Carbon nanoparticles with phenylsulfonate negative surface functionality (Emperor 2000, Cabot Corp.) are coated with positive chitosan followed by hydrothermal carbonization to give highly pH-responsive core-shell nanocarbon composite materials. With optimised core-shell ratio (resulting in an average shell thickness of ca. 4 nm, estimated from SANS data) modified electrodes exhibit highly pH-sensitive resistance, capacitance, and Faradaic electron transfer responses (solution based, covalently bound, or hydrothermally embedded). A shell "double layer exclusion" mechanism is discussed to explain the observed pH switching effects. Based on this mechanism, a broader range of future applications of responsive core-shell nanoparticles are envisaged.
Xia, F., Pan, M., Mu, S., Xiong, Y., Edler, K. J., Idini, I., ... Marken, F. (2012). Hydrothermal core-shell carbon nanoparticle films: Thinning the shell leads to dramatic pH response. Physical Chemistry Chemical Physics, 14(45), 15860-15865. https://doi.org/10.1039/c2cp42659e