Innovative magnetic bead-based electrochemical platform for rapid and sensitive cocaine detection in biological fluids.

Detecting psychoactive substances in biological samples presents significant challenges in clinical diagnostics, forensic analysis, and public health monitoring. This study introduces a highly sensitive electrochemical biosensing platform for the detection of cocaine, addressing the critical need for rapid, field-deployable testing methods. By integrating functionalized magnetic beads (MBs) with screen-printed carbon electrodes (SPCEs), we developed a competitive immunoassay system that leverages the superior molecular recognition capabilities of antibodies while maintaining operational simplicity. The biosensor operates via a competitive binding mechanism, in which cocaine present in the sample competes with cocaine-bovine serum albumin (BSA) conjugates immobilized on MBs for binding sites on horseradish peroxidase-labeled anti-cocaine antibodies (HRP-DAb). Electrochemical detection is achieved through amperometric measurement of enzyme activity using a redox system consisting of hydrogen peroxide/hydroquinone (H₂O₂/HQ). The optimized biosensor demonstrates excellent analytical performance with a linear response range from 0.3 to 300 ng mL^-1 and a detection limit of 0.1 ng mL^-1. Notably, the biosensor maintains its performance when analyzing cocaine in complex biological matrices, including human saliva and urine, successfully quantifying concentrations with minimal matrix interference. The platform offers significant advantages, including single-use disposable electrodes, rapid analysis time (< 30 min), minimal sample preparation requirements, and the potential for miniaturization into portable devices. These characteristics combined with high selectivity, a simple fabrication process, and cost-effectiveness, position this biosensor as a promising tool for point-of-care testing and field applications in clinical, forensic, and roadside testing scenarios.