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

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.