Layer-by-layer assembled AuNP/γ-MnO₂–chitosan modified GCE for ultrasensitive detection of carcinoembryonic antigen

The sensitive detection of carcinoembryonic antigen (CEA), a critical tumor marker, is paramount for early-stage cancer diagnosis and management. This study reports the development of a novel, label-free electrochemical immunosensor based on a layer-by-layer (LbL) assembly of gold nanoparticles (AuNPs) and a gamma-phase manganese dioxide–chitosan (γ-MnO₂–CS) nanocomposite on a glassy carbon electrode (GCE). The engineered sensing interface leverages the synergistic properties of its constituents: the porous, high-surface-area γ-MnO₂–CS matrix provides an ideal scaffold for high-density antibody immobilization, while the integrated AuNPs create a highly conductive network that significantly amplifies the electrochemical signal. The immunosensor operates by measuring the impedance to electron transfer from a [Fe(CN)₆]³ ⁻/⁴⁻ redox probe, which is proportionally hindered by the binding of CEA to surface-immobilized antibodies. The platform demonstrated exceptional analytical performance, exhibiting an ultra-wide linear dynamic range spanning seven orders of magnitude from 10 fg mL −1 to 100 ng mL −1 , with an extremely low limit of detection of 9.6 fg mL −1 . Furthermore, the sensor showed excellent precision, with inter-day CVs below 9 % for mid- and high-range concentrations, and demonstrated high selectivity against common interferents. Its practical utility was confirmed in diluted human serum, achieving spike-recovery rates between 94.1 % and 104.6 %, validating its potential as a powerful and reliable tool for clinical applications.