Nanopapers were fabricated as previously reported . In brief, Tollens' reagent containing 300 mM ammonia and 50 mM silver nitrate was prepared in a 2 L glass beaker in a 55 °C water bath. Glass microfiber papers were immersed in the solution, and 500 mm glucose solution was added to initiate the silver mirror reaction. After the reaction was complete, the filter papers were rinsed thoroughly with deionized water and 2-propanol.