Number 136 (Story #1), July 9, 1993 by Phillip F. Schewe and Ben Stein MOLECULAR-LEVEL "AND" LOGIC-GATE behavior has been observed by scientists at Queen's University, Belfast. In this case special polymer molecules are made to fluoresce strongly (constituting a sort of output signal) only when two hydrogen or two sodium ions (constituting the input) bind to each of two "recognition" sites on the molecule. This process cannot yet be employed in a logical device, however, because the necessary molecular circuitry ("wires" in the form of conducting molecules) for systematically conveying input signals---in the form of ions---to the molecule has not been developed. Meanwhile, certain forms of the receptor molecule can be used to monitor ion concentrations in some solutions. (A. de Silva et al., Nature, 1 July 1993.)