Here, we present three-dimensional-printed dual-channel flow-through miniaturized devices (3Dd) with dual electrochemical detection (EDd) integrating two working electrodes each in an in-channel configuration (3Dd-EDd). Prussian Blue (PB) shell-gold nanoparticles ((PB)AuNP) core-based electrochemistry was chosen for selective hydrogen peroxide determination. 3Dd-EDd devices exhibited impress stability, identical intrachannel and interchannel electrochemical performances, and excellent interdevice precision with values under 9%, revealing the reliability of the design and fabrication of the devices. 3Dd-EDd enabled long-term reliable hydrogen peroxide determination at physiological pH in Caco-2 cells under prooxidant stimulation demonstrating its outstanding electroanalytical performance. The results highlight the analytical versatility and trustworthiness of 3D-printing-based devices at miniaturized scale integrating advanced electrochemistry and its potential for real-time cell monitoring.