Authorizing multiple chemical passwords by a combinatorial molecular keypad lock.

A combinatorial fluorescent molecular sensor operates as a highly efficient molecular security system. The ability of a pattern-generating molecule to process diverse sets of chemical inputs, discriminate among their concentrations, and form multivalent and kinetically stable complexes is demonstrated as a powerful tool for processing a wide range of chemical "passwords" of different lengths. This system thus indicates the potential for obtaining unbreakable combination locks at the molecular scale.