Differential colorimetric pH measuring microfluidic manifold with embedded sensors and actuators for textile dyeing industry

This work presents a fully integrated microfluidic opto-electro-mechanical platform demonstrating a proof-of-concept for real-time colorimetric pH sensing in intensely colored textile solutions. The system features acrylic manifold with dual spectral sensors, an embedded magnetic mini-stirrer for rapid mixing, custom bidirectional syringe pumps, and automated fluid routing. An automated manifold-based implementation of differential colorimetry is presented, combining upstream and downstream absorbance measurements to mathematically compensate for background dye spectra. Mixing performance was validated using yellow and blue dyes (15 mL/hr flow rates), achieving complete homogenization within 0.1 s and consistent 1:1 dilution. pH sensing was evaluated using reactive blue dye (5 g/L) and reactive black dye (1 g/L) across pH 6.0–9.0. Conventional (uncompensated) measurements exhibited dye-dependent nonlinearity and suppressed sensitivity, whereas the differential method restored a linear response comparable to transparent samples (R² > 0.94). Within the indicator’s optimal working range (pH 6.8–8.2), the differential compensation algorithm achieved absolute measurement errors from 0.01 to 0.12, 0.07 to 0.09, and 0.14 to 0.27 pH units for transparent, black, and blue samples, respectively. These results demonstrate that the proposed platform effectively eliminates spectral interference from highly absorbing dyes, overcoming the specific bottleneck of high background absorbance, laying the groundwork for inline pH sensing in textile processing. The modular design provides a scalable foundation for broader multi-analyte chemical monitoring in industrial environments.