Wearable 3D-printed solid microneedle voltammetric sensors based on nanostructured gold for uric acid monitoring

Microneedle-based electrochemical sensors (MES) are developed as interface systems between the sensor and interstitial fluid (ISF), allowing the transdermal monitoring of analytes with clinical value. However, the widespread adoption of MES platforms to enable advances in devices for health monitoring is still a challenge. Herein, we propose an affordable and versatile wearable patch based on 3D-printed microneedle arrays to facilitate the development of electrochemical sensors. A plug-in design with a three-electrode setup allows a rapid configuration as a voltammetric sensor. Sputtering is employed to fabricate microneedle array electrodes based on nanostructured gold. The material highlights the excellent electrochemical performance due to the nanostructured surface and provides antibiofouling capability against protein. The ability of the MES to penetrate porcine skin without damage is successfully demonstrated, showing a decrease in the signal of only 8.4 % after four insertions. Thereafter, the analytical characterization for uric acid (UA) is completed in buffer solution, protein-enriched solution, emulated ISF, and in an ex vivo setup (slope 9.2 nA μM^-1), showing remarkable performance within the physiological range of UA (150-500 μM) and excellent reversibility while pierced in porcine skin (<3.3 % difference between upwards and downwards calibrations). Finally, a preliminary on-body test shows the capability of the MES to pierce the skin, proving the robustness of the wearable patch for on-body analysis and exhibiting a 5.8 % difference in the signal before and after the test. The results demonstrated a versatile microneedle-based electrochemical cell utilizing nanostructured gold, enabling the rapid development of innovative electrochemical sensors for ISF monitoring.