Hydrogel Film@Au Nanoparticle Arrays Based on Self‐Assembly Co‐Assisted by Electrostatic Attraction and Hydrogel‐Shrinkage for SERS Detection with Active Gaps

Abstract A facile route to fabricate the hydrogel film@Au nanoparticle array composite for a surface‐enhanced Raman scattering (SERS) substrate with high signal sensitivity and signal uniformity based on self‐assembly co‐assisted by electrostatic reaction and hydrogel‐shrinkage is developed. First, the positive‐charged Au nanoparticles (NPs) are self‐assembled on the hydrogel film with opposite charges due to electrostatic attraction to obtain non‐close‐packed Au NP films on both surface sides of the hydrogel film. Then, the non‐close‐packed Au NP films are densified to further form hexagonal close‐packed Au NP arrays on both surfaces due to the principle of minimum free energy during the hydrogel‐shrinkage process. The shrinkage of hydrogel film is proved to be a key process to form hexagonal close‐packed Au NP arrays by densifying the non‐closely packed Au NPs achieved by electrostatically self‐assembled on the hydrogel film. Constructed SERS substrate exhibits high signal sensitivity, colorant molecule amaranth with a concentration as low as 10 −8 m can be detected. This is caused by the uniform array structure with active gaps between neighboring NPs on a large area. Overall, this work paves a way to fabricate functional NP arrays on soft hydrogel, which will be highly helpful to prepare the micro/nano‐structured devices.