3D-printed miniaturized sensors integrated with hydrogels for semisolid-state electroanalysis.

The transition toward decentralized environmental monitoring demands the development of integrated, portable platforms capable of combining sampling, pre-concentration, and electrochemical detection into a single device. This study introduces a proof of concept for a novel semisolid-state electrochemical platform driven by low-cost poly(sodium acrylate) hydrogels integrated with unmodified 3D-printed miniaturized sensors. The devices were fabricated via 3D pen technology using conductive polylactic acid/graphite filaments and extensively characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Considering the advantage of the hydrogel's swelling dynamics, the proposed approach facilitates direct analyte uptake and provides a stable, highly controlled environment for the electrochemical process, significantly simplifying sample handling. To demonstrate the analytical feasibility of this semisolid system, sulfanilamide was selected as a representative model of veterinary antibiotic residues. Under optimized square wave voltammetry conditions (15 Hz frequency, 8 mV step potential, and 55 mV amplitude in 0.1 mol L-1 BR buffer, pH 10.0), the platform delivered a linear response from 10 to 50 µmol L-1 and a limit of detection of 5.55 µmol L-1. The architecture's robustness was validated through successful recovery trials (99% to 108%) in complex aquaculture water and pharmaceutical formulations. This hydrogel-based, 3D-printed platform establishes a baseline for a simple and low-cost alternative sampling strategy, representing a significant development in field-deployable tools for smart environmental monitoring.