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 (SP1) was synthesized and its metal-sensing properties were investigated using UV-vis spectrophotometry. The formation of a metal complex between SP1 and Cu2+ was associated with a color change that can be observed by the naked eye as low as 6 mu M and the limit of detection was found to be 0.11 mu M via UV-vis spectrometry. Colorimetric data showed linearity of response in a physiologically relevant range (0-20 mu M Cu2+) with high selectivity for Cu2+ ions over biologically and environmentally relevant metals such as Na+, K+, Mn2+, Ca2+, Zn2+, Co2+, Mg2+, Ni2+, Fe3+, Cd2+, and Pb2+. Since the color change accompanying SP1-Cu2+ complex formation could be detected at low micromolar concentrations, SP1 could be viable for field testing of trace Cu2+ ions.

Automated summary

This study demonstrated colorimetric copper sensing at low micromolar levels using dimethylamine-functionalized spiropyran (SP1). The SP1-Cu2+ complex formation led to a color change that could be observed by the naked eye as low as 6 μM, with a detection limit of 0.11 μM. SP1 showed high selectivity for Cu2+ ions and could be used for field testing of trace Cu2+ ions.