Affordable droplet-based flow analyzer with peristaltic micro-pumps for fluorescent ammonium sensing

An affordable droplet-based flow analyzer incorporating peristaltic micro-pumps has been developed for fluorescent ammonium sensing. The cost-effective peristaltic micro-pumps, modified using 3D-printing techniques, feature a 3D-printed pump base integrated with a Hall sensor to monitor the rotation of the pump motor. This setup generates a pulse flow instead of a continuous flow, delivering specific volumes (typically between 3 to 4 μL) of solution with each rotation. By using separate pumps to deliver the aqueous and oil phases, these phases merge to form a droplet flowing stream. The relative standard deviation (RSD) values for droplet volumes range from 3.97 % to 5.99 % (n=50) across different pumps. The analyzer utilizes a reaction between ammonium, ortho-phthalaldehyde, and sulfite to produce a fluorescent derivative, allowing for sensitive detection of low ammonium concentrations. A custom light-emitting diode (LED)-based fluorescence detector has been fabricated using 3D printing, ensuring cost-effective production. The analyzer provides a limit of detection of 0.02 μM (3σ) and an RSD of 0.15 % (n=10, 1 μM ammonium). This analyzer offers several practical advantages, including reduced reagent consumption and the potential for further development in distributed on-site analysis. The use of 3D printing facilitates rapid prototyping and customization, making the system adaptable to various analytical applications.