A facile and sensitive detection of pathogenic bacteria using magnetic nanoparticles and optical nanocrystal probes

We report a facile and sensitive analytical method for the detection of pathogenic bacteria. Salmonella bacteria in milk were captured by antibody-conjugated magnetic nanoparticles (MNPs) and separated from analyte samples by applying an external magnetic field. The MNP-Salmonella complexes were re-dispersed in a buffer solution then exposed to antibody-immobilized TiO2 nanocrystals (TNs), which absorb UV light. After magnetically separating the MNP-Salmonella-TN complexes from solution, the UV-Vis absorption spectrum of the unbound TN solution was obtained. Because the light absorption intensity was reversely proportional to the Salmonella concentration, the assay exhibited high sensitivity toward low concentrations of Salmonella bacteria. The detection limit of Salmonella in milk was found to be more than 100 cfu mL(-1).