Equipment-Free Quantitative Measurement for Microfluidic Paper-Based Analytical Devices Fabricated Using the Principles of Movable-Type Printing

Abstract

Microfluidic paper-based analytical devices (μPADs) are a growing class of low-cost chemo/biosensing technologies designed for point-of-use applications. In this article, we describe MTWP (movable-type wax printing), a facile method for the fabrication of μPADs. MTWP is inspired by the Chinese movable-type printing and requires only a hot plate and homemade small iron movable components. It is able to pattern various wax microstructures in paper via a simple adjustment of the number, patterning forms or types of the metal movable components. This inexpensive and versatile method may thus hold great potential for producing wax-patterned μPADs by untrained operators at minimized cost in developing countries. In addition, two novel equipment-free assay methods are further developed to render μPAD measurements straightforward and quantitative. They use the flow-through time of a detection reagent in a three-dimensional paper device and the number of colored detection microzones in a 24-zone paper device as the detection motifs. The timing method is based on the selective wettability change of paper from hydrophilic to hydrophobic that is mediated by enzymatic reactions. The counting method is carried out on the basis of oxidation-reduction reactions of a colored substance, namely iodine. Their utility is demonstrated with quantitative detection of hydrogen peroxide as a model analyte. These methods require only a timer or a cell phone with a timing function and the abilities of seeing color and of counting for quantitative μPAD measurement, thus making them simple, cost-efficient, and useful sensor technologies for a great diversity of point-of-need applications especially in resource-poor settings.

Paper and Fiber-Based Bio-Diagnostic Platforms: Current Challenges and Future Needs

“…A variety of techniques, including colorimetry [120][121][122][123], fluorescent [29,[123][124][125][126][127], luminescent [128], chemiluminiscent [128,129], photo-electro-chemiluminiscent, electrochemical [130,131], electro-chemiluminiscent [132,133], and photo-electrochemical [134] detections have been reported for paper and/or fiber-based bio-diagnostic platforms [2][3][4]135,136]. In the case of fluorescence readout, an important question is: "To what extent does the whiteness of the paper play a role in producing a background signal or perhaps participating in the bleaching effect?".…”

Highly Sensitive Paper-based Analytical Devices with the Introduction of a Large-Volume Sample via Continuous Flow

“…These techniques include time-based, [9][10][11][12] distancebased, [13][14][15][16] and titration-based detection. [17][18][19] Philips and coworkers demonstrated time-based detection using an enzymatic reaction wherein a color change took place at different times depending on the concentration of the analyte.…”

“…[13][14][15][16] Zhang and coworkers employed both the time and the number of the detection zones that changed color. 11,12,20 We also reported that titrimetric PADs where the endpoint is judged using only the naked eye to count the number of detection zones. 15,17 The method of counting the number of detection spots was also applied to a quantitative immunoassay.…”

Sustainable monitoring of Zn(II) in biological fluids using office paper

“…Especially in resource-limited areas where laboratory facilities are not accessible, wax offers an alternative technology for fabricating smart platforms for point-of-use devices. For instance, Songjaroen et al [20] produced a colorimetric PAD to detect glucose and BSA by simply wax dipping chromatographic paper, while Zhang et al [21] used heated patterned iron components, coated by wax, to stamp a wax pattern into chromatographic paper, detecting hydrogen peroxide. Among several chromatographic papers, Whatman #1 is often chosen as substrate in realizing these newgeneration diagnostic devices due to its surface area, cellulose purity, porosity, uniform thickness, and lightness [5].…”