The membranes of polydiacetylene backbone decorated with mannose can recognize Escherichia coli (E.coli) and bind with them. The binding leads to the color transition of the membranes which is readily visible to the naked eyes and can be quantified by visible absorption spectroscopy. The direct colorimetric detection by polydiacetylene membranes not only opens a new path for the use of these membranes in the area of biosensor development but also offers new possibilities for diagnostic applications and screening for binding ligand. In present paper

we utilized Langmuir-Blodgett technology to fabricate the mixed PDA/MPDA monolayers and measured the values of the colorimetric response when the mixed PDA/MPDA monolayers were incubated with various E.coli and physiological saline. On the basis of these measurements

we conclude the monolayers can be used to detect environmental E.coli. In order to understand the mechanism of the chromatic transition

the affinochromism properties of polydiacetylene are examined by Resonance Raman (RR) spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy. The results of RR spectroscopy demonstrate the bands of the double and triple bonds simultaneously shift to higher wavenumber during the affinochromism. At the same time

the bands intensity ratio of the double bonds to the triple bonds changes from a value 1.12 in the blue film to a value of about 2.5 in the red film

which can be explained by that the electronic structure in the polymer backbone changes from a acetylene to butatriene form when the blue to red chromatic transformation occurs. In addition

the results of FTIR spectroscopy also show that the side chains of polymer backbone perform rearrangement during the affinochromism. In conclusion

we demonstrate a simple and rapid method to detect E.coli and give a possible explanation to the mechanism of the affinochromism through RR and FTIR spectroscopy.