Rapid Detection of Listeriolysin O Toxin Based on a Nanoscale Liposome–Gold Nanoparticle Platform

Listeria monocytogenes (L. monocytogenes) is an important foodborne pathogen responsible for foodborne listeriosis, a significant issue for high risk groups such as pregnant women. Currently available detection techniques for this bacterium, primarily nucleic acid-based methods, can achieve low detection limits; however, the assays are generally complex and lengthy. This pathogen can also be indirectly detected via the sensing of Listeriolysin O (LLO), a pore-forming toxin secreted by L. monocytogenes. We present simple and rapid solution- and paper-based assays for the detection of pore-forming toxin LLO. Liposomes are used as the natural recognition element in this assay because LLO acts primarily on lipid membranes. Pore-forming LLO triggers the release of cysteine from liposomes, which subsequently induces a rapid aggregation of gold nanoparticles present in the assay. The colorimetric response elicited by this aggregation enables LLO detection as low as 7.6 μg mL–1 for the solution-based assay, and limits of detection of 12.9 and 19.5 μg mL–1 LLO in PBS and spiked human serum, respectively, were obtained in 5 min for the paper-based assay. The assay does not require separation, enzyme-associated amplification, or washing steps, which are superior features in relation to point-of-care applications. The simplicity and rapidness of the nanoscale assay provides an opportunity for further development of portable sensors, specifically in resource-limited regions.