Bacteria cause millions to suffer from a variety of infections every year. Current methods of identifying bacteria require expensive equipment or a great deal of time—the most common method for identifying bacteria, plating and culturing, requires at least 24 hours. A quicker method of identifying harmful bacteria would be beneficial to many fields, including medical diagnosis and food inspection.
Chemists have devised a sensor array to identify bacteria by fluorescence. The general design involves associating a negatively charged conjugated polymer with positively charged chemicals on the surface of a gold nanoparticle. The negatively charged conjugated polymer is fluorescent on its own but, when it’s associated with the nanoparticle, the fluorescence is quenched. Bacteria, which have negatively charged surfaces, can dissociate the conjugated polymer. Once the conjugated polymer has been freed, the fluorescence is restored. Different bacteria species may or may not trigger this reaction depending on the type of chemicals used on the surface of the gold nanoparticle.
In a recent Angewandte Chemie article, chemists used three hydrophobic nanoparticle designs (NP1-NP3) that interact with hydrophobic regions on the surface of the bacteria to enhance bacterial binding. Thus, both electrostatic and hydrophobic interactions are involved in the complexing of the bacteria to the nanoparticles. They also used a conjugated polymer dubbed Sw-CO2 as the fluorescence source.
They tested their sensor array by exposing their gold nanoparticles to a clean, buffered solution of bacteria for 15 minutes. The fluorescence intensities were then scored for 12 different bacterial species. Linear discriminant analysis, a statistical method, was able to cleanly differentiate and accurately classify the 12 bacteria.
These results show that sensor arrays with gold nanoparticles are potentially useful for identifying bacteria. However, more research is necessary before this technique is applicable outside of the laboratory. Real biological or environmental samples would not resemble a clean buffered solution. so the gold nanoparticles must be able to discern relevant bacteria within a hodgepodge of biomolecules.
Angewandte Chemie, 2008. DOI: 10.1002/anie.200703369