*Article* **Two Potential Clinical Applications of Origami-Based Paper Devices**

**Zong-Keng Kuo 1, Tsui-Hsuan Chang 2, Yu-Shin Chen 1, Chao-Min Cheng 2,\* and Chia-Ying Tsai 3,4,\***


Received: 2 November 2019; Accepted: 25 November 2019; Published: 26 November 2019

**Abstract:** Detecting small amounts of analyte in clinical practice is challenging because of deficiencies in specimen sample availability and unsuitable sampling environments that prevent reliable sampling. Paper-based analytical devices (PADs) have successfully been used to detect ultralow amounts of analyte, and origami-based PADs (O-PADs) offer advantages that may boost the overall potential of PADs in general. In this study, we investigated two potential clinical applications for O-PADs. The first O-PAD we investigated was an origami-based enzyme-linked immunosorbent assay (ELISA) system designed to detect different concentrations of rabbit IgG. This device was designed with four wing structures, each of which acted as a reagen<sup>t</sup> loading zone for pre-loading ELISA reagents, and a central test sample loading zone. Because this device has a low limit of detection (LOD), it may be suitable for detecting IgG levels in tears from patients with a suspected viral infection (such as herpes simplex virus (HSV)). The second O-PAD we investigated was designed to detect paraquat levels to determine potential poisoning. To use this device, we sequentially folded each of two separate reagen<sup>t</sup> zones, one preloaded with NaOH and one preloaded with ascorbic acid (AA), over the central test zone, and added 8 μL of sample that then flowed through each reagen<sup>t</sup> zone and onto the central test zone. The device was then unfolded to read the results on the test zone. The three folded layers of paper provided a moist environment not achievable with conventional paper-based ELISA. Both O-PADs were convenient to use because reagents were preloaded, and results could be observed and analyzed with image analysis software. O-PADs expand the testing capacity of simpler PADs while leveraging their characteristic advantages of convenience, cost, and ease of use, particularly for point-of-care diagnosis.

**Keywords:** origami-based paper analytic device; origami ELISA; IgG; paraquat
