Fabrication of Sensitive Voltammetric Sensors and Microsensors for Piroxicam by Modifying Nafion and MWCNTs Composite Film on the Electrode Surface (Supporting Information)

<p dir="ltr">Piroxicam is a common painkiller and anti-inflammatory drug. Precise monitoring of piroxicam levels can mitigate side effects, but current methods are often slow and complicated. An easily fabricated and highly sensitive voltammetric sensor for piroxicam was developed by drop-coating a composite of multi-walled carbon nanotubes (MWCNTs) and Nafion onto the electrode surface. The morphological and electrochemical characteristics of the Nafion-MWCNTs composite film were analyzed to reveal the synergistic effects of Nafion and MWCNTs. The composite film was then applied to modify a glassy carbon electrode (GCE), which served as a voltammetric sensor for the detection of piroxicam. When compared to previous reports, the sensor demonstrated efficient electrochemical oxidation of piroxicam with remarkable sensitivity, reproducibility, and stability. Under optimized conditions, the Nafion/MWCNTs/GCE exhibited a linear voltammetric response for piroxicam in the concentration range of 5 × 10⁻⁹ to 8 × 10⁻⁶ mol L⁻¹ and 8 × 10⁻⁶ to 6 × 10⁻⁵ mol L⁻¹ respectively, with a detection limit of 4 × 10⁻⁹ mol L⁻¹. The sensor was successfully applied to detect piroxicam in real tablet samples, providing satisfactory recovery values. Furthermore, the composite film was applied to the surface of a platinum microelectrode, resulting in a micro-sensor for piroxicam detection. With the typical small size and the radial diffusion field, the micro-sensor of piroxicam exhibited increased sensitivity and possessed unique properties. Particularly, fast and accurate response across various piroxicam concentrations was achieved without the necessity of additional forced-convection for preconcentration, demonstrating its great potential for in vivo determination of piroxicam.</p>