A rapid and sensitive label-free sensor for metoprolol detection based on MIPs-modified carbon nanocomposite

Electrochemical sensors utilizing molecularly imprinted polymers (MIPs) for metoprolol (MTP) often rely on its direct oxidation, which suffers from limited sensitivity due to the low electroactivity of MTP. Herein, a label-free electrochemical sensing platform was developed by electropolymerizing o-phenylenediamine (o-PD) on the carbon nano-onion (CNOs)-modified glassy carbon electrode (GCE). This MIPs/CNOs nanocomposite synergistically enhances the electron transfer rate and creates specific recognition sites. Consequently, the occupation of these sites by MTP hinders the diffusion of the redox probe, enabling sensitive quantification via a signal-off mechanism. Under optimized conditions, the sensor exhibits a wide linear range from 4.0 × 10^-8 to 8.0 × 10^-6 mol/L with a detection limit (LOD) of 1.33 × 10^-8 mol/L. Notably, this LOD is well below the minimum required performance level (MRPL) set by the World Anti-Doping Agency. The platform exhibits high selectivity against interfering substances and successfully determines MTP in commercial tablets and fortified urine samples with satisfactory recoveries (96.5-103.0%). These results demonstrate the practical applicability of the proposed label-free MIPs/CNOs sensor for sensitive MTP determination in complex matrices and provide a promising strategy for designing label-free electrochemical sensors.