Two Potential Clinical Applications of Origami-Based Paper Devices

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 reagent 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 reagent 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 reagent 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: IgG; origami ELISA; origami-based paper analytic device; paraquat.

Figure 1

The design of an origami-influenced paper-based analytic device (O-PAD) for enzyme-linked immunosorbent assay (ELISA). (a) Reagents were pre-loaded into the four-wing fashioned zones, and the central area was reserved as testing zone for sample loading. (b) The picture of our O-PAD.

Figure 2

Schematic illustrations demonstrating use of O-PAD ELISA. (a) Reagents were pre-loaded into reagent zone barrier wells. These reagents included the following: (1) 2 µL of BSA blocking buffer (2) 2 µL solution of alkaline phosphatase (ALP)-conjugated detection antibody (3) 2 µL BCIP/NBT substrate. After loading each reagent, the device was placed under ambient conditions for 5 to 10 min until the reagents dried. (b) Schematic illustrations for BSA blocking, antibody loading, and BCIP/NBT loading.

Figure 3

Results of rabbit IgG detection using the O-PAD. (a) Colorimetric response. (b) Calibration curve of rabbit IgG using mean gray-scale intensity versus several concentrations of rabbit IgG (n = 6).

Figure 4

Schematic illustrations of O-PAD for paraquat detection. (a) 5 µL of 5 N NaOH and 6 µL of 5% (w/v) ascorbic acid (AA) were preloaded onto the left and right parts of our PAD, respectively. (b) The reagent zones containing NaOH and AA were folded onto the test zone sequentially. 8 µL of test sample was loaded onto the test zone, and the device stood for 10 min at 25 °C. Paraquat, in contact with NaOH and AA, changed to paraquat radical ion (blue color).

Figure 5

Result of paraquat detection using the O-PAD. (a) Colorimetric response. (b) The calibration curve of paraquat using mean RGB intensity versus several concentrations of paraquat (n = 3).