Authors: Zhu, Donghua; White, R.D.; Hardy, Peter A.; Weerapreeyakul, Natthida; Sutthanut, Khaetthareeya; Jay, Michael

Source: Journal of Nanoscience and Nanotechnology, Volume 6, Number 4, April 2006 , pp. 996-1003(8)

Publisher: American Scientific Publishers

Abstract:

In this article, we use a nanotemplate engineering approach to prepare biodegradable nanoparticles composed of FDA-approved materials and possessing accessible gadolinium (Gd) atoms and demonstrate their potential as a Magnetic Resonance Imaging (MRI) contrast agent. Nanoparticles containing dimyristoyl phosphoethanolamine diethylene triamine penta acetate (PE-DTPA) were prepared using 3.5 mg of Brij 78, 2.0 mg of emulsifying wax and 0.5 mg of PE-DTPA/ml from a microemulsion precursor. After the addition of GdCl₃, the presence of Gd on the surface of nanoparticles was characterized using inductively coupled plasma atomic emission spectroscopy and Scanning Transmission Electron Microscopy (STEM). The in vitro relaxivities of the PE-DTPA-Gd nanoparticles in different media were assessed at different field strengths. The conditional stability constant of Gd binding to the nanoparticles was determined using competitive spectrophotometric titration. Transmetallation kinetics of the gadolinium ion from PE-DTPA-Gd nanoparticles with zinc as the competing ionic was measured using the relaxivity evolution method. Nanoparticles with a diameter of ∼130 nm possessing surface chelating functions were made from GRAS (Generally Regarded As Safe) materials. STEM demonstrated the uniform distribution of Gd³⁺ on the surface of the nanoparticles. The thermodynamic binding constant for Gd³⁺ to the nanoparticles was ∼10¹⁸ M⁻¹ and transmetallation studies with Zn²⁺ yielded kinetic constants K₁ and K₋₁ of 0.033 and 0.022 1/h, respectively, with an equilibrium constant of 1.5. A payload of ∼10⁵ Gd/nanoparticle was achieved; enhanced relaxivities were observed, including a pH dependence of the transverse relaxivity (r₂). Nanoparticles composed of materials that have been demonstrated to be hemocompatible and enzymatically metabolized and possessing accessible Gd ions on their surface induce relaxivities in the bulk water signal that make them potentially useful as next-generation MRI tumor contrast enhancement agents.

Keywords: GADOLINIUM; NANOPARTICLE; BINDING STABILITY; TRANSMETALLATION KINETICS; RELAXIVITY

Document Type: Research article

DOI: http://dx.doi.org/10.1166/jnn.2006.169

Publication date: 2006-04-01

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• Journal for Nanoscience and Nanotechnology (JNN) is an international and multidisciplinary peer-reviewed journal with a wide-ranging coverage, consolidating research activities in all areas of nanoscience and nanotechnology into a single and unique reference source. JNN is the first cross-disciplinary journal to publish original full research articles, rapid communications of important new scientific and technological findings, timely state-of-the-art reviews with author's photo and short biography, and current research news encompassing the fundamental and applied research in all disciplines of science, engineering and medicine.
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