Core-brush hybrid nanoparticles containing PEG surface functions are highly interesting as biologically inert and smart stimuli-responsive materials for future applications in biosensors, drug delivery, tissue engineering and optical systems. In this context, surface modification methodologies are critical to exert a thorough control of morphological and functional aspects such as grafting density, polymer conformation or colloidal dispersability. In this work, we present core-brush hybrid nanoparticles synthesis from SiO2 particles and an oligo(ethyleneglycol)-based polymer. Di(ethylene glycol) methyl ether methacrylate (DEGMA) was successfully grafted using the grafting-from approach. In particular, we compared DEGMA grafting on SiO2 particles using three pathways, where route 1 and 2 corresponds to a surface-initiated atom radical polymerization (SI-ATRP), while pathway 3 consists in a photo-grafting polymerization. The polymer density grafted on the SiO2 surface,
We present the study of the anchoring of carboxylic groups on SiO2 nanoparticles from different approximations based on the photochemical radical thiol-ene addition (PRTEA) reaction: a photografting approach between mercaptosuccinic acid (MSA) and vinyl-modified SiO2 nanoparticles and the post-grafting on the surface of silica colloids of the silane precursor 2-((2-(trimethoxysilyl)ethyl)thio)succinic acid (TMSMSA), obtained from the PRTEA. These synthetic strategies were compared with a widely common derivatization methodology based on the nucleophilic attack of surface-anchored amino groups with succinic anhydride. The successful functionalization of the colloidal silica was confirmed by infrared spectroscopy (FTIR), zeta potential at different pH and contact angle measurements. We found that although these three approaches were valid for -COOH immobilization, they had a noticeable impact on the dispersability and agglomeration of the colloidal suspension at the end of the synthesis. Scanning electron microscopy, dynamic light scattering (DLS) and fluorescence correlation spectroscopy (FCS) measurements indicated that the PRTEA photografting between MSA and vinyl-modified SiO2 resulted in highly dispersed colloidal particles. On the other hand, the presence of surface -COOH groups was highly beneficial for redispersion of the colloidal material after lyophilization or freeze-drying procedures.
Smart nanosystems that transduce external stimuli to physical changes are an inspiring challenge in current materials chemistry. Hybrid organic−inorganic materials attract great attention due to the combination of building blocks responsive to specific external solicitations. In this work, we present a sequential method for obtaining an integrated core-shell-brush nanosystem that transduces light irradiation into a particle size change through a thermoplasmonic effect. We first synthesize hybrid monodisperse systems made up of functionalized silica colloids covered with controllable thermoresponsive poly(Nisopropylacrylamide), PNIPAm, brushes, produced through radical photopolymerization. This methodology was successfully transferred to Au@SiO 2 nanoparticles, leading to a core-shell-brush architecture, in which the Au core acts as a nanosource of heat; the silica layer, in turn, adapts the metal and polymer interfacial chemistries and can also host a fluorescent dye for bioimaging. Upon green LED irradiation, a light-to-heat conversion process leads to the shrinkage of the external polymer layer, as proven by in situ DLS. Our results demonstrate that modular hybrid nanosystems can be designed and produced with photothermo-physical transduction. These remote-controlled nanosystems present prospective applications in smart carriers, responsive bioscaffolds, or soft robotics.
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