Highly Sensitive and Selective Spiropyran-Based Sensor for Copper(II) Quantification.

The metal-binding capabilities of the spiropyran family of molecular switches have been explored for several purposes from sensing to optical circuits. Metal-selective sensing has been of great interest for applications ranging from environmental assays to industrial quality control, but sensitive metal detection for field-based assays has been elusive. In this work, we demonstrate colorimetric copper sensing at low micromolar levels. Dimethylamine-functionalized spiropyran () was synthesized and its metal-sensing properties were investigated using UV-vis spectrophotometry. The formation of a metal complex between and Cu was associated with a color change that can be observed by the naked eye as low as ≈6 μM and the limit of detection was found to be 0.11 μM via UV-vis spectrometry. Colorimetric data showed linearity of response in a physiologically relevant range (0-20 μM Cu) with high selectivity for Cu ions over biologically and environmentally relevant metals such as Na, K, Mn, Ca, Zn, Co, Mg, Ni, Fe, Cd, and Pb. Since the color change accompanying -Cu complex formation could be detected at low micromolar concentrations, could be viable for field testing of trace Cu ions.