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The assembly state between magnetic nanosensors and their targets orchestrates their magnetic relaxation response.

ABSTRACT: The target-induced clustering of magnetic nanoparticles is typically used for the identification of clinically relevant targets and events. A decrease in the water proton transverse NMR relaxation time, or T(2), is observed upon clustering, allowing the sensitive and accurate detection of target molecules. We have discovered a new mechanistically unique nanoparticle-target interaction resulting in a T(2) increase and demonstrate herein that this increase, and its associated r(2) relaxivity decrease, are also observed upon the interaction of the nanoparticles with ligands or molecular entities. Small molecules, proteins, and a 15-bp nucleic acid sequence were chemically conjugated to polyacrylic-acid-coated iron oxide nanoparticles, and all decreased the original nanoparticle r(2) value. Further experiments established that the r(2) decrease was inversely proportional to the number of ligands bound to the nanoparticle and the molecular weight of the bound ligand. Additional experiments revealed that the T(2)-increasing mechanism was kinetically faster than the conventional clustering mechanism. Most importantly, under conditions that result in T(2) increases, as little as 5.3 fmol of Bacillus anthracis plasmid DNA (pX01 and pX02), 8 pmol of the cholera toxin B subunit (Ctb), and even a few cancer cells in blood were detected. Transition from the binding to the clustering mechanism was observed in the carbohydrate-, Ctb-, and DNA-sensing systems, simply by increasing the target concentration significantly above the nanoparticle concentration, or using Ctb in its pentameric form as opposed to its monomer. Collectively, these results demonstrate that the molecular architectures resulting from the interaction between magnetic nanosensors and their targets directly govern water proton NMR relaxation. We attribute the observed T(2) increases to the bound target molecules partially obstructing the diffusion of solvent water molecules through the superparamagnetic iron oxide nanoparticles' outer relaxation spheres. Finally, we anticipate that this novel interaction can be incorporated into new clinical and field detection applications, due to its faster kinetics relative to the conventional nanoparticle-clustering assays.

SUBMITTER: Kaittanis C

PROVIDER: S-EPMC3053437 | biostudies-other | 2011 Mar

REPOSITORIES: biostudies-other

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The assembly state between magnetic nanosensors and their targets orchestrates their magnetic relaxation response.

Kaittanis Charalambos C Santra Santimukul S Santiesteban Oscar J OJ Henderson Terry J TJ Perez J Manuel JM

Journal of the American Chemical Society 20110222 10

The target-induced clustering of magnetic nanoparticles is typically used for the identification of clinically relevant targets and events. A decrease in the water proton transverse NMR relaxation time, or T(2), is observed upon clustering, allowing the sensitive and accurate detection of target molecules. We have discovered a new mechanistically unique nanoparticle-target interaction resulting in a T(2) increase and demonstrate herein that this increase, and its associated r(2) relaxivity decre ...[more]

PMID: 21341659

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Project description:Purpose Brain imaging has provided puzzle pieces in the understanding of language. In neurologically healthy populations, the structure of certain brain regions is associated with particular language functions (e.g., semantics, phonology). In studies on focal brain damage, certain brain regions or connections are considered sufficient or necessary for a given language function. However, few of these account for the effects of lesioned tissue on the "functional" dynamics of the brain for language processing. Here, functional connectivity (FC) among semantic-phonological regions of interest (ROIs) is assessed to fill a gap in our understanding about the neural substrates of impaired language and whether connectivity strength can predict language performance on a clinical tool in individuals with aphasia. Method Clinical assessment of language, using the Western Aphasia Battery-Revised, and resting-state functional magnetic resonance imaging data were obtained for 30 individuals with chronic aphasia secondary to left-hemisphere stroke and 18 age-matched healthy controls. FC between bilateral ROIs was contrasted by group and used to predict Western Aphasia Battery-Revised scores. Results Network coherence was observed in healthy controls and participants with stroke. The left-right premotor cortex connection was stronger in healthy controls, as reported by New et al. (2015) in the same data set. FC of (a) connections between temporal regions, in the left hemisphere and bilaterally, predicted lexical-semantic processing for auditory comprehension and (b) ipsilateral connections between temporal and frontal regions in both hemispheres predicted access to semantic-phonological representations and processing for verbal production. Conclusions Network connectivity of brain regions associated with semantic-phonological processing is predictive of language performance in poststroke aphasia. The most predictive connections involved right-hemisphere ROIs-particularly those for which structural adaptions are known to associate with recovered word retrieval performance. Predictions may be made, based on these findings, about which connections have potential as targets for neuroplastic functional changes with intervention in aphasia. Supplemental Material https://doi.org/10.23641/asha.12735785.

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The assembly state between magnetic nanosensors and their targets orchestrates their magnetic relaxation response.

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The assembly state between magnetic nanosensors and their targets orchestrates their magnetic relaxation response.

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