PH-activated off/on nanosystem for combined photothermal/chemodynamic antibacterial application

Photothermal therapy (PTT) holds great promise for the treatment of bacterial infections, but the traditional “always-on” photothermal agents severely restrict further clinical applications. Here, a pH-activated off/on PTT/CDT nanosystem for synergistic antibacterial/antibiofilm application was reported. Using mesoporous silica as a nanocarrier, such activatable photoagent was achieved via specific redox reactions between 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and Fe(III), which could switch PTT/CDT from “off” to “on” in response to pH. Under neutral conditions, the nanosystem was “off state” due to the isolation of Fe(III) and ABTS. Whereas under acidic conditions, the nanosystem selectively activated to “on state”. The released Fe(III) can oxidize ABTS to photothermal reagent of ABTS •+ , and itself was reduced to Fe(III)/Fe(II) pairs. The Fe(II)/Fe(III) pairs can catalyze the H 2 O 2 to hydroxyl radicals (•OH) via Fenton reactions for chemodynamic therapy (CDT). The in vitro results showed that the pH-activated off/on PTT/CDT nanosystem have an excellent antibacterial efficiency (˃90 %) and enhanced antibiofilm activity for Escherichia coli ( E. coli ) and Staphylococcus aureus ( S. aureus ).