Colorimetric determination of Listeria monocytogenes using aptamer and urease dual-labeled magnetic nanoparticles and cucurbit[7]uril-mediated supramolecular assembly of gold nanoparticle.

A host-guest colorimetric strategy is described for the detection of Listeria monocytogenes (L. monocytogenes). The optical probes were self-assembled based on the supramolecular interactions between the carbonyl groups of cucurbit[7]uril portals and gold nanoparticles (CB[7]-AuNPs). Aptamer and urease modified magnetic nanoparticles were used to specifically recognize and binding to L. monocytogenes, simultaneously hydrolyzing urea to produce ammonium ion (NH 4 + ) that can reverse CB[7] induced AuNPs aggregation. In the presence of L. monocytogenes, the above-mentioned magnetic conjugates preferentially bind to the bacterial surface, which results in blocking the catalytic active sites, thus inhibiting the production of ammonium ions. The normalized absorbance ratio of A 700 nm /A 525 nm was proportional to the L. monocytogenes concentration ranging from 10 to 10 6  cfu·mL -1 , and the visual determination can be done down to 10 cfu·mL -1 . For spiked food samples analyzed without pre-enrichment, recoveries of 98.4% to 99.3% were achieved could be verified and RSD were less than 10%. This work may offer a broad prospect for sensitive and specific determination  of pathogens.