Development of a carbon paper-based electrochemical immunosensor for trimethoprim detection in fishery species: monitoring antibiotic contaminants.

BACKGROUND AND PURPOSE: Monitoring antibiotic drugs in the environment is particularly relevant given their role in fostering microbial resistance, impacting aquatic species and human health. Therefore, this work addresses the lack of a sustainable and cost-effective analytical approach and reports the development of a competitive electrochemical immunosensor for the rapid analysis of trimethoprim (TMP), an aquatic contaminant of emerging concern, overcoming the limitations of conventional methods that are often costly and time-consuming. EXPERIMENTAL APPROACH: A miniaturized 3-electrode system was developed to support the analyses of a low-volume sample (200 μL), using a low-cost carbon-paper working electrode, pencil graphite lead auxiliary electrode and a stainless-steel needle reference electrode. Scanning electron microscopy was used to characterize the transducer, revealing a network of randomly arranged carbon fibres, significant for efficient antibody immobilization. For the immunoassay construction, an anti-TMP antibody was physically adsorbed to a small-sized transducer (d = 4 mm) for the specific recognition of TMP, followed by incubation with the enzyme-conjugate (horseradish peroxidase) and the enzyme-substrate (tetramethylbenzidine). KEY RESULTS: The analytical signal was recorded by chronoamperometry (1-minute reaction) and yielded a limit of detection of 34 ng L-1. The 45-minute assay demonstrates accuracy (92.0 to 103.2 % in fishery species including codfish, mackerel, crab, and hake), reproducibility (6.1 and 9.3 % for repeatability and inter-day variation coefficient) and high selectivity (bias less than 5 %) analysis. The sensor's performance was validated against a conventional Enzyme-Linked Immunosorbent Assay. CONCLUSION: This study introduces a sustainable electrochemical immunosensor, offering a portable and eco-friendly alternative for the rapid detection of TMP in fishery species, addressing the limitations of traditional methods.