Exclusive detection of sub-nanomolar levels of palladium(II) in water: an excellent probe for multiple applications.

A new colorimetric probe has been developed for the detection and estimation of Pd(II) at sub-nanomolar concentrations. The probe consisted of rhodamine (signaling unit), which was linked with a bis-picolyl moiety (binding site) through a phenyl ring. Pd(II) induced opening of the spirolactam ring of the probe with the generation of a prominent pink color. The excellent selectivity of the probe towards Pd(II) over Pd(0) or Rh(II) ensured its potential utility for the detection of residual palladium contamination in pharmaceutical drugs and in Pd-catalyzed reactions. The probe showed a "turn-on" (bright yellow) fluorescence upon the addition of Pd(II), which made it suitable for the detection of Pd contaminants in mammalian cells.