Enhanced detection of live bacteria using a dendrimer thin film in an optical biosensor

Here we describe the detection of live Pseudomonas aeruginosa using a sensing film containing a fourth-generation hydroxy-terminated polyamidoamine (PAMAM) dendrimer (i.e., G4-OH) and SYTOX Green fluorescent nucleic acid stain. The films are configured on simple, disposable plastic coupons or optical fibers and are interrogated using a miniature fiber-optic spectrometer. SYTOX Green is generally considered a dead cell stain because it is not able to cross the membranes of live cells. In the presence of PAMAM-OH (G4-OH) in water, the bacterial cell becomes permeable to the SYTOX dye and the fluorescence is significantly enhanced. The fluorescence increases with the bacteria concentration, and the intensity at 5.4 x 10(7) cells mL(-1) is 350% higher than the liquid controls without PAMAM-OH. We also demonstrate that dendrimers stabilize the sensing film. After drying and desiccation, the SYTOX Green/PAMAM-OH films are still able to quantitatively detect P. aeruginosa in water. Incorporation of glucose into the SYTOX Green/ PAMAM-OH film may improve the homogeneity of the film and enhances the fluorescence signal an additional 11-25%.