A sensor, system, and method of making a sensor are disclosed. The sensor includes a solid polymer material, and a dopant-containing region of discrete thickness at a surface of the solid polymer. The method of creating the sensor includes impregnating the polymer material with the dopant by contact with a solvent solution containing the dopants. A polymer/solvent gel-layer, whose depth increases with impregnation time, forms after contact of the polymer material in the solvent solution. The dopants are diffused into the polymer material, forming a dopant-containing region of discrete thickness at a surface of the solid polymer.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made with Government support under Contract DE-AC0576RLO1830 awarded by the U.S. Department of Energy. The Government has certain rights in the invention.