Photophysical properties of an amino acid (tryptophan) have been studied in different aqueous micellar environments at various pH using steady-state emission spectroscopy. We report herein tuning of the sensory capability of tryptophan in biomimicking ionic micellar nanocage at various pH. In an un-buffered aqueous solution (or at pH 7) and pH 4 the fluorescence quenching efficiency of tryptophan in the presence of trace metal ion Cu2+ increases significantly around critical micelle concentration (CMC) of an anionic surfactant sodium dodecyl sulfate (SDS). At pH 11 fluorescence quenching efficiency of tryptophan increases significantly around CMC of a cationic surfactant cetyl trimethyl ammonium bromide (CTAB). (C) 2008 Elsevier B.V. All rights reserved.