The article describes synthesis and thermally triggered self-assembly of a Poly (ethylene oxide)-block-poly (N-insopropylacrylamide) (PEO-b-PNIPAm) in aqueous medium. At rt, the polymer remains as unimer, however, at lower critical solution temperature (LCST) of PNIPAm (32 degrees C), it forms a rather large undefined aggregate which at slightly elevated temperature (similar to 40 degrees C) converges to well defined polymersome structure (Critical aggregation concentration = 0.45 mg/mL) with hydrodynamic diameter of 40-50 nm. By lowering the temperature, initial swelling of the compact vesicle followed by reversible disassembly to unimer was noticed. The polymersome exhibits encapsulation ability to a hydrophilic dye Calcein which can be spontaneously released by lowering the temperature below cloud point. Likewise a hydrophobic dye namely 8-Anilino-1-naphthalenesulfonic acid (ANS) can also be encapsulated and released by thermal trigger. Detail photoluminescence studies reveal ANS dye can be used as a generalized probe molecule for detecting LCST of a thermoresponsive polymer by "fluorescence on" above LCST even by cursory observation. (C) 2015 Wiley Periodicals, Inc.