Ultrafast Microwave-Synthesized\n2D/1D MnO<sub>2</sub>/Carbon Nanotube Hybrid for Bilirubin Detection\nin Simulated Blood\nSerum

Hybridization of carbon nanotubes (CNTs) and manganese\ndioxide\n(MnO<sub>2</sub>) integrates the biocompatibility and outstanding\nelectrocatalytic activity of MnO<sub>2</sub> with the exceptional\nconductivity of CNTs, thus providing a superior synergistic sensing\nplatform for the detection of biomolecules. However, the existing\nmethods for synthesizing MnO<sub>2</sub>/CNT hybrids are complex and\ninefficient, resulting in low yields and limited surface functionalities.\nHence, in this study, we present a low-cost and ultrafast solid-phase\nsynthesis of the MnO<sub>2</sub>/CNT hybrid using a facile microwave\ntechnique to detect a crucial biomolecule bilirubin. The successful\nsynthesis of the MnO<sub>2</sub>/CNT hybrid is confirmed through characteristic\nRaman and X-ray diffraction peaks, while morphology is analyzed by\nimaging techniques such as FESEM and HRTEM. The MnO<sub>2</sub>/CNT/nickel\nfoam (NF) sensor is thereafter used for the electrochemical detection\nof bilirubin. The sensor demonstrates a wide linear detection range\nfrom 10 nM to 1 mM, with a sensitivity of 6.87 mA nM<sup>–1</sup> cm<sup>–2</sup> toward bilirubin, as determined through the\ndifferential pulse voltammetry technique. The lower limit of detection\nis noted at 3.3 nM (=3.3 <i>S</i>/<i>m</i>). Furthermore,\nthe as-fabricated sensor showcases high selectivity against the interfering\nspecies. Real-time analysis conducted in simulated blood serum using\nthe standard addition method reveals an outstanding recovery percentage\nof approximately 98%. The conductive MnO<sub>2</sub>/CNT hybrid interacts\nrobustly with bilirubin, aided by the porous NF substrate for stability,\ncatalytic activity, and rapid electron transfer, enabling sensitive\nbilirubin detection. The work provides an ultrafast, low-cost, and\nhigh-yield solid-phase microwave synthesis of MnO<sub>2</sub>/CNT\nhybrid material and broadens its application in the detection of biological\nspecimens for clinical diagnosis and biomedical research.