A selective sensing technique for Hg^II ions has been developed utilizing an amino acid based probe. The design, synthesis and efficacy of the chemosensor have been described. The probe (SALTYR) was successfully synthesized from a naturally occurring amino acid after sequential functional group modifications. Recognition studies were performed against a wide variety of metal cations and anions including real water samples. All the analyses were carried out utilizing UV–vis and fluorescence techniques with micromolar concentrations of the probe in HEPES buffer. The selectivity of the probe was found to be very specific for Hg^II with quenching of the fluorescence in a turn-off mechanism. The detection limit of the probe SALTYR was calculated and found to be 5.9 × 10⁻⁶ M. Quantum chemical calculations demonstrated the stability of the Hg^II complex in the context of binding energy. Furthermore, the change of the pattern of emission spectra has been rationalized with a logic gate model.