Non-monotonic plasmonic alignment governed by liquid-crystalline DNA hydrogel networks

Abstract

Liquid-crystalline ordering in biopolymer networks provides a powerful yet unexplored route for controlling anisotropy in soft materials. Here, we report a DNA–gold nanorod (GNR) hydrogel that exhibits a non-monotonic dependence of strain-induced plasmonic alignment on DNA concentration. The hydrogel is fabricated through a simple thermal annealing process based on DNA denaturation and rehybridization, forming physically crosslinked networks without chemical crosslinkers. Pronounced mechano-responsive color modulation is observed only within a limited concentration regime. When liquid-crystalline (LC) ordering is insufficiently developed, deformation of the matrix is not effectively transferred to the embedded nanorods. Conversely, when DNA packing becomes excessive, the LC phase evolves into densely polydomain textures, in which abundant domain boundaries disrupt long-range strain propagation and suppress nanorod reorientation despite increased bulk stiffness. Rheological measurements, birefringence imaging, and directional FT-IR spectroscopy consistently support this behavior by revealing concentration-dependent differences in network reorganization and deformation continuity. Finally, spatially programmable mechano-optical encryption is demonstrated as a functional example enabled by concentration-controlled DNA-based hydrogels.