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Biomimetic monolayer-protected gold nanoparticles for immunorecognition.

ABSTRACT: Gold nanoparticles (AuNPs) protected by self-assembled monolayers (SAMs) are capable of presenting precisely engineered surfaces at the nanoscale, allowing the mimicry of biomacromolecules on an artificial platform. Here we review the generation, characterization, and applications of monolayer-protected AuNPs that have been designed for immunorecognition by the integration of an oligopeptide epitope into the protecting monolayer. The resulting peptide-AuNP conjugate is an effective platform for biomimesis, as demonstrated by multiple studies. Recent work is presented and future directions for this field of research are discussed.

SUBMITTER: Harkness KM

PROVIDER: S-EPMC3376232 | biostudies-literature | 2012 Jul

REPOSITORIES: biostudies-literature

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Biomimetic monolayer-protected gold nanoparticles for immunorecognition.

Harkness Kellen M KM Turner Brian N BN Agrawal Amanda C AC Zhang Yibin Y McLean John A JA Cliffel David E DE

Nanoscale 20120529 13

Gold nanoparticles (AuNPs) protected by self-assembled monolayers (SAMs) are capable of presenting precisely engineered surfaces at the nanoscale, allowing the mimicry of biomacromolecules on an artificial platform. Here we review the generation, characterization, and applications of monolayer-protected AuNPs that have been designed for immunorecognition by the integration of an oligopeptide epitope into the protecting monolayer. The resulting peptide-AuNP conjugate is an effective platform for ...[more]

PMID: 22641221

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Project description:In order to determine how functionalized gold nanoparticles (AuNPs) interact in a near-physiological environment, we performed all-atom molecular dynamics simulations on the icosahedral Au144 nanoparticles each coated with a homogeneous set of 60 thiolates selected from one of these five (5) types: 11-mercapto-1-undecanesulfonate -SC11H22(SO3(-)), 5-mercapto-1-pentanesulfonate -SC5H10(SO3(-)), 5-mercapto-1-pentaneamine -SC5H10(NH3(+)), 4-mercapto-benzoate -SPh(COO(-)), or 4-mercapto-benzamide -SPh(CONH3(+)). These thiolates were selected to elucidate how the aggregation behavior of AuNPs depends on ligand parameters, including the charge of the terminal group (anionic vs. cationic), and its length and conformational flexibility. For this purpose, each functionalized AuNP was paired with a copy of itself, placed in an aqueous cell, neutralized by 120 Na(+)/Cl(-) counter-ions and salinated with a 150 mM concentration of NaCl, to form five (5) systems of like-charged AuNPs pairs in a saline. We computed the potential of mean force (the reversible work of separation) as a function of the intra-pair distance and, based on which, the aggregation affinities. We found that the AuNPs coated with negatively charged, short ligands have very high affinities. Structurally, a significant number of Na(+) counter-ions reside on a plane between the AuNPs, mediating the interaction. Each such ion forms a "salt bridge" (or "ionic bonds") to both of the AuNPs when they are separated by its diameter plus 0.2-0.3 nm. The positively charged AuNPs have much weaker affinities, as Cl(-) counter-ions form fewer and weaker salt bridges between the AuNPs. In the case of Au144(SC11H22(SO3(-)))60 pair, the flexible ligands fluctuate much more than the other four cases. The large fluctuations disfavor the forming of salt bridges between two AuNPs, but enable hydrophobic contact between the exposed hydrocarbon chains of the two AuNPs, which are subject to an effective attraction at a separation much greater than the AuNP diameter and involve a higher concentration of counter ions in the inter-pair space.

Project description:Gold nanoparticles covered with a mixture of ligands of which one type contains solubilizing triethylene glycol residues and the other peripheral zinc(II)-dipicolylamine (DPA) complexes allowed the optical detection of hydrogenphosphate, diphosphate, and triphosphate anions in water/methanol 1:2 (v/v). These anions caused the bright red solutions of the nanoparticles to change their color because of nanoparticle aggregation followed by precipitation, whereas halides or oxoanions such as sulfate, nitrate, or carbonate produced no effect. The sensitivity of phosphate sensing depended on the nature of the anion, with diphosphate and triphosphate inducing visual changes at significantly lower concentrations than hydrogenphosphate. In addition, the sensing sensitivity was also affected by the ratio of the ligands on the nanoparticle surface, decreasing as the number of immobilized zinc(II)-dipicolylamine groups increased. A nanoparticle containing a 9:1 ratio of the solubilizing and the anion-binding ligand showed a color change at diphosphate and triphosphate concentrations as low as 10 μmol/L, for example, and precipitated at slightly higher concentrations. Hydrogenphosphate induced a nanoparticle precipitation only at a concentration of ca. 400 μmol/L, at which the precipitates formed in the presence of diphosphates and triphosphates redissolved. A nanoparticle containing fewer binding sites was more sensitive, while increasing the relative number of zinc(II)-dipicolylamine complexes beyond 25% had a negative impact on the limit of detection and the optical response. Transmission electron microscopy provided evidence that the changes of the nanoparticle properties observed in the presence of the phosphates were due to a nanoparticle crosslinking, consistent with the preferred binding mode of zinc(II)-dipicolylamine complexes with phosphate anions which involves binding of the anion between two metal centers. This work thus provided information on how the behavior of mixed monolayer-protected gold nanoparticles is affected by multivalent interactions, at the same time introducing a method to assess whether certain biologically relevant anions are present in an aqueous solution within a specific concentration range.

Dataset Information

Biomimetic monolayer-protected gold nanoparticles for immunorecognition.

Publications

Biomimetic monolayer-protected gold nanoparticles for immunorecognition.

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