Plasmonic control of drug release efficiency in agarose gel loaded with gold nanoparticle assemblies

Plasmonic nanoparticles (NPs) are exploited to concentrate light, provide local heating and enhance drug release when coupled to smart polymers. However, the role of NP assembling in these processes is poorly investigated, although their superior performance as nanoheaters has been theoretically predicted since a decade. Here we report on a compound hydrogel (agarose and carbomer 974P) loaded with gold NPs of different configurations. We investigate the dynamics of light-heat conversion in these hybrid plasmonic nanomaterials via a combination of ultrafast pump-probe spectroscopy and hot-electrons dynamical modeling. The photothermal study ascertains the possibility to control the degree of assembling via surface functionalization of the NPs, thus enabling a tuning of the photothermal response of the plasmon-enhanced gel under continuous wave excitation. We exploit these assemblies to enhance photothermal release of drug mimetics with large steric hindrance loaded in the hydrogel. Using compounds with an effective hydrodynamic diameter bigger than the mesh size of the gel matrix, we find that the nanoheaters assemblies enable a two orders of magnitude faster cumulative drug release toward the surrounding environment compared to isolated NPs, under the same experimental conditions. Our results pave the way for a new paradigm of nanoplasmonic control over drug release.