Plasmonic Biosensing with Aluminum Thin Films under the Kretschmann Configuration

Aluminum has recently attracted considerable interest as a plasmonic material due to its unique optical properties, but most work has been limited to nanostructures. We report here SPR biosensing with aluminum thin-films using the standard Kretschmann configuration that has previously been dominated by gold films. Electron-beam physical vapor deposition (EBPVD)-prepared Al films oxidize in air to form a nanofilm of Al₂O_3, yielding robust stability for sensing applications in buffered solutions. FDTD simulations revealed a sharp plasmonic dip in the visible range that enables measurement of both angular shift and reflection intensity change at a fixed angle. Bulk and surface tests indicated that Al films exhibited superb sensitivity performance in both categories. Compared to Au, the Al/Al₂O₃ layer showed a marked effect of suppressing nonspecific binding from proteins in human serum. Further characterization indicated that Al film demonstrated a higher sensitivity and a wider working range than Au films when used for SPR imaging analysis. Combined with its economic and manufacturing benefits, the Al thin-film has the potential to become a highly advantageous plasmonic substrate to meet a wide range of biosensing needs in SPR configurations.