Luminescent carbon nanoparticles immobilized in polymer hydrogels for pH sensing

Luminescent O, N-containing carbon nanoparticles (O, N-CNPs) were synthesized by the one-step method. Their surface chemistry was studied by TPD-MS, TGA, and 1 H NMR. Different groups, carboxyl, imide, and amide groups, were found. The small (O, N)-CNPs dispersed in water have a high quantum yield of 0.26 with respect to quinine sulfate in 0.05 M sulfuric acid. We investigated the change in the fluorescence emission intensity using a titration of a colloidal solution of (O, N)-CNPs with unimolar solutions of KOH, HCl, or NaCl. The quenching efficiency strongly depends on the pH and is less dependent on the content of indifferent electrolytes. The small (O, N)-CNPs showed high fluorescence emission intensity in a neutral buffer in a Krebs solution. Besides, they showed a pronounced pH-dependent fluorescence quenching at acidic pH levels. These small (O, N)-CNPs are promising materials for biomedical applications as fluorescent probes with high acidic sensitivity because of high stability and high intensive fluorescence in a complex water matrix. With this aim, polymer hybrid hydrogels for wound dressings were modified with (O, N)-CNPs. Some of the obtained composites are potentially effective for fluorescence pH-sensitive testing and the screening monitoring of wound healing.