To monitor and manage hydrological systems such as brooks, streams, rivers, the use of tracers is a well-established process. Limited number of potential tracers such as salts, isotopes and dyes, make study of hydrological processes a challenge. Traditional tracers find limited use due to lack of multiplexed, multipoint tracing and background noise, among others. In this regard, DNA based tracers possess remarkable advantages including, environmentally friendly, stability, and high sensitivity in addition to showing great potential in the synthesis of ideally unlimited number of unique tracers capable of multipoint tracing. To prevent unintentional losses in the environment during application and easy recovery for analysis, we hereby report DNA encapsulation in silica containing magnetic cores (iron oxide) of two different shapes—spheres and cubes. The iron oxide nanoparticles having size range 10–20 nm, have been synthesized using co-precipitation of iron salts or thermal decomposition of iron oleate precursor in the presence of oleic acid or sodium oleate. Physico-chemical properties such as size, zeta potential, magnetism etc. of the iron oxide nanoparticles have been optimized using different ligands for effective binding of dsDNA, followed by silanization. We report for the first time the effect of surface coating on the magnetic properties of the iron oxide nanoparticles at each stage of functionalization, culminating in silica shells. Efficiency of encapsulation of three different dsDNA molecules has been studied using quantitative polymerase chain reaction (qPCR). Our results show that our DNA based magnetic tracers are excellent candidates for hydrological monitoring with easy recoverability and high signal amplification. Graphic Abstract

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We report the synthesis and properties of temperature- and pH-responsive p([NIPAm-co-PEGMA] (core)/[NIPAm-co-AAc] (shell)) nanogels with narrow size distributions, tunable sizes and increased drug loading efficiencies. The core-shell nanogels were synthesized using an optimized two-stage seeded polymerization methodology. The core-shell nanogels show a narrow size distribution and controllable physico-chemical properties. The hydrodynamic sizes, charge distributions, temperature-induced volume phase transition behaviors, pH-responsive behaviors and drug loading capabilities of the core-shell nanogels were investigated using transmission electron microscopy, zeta potential measurements, dynamic light scattering and UV-Vis spectroscopy. The size of the core-shell nanogels was controlled by polymerizing NIPAm with crosslinker poly(ethylene glycol) dimethacrylate (PEGDMA) of different molecular weights (Mn-200, 400, 550 and 750 g/mol) during the core synthesis. It was found that the swelling/deswelling kinetics of the nanogels was sharp and reversible; with its volume phase transition temperature in the range of 40–42 °C. Furthermore, the nanogels loaded with l-3,4-dihydroxyphenylalanine (L-DOPA), using a modified breathing-in mechanism, showed high loading and encapsulation efficiencies, providing potential possibilities of such nanogels for biomedical applications.

Here, a synthetic method has been optimized for the synthesis of thermo and pH responsive poly(N-isopropylacrylamide-co-acrylic acid) nanogels which are subsequently loaded with Cytochrome C using a modified breathing-in mechanism. Physico-chemical properties mapped using dynamic light scattering (DLS) and differential scanning calorimetry (DSC) confirm the swelling/de-swelling kinetics as reversible with a volume phase transition temperature (VPTT) of ~ 39 °C. Fe@Au nanoparticles were incorporated inside the nanogel networks 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 using a dialysis setup and monitored 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, incorporation and presence of Fe@Au nanoparticles and drug incorporation method are found to control both the drug release mechanism and kinetics. KEYWORDS ((Nanogels, core-shell nanoparticles, Volume phase transition temperature, programmed drug release, breathing-in)) Incorporation of Fe@Au nanoparticles into multiresponsive pNIPAM-AAc colloidal gels modulates drug uptake and release. Supporting Information.

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