Colorimetric detection and typing of E. coli lipopolysaccharides based on a dual aptamer-functionalized gold nanoparticle probe.

A rapid method for identification and typing of lipopolysaccharides (LPS) was developed by utilizing the different binding affinities between two kinds of gold nanoparticles (AuNPs) functionalized with two aptamers. Aptamers against ethanolamine and E. coli O111:B4 LPS were used to functionalize the AuNPs. The AuNPs functionalized with ethanolamine aptamer can bind to ethanolamine and are termed general probe (G-probe). The G-probe can recognize any type of LPS because ethanolamine is a component of every type of LPS. This causes a sandwich-mediated aggregation of the AuNPs and a color change from red to blue. The AuNPs functionalized with aptamer against the LPS of E. coli O111:B4 specifically bind to O111:B4 LPS and are termed specific probe (S-probe). By using these two probes, a logic typing method was developed. It can detect LPS in concentrations between 2.5 and 20 μg·mL-1 and with a 1 μg·mL-1 detection limit. In the authors' perception, the use of a dual aptamer-based colorimetric method has a large potential in terms of selective detection of microorganisms. Graphical abstract Two aptamer functionalized AuNP probes, G-probe and S-probe, were prepared for LPS typing and detecting. E. coli O111:B4 LPS was easily distinguished from O55:B5 LPS according to the signal output configurations (On & On Vs On & Off) of a general probe (G-probe) and a specific probe (S-probe).