Response of paper-based gas sensor with different coating formulations to various amounts of ammonium hydroxide solution (a), 6g/m2 coat weight and 0.5 part dye; (b), 20 g/m2 coat weight and 0.5 part dye; (c), 6 g/m2 coat weight and 1 part dye addition; and (d), 20 g/m2 coat weight and 1 part dye.