Naked-eye detection of Listeria monocytogenes using smart chromogenic polymers with tuneable surface morphologies

Abstract

Listeria monocytogenes is a major foodborne pathogen associated with listeriosis, with a mortality rate of up to 30 %. Conventional detection methods are often time-consuming and require sophisticated equipment or complementary techniques to ensure sensitivity and specificity. This study presents a smart chromogenic polymeric sensor for the rapid detection of L. monocytogenes based on the activity of phosphatidylinositol-specific phospholipase C (PI-PLC). Six hydrophilic polymer films with identical compositions but different surface properties were developed, incorporating a chromogenic substrate that produces a visible colour change upon enzymatic hydrolysis, allowing the direct visual identification of L. monocytogenes. The sensitivity and specificity were assessed against a panel of foodborne bacteria, with detection limits of 104 CFUs/mL. Among the tested materials, NC2sf, Ff, and Sf showed the highest sensitivity and limited cross-reactivity with L. ivanovii, Staphylococcus aureus, and Bacillus cereus. Biocompatibility assays in HepG2 cells confirmed acceptable cytocompatibility, underscoring the importance of substrate selection for minimising adverse cellular effects. A proof-of-concept test on chicken breast slices and fresh-cut melon demonstrated the specific detection of L. monocytogenes and clear discrimination from non-pathogenic L. innocua, confirming the robustness and selectivity of the system. Finally, a Life Cycle Assessment highlighted the environmental impact of the sensing materials and provided insights into their potential pre-industrial scalability.