Nanostructured Titania-Gold biosensor platforms for dual-mode optical and electrochemical biomolecular recognition

• Au-decorated TiO2 nanotubes are presented as a dual-mode biosensor platform. • Smallest AuNPs enhance fluorescence and charge transfer response. • DNA hybridisation yields 5× stronger PL and 69 % RCT increase for 5Au-TiO₂. • Electric field subtly modulates signal via SVD-aided DEIS analysis. • Scalable fabrication via sputtering and anodisation ensures reproducibility. This study presents the fabrication of a novel biosensor platform based on semitransparent titania nanotubes (TiO2NTs) decorated with thermally treated gold layers. The platform is designed for multimodal opto-impedimetric monitoring, exploring the impact of gold coverage and morphology on physicochemical properties and electrochemical activity. When annealed, the gold layer of different thicknesses results in various nanoarchitectures, modulating charge transfer kinetics, plasmonic effects, and steric hindrance within the receptor layer. The proof-of-concept aptamer-based platform for biomolecular recognition is also discussed. Furthermore, the investigation explores electric field modulation through voltammetry to identify efficient analyte-to-receptor binding, verified by singular value decomposition (SVD) for rapid diagnostics. A non-trivial, electrostatic-driven behaviour of DNA conformation at the electrode surface was identified and discussed. A surface-enhanced fluorescence effect was achieved for the smallest gold layer thickness of 5 nm, where DNA hybridisation is most effective due to the highest surface curvature. This approach leverages both biosensor surface nanostructurization and multiparametric impedance discriminant analysis (MIDA)-aided signal processing to enhance biosensor performance. Our platform offers a promising route for developing advanced biosensors with dual-mode capabilities, integrating optical and electrochemical tools. Moreover, the methods employed for fabricating this novel platform, namely magnetron sputtering and anodisation, are scalable and cost-effective while offering high uniformity and precise control over nanostructure dimensions, making them ideal for various applications.