This study investigated a method that simultaneously detects three bacteria, Salmonella typhimurium, Escherichia coli,
and Staphylococcus aureus via an approach that combines un-immunized magnetic nanoparticles for the enrichment and
antibody-conjugated quantum dots (QDs) as fluorescence markers, by using a laboratory-made system. In the
enrichment procedure, the un-immunized superparamagnetic polymer nanoparticles and the three bacteria formed "beadcell"
complex. Magnetic nanoparticles with different size were used and some interferents were added into the bacteria
suspension respectively to check the influence on concentration efficiency. In the immuno-fluorescence labeling
procedure, QDs with different emission wavelenghs were immobilized with antibody. Antibody conjugated QDs capture
the bacteria selectively and specifically so that "sandwich" complex were formed. The suspension of the labeled bacteria
was trickled onto a microporous membrane. A 450nm semiconductor laser was used as a part of the laboratory-made
system to excite the QDs. Three PMT detectors were utilized to detect the fluorescence intensity. These un-immunized
magnetic nanoparticles can be applied in nonspecific separation and enrichment of bacteria from environmental samples,
and this method, of which the detection procedures are completed within 2 h, can be applied to the cost-effective and
rapid detecting of bacterial contamination.