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Screen-based analysis of magnetic nanoparticle libraries formed using peptidic iron oxide ligands.

ABSTRACT: The identification of effective polypeptide ligands for magnetic iron oxide nanoparticles (IONPs) could considerably accelerate the high-throughput analysis of IONP-based reagents for imaging and cell labeling. We developed a procedure for screening IONP ligands and applied it to compare candidate peptides that incorporated carboxylic acid side chains, catechols, and sequences derived from phage display selection. We found that only l-3,4-dihydroxyphenylalanine (DOPA)-containing peptides were sufficient to maintain particles in solution. We used a DOPA-containing sequence motif as the starting point for generation of a further library of over 30 peptides, each of which was complexed with IONPs and evaluated for colloidal stability and magnetic resonance imaging (MRI) contrast properties. Optimal properties were conferred by sequences within a narrow range of biophysical parameters, suggesting that these sequences could serve as generalizable anchors for formation of polypeptide-IONP complexes. Differences in the amino acid sequence affected T1- and T2-weighted MRI contrast without substantially altering particle size, indicating that the microstructure of peptide-based IONP coatings exerts a substantial influence and could be manipulated to tune properties of targeted or responsive contrast agents. A representative peptide-IONP complex displayed stability in biological buffer and induced persistent MRI contrast in mice, indicating suitability of these species for in vivo molecular imaging applications.

SUBMITTER: Barch M

PROVIDER: S-EPMC4160280 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature

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Project description:Iron oxides are chemical compounds which have different polymorphic forms, including ?-Fe2O3 (maghemite), Fe3O4 (magnetite), and FeO (wustite). Among them, the most studied are ?-Fe2O3 and Fe3O4, as they possess extraordinary properties at the nanoscale (such as super paramagnetism, high specific surface area, biocompatible etc.), because at this size scale, the quantum effects affect matter behavior and optical, electrical and magnetic properties. Therefore, in the nanoscale, these materials become ideal for surface functionalization and modification in various applications such as separation techniques, magnetic sorting (cells and other biomolecules etc.), drug delivery, cancer hyperthermia, sensing etc., and also for increased surface area-to-volume ratio, which allows for excellent dispersibility in the solution form. The current methods used are partially and passively mixed reactants, and, thus, every reaction has a different proportion of all factors which causes further difficulties in reproducibility. Direct active and complete mixing and automated approaches could be solutions to this size- and shape-controlled synthesis, playing a key role in its exploitation for scientific or technological purposes. An ideal synthesis method should be able to allow reliable adjustment of parameters and control over the following: fluctuation in temperature; pH, stirring rate; particle distribution; size control; concentration; and control over nanoparticle shape and composition i.e., crystallinity, purity, and rapid screening. Iron oxide nanoparticle (IONP)-based available clinical applications are RNA/DNA extraction and detection of infectious bacteria and viruses. Such technologies are important at POC (point of care) diagnosis. IONPs can play a key role in these perspectives. Although there are various methods for synthesis of IONPs, one of the most crucial goals is to control size and properties with high reproducibility to accomplish successful applications. Using multiple characterization techniques to identify and confirm the oxide phase of iron can provide better characterization capability. It is very important to understand the in-depth IONP formation mechanism, enabling better control over parameters and overall reaction and, by extension, properties of IONPs. This work provides an in-depth overview of different properties, synthesis methods, and mechanisms of iron oxide nanoparticles (IONPs) formation, and the diverse range of their applications. Different characterization factors and strategies to confirm phase purity in the IONP synthesis field are reviewed. First, properties of IONPs and various synthesis routes with their merits and demerits are described. We also describe different synthesis strategies and formation mechanisms for IONPs such as for: wustite (FeO), hematite (?-Fe2O3), maghemite (?-Fe2O3) and magnetite (Fe3O4). We also describe characterization of these nanoparticles and various applications in detail. In conclusion, we present a detailed overview on the properties, size-controlled synthesis, formation mechanisms and applications of IONPs.

Project description:The use of inorganic nanoparticles (NPs) as vectors for the delivery of oligonucleotides for in vitro and in vivo applications is rapidly gaining momentum. Some of the reasons making them especially good candidates for this purpose are their ease of synthesis in a range of sizes and surface coatings, their propensity to penetrate cell membranes, their stability and biocompatibility, and their unique size-dependent physical properties that impart additional diagnostic and therapeutic tools. Notwithstanding these notable attributes, a major obstacle to their practical use is given by the typically low oligonucleotide loading levels attainable through conventional bioconjugation procedures. This shortcoming is especially worrisome as toxicity concerns have been associated with codelivery of NPs. In this paper we are analytically analyzing the formation of electrostatic complexes between negatively charged ssDNA and positively charged iron oxide nanoparticles (SPIO-NP) with the purpose of identifying the optimal conditions leading to stable formulations at high oligo loading levels. The formation and loading levels of ssDNA:SPIO-NP complexes have been investigated at different oligo:NP ratios and under different ionic strengths through dynamic light scattering, fluorescence quenching experiments, and pull-down assays. Through these studies we have identified optimal conditions for attaining maximal oligo loading levels, and we are proposing a simple model to explain an unusual behavior observed in the formation of the complexes. Finally, we introduce an alternative loading method relying on the electrostatic coloading of an oligo sequence in the presence of a negatively charged PEGylated block copolymer, yielding very stable and high loading PEGylated ssDNA:SPIO-NPs. The findings that we are reporting are of general validity, and similar conditions could be easily translated to the electrostatic formation of ssDNA:NP complexes consisting of different NP materials and sizes.

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Screen-based analysis of magnetic nanoparticle libraries formed using peptidic iron oxide ligands.

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