A sensing device for determining the presence of hydrogen peroxide is disclosed. The sensing device comprises a light guide having a distal portion terminating at a light guide tip and a proximal portion, wherein the light guide tip is proximal to a layer of Prussian blue (PB), which is pure (or essentially free of contaminants). The sensing device produces a fast linear response and is durable, due to the robustness and purity of the PB. The PB is chemically deposited proximal to, or on, the light guide tip using a single-source precursor technique. Methods of making and using the device also are disclosed herein.