Aqueous transition metal dications Cu2+ and Zn2+ bind to the amide groups of the responsive polymer poly(N-isopropylacrylamide) (PNIPAm). Ratiometric detection by the response of PNIPAm is based on the effect of metal ion binding to ligands that are copolymerized into PNIPAm. Metal ions bound to copolymerized ligands cause a polarity change that shifts the ratio of coil and globule polymer phases, whereby the coil:globule state is monitored by the FRET process of a pair of fluorophores distributed throughout the polymer. This work discusses the interaction of Cu2+ and Zn2+ with PNIPAm amide groups, in competition with the copolymerized ligands. Several aggregation processes are implicated based on [Cu2+] or [Zn2+] from 8 x 10-5 to 2.5 x 10-2 M. These processes are fully reversible by reducing the sample temperature.

Ratiometric Copper(II) and Zinc(II) sensors based on phase change and aggregation of (N-isopropylacrylamide)

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