The unique and intriguing colorimetric transition of polydiacetylene (PDA) from blue to red color when exposed to different external stimuli makes it a perfect candidate for various bio-sensing applications. In this study, in an effort to tune the PDA phase behavior, a PDA derivative 10, 12-pentacosadiynoic acid (PCDA) mixed with a cholesterol derivative Cholestane-3β,5α,6β-triol (Chol) have been investigated employing Langmuir–Blodgett technique. Pressure-Area isotherm, excess area analysis, Gibb’s free energy as well as compressibility analysis indicate that incorporation of cholesterol largely influences the thermodynamic behavior of PCDA in the mixed film and hence, the PCDA phase transition. Brewster Angle Microscopy (BAM) and absorption spectroscopic studies also confirmed this. It has been observed that in most of the cases repulsive interaction occurred among the binary component in the PCDA-Chol mixed Langmuir film. Upon UV exposure, both blue and red phases co-exist in case of pure PCDA film. However, all PCDA converted into red phase at 45 ℃. On the other hand, in case of PCDA-Chol mixed film both blue and red phase co-existed upon UV exposure except 0.6 molar ratio of PCDA. Interestingly, here all PCDA molecule could be converted into red phase upon UV exposure. PCDA-Chol mixed system only at this mole fraction (0.6) is found to detect the presence of a pathogenic bacteria through blue to red color change visible under naked eye. Based on this, a paper-based low cost colorimetric bacteria sensor has been proposed.
