1：Experimental Design and Method Selection:

The study involved designing and fabricating 3D printed photometric and fluorometric flow-through detectors using Fused Filament Fabrication (FFF) technology. The designs were customizable with variations in aperture (internal diameter of flow channel) and optical path length. Two detection methods were covered: photometric and fluorometric, using LEDs as light emitters and CCD spectrophotometers or LEDs as detectors.

2：Sample Selection and Data Sources:

Model dyes bromothymol blue (for photometry) and fluorescein sodium salt (for fluorometry) were used. Stock solutions were prepared in sodium tetraborate buffer (pH 9.18). Deionized water was used throughout.

3：18). Deionized water was used throughout. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: A Flashforge Dreamer FFF 3D printer with PLA (polylactide) and Ninjaflex (thermoplastic polyurethane) filaments; standard cuvettes from Sarstedt; Teflon tubing, solenoid valves, and micropumps from Cole Parmer and Bio-Chem Fluidics; Arduino-based controller; Ocean Optics USB2000FLG CCD detector; LEDs for light emission and detection; Agilent U1231A multimeter; chemicals from Avantor Performance Materials.

4：Experimental Procedures and Operational Workflow:

A multicommutated flow analysis system was set up with two parallel lines for sample injection and dilution. Analytical protocols involved standard injections with specific valve and pump actuation sequences. Detectors were assembled by inserting polystyrene glasses and rubber inserts into 3D printed housings, with tubing connected and sealed. Calibration curves were generated for various detector geometries.

5：Data Analysis Methods:

Signals were recorded using CCD detectors via USB interface or LED detectors with a multimeter in voltmeter mode. Data was analyzed for peak heights, calibration curves, and relative standard deviations (RSD) to assess repeatability and performance.