Nanostructured Copper by GLAD for Non-Enzymatic L-Lactic Acid Sensors

The advancement of biochemical sensing technologies relies heavily on the development of nanostructured sensors with superior electrochemical performance. In this work, a high-sensitivity, non-enzymatic L-lactic acid sensor was fabricated by coating a screen-printed carbon electrode with copper using the glancing angle deposition (GLAD) technique. During deposition, the substrate was positioned at an 80° tilt relative to the target while undergoing continuous rotation. Coatings were applied for 10 and 15 minutes at rotation speeds of 0 rpm and 45 rpm. Electrochemical characterization revealed a fast response and high sensitivity toward L-lactic acid. The GLAD-modified sensor (45 rpm, 15 minutes) achieved an active surface area of 14.14 mm²—an 11.1% increase compared to the apparent surface area of the unmodified carbon electrode (12.57 mm²), as determined using the Randles–Sevcík equation.

Atomic force microscopy confirmed a 16.3% increase in surface area, attributed to the growth of smaller nanostructures during rotation. Scanning electron microscopy images showed a porous, stacked morphology composed of copper (Cu) and copper oxide (CuO). The sensor detected L-lactic acid across the 0.75–10 mM range, with a sensitivity of 3.98 μA/mM and a detection limit of 0.56 μM. These results demonstrate that copper nanostructures engineered via GLAD can substantially enhance the selectivity and sensitivity of electrochemical sensors, offering a promising route for the development of next-generation sensing platforms.