Selective capture and sensitive fluorometric determination of Pseudomonas aeruginosa by using aptamer modified magnetic nanoparticles.

A fluorometric assay is described for the detection of the food pathogen Pseudomonas aeruginosa (P. aeruginosa). It is based on the hybridization of aptamer and fluorescein-labeled complementary DNA (FAM-cDNA) in combination with magnetic separation. In the absence of P. aeruginosa, FAM-cDNA is assembled on the surface of aptamer modified magnetic particles (MNPs) via hybridization between aptamer and cDNA. Upon addition of P. aeruginosa, FAM-cDNA is replaced by the bacteria and released from the MNPs since the aptamer preferentially binds to bacteria. After magnetic separation, the amount of bacteria can be quantified by determination of the fluorescence intensity (λexc/em = 494/525 nm) of the supernatant containing the released FAM-cDNA. This kind of assay allows for both selective enrichment and sensitive fluorometric determination of bacteria in a single step. The assay has a response to the logarithm of P. aeruginosa concentration that is linear in the range between 10 and 108 cfu·mL-1, with a detection limit as low as 1 cfu·mL-1. The detection process can be finished within <1.5 h. The feasibility of the assay was verified by detecting P. aeruginosa in spiked food samples. Graphical abstract Hybridization of aptamer and carboxyfluorescein labeled complementary DNA is combined with magnetic separation for detection of as low as 1 cfu·mL-1 Pseudomonas aeruginosa. This kind of assay allows for both selective enrichment and sensitive fluorometric determination of bacteria in a single step.