Temperature-induced fluorescence enhancement of GFP chromophore containing copolymers for detection of Bacillus thermophilus

Abstract

Green fluorescent protein (GFP) chromophore based copolymers with temperature-induced emission enhancement properties were successfully prepared and applied for biodetection. First, diblock copolymers (PEG-b-PNIPAM-c) with different poly(N-isopropylacrylamide) (PNIPAM) chain lengths were synthesized by atom transfer radical polymerization (ATRP) employing a poly(ethylene glycol) (PEG) macroinitiator and then modified with a GFP chromophore at one chain end through a click reaction. Owing to the different PNIPAM chain lengths, the block copolymers exhibited thermoresponsive phase transitions with adjustable lower critical solution temperature (LCST). Above the LCST, the fluorescence intensity of PEG-b-PNIPAM-c was enhanced dramatically, which could be attributed to the chromophore's conformational restriction by the collapse of PNIPAM blocks. Moreover, the emission intensity of PEG-b-PNIPAM-c increased with the PNIPAM chain length. Correspondingly, the temperature-dependent fluorescence enhancement properties of PEG-b-PNIPAM-c were successfully applied in the highly sensitive detection of Bacillus thermophilus with a 10² cfu per mL detection limit.