Analysis and Modification of a Colorimetric Nanosensor for Rapid Detection of IEscherichia coli/I in Water

This research analyzed the mechanisms of work and modified a colorimetric nanosensor to make it more cost-effective for the detection of Escherichia coli (E. coli) in water. The base nanosensors modified herein rely on a competitive binding detection mechanism, where positively charged gold nanoparticles coated with polyethyleneimine (PEI-AuNPs) preferably bind to negatively charged E. coli in the presence of β-galactosidase (β-Gal) enzymes and chlorophenol red β-d-galactopyranosides (CPRG). The positive surface charge of the nanoparticle, rather than nanoparticle composition or type of chemical coating on its surface, was hypothesized herein as the governing factor for the nanosensor functionality. Thus, positively charged nanoparticles and polymers were tested as potential alternatives for gold nanoparticles for detecting E. coli. Positively charged silver and iron oxide nanoparticles coated with branched PEI detected E. coli as low as 10[sup.5] and 10[sup.7] colony-forming units per milliliter (CFU/mL), respectively. Furthermore, the branched PEI polymer itself (without nanomaterial) detected E. coli at 10[sup.7] CFU/mL. These findings suggest that the positive charge, rather than the nanoparticle type was likely responsible for the detection of E. coli using the competitive binding approach. Therefore, other types of recyclable and cost-effective nanomaterials and polymers can be developed for E. coli detection using this rapid colorimetric sensing technique.