Magnetophoretic Chromatography Technique for the Detection of Pathogenic Bacteria with the Naked Eye

INTRODUCTION

Since microorganisms tend to proliferate over time, the detection of pathogenic bacteria at an early stage is crucial for preventing food-borne illnesses. To address these problems, we have developed a novel method for the detection of pathogenic bacteria that uses simple magnetic separation in a precision pipette. After separation of Salmonella bacteria from milk using antibody-conjugated magnetic nanoparticle clusters (MNCs), the Salmonella-containing solution and viscous polymer solution are successively loaded into pipette tip placed above a permanent magnet. The MNCs-Salmonella complexes are attracted to the bottom of the tip whereas most of the free particles are trapped at the interface between the solutions, which is called as magnetophoretic chromatography. Once the separation is completed, the presence of Salmonella bacteria can be determined with the naked eye. The detection limit is 100 cfu/mL, which is comparable to results obtained with light absorption measurements.

RESULT

Fig. 1 shows schematic illustrations and the corresponding optical images of the magnetophoretic chromatography setup before and after the separation of Au/MNC−Salmonella complexes from free Au/MNCs respectively. Fig. 2 shows optical images of the pipette tips after 10 min of magnetophoretic chromatography. As the concentration of Salmonella bacteria increases, the color at the end of the tip becomes dark whereas the color of the interface of the solutions becomes pale. The Au/MNCs-Salmonella complexes become concentrated at the narrow tip of the pipette, so the presence of Salmonella bacteria can be confirmed with the naked eye for concentrations down to 100 cfu/mL.

Conclusion

We have developed a magnetophoretic chromatography separation technique that uses a precision pipette and applied this method to the detection of Salmonella bacteria in milk with the naked eye. Because the experimental set-up requires only a permanent magnet and a precision pipette, the developed method is simple and cost-efficient, which means that it can be used in the rapid on-site detection of bacteria at restaurants, hospitals, and even homes for food safety monitoring. As a result, this assay will play a key role in preventing the outbreak of foodborne diseases caused by microorganisms, especially in developing countries.