Arsonic acid-presenting superparamagnetic iron oxide for pH-responsive aggregation under slightly acidic conditions

Stimulus-Responsive Nanoparticle Magnetic Resonance Imaging Contrast Agents: Design Considerations and Applications

Magnetic resonance imaging (MRI) has been widely used for disease diagnosis because it can noninvasively obtain anatomical details of various diseases through accurate contrast between soft tissues. Over one-third of MRI examinations are performed with the assistance of contrast agents. Traditional contrast agents typically display an unchanging signal, thus exhibiting relatively low sensitivity and poor specificity. Currently, advances in stimulus-responsive contrast agents which can alter the relaxation signal in response to a specific change in their surrounding environment provide new opportunities to overcome such limitation. The signal changes based on stimulus also reflects the physiological and pathological conditions of the site of interests. In this review, how to design stimulus-responsive nanoparticle MRI contrast agents from the perspective of theory and surface design is comprehensively discussed. Key structural features including size, clusters, shell features, and surface properties are used for tuning the T₁ and T₂ relaxation properties. The reversible or non-reversible signal changes highlight the contrast agents have undergone structural changes based on certain stimulus, as an indication for disease diagnosis or therapeutic efficacy.

Microwave-driven enzyme deactivation using imidazolium salt-presenting silica nanoparticles

Thermal enzyme deactivation by the imidazolium-presenting silica nanoparticles with the microwave irradiation is presented in this manuscript. The modified nanoparticles were synthesized, and it was observed that the modified nanoparticles can be a heat source in the buffer under the weak-power microwave irradiation. Finally, based on the heat-generating ability of these nanoparticles, deactivation of glutathione reductase and alkaline phosphatase with the modified nanoparticles were demonstrated.

pH-Sensitive MR Responses Induced by Dendron-Functionalized SPIONs

We report a series of investigations of the pH-sensitive magnetic resonance (MR) responses of various surface-functionalized SPIONs (superparamagnetic iron oxide nanoparticles). First, functionalization of ~12 nm highly monocrystalline SPION cores with three different generations of melamine-dendrons was optimized to give agents with high molar relaxivities (e.g. R2m ~300 mM-1·s-1 at 7 T and R1m ~20-30 mM-1·s-1 at 0.5 T) and excellent aqueous stabilities. Molar relaxivities were found to exhibit great sensitivity to pH at physiologically-relevant ionic strengths, with sharp inflections observed at pH values near the pKa of the melamine monomer. The strength of the effect was observed to grow with increasing dendron generation (with concomitant shift in the position of the main pH inflection). Opposing behavior in R2m and R2m * trends may be exploited to provide a ratiometric MR response to pH. Combined with TEM and corresponding MR measurements from solutions of varying ionic strengths, these results are consistent with the pH-sensitive behavior originating from transient, reversible SPION clustering modulated by an interplay between SPION surface charge density and solution ionic strength. Studies of SPION cellular uptake and MR response in HeLa cell cultures are also presented. Finally, comparisons with the MR responses of SPIONs with alternative functionalities-derivatives of nitrilotriacetic acid or poly(1-vinylimidazole)-indicate that these types of pH-sensitive MR responses can be highly dependent upon the chemical composition of the surface species (and thus amenable to modulation through rational design).