Monitoring gelation using magnetic nanoparticles

Abstract

The temperature dependent response of magnetic nanoparticles in oscillating magnetic fields was used to monitor gelation of the surrounding fluid at the size scale of the nanoparticles. The dynamic susceptibility of PEG-coated cobalt ferrite nanoparticles suspended in an aqueous gelatin solution had sharp transitions which correlated with gelation and melting observed using macroscale rheological measurements. The reported method requires small sample volumes and provides information on network formation at the scale of the probe nanoparticles.

Assessing magnetic nanoparticle aggregation in polymer melts by dynamic magnetic susceptibility measurements

“…We have previously shown that quantitative nanoscale viscosity measurements can be obtained from DMS measurements [46]. We have also used this technique to monitor phase transitions in the surrounding media, colloidal stability of MNPs in simple fluids, and adsorption of proteins to MNPs [47][48][49]. Others have also applied this technique to evaluate the mobility of nanoparticles in polymer hydrogels [50] and to evaluate the rheological properties of the suspending fluid [51].…”

Influence of aging time of oleate precursor on the magnetic relaxation of cobalt ferrite nanoparticles synthesized by the thermal decomposition method

“…Because the particles are nanometers in size, they can be used to probe fluid properties at the nanoscale. Recently, we have used this response to follow changes in the size and aggregation state of polymer-coated magnetic nanoparticles [20] and to determine the nanoscale viscosity of a test fluid by measuring the rotational hydrodynamic resistance on the particles in an oscillating magnetic field [18,19]. Additionally, the response of the peak frequency of the AC susceptibility can be used to design nanobiosensors based on Brownian relaxation [7,24,25].…”

“…Such could be the case when cobalt ferrite is synthesized and a mixture of cobalt ferrite and magnetite/ maghemite (or another superparamagnetic phase) is obtained. The response of the frequency peak of the AC susceptibility of magnetic nanoparticles with thermally blocked dipoles can be used to monitor changes occurring in the surrounding fluid matrix [18][19][20]. Because the particles are nanometers in size, they can be used to probe fluid properties at the nanoscale.…”

“…), which display attractive magnetic properties, making them useful for a wide range of applications such as in magnetic recording, catalysis, biotechnology, biomedicine, and magnetic separations [5][6][7][8][9]. Besides magnetite, cobalt ferrite is one of the most widely studied ferrites, due to its room temperature coercivity and high magnetocrystalline anisotropy, which makes it attractive for high-capacity magnetic storage [10,11], MRI contrast agents [6,12], cancer thermotherapy [8,12,13], nanobiosensors based on the Brownian relaxation mechanism [14,15], and nanoscale mechanical probes [16][17][18][19][20].…”

Demagnetization Treatment of Remanent Composite Microspheres Studied by Alternating Current Susceptibility Measurements

“…With magnetic particles, bio-assays have been developed that magnetically detect the slowdown of rotational diffusion that occurs when molecules adsorb to the particle surface, enlarging the hydrodynamic radius [4–8]. Moreover, cobalt ferrite nanoparticles have been used as rheological probes on the nanoscale [9] for instance to monitor the gelation of gelatin solutions [10] and to characterize the mechanical properties of ferrohydrogels [11]. …”