ORIGINAL PAPER: SOL-GEL, HYBRIDS AND SOLUTION CHEMISTRIES Sol–gel based optically active phenolphthalein encapsulated nanomatrices for sensing application Shumaila Islam 1 • Noriah Bidin 1 • Saira Riaz 2 • Ganesan Krishnan 1,3 • Suzairi Daud 1,3 • Shahzad Naseem 2 • Faridah M. Marsin 4 Received: 27 December 2015 / Accepted: 4 April 2016 Ó Springer Science+Business Media New York 2016 Abstract In this work, synthesis and characterization of phenolphthalein-immobilized titania (T-phph) and silica– titania (ST-phph) nanomatrix is reported. The thin films are deposited by sol–gel method at low temperature. The effect of host–guest chemistry in matrices, on the surface struc- tures, optical and sensing activity of the resultant thin films is studied. The phenolphthalein-immobilized fabricated nanoparticles/nanomatrices are analyzed by field emission scanning electron microscope, energy-dispersive X-ray spectroscopy, atomic-force microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, surface analysis, thermogravimetric analysis, and UV–Vis spectroscopy. Thermally stable and high surface area homogeneous nanoparticles, containing nanocrystalline anatase phase with low refractive index (1.58), low roughness (5.5 nm), and high transparency (95 %) are obtained for phenolph- thalein-immobilized ST-phph nanomatrix. Moreover, smaller nanoparticles (56–121 nm) with good incorpora- tion of dye and good response of sensing are obtained. The sensor response is optimized at pH 12 with 10.1 pKa value at 555 nm. & Noriah Bidin noriah@utm.my Shumaila Islam shumaila@utm.my Saira Riaz Saira_cssp@yahoo.com Ganesan Krishnan k.ganesan@utm.my Suzairi Daud suzairidaud@utm.my Shahzad Naseem shahzad_naseem@yahoo.com Faridah M. Marsin fmarsin@kimia.gov.my 1 Laser Centre, Ibnu Sina Institute for Scientific and Industrial Research, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia 2 Centre of Excellence in Solid State Physics, University of the Punjab, QAC, Lahore 54590, Pakistan 3 Physics Department, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia 4 Chemistry Department Malaysia (Johor Branch), Ministry of Science, Technology and Innovation (MOSTI), Johor Bahru, Malaysia 123 J Sol-Gel Sci Technol DOI 10.1007/s10971-016-4041-0