Spiropyran-Based Soft Substrate with SPR, Anti-Reflection and Anti-NRET for Enhanced Visualization/Fluorescence Dual Response to Metal Ions

The photoluminescence of modified spiropyran on solid surfaces is poor, and the fluorescence intensity of its MC form is weak, which affects its application in the field of sensing. In this work, a PMMA layer containing Au nanoparticles and a spiropyran monomolecular layer are coated on the surface of a PDMS substrate with inverted micro-pyramids successively by means of interface assembly and soft lithography, and the overall structure is similar to insect compound eyes. The anti-reflection effect of the bioinspired structure, the SPR (surface plasmon resonance) effect of the Au nanoparticles and the anti-NRET (non-radiation energy transfer) effect of the PMMA isolation layer raise the fluorescence enhancement factor of the composite substrate vs. the surface MC form of spiropyran to 5.06. In the process of metal ion detection, the composite substrate can achieve both colorimetric and fluorescence response, and the detection limit for Zn2+ can reach 0.281 μM. However, at the same time, the lack of the ability to recognize specific metal ions is expected to be further improved by the modification of spiropyran.