A new 3D printing milli-fluidic device with integrated nanojunction for on-site colorimetric analysis of iron in water and soil samples

Fabrication and bonding represent significant challenges in the production of micro- and milli-fluidic devices with integrated functions. Here, to investigate the formation of nanojunction through controlled dielectric breakdown, a thermoplastic material was utilized to create a three-dimensional (3D) printed milli-fluidic device. The device was constructed using a fused deposition modeling 3D printer with acrylonitrile butadiene styrene (ABS). With the application of a voltage between 20 and 25 kV, which was cut off when the current threshold was reached, a controlled dielectric breakdown was used to create a nanojunction in the thin slice of ABS. Both altering the current threshold and the electrolyte ionic strength used for breakdown allowed for different sizes of the nanojunction to be created. The size and transport characteristics of the nanojunctions were observed using electrophoretic transport of two proteins: fluorescamine-labeled bovine serum albumin (f-BSA; 2–4 nm) and R-phycoerythrin (RPE; <10 nm in size), and a small molecule (fluorescein, ∼0.5–1.0 nm) and ions (thiocyanate, ∼0.3 nm). Colorimetric measurement of iron from water and soil slurry samples was utilized to examine the suitability of the 3D-printed device for on-site analysis. Samples were freshly introduced to the 3D-printed milli-fluidic device after Fe 3+ was reduced to Fe 2+ using hydroxylammonium chloride. The nanojunction captured particle matter, allowing for particulate-free smartphone camera detection for imaging the orange-brown complex produced using 1,10-phenanthroline. The calibration curve covered 1 to 100 µg/mL of Fe 2+ using the 3D printed device, which showed good agreement (97.5%) with ICP-MS.