Colorimetric and test stripe-based assay of bacteria by using vancomycin-modified gold nanoparticles

Bacteria are the most principal pathogens threatening human health. Rapid, simple, and sensitive identification and assay for bacteria are greatly desired for clinical diagnosis and environmental monitoring. In this work, a commonly used antibiotic vancomycin (Van) was used to synthesize gold nanoparticles (Au NPs) by a simple one-pot reaction, and the resultant Van-coated Au NPs (denoted as Van-AuNPs) can selectively interact with Gram-positive bacteria and thus be used to differentiate Gram-positive bacteria from Gram-negative ones through the change of their red color. On this basis, Van-AuNPs-based visual colorimetric assay was established for Gram-positive bacteria. The detection limits of bare eyes for Gram-positive S. aureus, M. luteus, and B. subtilis are 1x10(9), 1x10(9), and 1x10(9) cells/mL, respectively, according to the color of the spots on the test strip without the use of any microscopic devices. We also used this method to detect S. aureus in orange juice and tap water with excellent recoveries. Compared with conventional bacterial identification methods, this assay is rapid and easy, and is promising to be used as a rapid method for the identification and quantification of bacteria in clinics, environment, and fieldwork.