Deposition methods govern the electrochemical performance of graphene-derivative functionalized screen-printed electrodes: a practical framework for electrode surface characterization

• Deposition methods govern the electrochemical performance of modified electrode • Structured protocol links electrode surface characterization to electrochemistry • Inkjet printing yields uniform functionalization versus drop-casting on electrodes • Coverage uniformity and layer thickness explain impedance and voltammetric response • Electrochemical response follows accessible active sites, not deposited mass The performance of functionalized electrochemical sensors is commonly linked to the intrinsic properties of the material used for electrode surface modification. However, the role of the deposition method itself is often overlooked, even though it critically defines the interfacial structure and batch-to-batch reproducibility. In addition, electrode functionalization is rarely accompanied by comprehensive surface characterization, which limits mechanistic interpretation and transferability of results. Here, we introduce a structured, multiscale characterization framework that isolates how deposition methods define the electrochemical interface on printed electrodes. A commercial screen-printed carbon electrode platform was functionalized with nitrogen-doped graphene acid using conventional drop-casting and inkjet printing as a controlled deposition strategy. Complementary local and electrode-scale analyses were used to quantify film homogeneity, thickness distribution, microtopography, wetting behavior, and coating integrity. These interfacial descriptors were systematically correlated with electrochemical performance using impedance spectroscopy and voltammetric benchmarking. Inkjet printing produced thin, laterally uniform coatings with enhanced wetting and significantly reduced electrode-to-electrode variability. In contrast, drop-casting resulted in edge-enriched films dominated by coffee-ring drying and pronounced interfacial heterogeneity. The electrochemical response was governed by the spatial accessibility and distribution of the functional layer rather than by the nominal deposited mass. This positions deposition technique among primary design parameters in electrochemical sensor development. The framework presented here provides a practical characterization and reporting protocol that supports reproducible and mechanistically interpretable optimization of functionalized electrochemical interfaces. Electrochemical performance is governed by how a functional layer is structured and coupled to the electrode: continuity, electronic connectivity, and mechanical robustness determine kinetics and reproducibility. Spatially resolved, complementary interface characterization is essential to translate surface architecture into reliable device performance.