This study presents a novel, rapid method for in situ functionalization of carbon electrodes using redox-active form of the 6-hydroxyflavone. The resulting multiwalled carbon nanotubes with redox-active HFLA (MWCNT@HFLA-Redox) electrode enables sensitive, selective detection of toxic phenylhydrazine, with excellent performance (limit of detection: 7 nM), stability, and eco-compatibility, offering a cost-effective alternative to conventional sensing techniques.

The development of simple and rapid methods for preparing redox-active molecular catalyst-functionalized carbon electrodes for electrocatalytic applications is a significant research area. 6-Hydroxyflavone (HFLA), a naturally occurring flavonoid with known anxiolytic properties, also acts as a noncompetitive inhibitor of cytochrome. This study focuses on the in situ functionalization of multiwalled carbon nanotubes (MWCNTs) with redox-active HFLA, resulting in a modified electrode denoted as GCE/MWCNT@HFLA-Redox, where HFLA-Redox represents the redox-active product of HFLA. The constructed-modified electrode exhibits a well-defined and stable surface-confined redox response at E° of 0.55 V versus Ag/AgCl, with a surface excess of 6.26 × 10⁻⁹ mol cm⁻² in a pH 2 KCl-HCl solution. The modified electrode is characterized by Fourier transform infrared, Raman, UV–vis, field-emission scanning electron microscopy, high-resolution mass spectrometry (organic extract), and control electrochemical studies. This GCE/MWCNT@HFLA-Redox electrode selectively oxidizes phenylhydrazine (PhHyd) in a pH 2 KCl-HCl solution. A screen-printed-modified electrode facilitates highly selective electrocatalytic oxidation of PhHyd via amperometric i–t measurements and batch injection analysis, without interference from hydrazine or other common electroactive species. This method exhibits an excellent linear calibration curve (200 nM to 2 μM), demonstrating a high-current sensitivity of 0.413 μA μM⁻¹ cm⁻² and a detection limit of 7 nM (signal-to-noise ratio of 3).