We report on the effect of different stimuli-responsive polymer shells on Fe@Au core-shell nanoparticles (NPs) with respect to thermoresponse as well as loading and release characteristics. The hybrid NP systems were investigated using a wide array of characterization techniques including dynamic light scattering, electrophoretic mobility, UV-visible spectroscopy, and scanning transmission electron microscopy. Three different polymeric shells were selected for loading and release of l-dopa: thiolated polyethylene glycol (PEG), poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAAM_AAc) microgel crosslinked with N,N′-methylenebis(acrylamide) (BIS), and finally concomitant PEG and PNIPAAM_AAc microgel (Fe@Au_PEG_Microgel). All three shells were found to exhibit high loading (∼10%) and encapsulation efficiencies up to 100 μg l-dopa/mg. Although the loading efficiencies are comparable for the three systems, Fe@Au_PEG_Microgel has the highest release (87%) at elevated temperature and acidic conditions. The attenuated release from the PEG-based systems can be attributed to stronger dipole-dipole interactions between the carboxyl group of PEG and the amino group of l-dopa. [Figure not available: see fulltext.]@en

Here, a synthetic method has been optimized for the synthesis of thermoresponsive and pH-responsive poly(N-isopropylacrylamide-co-acrylic acid) nanogels which are subsequently loaded with cytochrome C by using a modified breathing-in mechanism. Physico-chemical properties mapped by using dynamic light scattering (DLS) and differential scanning calorimetry (DSC) confirm the swelling/deswelling kinetics as reversible with a volume phase transition temperature (VPTT) of ~39 °C. Fe@Au nanoparticles were incorporated inside the nanogel networks by using two different methods: coating and in situ growth. The latter bears closer resemblance to the nanogels only, while the former follows the trend of bare Fe@Au nanoparticles. High loading (~96 %) and encapsulation (500 μg/mg of nanogels) of cytochrome C were obtained. Release experiments performed by using a dialysis set-up and monitored by using UV-vis spectroscopy show the highest release at 40 °C and pH 3.2 (high temperature, low pH), with maximum release from the Fe@Au-coated nanogels that also show a reverse swelling-collapse trend. The location of the drug, the incorporation and presence of Fe@Au nanoparticles and the drug incorporation method are found to control both the drug release mechanism and kinetics. [Figure not available: see fulltext.]

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