Towards a single bioactive substrate combining SERS-effect and drug release control based on thin anodic porous alumina coated with gold and with lipid bilayers

Thin anodic porous alumina (tAPA), engineered by electrochemical anodization of aluminum and post-fabrication etching, has already shown surface-enhanced Raman scattering (SERS) activity, after overcoating with a thin gold film. On the other hand, the tAPA nanoporous surface, which is biocompatible and presents controlled roughness, has been extensively investigated as a substrate for living cell cultures. Here, we are interested in exploiting the nanoporosity of tAPA as a drug reservoir and demonstrating drug-delivery capabilities of these substrates which can be combined with the above cell-seeding and SERS activities. We focused on the loading/elution of a test drug, the nonsteroidal anti-inflammatory and analgesic molecule Diclofenac. We carried out pore loading of differently concentrated aqueous solutions of the test drug, and characterized the elution profiles by UV-Vis absorbance, using the lipid bilayers coated on the top surface as a mechanism for retarded elution from the pores, providing a more sustained release. We also demonstrated that, by changing an environmental parameter such as the pH, we can trigger an increased release of the drug. Additionally, we investigated the tAPA adsorption properties by quartz crystal microbalance technique with dissipation monitoring (QCM-D). For the purpose, anodization was carried out on an Al-coated quartz, which resulted in successful fabrication of tAPA on the sensor. Finally, the process of lipid bilayer formation on the nanoporous sensor, as well as the test drug loading, was demonstrated by QCM-D.