Indium tin oxide (ITO) is a transparent conducting material with exceptional electrical and optical properties, widely used in biosensing and bioelectronics. Functionalization of ITO with linker molecules enables covalent attachment of biomolecules, allowing for dual-mode optical and electrochemical detection. Carbonic anhydrase IX (CA IX), a transmembrane enzyme overexpressed in hypoxic tumors, is a promising biomarker for cancer diagnostics due to its restricted expression in normal tissues. However, conventional detection methods are time-intensive and unsuitable for point-of-care applications. In this study, ITO surfaces were functionalized using silane-based chemistry to immobilize CA IX-specific antibodies, creating a novel biosensing platform. The biosensor utilized a secondary horseradish peroxidase (HRP)-conjugated antibody to catalyze the oxidation of luminol in the presence of hydrogen peroxide, producing a chemiluminescent and electrochemical signal. Characterization of the biosensor via a dual-mode optical and electrochemical approach revealed efficient antibody immobilization. Due to the high variation observed in the optical approach, limit of detection (LOD) experiments were conducted exclusively with electrochemistry, yielding an LOD of 266.4 ng/mL. These findings demonstrate the potential of ITO-based electrochemical biosensors for sensitive and selective CA IX detection, highlighting their applicability in cancer diagnostics and other biomedical fields.

Indium tin oxide (ITO) is the benchmark transparent conductor for displays and for electrochemical and optical sensors, but its brittleness, cost, and indium supply risk limit its use in flexible, large-area devices. Oxide/metal/oxide multilayers, namely transparent conducting oxide (TCO)/metal/TCO stacks such as ITO/metal/ITO (IMI) and dielectric–metal–dielectric (DMD) stacks, decouple sheet resistance from transmittance: a ductile ultrathin metal core carries the current, while the outer oxides act as anti-reflection layers. This review compares the design rules, deposition routes, and characterisation of these electrodes. Single-study tables relate architecture, substrate, and processing conditions to electrical, optical, and mechanical performance, and the review explains why reported figures of merit are rarely comparable. Ag-based TCO/metal/TCO stacks are the most mature option for flexible displays, and asymmetric stacks with nucleation-controlled Ag are a promising indium-free route. Open limits include ultrathin-metal growth, metal absorption, Ag/Cu stability, and oxide cracking. No biosensor built on a multilayer electrode has been reported; ITO already enables dual electrochemical and optical readout, so testing multilayers against ITO is the next step. Artificial intelligence (AI)-assisted design of multilayer electrodes is at an early stage.