Poly(N-isopropylacrylamide) (PNIPAM), which undergoes a temperature dependent transition from hydrophilic to hydrophobic, has played a crucial role in the development of stimuli-responsive multifunctional nanoparticles. In particular, iron oxide nanoparticles coated with PNIPAM have been effectively developed to enable stimuli responsive drug delivery and imaging agents. However, the PNIPAM transition from hydrophilic to hydrophobic at physiologically relevant temperatures renders colloidal nanoparticles unstable resulting in aggregation and precipitation from solution. Consequently, a direct correlative analysis of the effect of the thermally induced phase transition of PNIPAM on the magnetic resonance properties of nanoparticles has not been possible as the changes in proton relaxivity have been dominated by the colloidal agglomeration of the nanoparticles. Herein, we report colloidally stable thermoresponsive PNIPAM-grafted-PGMA coated magnetite core/shell nanoparticles (PNIPAM–PGMA–NPs) that enable the direct analysis of the effect of PNIPAM phase changes in solution on the overall magnetic resonance relaxivity of nanoparticles in suspension.

中文翻译：

---

PNIPAM热转变与氧化铁纳米粒子的磁共振弛豫的直接相关

聚（N-异丙基丙烯酰胺（PNIPAM）经历了从亲水性到疏水性的温度依赖性转变，在刺激响应性多功能纳米颗粒的开发中起着至关重要的作用。特别是，已经有效地开发了涂覆有PNIPAM的氧化铁纳米颗粒，以实现刺激响应性药物输送和显像剂。但是，PNIPAM在生理相关温度下从亲水性转变为疏水性使胶体纳米颗粒不稳定，从而导致溶液中的聚集和沉淀。所以，由于质子弛豫度的变化已被纳米粒子的胶体团聚所支配，因此不可能对PNIPAM的热诱导相变对纳米粒子的磁共振特性的影响进行直接的相关分析。在此，我们报道了胶体稳定的热响应性PNIPAM-接枝了-PGMA涂层的磁铁矿核/壳纳米粒子（PNIPAM–PGMA–NPs），可以直接分析溶液中PNIPAM相变对悬浮液中纳米粒子总体磁共振弛豫的影响。