Portable Lab for Shipping (POLS): A Biosensor-Based System for Rapid Onboard Detection of Escherichia coli and Enterococcus spp. in Ballast Water

Ballast water (BW) is a major pathway for the spread of invasive microorganisms and pathogens, posing significant ecological and public health risks. The International Maritime Organization (IMO) has established strict discharge standards, yet routine monitoring remains limited, and no reliable onboard test is currently available to assist crews in verifying BW quality before discharge. This study presents the development of a rapid, portable method for onboard microbiological assessment of BW, based on potentiometric detection and biosensors engineered with the Bioelectric Recognition Assay (BERA). Two complementary approaches were evaluated: (i) direct potentiometric measurements of contaminated and non-contaminated samples, which confirmed the feasibility of detecting microbial presence but were restricted by high detection limits, and (ii) development of biosensors specifically engineered for <i>Escherichia coli</i> and <i>Enterococcus</i> spp. to improve specificity and lower the limit of detection (LOD). Results demonstrated successful detection of both microorganisms, with performance characteristics of 83.3% sensitivity and 81.9% accuracy for <i>Enterococcus</i> spp. (LOD: 10² CFU 100 mL^-1), and 89.8% sensitivity and 85.1% accuracy for <i>Escherichia coli</i> (LOD: 250 CFU 100 mL^-1). These findings underscore the potential of biosensor-based systems as practical, crew-operated tools for early warning and real-time monitoring of ballast water quality, supporting compliance with IMO standards and contributing to safer, more sustainable maritime operations.