Additively Manufactured <i>in planta</i> Integrated Microneedle–Microfluidic Sensing: Nondestructive Electrochemical Tracking of Glucose and Water Stress in Agricultural Crop Plants

High Resolution Image Download MS PowerPoint Slide Timely quantification of crop stress physiology remains challenging because conventional assays are destructive, labor-intensive, and poorly suited for continuous monitoring and field deployment. Here, we report a microneedle-enabled electrochemical biosensing platform with smartphone-based data collection for the in planta monitoring of plant stress that integrates three design innovations in a single architecture: (i) a fully integrated hollow microneedle–microfluidic measurement pathway for sap access, (ii) physical isolation of the metal electrodes from direct tissue contact to reduce insertion-zone abrasion of the sensing interface, improving biocompatibility and potentially lowering fouling pathways, and (iii) lithography-free fabrication of a modular transducer on an additively manufactured substrate. The platform comprises a three-electrode gold (Au) transducer modified with a nanostructured reduced graphene oxide (rGO)–chitosan layer. The biosensing platform enabled dual sensing channels via functionalized glucose oxidase (GO x ) and horseradish peroxidase (HRP) for the detection of glucose and water stress-associated hydrogen peroxide (H 2 O 2 ), respectively. The glucose channel showed a strong linear calibration over the tested range, with Pearson’s r = 0.99, R 2 = 0.98, sensitivity of 62.34 μA/mM, and a limit of detection (LOD) of 102.50 μM (∼1.85 mg/dL), while the H 2 O 2 channel exhibited Pearson’s r = 0.99, R 2 = 0.99, sensitivity of 3.65 μA/decade, and an LOD of 3.22 μM. Repeatability across measured standards remained high for both channels, with mean coefficients of variation of 1.31% for glucose and 1.16% for H 2 O 2 . Ex vivo measurements in plant sap, including standard-addition experiments and comparison with commercial benchmark assays, provided validation of analyte concentration determination in plant-derived samples. In planta measurements on maize plants ( Zea mays L.) grown under graded watering treatments revealed statistically significant treatment-dependent glucose and H 2 O 2 signatures over time ( p < 0.05), consistent with carbon-status and oxidative-stress responses to water deficit, respectively. This integrated, manufacturable platform provides a practical route toward real-time, data-driven crop management using minimally invasive electrochemical readouts.