A trigger-based aggregation of aptamer-functionalized gold nanoparticles for colorimetry: An example on detection of Escherichia coli O157:H7

A pH-triggered colorimetric assay has been established by using aptamer anchored gold nanoparticles to detect Escherichia coli O157:H7 ( E. coli O157:H7). Gold nanoparticles (AuNPs) functionalized by aptamer via thiol groups were used as probes ( [email protected] ).Solvents of HCl (acid), NaOH (alkaline) and MgCl 2 (nearly neutral) were used as triggers to initiate the movement of [email protected] in the presence of E. coli O157:H7 bacteria respectively. Due to the pH effect of trigger on the surface charges of E. coli O157:H7 and the contribution of aptamer to capture E. coli O157:H7, the movement of [email protected] with the presence of E. coli O157:H7 exhibit dispersion and aggregation respectively, which leads the change of colorimetric signal to an opposite direction. Taking the solvent of NaCl frequently used as trigger for gold nanoparticle based colorimetric sensor into consideration, the utilization of pH dependent triggers provide an alternative for this kind of trigger-based sensor. Design of gold nanoparticle-based colorimetric biosensing assay suiting a wide range of trigger is more flexible for specific diagnosis. These results demonstrate a great potential to design bacterial sensor with high sensitivity to defend public health.