Magnetic Gold Nanoshells: Stepwise Changing of Magnetism through Stepwise Biofunctionalization

Abstract

We report step-wise changing of magnetic behavior of iron oxide core gold shell nanoparticles from super paramagnetic to permanent magnetism at room temperature, on step-wise biofunctionalization with leutenizing hormone and releasing hormone (LHRH) through cysteamine linker. The observed permanent magnetism at room temperature in LHRH-capped gold nanoshells provides opportunities to extend fundamental investigations of permanent magnetism to other novel nanostructures and biofunctionalized nano gold architectures, simultaneously opening the way to newer applications, especially to those in biomedicine. KeywordsIron oxide nanoparticles; SPION; Gold nanoshell; SPION@Au; Thiol capping; leutenizing hormone and releasing hormone (LHRH); Biofunctionalization It is well known that bulk gold is diamagnetic due to counteraction of paramagnetic behavior of conduction electrons by orbital and ionic core diamagnetism. On the other hand, single gold atoms are paramagnetic because of the unpaired 6s electron. 1 There is a distinct change in the magnetism as one goes from gold atoms to nano gold and further to bulk gold and these fundamental changes in the magnetism are interesting from basic research as well as practical applications. Adding to this is recently reported chemically induced ferromagnetism in thiol-capped gold nanoparticles. 2 The chemically induced permanent magnetism was also extended to Ag and Cu nano clusters. 3 The surprising induction of permanent magnetism, under some conditions of chemisorptions, in small nanoparticles of a bulk-diamagnetic metal is likely through an interaction of s and p orbitals of adsorbates such as thiolates with 5d-orbitals of metal atoms. This interaction is anticipated to lead to emergence of 5d-localized holes as a result of significant charge transfer occurring from the metal atoms to sulfur atoms in the adsorbate molecule. The Au L3-edge extended X-ray absorption near-edge structure (EXAFS) measurements confirm the existence of these holes in Au nanoparticles capped with thiolates. 4 , 5 This interaction between the orbitals of S and Au is ultimately responsible for the onset of magnetism in thiol-capped gold nanoclusters. Recent literature reports indicate that different types of thiol-capped Au nanoparticles showed a great variety of effects going from giant paramagnetism, 6 superparamagnetism, 7 and even to permanent magnetism. 2 , 8 * Corresponding Author: To whom correspondence should be addressed. ckumar1@lsu.edu . Supplementary Figures S1-S7 and Table S1. This material is available free of charge via the Internet at http://pubs.acs.org. We synthesized SPIONs (Fe 3 O 4 ) and gold coated SPIONs (Fe 3 O 4 @Au) modifying the procedure described previously. 16 The SPIONs@Au nanoparticles were purified magnetically making them free of unwanted residual amount of pure Au nanoparticles. The HRTEM measurements show their spherical nature and the mean size of SPIONs@Au is 6.3 ± 0.7 nm compared to 5.4 ± 0.4 nm for SPIONs (Figure 1 and S1). The particles are well dispersi...

Chemically Induced Magnetism in Atomically Precise Gold Clusters

“…[ 6 ] We have also recently demonstrated ferromagnetism in peptide-capped gold nanoshells ( ∼ 0.5 nm thick) and the possibility to modulate their magnetic behavior by step-wise functionalization of stabilizing ligands. [ 7 ] It is generally observed that ferromagnetism at room temperature in gold nanoparticles prevails in thiol-stabilized Au nanoparticles. [ 8 ] The crucial electronic event involved on the onset of magnetization in capped gold nanoparticles is a spin symmetry breaking associated with the 5 d and 6 s electrons of the Au atoms involved in the chemical bond with the ligands, which in turn modifi es the relative spin densities at the Fermi energy thus creating a non-zero magnetic moment and a corresponding magnetization.…”

Polymeric nanoparticles for therapy and imaging

“…Table 3 discusses some advantages of MNP-based hyperthermia, which have been proved by many studies throughout the past decade. [51,[84][85][86][87][88] It is also shown to be superior over traditional ones. Some of these advantages are discussed next: (I) MNPs have small particle size that can pass through the biological barrier, even to brain; (II) MNPs targeting can be enhanced by specific agents to increase the effectiveness of hyperthermia at targeted site; (III) MNPs not only provide hyperthermia treatment but also can be utilized as a diagnostic agent for MRI; and (IV) it can be heated though alternating magnetic fields.…”

Targeted hyperthermia-induced cancer cell death by superparamagnetic iron oxide nanoparticles conjugated to luteinizing hormone-releasing hormone

“…SPIONs@Au-LHRH were synthesized as described in our previous publications [18,19]. Briefly, following synthesis of SPIONs of Fe 3 O 4 (average diameter: 5.1 nm) by reduction of Fe(II) acetylacetonate at 210°C using 1,2 hexadecanediol in the presence of surfactants (oleic acid and oleylamine), they were coated with Au in situ through reduction of Au(III) acetylacetonate.…”

“…Based on the Leuschner's study, which showed a practical application of LHRH-SPIONs for targeted delivery, we have reasoned that MNPs bound to LHRH would also serve as ideal candidates for targeted hyperthermia when applied in conjunction with external magnetic fields. Toward realizing this goal, we have previously reported a synthetic strategy to obtain gold-coated SPIONs (SPIONs@Au) and subsequently bound them to LHRH through cysteamine crosslinker [18]. The SPIONs@Au-LHRH thus synthesized were found to have a mean diameter of 6.7 ± 0.8 nm with saturation magnetization (Ms) of 32 emu/g (at 27°C) and a blocking temperature (T B ) of ∼300 K [18,19].…”

“…Toward realizing this goal, we have previously reported a synthetic strategy to obtain gold-coated SPIONs (SPIONs@Au) and subsequently bound them to LHRH through cysteamine crosslinker [18]. The SPIONs@Au-LHRH thus synthesized were found to have a mean diameter of 6.7 ± 0.8 nm with saturation magnetization (Ms) of 32 emu/g (at 27°C) and a blocking temperature (T B ) of ∼300 K [18,19].…”