High Relaxivity Gd(III)–DNA Gold Nanostars: Investigation of Shape Effects on Proton Relaxation

Gadolinium(III) nanoconjugate contrast agents (CAs) have distinct advantages over their small-molecule counterparts in magnetic resonance imaging. In addition to increased Gd(III) payload, a significant improvement in proton relaxation efficiency, or relaxivity (<i>r</i>₁), is often observed. In this work, we describe the synthesis and characterization of a nanoconjugate CA created by covalent attachment of Gd(III) to thiolated DNA (Gd(III)–DNA), followed by surface conjugation onto gold nanostars (DNA–Gd@stars). These conjugates exhibit remarkable <i>r</i>₁ with values up to 98 mM^–1 s^–1. Additionally, DNA–Gd@stars show efficient Gd(III) delivery and biocompatibility <i>in vitro</i> and generate significant contrast enhancement when imaged at 7 T. Using nuclear magnetic relaxation dispersion analysis, we attribute the high performance of the DNA–Gd@stars to an increased contribution of second-sphere relaxivity compared to that of spherical CA equivalents (DNA–Gd@spheres). Importantly, the surface of the gold nanostar contains Gd(III)–DNA in regions of positive, negative, and neutral curvature. We hypothesize that the proton relaxation enhancement observed results from the presence of a unique hydrophilic environment produced by Gd(III)–DNA in these regions, which allows second-sphere water molecules to remain adjacent to Gd(III) ions for up to 10 times longer than diffusion. These results establish that particle shape and second-sphere relaxivity are important considerations in the design of Gd(III) nanoconjugate CAs

Gd(III)-Dithiolane Gold Nanoparticles for <i>T</i>₁‑Weighted Magnetic Resonance Imaging of the Pancreas

Pancreatic adenocarcinoma has a 5 year survival of approximately 3% and median survival of 6 months and is among the most dismal of prognoses in all of medicine. This poor prognosis is largely due to delayed diagnosis where patients remain asymptomatic until advanced disease is present. Therefore, techniques to allow early detection of pancreatic adenocarcinoma are desperately needed. Imaging of pancreatic tissue is notoriously difficult, and the development of new imaging techniques would impact our understanding of organ physiology and pathology with applications in disease diagnosis, staging, and longitudinal response to therapy in vivo. Magnetic resonance imaging (MRI) provides numerous advantages for these types of investigations; however, it is unable to delineate the pancreas due to low inherent contrast within this tissue type. To overcome this limitation, we have prepared a new Gd­(III) contrast agent that accumulates in the pancreas and provides significant contrast enhancement by MR imaging. We describe the synthesis and characterization of a new dithiolane-Gd­(III) complex and a straightforward and scalable approach for conjugation to a gold nanoparticle. We present data that show the nanoconjugates exhibit very high per particle values of <i>r</i>₁ relaxivity at both low and high magnetic field strengths due to the high Gd­(III) payload. We provide evidence of pancreatic tissue labeling that includes MR images, post-mortem biodistribution analysis, and pancreatic tissue evaluation of particle localization. Significant contrast enhancement was observed allowing clear identification of the pancreas with contrast-to-noise ratios exceeding 35:1

Shape-Dependent Relaxivity of Nanoparticle-Based <i>T</i>₁ Magnetic Resonance Imaging Contrast Agents

Gold nanostars functionalized with Gd­(III) have shown significant promise as contrast agents for magnetic resonance imaging (MRI) because of their anisotropic, branched shape. However, the size and shape polydispersity of as-synthesized gold nanostars have precluded efforts to develop a rigorous relationship between the gold nanostar structure (e.g., number of branches) and relaxivity of surface-bound Gd­(III). This paper describes the use of a centrifugal separation method that can produce structurally refined populations of gold nanostars and is compatible with Gd­(III) functionalization. Combined transmission electron microscopy and relaxivity analyses revealed that the increased number of nanostar branches was correlated with enhanced relaxivity. By identifying the underlying relaxivity mechanisms for Gd­(III)-functionalized gold nanostars, we can inform the design of high-performance MRI contrast agents

Gd(III)-Gold Nanoconjugates Provide Remarkable Cell Labeling for High Field Magnetic Resonance Imaging

In vivo cell tracking is vital for understanding migrating cell populations, particularly cancer and immune cells. Magnetic resonance (MR) imaging for long-term tracking of transplanted cells in live organisms requires cells to effectively internalize Gd­(III) contrast agents (CAs). Clinical Gd­(III)-based CAs require high dosing concentrations and extended incubation times for cellular internalization. To combat this, we have devised a series of Gd­(III)-gold nanoconjugates (Gd@AuNPs) with varied chelate structure and nanoparticle-chelate linker length, with the goal of labeling and imaging breast cancer cells. These new Gd@AuNPs demonstrate significantly enhanced labeling compared to previous Gd­(III)-gold-DNA nanoconstructs. Variations in Gd­(III) loading, surface packing, and cell uptake were observed among four different Gd@AuNP formulations suggesting that linker length and surface charge play an important role in cell labeling. The best performing Gd@AuNPs afforded 23.6 ± 3.6 fmol of Gd­(III) per cell at an incubation concentration of 27.5 μMthis efficiency of Gd­(III) payload delivery (Gd­(III)/cell normalized to dose) exceeds that of previous Gd­(III)-Au conjugates and most other Gd­(III)-nanoparticle formulations. Further, Gd@AuNPs were well-tolerated in vivo in terms of biodistribution and clearance, and supports future cell tracking applications in whole-animal models

Graphene Oxide Enhances Cellular Delivery of Hydrophilic Small Molecules by Co-incubation

The delivery of bioactive molecules into cells has broad applications in biology and medicine. Polymer-modified graphene oxide (GO) has recently emerged as a <i>de facto</i> noncovalent vehicle for hydrophobic drugs. Here, we investigate a different approach using native GO to deliver hydrophilic molecules by co-incubation in culture. GO adsorption and delivery were systematically studied with a library of 15 molecules synthesized with Gd(III) labels to enable quantitation. Amines were revealed to be a key chemical group for adsorption, while delivery was shown to be quantitatively predictable by molecular adsorption, GO sedimentation, and GO size. GO co-incubation was shown to enhance delivery by up to 13-fold and allowed for a 100-fold increase in molecular incubation concentration compared to the alternative of nanoconjugation. When tested in the application of Gd(III) cellular MRI, these advantages led to a nearly 10-fold improvement in sensitivity over the state-of-the-art. GO co-incubation is an effective method of cellular delivery that is easily adoptable by researchers across all fields

Mechanisms of Gadographene-Mediated Proton Spin Relaxation

Gd­(III) associated with carbon nanomaterials relaxes water proton spins at an effectiveness that approaches or exceeds the theoretical limit for a single bound water molecule. These Gd­(III)-labeled materials represent a potential breakthrough in sensitivity for Gd­(III)-based contrast agents used for magnetic resonance imaging (MRI). However, their mechanism of action remains unclear. A gadographene library encompassing GdCl₃, two different Gd­(III) complexes, graphene oxide (GO), and graphene suspended by two different surfactants and subjected to varying degrees of sonication was prepared and characterized for their relaxometric properties. Gadographene was found to perform comparably to other Gd­(III)–carbon nanomaterials; its longitudinal (<i>r</i>₁) and transverse (<i>r</i>₂) relaxivity are modulated between 12–85 mM^–1 s^–1 and 24–115 mM^–1 s^–1, respectively, depending on the Gd­(III)–carbon backbone combination. The unusually large relaxivity and its variance can be understood under the modified Florence model incorporating the Lipari–Szabo approach. Changes in hydration number (<i>q</i>), water residence time (τ_M), molecular tumbling rate (τ_R), and local motion (τ_fast) sufficiently explain most of the measured relaxivities. Furthermore, results implicated the coupling between graphene and Gd­(III) as a minor contributor to proton spin relaxation

Forage Utilization for Pasture-Based Livestock Production (NRAES 173)

This 185 page publication (NRAES-173) was originally published by the Natural Resource, Agriculture, and Engineering Service (NRAES, previously known as the Northeast Regional Agricultural Engineering Service), a multi-university program in the Northeast US disbanded in 2011. Plant and Life Sciences Publishing (PALS) was subsequently formed to manage the NRAES catalog. Ceasing operations in 2018, PALS was a program of the Department of Horticulture in the College of Agriculture and Life Sciences (CALS) at Cornell University. PALS assisted university faculty in publishing, marketing and distributing books for small farmers, gardeners, land owners, workshops, college courses, and consumers.Essential information on grazing management and harvesting excess forage for livestock produced in a pasture-based system including chapters on fencing, watering systems, lanes and feeding pads, animal-handling facilities, and more