Rapid flow in multilayer microfluidic paper-based analytical devices

Abstract

Microfluidic paper-based analytical devices (μPADs) are a versatile and inexpensive point-of-care (POC) technology, but their widespread adoption has been limited by slow flow rates and the inability to carry out complex in field analytical measurements. In the present work, we investigate multilayer μPADs as a means to generate enhanced flow rates within self-pumping paper devices. Through optical and electrochemical measurements, the fluid dynamics are investigated and compared to established flow theories within μPADs. We demonstrate a ∼145-fold increase in flow rate (velocity = 1.56 cm s, volumetric flow rate = 1.65 mL min, over 5.5 cm) through precise control of the channel height in a 2 layer paper device, as compared to archetypical 1 layer μPAD designs. These design considerations are then applied to a self-pumping sequential injection device format, known as a three-dimensional paper network (3DPN). These 3DPN devices are characterized through flow injection analysis of a ferrocene complex and anodic stripping detection of cadmium, exhibiting a 5× enhancement in signal compared to stationary measurements.

Emerging Considerations for the Future Development of Electrochemical Paper‐Based Analytical Devices

“…Paper is an excellent substrate for automatic multistep processes, since it integrates a passive fluid pumping through the capillary forces of cellulose fibers; however, this property is dependent on not only paper type but also many other parameters. It is dependent on the geometry of the microfluidic channel, the presence of wax boundaries, the ambient conditions (such as temperature and moisture),, the confinement of the space,, etc. These articles give insights into the physical mechanisms involved in the passive pumping of paper, making the subject possible to be studied by anyone, since it is observed by the naked eye.…”

“…For electrochemical sensing, the articles by Nery et al . investigated how the device shape influences the flow of glucose and uric acid, and later, Channon et al . showed that a multilayer device must to be optimized for the analyte and the electrochemical technique used to obtain the analytical signal.…”

“…Wicking behavior is a fundamental property of paper that is often neglected in the device construction, but it should be accounted for and properly characterized for further advances in these devices. For colorimetric tests, more efforts are being made to optimize devices in order to enhance their analytical responses relative to the responses of electrochemically based assays; these efforts include optimizing the device shape to reduce sample loss in the microfluidic channel and thus obtain a maximum response, quantifying the distribution of proteins on devices, and accounting for the interactions of the proteins on the cellulose fibers . Even though the fundamental characteristics of both types of devices are the same, there are differences that must be accounted for and properly characterized.…”

Rotary manifold for automating a paper-basedSalmonellaimmunoassay

“…27 Since then, many other devices have been proposed including key shaped devices, sliding mPADs, rotating devices, dissolving sugar bridges, and complex channel geometries. 26,[28][29][30][31][32] Although they accomplish the goal of sequential reagent delivery, many of these devices suffer from inconsistent results, as the end user is ultimately performing the folding or sliding, and others require multiple pipetting steps to continually add buffer. 33 Additionally, the more complex channels necessary for sequential delivery in these systems can result in lost analyte to the cellulose bers and decreased sensitivity.…”

Simplified White Blood Cell Differential: An Inexpensive, Smartphone- and Paper-Based Blood Cell Count

“…Paper substrates offer two major benefits over the popularlyused silicone-based microfluidic platforms: 1) its ability to filter out blood cells from plasma, or even isolating WBCs from RBCs without using lysing solution, and 2) spontaneous flow by capillary action, dismissing the requirement of external pumping [13], [14], [15], [16]. However, to the best of our knowledge, no work has been demonstrated to utilize these advantages of paper-based microfluidic platforms toward cell sorting and quantification of WBC components.…”