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 (˜í¬¿PADs), and development of selected applications for (bio)chemical point-of-care analysis. Chapter 1 provides insights into the principles and evolution of ˜í¬¿PADs, particularly those based on the distance-based detection method. Chapter 2 introduces a new facile fabrication technique for (distance-based) ˜í¬¿PADs using a low-cost desktop electronic craft plotter/cutter. This simple approach enabled rapid prototyping of ˜í¬¿PADs 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 ˜í¬¿PADs with various designs, while the deposition volume could be precisely quantified gravimetrically. Chapter 4 demonstrates the effect of the ˜í¬¿PAD device geometry on the distance signal obtained from the fabricated distance-based ˜í¬¿PADs. 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 ˜í¬¿PADs from as little as 5 ˜í¬¿L 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 ˜í¬¿PADs, 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) ˜í¬¿PADs and provides further insight and direction for future research.