Gold nanoparticles as colorimetric sensor: A case study on E. coli O157:H7 as a model for Gram-negative bacteria

A novel and sensitive colorimetric method for assay of Escherichia coli O157:H7 was developed as a model for Gram-negative bacteria by a mercaptoethylamine-modified gold nanoparticles (MEA-AuNPs) sensor. Mercaptoethylamine (MEA) molecule binded with E. coli O157:H7 via electrostatic adhesion between the positive electricity of MEA and the negative electricity of E. coli O157:H7. Furthermore MEA can be easily conjugated to AuNPs through –SH group. Thus, the MEA-AuNPs can be cross linked in the presence of certain amount of E. coli O157:H7, resulting in a dramatic color change from red to blue. It is worth noting that the absorption ratio (A625/A520) of the modified AuNPs exhibited a linear correlation with E. coli O157:H7 concentration. Therefore, the concentration of E. coli O157:H7 can be detected by the naked eyes. This bioassay is rapid, takes less than 5 min from bacterium binding to detection and analysis, and is also convenient. Therefore, MEA-AuNPs system as a novel, on-site, real-time and low-cost Gram-negative bacteria sensor, would have a wide range of practical applications.