Zirconium-MOF-Based Fluorescent and Conductive Bioprobes for Carbohydrate-Mediated Bacterial Detection

Bacterial contamination in food and water remains a pressing global health concern, necessitating the development of rapid, selective, and reliable detection platforms. Nanostructured biosensors, particularly those possessing luminescent and conductive features, offer promising avenues for sensitive and versatile detection. Among these, metal–organic frameworks (MOFs) are emerging as attractive candidates due to their structural rigidity and tunable luminescence. However, their limited intrinsic conductivity restricts their application in electrochemical sensing. In this study, we report the design and development of zirconium-based MOF (UiO-66(COOH)2)-derived fluorescent and conductive bioprobes for detecting common foodborne and waterborne bacterial pathogens. The synthesized ZrMOF exhibited inherent luminescent properties, while its conductivity was significantly enhanced by covalent integration with polyaniline-grafted chitosan (CS-g-PANI), forming a stable conductive composite. To impart biorecognition specificity, both the pristine ZrMOF and the composite were functionalized with 4-aminophenyl-α-d-mannopyranoside (4APM) and 4-aminophenyl-β-d-galactopyranoside (4APG) via carbodiimide-mediated coupling, exploiting lectin–carbohydrate interactions for selective bacterial targeting. The resulting fluorescent (4APM@ZrMOF and 4APG@ZrMOF) and conductive (4APM@ZrMOF/CS-g-PANI/SPCE and 4APG@ZrMOF/CS-g-PANI/SPCE) biosensing platforms demonstrated excellent sensitivity and a linear response. Detection limits of 48 and 140 CFU/mL were achieved for Escherichia coli and Pseudomonas aeruginosa, respectively, using the fluorescent bioprobes, while the conductive bioprobes achieved LODs of 67 and 44 CFU/mL, respectively. Both platforms exhibited high selectivity toward their target bacteria and lectins (Concanavalin A and PA-1), with minimal interference. Furthermore, the conductive bioprobes achieved satisfactory recovery rates in spiked real samples, ranging from 80 to 89% in milk and from 79 to 86% in juice. Overall, this study establishes an innovative material-driven approach to designing multifunctional MOF-based fluorescent and electrochemical bioprobes for effective detection of food- and waterborne pathogens.