Scalable 3D printing method for the manufacture of single-material fluidic devices with integrated filter for point of collection colourimetric analysis

Assembly and bonding are major obstacles in manufacturing of functionally integrated fluidic devices. Here we demonstrate a single-material 3D printed device with an integrated porous structure capable of filtering particulate matter for the colourimetric detection of iron from soil and natural waters. Selecting a PolyJet 3D printer for its throughput, integrated filters were created exploiting a phenomenon occurring at the interface between the commercially available build material (Veroclear-RGD810) and water-soluble support material (SUP707). The porous properties were tuneable by varying the orientation of the print head relative to the channel and by varying the width of the build material. Porous structures ranging from 100 to 200 μm in thickness separated the sample and reagent chambers, filtering particles larger than 15 μm in diameter. Maintaining the manufacturing throughput of the Polyjet printer, 221 devices could be printed in 1.5 h (∼25 s per device). Including the 12 h post-processing soak in sodium hydroxide to remove the solid support material, the total time to print and process 221 devices was 13.5 h (3.6 min per device), with a material cost of $2.50 each. The applicability of the fluidic device for point of collection analysis was evaluated using colourimetric determination of iron from soil slurry and environmental samples. Following the reduction of Fe³⁺ to Fe²⁺ using hydroxylammonium chloride, samples were introduced to the fluidic device where particulate matter was retained by the filter, allowing for particulate-free imaging of the red complex formed with 1,10-phenanthroline using a smartphone camera. The calibration curve ranged from of 1-100 mg L^-1 Fe²⁺ and good agreement (95%) was obtained between the point of collection device and Sector Field ICP-MS.