Fluorescent Polymeric Nanofibers as Ratiometric Multiplexed Skin Sensors of pH and Oxygen

Monitoring wound healing requires the development of multiplexed sensors with remote readout. Here, we report fluorescent polymeric nanofibers and nanorods as ratiometric sensors of two important physiological parameters: pH and oxygen. These nanofibers operate by dual Forster resonance energy transfer (FRET) between large number of energy donor dyes (reference) and limited number of two distinct energy acceptors sensitive to these two analytes. This configuration ensures signal amplification of analyte-sensitive energy acceptor by light-harvesting principle. The oxygen sensor is based on encapsulation of cationic donor dyes (cyanine or rhodamine derivatives) with bulky hydrophobic counterions as FRET donors and Pt-porphyrins as energy acceptors inside the nanofibers. In the pH sensor, nanofibers loaded with donor dyes are functionalized at the surface with the rhodamine-derived energy acceptor, which ensures sensitivity to pH. The developed nanosensors show ratiometric response to the analytes by changing the intensity ratio of the analyte-sensitive acceptor vs the reference donor dye. Finally, a multiplexing device combining oxygen- and pH-sensing modalities is developed, which enable sensing both pH and oxygen in a wound model by recording its emission in the red, green, and blue channels. The obtained materials will find numerous biomedical applications, including monitoring wound healing, compatible with simple smartphone-based detection.