Development and characterization of litmus-based pH sensor films for real-time monitoring in 3D printed microreactor channels

This study aimed to develop and characterize pH sensor films prepared by immobilizing a litmus indicator in a silane matrix coated within microreactor channels. The microreactors were fabricated using fused filament fabrication (FFF) technology with polyethylene terephthalate glycol (PETG) filament. A sol-gel method was employed to produce thin pH sensor films, using tetraethoxysilane (TEOS) and phenyltrimethoxysilane (PTMS) as precursors, with the litmus indicator incorporated into the silane matrix. To evaluate the performance of the pH sensor films, RGB analysis software was utilized to detect color changes when the system was exposed to acidic and basic solutions. Characterization techniques also included contact angle measurements with water and diiodomethane, as well as Fourier-transform infrared spectroscopy (FTIR). After the comprehensive analysis of the pH sensor films on the test plates, the sensor films that exhibited the most significant color changes were applied to the microreactor channels. Both on test plates and in microreactor channels, the pH sensor films responded to the changes in pH with observable color shifts within a few seconds. These reusable pH-sensitive films within microreactor channels exhibit rapid response time of less than 5 s, making them ideal for real-time monitoring in smart sensor applications, including Industry 4.0 and Internet-of-Things-based (IoT) sensor networks.

Graphical Abstract