Development of Novel pH-Sensitive Dyes for Early Stage Wound Infection Detection and Monitoring

Early-stage wound infections are challenging to detect; however, a timely diagnosis significantly improves healing outcomes and reduces the risk of scarring or systemic complications. Healthy skin is mildly acidic (average pH ~4.7), while chronic or infected wounds remain alkaline (7.15–8.9) and gradually return to acidic during healing. Real-time monitoring of wound pH has emerged as a valuable tool for tracking the progression of healing, providing an early warning of potential bacterial infection, and reducing unnecessary antibiotic therapy. pH-sensitive dyes that undergo visible color changes within carrier materials present a simpler and cost-effective approach for wound pH monitoring. Current pH indicators, however, suffer from low photostability and dye leaching, limiting their practical use. This work presents the design, synthesis, and functional evaluation of carborhodol dyes, developed as photostable alternatives to conventional pH indicators, optimized for the physiological pH range. Nine novel carborhodols were synthesized from their respective carbopyronine precursors through hydrolytic deamination, with structural modifications designed to enhance photostability, solubility, and bioconjugation potential. The dyes exhibit distinct pH-dependent optical properties, with pKa values in the physiologically relevant range (5–7). Deprotonation leads to increases in absorption, quantum yield, and fluorescence lifetime, enabling sensitive detection of pH changes by both colorimetric and fluorogenic modes. Compared to the standard indicator fluorescein and the common biological label Cy5, carborhodols display superior photostability, addressing a key limitation of existing probes. Additionally, the basic forms exhibit pronounced positive solvatochromism, indicating their utility as polarity-sensitive probes. To demonstrate practical applications, the dyes were incorporated into polymer-based systems. Encapsulation in PEG-b-PLA vesicles resulted in an increase in fluorescence intensity with rising pH levels, whereas covalent grafting to chitosan films yielded hydrogel dressings capable of reversible, real-time pH monitoring within the wound-relevant range. These hybrid materials combine high stability and biocompatibility, with pH-dependent color changes visible to the naked eye under ambient light, and fluorescence turn-on readily detectable by the eye under UV illumination, showing the successful translation of molecular dye properties into functional biomedical platforms, and highlighting their promise for smart wound dressings and related diagnostic devices.