Photo physical and spectral property of indomethacin has been harnessed to sense the cluster structures that exist at the microscopic level in binary mixtures of 1-propanol-water. The ability of indomethacin to switch from a fluorescent complex with alcohol self-association cluster at low water content, to a non-fluorescent complex with hydrogen-bonded water cluster at high water content, imparts the drug with its unique microheterogeneity sensing property. Similar results are obtained for methanol-water and 1-butanol-water binary mixtures. (C) 2010 Elsevier B. V. All rights reserved.