends the applicability of the distance-based detection method to assays which involve water-soluble anionic chromogenic reagents, not readily immobilized on the standard filter paper. Finally, Chapter 6 of this thesis discusses the limitations of (distance-based) μPADs and provides further insight and direction for future research