Colorimetric Detection of Bacteria Using Litmus Test

J Vis Exp. 2016 Sep 17;(115):54546. doi: 10.3791/54546.


There are increasing demands for simple but still effective methods that can be used to detect specific pathogens for point-of-care or field applications. Such methods need to be user-friendly and produce reliable results that can be easily interpreted by both specialists and non-professionals. The litmus test for pH is simple, quick, and effective as it reports the pH of a test sample via a simple color change. We have developed an approach to take advantage of the litmus test for bacterial detection. The method exploits a bacterium-specific RNA-cleaving DNAzyme to achieve two functions: recognizing a bacterium of interest and providing a mechanism to control the activity of urease. Through the use of magnetic beads immobilized with a DNAzyme-urease conjugate, the presence of bacteria in a test sample is relayed to the release of urease from beads to solution. The released urease is transferred to a test solution to hydrolyze urea into ammonia, resulting in an increase of pH that can be visualized using the classic litmus test.

Publication types

  • Video-Audio Media

MeSH terms

  • Ammonia / analysis
  • Bacteria / enzymology
  • Bacteria / isolation & purification*
  • Bacteriological Techniques / methods*
  • Colorimetry / methods*
  • DNA, Catalytic / chemistry
  • Enzymes, Immobilized / chemistry
  • Hydrogen-Ion Concentration
  • Point-of-Care Systems
  • Urease / chemistry


  • DNA, Catalytic
  • Enzymes, Immobilized
  • Ammonia
  • Urease