Fluorescent water-soluble responsive polymers site-specifically labeled with FRET dyes possessing pH- and thermo-modulated multicolor fluorescence emissions as dual ratiometric probes
作者:Xuejuan Wan、Shiyong Liu
DOI:10.1039/c1jm10332f
日期:——
We reported on the synthesis of well-defined thermoresponsive polymers labeled with fluorescence resonance energy transfer (FRET) pairs at chain middle and terminals, which can act as single chain-based dual ratiometric fluorescent probes for pH and temperature under extremely dilute conditions. Starting from difunctional initiator containing a 7-nitro-2,1,3-benzoxadiazole (NBD) moiety, the atom transfer radical polymerization (ATRP) of oligo(ethylene glycol) monomethyl ether methacrylate (OEGMA) and di(ethylene glycol) monomethyl ether methacrylate (DEGMA), and the subsequent terminal group functionalization with Rhodamine B (RhB)-ethylenediamine derivative afforded thermoresponsive NBD-P(OEGMA-co-DEGMA)-RhB2, which were labeled with FRET donor (NBD) and acceptor moieties (RhB) at the chain middle and terminals. The fluorescence emission of terminal RhB functionalities is highly pH-dependent, i.e, non-fluorescent in neutral or alkaline media (spirolactam form) and highly fluorescent in acidic media (ring-opened acyclic form), thus the off/on switching of FRET process can be facilely modulated by solution pH. Moreover, at acidic pH and highly dilute conditions, the thermo-induced chain collapse and extension of NBD-P(OEGMA-co-DEGMA)-RhB2 can effectively modulate the spatial distance between FRET donor and acceptor moieties, leading to prominent changes in FRET efficiencies. The site-specific incorporation of one FRET donor and two pH-switchable acceptors at the chain middle and terminals of thermoresponsive polymers allows for the effective off/on switching and the modulation of efficiency of FRET processes by dually playing with solution pH and temperatures. This work represents the first report of single thermoresponsive polymer chains acting as dual ratiometric fluorescent probes under highly dilute conditions.
我们报道了在链中部和末端用荧光共振能量转移(FRET)对标记的明确热响应聚合物的合成,该聚合物可以作为基于单链的双比率荧光探针,在极稀条件下检测 pH 和温度。以含有7-硝基-2,1,3-苯并恶二唑(NBD)部分的双官能引发剂为原料,低聚(乙二醇)单甲醚甲基丙烯酸酯(OEGMA)和二(乙二醇)单甲醚进行原子转移自由基聚合(ATRP)甲基丙烯酸酯 (DEGMA),随后用罗丹明 B (RhB)-乙二胺衍生物进行端基官能化,得到热响应性 NBD-P(OEGMA-co-DEGMA)-RhB2,并用 FRET 供体 (NBD) 和受体部分 (RhB) 标记在链条中间和末端。末端 RhB 官能团的荧光发射高度依赖于 pH 值,即在中性或碱性介质(螺内酰胺形式)中不发出荧光,而在酸性介质(开环无环形式)中发出高度荧光,因此 FRET 过程的关闭/开启切换可以通过溶液 pH 值轻松调节。此外,在酸性pH和高度稀释的条件下,热诱导的NBD-P(OEGMA-co-DEGMA)-RhB2链断裂和延伸可以有效调节FRET供体和受体部分之间的空间距离,导致FRET发生显着变化效率。在热响应聚合物的链中部和末端位点特异性结合一个 FRET 供体和两个 pH 可切换受体,可以通过溶液 pH 和温度的双重作用实现有效的开/关切换和 FRET 过程效率的调节。这项工作代表了在高度稀释条件下单热敏聚合物链充当双比率荧光探针的首次报告。