Towards green monitoring of antibiotics: a direct biochar-based electrochemical sensor for ampicillin detection in biomedical and environmental matrices.

Abstract

Antimicrobial resistance (AMR) represents a global health burden, requiring effective monitoring of antibiotic residues across the clinical-environmental chain. However, reference methods remain laboratory-based and solvent-intensive. To address this need in an ecologically responsible manner, this study exploits KOH-activated biochar derived from spent coffee grounds (BCK-KOH) as a screen-printed carbon electrode modifier for the direct detection of ampicillin (AMP); the corresponding non-activated material is denoted BCK. Characterization by N2 adsorption, FTIR, XPS and SEM-EDS revealed a 168-fold increase in BET surface area and substantial enrichment in surface carboxyl groups following activation. Modification with a PEI/BCK-KOH composite produced a ∼370 mV cathodic shift of the AMP oxidation signal compared with the unmodified electrode. Under optimized differential pulse voltammetry (DPV), the platform exhibited a linear range of 0.01-5 μM, an LOD of 3.3 nM, an LOQ of 10 nM and a sensitivity of 64.7 μA μM-1 (R2 = 0.997). The sensor showed acceptable interference tolerance toward the tested antibiotics and common endogenous compounds. Validation in artificial and ICU-patient serum, milk and water samples yielded recoveries of 88.5-111.4% with RSDs below 5.6% (n = 3), without pre-treatment. Because the LOQ closely matches the EU maximum residue limit (MRL) for AMP in milk, the platform enabled quantitative determination at approximately the MRL, 1.5×MRL and 2×MRL, with recoveries of 90.9%, 101.9% and 100.9%, respectively, while also supporting qualitative MRL screening in diluted samples complementary to confirmatory LC-MS/MS. AGREE (0.75) and BAGI (67.5) scores confirmed a substantially greener analytical platform than LC-MS/MS (AGREE 0.43) with practical applicability.