Zinc-ed in: A highly fluorescent zinc complex of triazole-linked calix[4]arene (see scheme), [ZnL], for the selective recognition of Cys and other protein-bound/free thiols in the blood-serum milieu by mimicking the Zn 2+-induced redox switch has been developed. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.