Fig. 3.

Preparation of PDA-coated PVDF strips. (A) PVDF strips are dipped into chloroform solution containing DA monomers conjugated with Zn²⁺ aptamer, unmodified DA monomers, and DMPE (left) and subsequently photopolymerized by 254 nm UV irradiation under a mask to yield a blue-colored device (middle). Dipping the device in Zn²⁺ solution causes a blue to pink/red color transition as a result of direct interaction between Zn²⁺ ions in solution and Zn²⁺ aptamers (right). (B) Prepared devices before (left) and after (right) color transition. Scale bar = 2.5 mm. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)