Fig. 1. Overview of the test construction and image acquiring devices.

a Exploded scheme of the cellulose testing unit, comprising 2 pieces of acrylic manifold to hold the testing unit together, 3 layers of the folded and printed cellulose test strip whereby hydrophobic ink (black area) was used to determine liquid flow path and folded Kim Wipes which is used as an absorbent pad. b An Image of the assembled cellulose testing unit which is held together using paper binders. c An image the top piece of the acrylic manifold which contains an opening to access the cellulose test strip. d An image of cellulose test strip. The strip was printed and cut as one piece. Wax ink was used for printing (black area) to define the liquid flow path. To create 3 layers of the test strip, the printed paper is folded in a zig-zag motion until the hydrophobic regions are aligned (inset). The top most layer of the cellulose paper contains a circular testing region (white, hydrophilic area without ink) with a diameter of 5 mm whereas the lower two layers, each, contain hydrophilic regions with a diameter of 6 mm. Each cellulose testing unit contains two test zones for testing of two reactions. e An image of the folded Kim Wipes which was folded in half for 6 times and used as absorbent material. f An image of the lower piece of the acrylic manifold which contain 3 mm spacers at two ends. The spacers are used to control consistent pressure that applies to different cellulose testing units. g An image of the light box with the phone placed at the top face. h An image of a slight opened light box showing phone fixture and a void for phone camera access at the top face. i An image of opened light box showing internal structure of the box. Warm-white LED light strips were attached to the inner top face of the light box to provide consistent lighting for all images. Cylindrical, white papers were covered parts of the LED strips to diffuse light from the strip, prevent shadow which may form on the cellulose test unit. Fixture was placed at the base of the light box to provide a fixed location to place the cellulose test unit.