Preparation of Multi-stimulus Responsive Polymer Nanospheres Based on AIE Effect and Its Cell Tracing Application

Abstract

In recent years, fluorescent bioimaging technology has great advantages in the fields of life science research and medical diagnosis because of its advantages of fast and effective, high sensitivity, easy realization of multi-channel imaging and economic efficiency. Organic fluorescent dyes have been widely used as biological imaging reagents due to their excellent photoelectric properties, functional modification, adjustable optical properties, and good biocompatibility. However, conventional organic fluorescent molecules cause aggregation-caused quenching (ACQ) due to π-π stacking in the aggregated state, limiting their bioimaging applications in aggregated or high concentrations. Since the discovery of the unique luminescence phenomenon of aggregation-induced emission (AIE), the ACQ phenomenon of traditional fluorescent materials has been eliminated. Stimulating responsive polymer nanoparticles have been widely used in the life sciences due to their combination of nanoparticle and polymer advantages and their ability to respond intelligently with environmental changes. Therefore, nanomaterials with excellent aggregation-induced emission (AIE) property, environmental stimuli responsiveness and biocompatibility based on AIE molecules and smart responsive polymers have shown attractive application prospects in the life sciences. A kind of multi-responsive AIE-active polymer nanospheres, which were composed of tetraphenylethylene (TPE) and stimuli-responsive poly[N]-2-(diethylamino)-ethyl]acrylamide (PDEAEAM), were constructed in this study. Firstly, a multi-stimulation responsive monomer N-[2-(diethylamino)ethyl]acrylamide (DEAEAM) and TPE derivative tetraphenylethene-4-(12-hydroxydodecyl-2-methylpropionyl) (TPE-BIB) with propionyl bromide were synthesized, respectively, and a multi-stimuli-responsive amphiphilic polymer of tetraphenylethene-graft-poly[N-[2-(diethylamino)ethyl]acrylamide] (TPE-g-PDEAEAM) was then successfully synthesized by atom transfer radical polymerization (ATRP) using TPE-BIB as initiator. Lastly, polymer nanospheres TPE-g-PDEAEAM of approximately 200 nm were formed by a self-assembling process. The results of the performed experiments showed that the LCST of TPE-g-PDEAEAM in aqueous solution is about 60℃. Meanwhile, the luminescence change of TPE-g-PDEAEAM at different temperatures from 20 to 66℃ was observed. The fluorescence intensity of TPE-g-PDEAEAM firstly decreased with increasing temperature from 20 to 58℃, and the fluorescence intensity increased with increasing temperature from 58 to 66℃. The phase transfer of PDEAEAM in TPE-g-PDEAEAM may be the reason of luminescence change which may lead to the fluorescent temperature response. Moreover, the fluorescence intensity of TPE-g-PDEAEAM nanospheres in aqueous solution increased with increasing temperature pH. Besides, the fluorescence intensity of TPE-g-PDEAEAM decreased dramatically when the volume of CO2 increased from 0.0 to 1.2 mL. Therefore, TPE-g-PDEAEAM was a new temperature and pH/CO2 responsive materials and might be used as multi-functional smart fluorescent sensors. More importantly, the fluorescent signals were significantly strong in HeLa cells after cells were incubated with TPE-g-PDEAEAM for 24 h based on the characteristic of AIE fluorescence and low cytotoxicity. The resultant nanospheres were able to be internalized by the cancer cells and effectively track the HeLa cells for as long as 11 passages. So, the polymer nanomaterial is an ideal living cell fluorescent tracer probe, which is expected to be applied as biosensors, long-term cell traces and medical biomaterials.