An anion responsive molecular valve comprised of poly(4-vinylpyridine) gel-coated Au mesh was developed. At pH 3 the valve closed when the concentration of anions such as Cl-, ClO4-, SCN-, and HSO4- was low, whereas automatically opened upon an increase in the concentration of anion due to collapse of the gel. The valve re-closed upon a loading of a 1 x 10(-3) M HCl solution. The concentration where the valve opens was found to increase in the order of HSO4- < ClO4- = SCN- < Cl- (5 x 10(-3), 8 x 10(-3), 8 x 10(-3), and 8 x 10(-2) M, respectively). This order was consistent with that of a concentration where the gel shrinks and was rationalized by affinity between an anion and pyridyl group of the gel. The valve exhibited repeated opening and closing 5 cycles upon alternative loading of NaClO4 (pH 3) and 1 x 10(-3) M HCl solutions, and 20 cycles for Na2SO4 (pH 3) and HCl solutions. The effect of cation was also studied. (C) 2013 Elsevier B.V. All rights reserved.