Gold nanoparticles for biology and medicine

Biological applications of magnetic nanoparticles

In this review an overview about biological applications of magnetic colloidal nanoparticles will be given, which comprises their synthesis, characterization, and in vitro and in vivo applications. The potential future role of magnetic nanoparticles compared to other functional nanoparticles will be discussed by highlighting the possibility of integration with other nanostructures and with existing biotechnology as well as by pointing out the specific properties of magnetic colloids. Current limitations in the fabrication process and issues related with the outcome of the particles in the body will be also pointed out in order to address the remaining challenges for an extended application of magnetic nanoparticles in medicine.

Tuning ratios, densities, and supramolecular spacing in bifunctional DNA-modified gold nanoparticles

Methods for combining multiple functions into well-defined nanomaterials are still lacking, despite their need in nanomedicine and within the broader field of nanotechnology. Here several strategies for controlling the amount and the ratio of combinations of labeled DNA on 13-nm gold nanoparticles using self-assembly of thiolated DNA and/or DNA-directed assembly are explored. It is found that the self-assembly of mixtures of fluorescently labeled DNA can lead to a higher amount of labeled DNA per particle; however, the ratio of fluorophores on the nanoparticles differs greatly from that in the self-assembly solution. In contrast, when fluorescently labeled DNA are hybridized to DNA-modified gold nanoparticles, the fluorophore ratio on the nanoparticles is much closer to their ratio in solution. The use of bifunctional DNA-doublers in self-assembly and DNA-directed assembly is also explored to increase the complexity of these materials and control their composition. Finally, tuning the distance between the labels from 2.9 to 5.4 nm was achieved using different hybridized DNA clamp complexes. Fluorescent results suggest that assembling these clamps on nanoparticle surfaces may be possible, although the resulting label spacing could not be quantified.

One-pot aqueous phase growth of biocompatible 15-130 nm gold nanoparticles stabilized with bidentate PEG

We describe a new, single pot, aqueous phase method for synthesizing water soluble gold nanoparticles (AuNPs) over a size range of 15-130 nm. Poly(ethylene glycol)-appended thioctic acid ligands were used to control the growth rates and stabilize the AuNPs. Critical factors that enable the controlled growth of the AuNPs over this size range include the pH, the choice of reducing agent, the reaction temperature and the sequential addition of gold precursor and ligand with specific ligand-to-gold ratios. We describe the synthetic procedure in detail. Optical and structural characterization of the AuNPs was accomplished using UV-vis absorption spectroscopy, dynamic light scattering, and transmission and scanning electron microscopy.

Highly size- and shape-controlled synthesis of silver nanoparticles via a templated Tollens reaction

A mild, facile one-step synthetic strategy for the preparation of size- and shape-controlled silver nanoparticles (AgNPs) is presented. The high degree of size- and shape-control of these AgNPs is achieved by the use of triazole sugar ligands scaffolded by a central resorcinol ether core. Both the triazoles and the resorcinol ether core mediate the nucleation, growth, and passivation phases of the preparation of AgNP in the presence of the Tollens reagent as the silver source. Kinetic and (1)H NMR titration data is presented describing the nature of the interactions between the Tollens reagent and these ligands.

Surface science of DNA adsorption onto citrate-capped gold nanoparticles

Single-stranded DNA can be adsorbed by citrate capped gold nanoparticles (AuNPs), resulting in increased AuNP stability, which forms the basis of a number of biochemical and analytical applications, but the fundamental interaction of this adsorption reaction remains unclear. In this study, we measured DNA adsorption kinetics, capacity, and isotherms, demonstrating that the adsorption process is governed by electrostatic forces. The charge repulsion among DNA strands and between DNA and AuNPs can be reduced by adding salt, reducing pH or by using noncharged peptide nucleic acid (PNA). Langmuir adsorption isotherms are obtained, indicating the presence of both adsorption and desorption of DNA from AuNPs. While increasing salt concentration facilitates DNA adsorption, the desorption rate is also enhanced in higher salt due to DNA compaction. DNA adsorption capacity is determined by DNA oligomer length, DNA concentration, and salt. Previous studies indicated faster adsorption of short DNA oligomers by AuNPs, we find that once adsorbed, longer DNAs are much more effective in protecting AuNPs from aggregation. DNA adsorption is also facilitated by using low pH buffers and high alcohol concentrations. A model based on electrostatic repulsion on AuNPs is proposed to rationalize the DNA adsorption/desorption behavior.

A nanoscale drug delivery carrier using nucleic acid aptamers for extended release of therapeutic

We have synthesized, characterized, and optimized a novel nano drug-delivery carrier that utilizes the versatile properties of nucleic acid for programmable and on-demand drug release. The drug-delivery carrier consists of 15 nm gold nanoparticles (AuNPs) functionalized with drug binding DNA aptamers via single-stranded (ss) anchor DNA. The presence of anchor DNA makes the nanocarrier flexible to be reprogrammed with various aptamers. Under the optimum binding conditions (0.4 M NaCl and 4 μM DNA), a maximum of 101 ± 8 anchor DNA strands were conjugated per particle. On binding DNA-aptamer:drug complexes to AuNPs, a maximum of 35 neomycin molecules were bound per AuNP. Controlled and extended release of drug from the synthesized carrier was obtained by temperature and affinity modulations. Furthermore, for the first time, we demonstrated that neomycin could bind to DNA with very high affinity (K(d) = 98.101 nM). This DNA-based nanocarrier, designed using the principles of molecular biology, is expected to impact a number of treatment strategies.

FROM THE CLINICAL EDITOR

In this basic science work, the authors demonstrate the feasibility of utilizing a novel nano drug-delivery carrier with the versatile properties of nucleic acid for programmable and on-demand drug release.

Ex vivo impact of functionalized carbon nanotubes on human immune cells

Aim: Different studies, carried out by us and others, have investigated the impact of carbon nanotubes (CNTs) in vitro and in animal models. To date, only a few studies have been performed on human cells ex vivo. There is also a lack of comparison between CNTs with varied functionalization and structural properties and their impact on different cell types. Materials & Methods: The present ex vivo human study focuses on the impact of a series of functionalized multiwalled CNTs on human T and B lymphocytes, natural killer (NK) cells and monocytes. Results: Smaller diameter nanotubes are internalized more efficiently. Viability assays displayed the absence of cytotoxicity of all multiwalled CNTs used. Activation assay demonstrated a strong effect on monocytes and NK cells. Conclusion: Our results, on human cells ex vivo, confirmed previous studies demonstrating appropriately functionalized CNTs are nontoxic. The effects on cell functionality were significant for the monocytes and NK cells. These findings encourage the possible use of CNTs for biomedical applications either as carriers of therapeutic molecules or as immune modulator systems.

Towards in vitro molecular diagnostics using nanostructures

Nanostructures appear to be promising for a number of applications in molecular diagnostics, mainly due to the increased surface-to-volume ratio they can offer, the very low limit of detection achievable, and the possibility to fabricate point-of-care diagnostic devices. In this paper, we review examples of the use of nanostructures as diagnostic tools that bring in marked improvements over prevalent classical assays. The focus is laid on the various sensing paradigms that possess the potential or have demonstrated the capability to replace or augment current analytical strategies. We start with a brief introduction of the various types of nanostructures and their physical properties that determine the transduction principle. This is followed by a concise collection of various functionalization protocols used to immobilize biomolecules on the nanostructure surface. The sensing paradigms are discussed in two contexts: the nanostructure acting as a label for detection, or the nanostructure acting as a support upon which the molecular recognition events take place. In order to be successful in the field of molecular diagnostics, it is important that the nanoanalytical tools be evaluated in the appropriate biological environment. The final section of the review compiles such examples, where the nanostructure-based diagnostic tools have been tested on realistic samples such as serum, demonstrating their analytical power even in the presence of complex matrix effects. The ability of nanodiagnostic tools to detect ultralow concentrations of one or more analytes coupled with portability and the use of low sample volumes is expected to have a broad impact in the field of molecular diagnostics.

Monolayer coated gold nanoparticles for delivery applications

Gold nanoparticles (AuNPs) provide attractive vehicles for delivery of drugs, genetic materials, proteins, and small molecules. AuNPs feature low core toxicity coupled with the ability to parametrically control particle size and surface properties. In this review, we focus on engineering of the AuNP surface monolayer, highlighting recent advances in tuning monolayer structures for efficient delivery of drugs and biomolecules. This review covers two broad categories of particle functionalization, organic monolayers and biomolecule coatings, and discusses their applications in drug, DNA/RNA, protein and small molecule delivery.

Susceptibility to gold nanoparticle-induced hepatotoxicity is enhanced in a mouse model of nonalcoholic steatohepatitis

Although the safety of gold nanoparticle (AuNP) use is of growing concern, most toxicity studies of AuNPs had focused on their chemical characteristics, including their physical dimensions, surface chemistry, and shape. The present study examined the susceptibility of rodents with healthy or damaged livers to AuNP-induced hepatotoxicity. To induce a model of liver injury, mice were fed a methionine- and choline-deficient (MCD) diet for 4 weeks. Sizes and biodistribution of 15-nm PEGylated AuNPs were analyzed by transmission electron microscopy. Levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were estimated with an automatic chemical analyzer, and liver sections were subjected to pathological examination. Activities of antioxidant enzymes were determined by biochemical assay. Lateral tail vein injection of MCD diet-fed mice with 5 mg kg(-1) AuNPs significantly elevated the serum ALT and AST levels compared to MCD diet-fed mice injected with mPEG (methylpolyethylene glycol). Similarly, severe hepatic cell damage, acute inflammation, and increased apoptosis and reactive oxygen species (ROS) production were observed in the livers of AuNP-injected mice on the MCD diet; these liver injuries were attenuated in mice fed a normal chow diet. The results suggest that AuNPs display toxicity in a stressed liver environment by stimulating the inflammatory response and accelerating stress-induced apoptosis. These conclusions may point to the importance of considering health conditions, including liver damage, in medical applications of AuNPs.

Regiospecific plasmonic assemblies for in situ Raman spectroscopy in live cells

Multiple properties of plasmonic assemblies are determined by their geometrical organization. While high degree of complexity was achieved for plasmonic superstructures based on nanoparticles (NPs), little is known about the stable and structurally reproducible plasmonic assemblies made up from geometrically diverse plasmonic building blocks. Among other possibilities, they open the door for the preparation of regiospecific isomers of nanoscale assemblies significant both from a fundamental point of view and optical applications. Here, we present a synthetic method for complex assemblies from NPs and nanorods (NRs) based on selective modification of NRs with DNA oligomers. Three types of assemblies denoted as End, Side, and Satellite isomers that display distinct elements of regiospecificity were prepared with the yield exceeding 85%. Multiple experimental methods independently verify various structural features, uniformity, and stability of the prepared assemblies. The presence of interparticle gaps with finely controlled geometrical parameters and inherently small size comparable with those of cellular organelles fomented their study as intracellular probes. Against initial expectations, SERS intensity for End, Side, and Satellite isomers was found to be dependent primarily on the number of the NPs in the superstructures rationalized with the help of electrical field simulations. Incubation of the label-free NP-NR assemblies with HeLa cells indicated sufficient field enhancement to detect structural lipids of mitochondria and potentially small metabolites. This provided the first proof-of-concept data for the possibility of real-time probing of the local organelle environment in live cells. Further studies should include structural optimization of the assemblies for multitarget monitoring of metabolic activity and further increase in complexity for applications in transformative optics.

Tailoring of biomimetic high-density lipoprotein nanostructures changes cholesterol binding and efflux

Gold nanoparticles (Au NPs) were employed as templates to synthesize spherical, high-density lipoprotein (HDL) biomimics (HDL Au NPs) of different sizes and surface chemistries. The effect of size and surface chemistry on the cholesterol binding properties and the ability of the HDL Au NPs to efflux cholesterol from macrophage cells were measured. Results demonstrate that Au NPs may be utilized as templates to generate nanostructures with different physical characteristics that mimic natural HDL. Furthermore, the properties of the HDL Au NPs may be tailored to modulate the ability to bind cholesterol in solution and efflux cholesterol from macrophages. From the conjugates tested, the optimum size and surface chemistry for preparing functional Au NP-templated HDL biomimics were identified.

One-pot synthesis of polypeptide-gold nanoconjugates for in vitro gene transfection

We present a general strategy to create polypeptide-gold nanoconjugates by a one-pot synthesis approach, where polypeptides act not only as capping agents but also as reductants for the formation of gold nanoparticles without the need of an additional reducing agent. The present approach is environmentally benign, facile, and flexible for the design of functional polypeptide-gold nanoconjugates. As a demonstration of as-synthesized nanoconjugates for biomedical applications, the resulting positively charged polypeptide-conjugated gold nanoparticles are applied for gene delivery. A gradual and prolonged intracellular uptake and transfection is achieved, and transfection activity is maintained for almost two weeks with no obvious cytotoxicity. The biologically based method presented in this work will provide a new alternative in creating a variety of multifunctional polypeptide-metallic nanoconjugates in a simple and straightforward manner, which will be more advantageous for their applications in biomedicine.

Au-Ag hybrid nanoparticle patterns of tunable size and density on glass and polymeric supports

This paper describes a method to pattern surfaces with Au-Ag hybrid nanoparticles. We used block copolymer micelle lithography of Au nanoparticles and electroless deposition of Ag. The combination of these two methods enables independent tuning of nanoparticle spacing and Ag-shell size. For this purpose, 8 nm large patterned Au nanoparticle seeds served as nuclei for the electroless deposition of silver that is based on a modified Tollens process with glucose. By adjusting the reaction conditions, specific growth of Ag on top of the Au seeds has been accomplished and analyzed by SEM, HRTEM, XEDS, and UV-vis spectroscopy. We could show that this versatile and green method is feasible on glass as well as on biomedical-relevant polymers like poly(ethylene glycol) hydrogels and amorphous Teflon. In conclusion, this method provides a new route to pattern glass and polymeric surfaces with Au-Ag hybrid nanoparticles. It will have many uses in applications such as surface enhanced Raman spectroscopy (SERS) or antimicrobial coatings for which hybrid nanoparticle density, size, and morphology are important.

Programmable multivalent display of receptor ligands using peptide nucleic acid nanoscaffolds

Multivalent effects dictate the binding affinity of multiple ligands on one molecular entity to receptors. Integrins are receptors that mediate cell attachment through multivalent binding to peptide sequences within the extracellular matrix, and overexpression promotes the metastasis of some cancers. Multivalent display of integrin antagonists enhances their efficacy, but current scaffolds have limited ranges and precision for the display of ligands. Here we present an approach to studying multivalent effects across wide ranges of ligand number, density, and three-dimensional arrangement. Using L-lysine γ-substituted peptide nucleic acids, the multivalent effects of an integrin antagonist were examined over a range of 1-45 ligands. The optimal construct improves the inhibitory activity of the antagonist by two orders of magnitude against the binding of melanoma cells to the extracellular matrix in both in vitro and in vivo models.

Interactions of human endothelial cells with gold nanoparticles of different morphologies

The interactions between noncancerous, primary endothelial cells and gold nanoparticles with different morphologies but the same ligand capping are investigated. The endothelial cells are incubated with gold nanospheres, nanorods, hollow gold spheres, and core/shell silica/gold nanocrystals, which are coated with monocarboxy (1-mercaptoundec-11-yl) hexaethylene glycol (OEG). Cell viability studies show that all types of gold particles are noncytotoxic. The number of particles taken up by the cells is estimated using inductively coupled plasma (ICP), and are found to differ depending on particle morphology. The above results are discussed with respect to heating efficiency. Using experimental data reported earlier and theoretical model calculations which take into account the physical properties and distribution of particles in the cellular microenvironment, it is found that collective heating effects of several cells loaded with nanoparticles must be included to explain the observed viability of the endothelial cells.

Aptasensor for ampicillin using gold nanoparticle based dual fluorescence-colorimetric methods

A gold nanoparticle based dual fluorescence-colorimetric method was developed as an aptasensor to detect ampicillin using its single-stranded DNA (ssDNA) aptamer, which was discovered by a magnetic bead-based SELEX technique. The selected aptamers, AMP4 (5'-CACGGCATGGTGGGCGTCGTG-3'), AMP17 (5'-GCGGGCGGTTGTATAGCGG-3'), and AMP18 (5'-TTAGTTGGGGTTCAGTTGG-3'), were confirmed to have high sensitivity and specificity to ampicillin (K(d), AMP7 = 9.4 nM, AMP17 = 13.4 nM, and AMP18 = 9.8 nM, respectively). The 5'-fluorescein amidite (FAM)-modified aptamer was used as a dual probe for observing fluorescence differences and color changes simultaneously. The lower limits of detection for this dual method were a 2 ng/mL by fluorescence and a 10 ng/mL by colorimetry for ampicillin in the milk as well as in distilled water. Because these detection limits were below the maximum residue limit of ampicillin, this aptasensor was sensitive enough to detect antibiotics in food products, such as milk and animal tissues. In addition, this dual aptasensor will be a more accurate method for antibiotics in food products as it concurrently uses two detection methods: fluorescence and colorimetry.

Gold nanoparticles in the clinical laboratory: principles of preparation and applications

In order to meet the challenges of effective healthcare, the clinical laboratory is constantly striving to improve testing sensitivity while reducing the required time and cost. Gold nanoparticles (AuNPs) are proposed as one of the most promising tools to meet such goals. They have unique optophysical properties which enable sensitive detection of biomarkers, and are easily amenable to modification for use in different assay formats including immunoassays and molecular assays. Additionally, their preparation is relatively simple and their detection methods are quite versatile. AuNPs are showing substantial promise for effective practical applications and commercial utilization is already underway. This article covers the principles of preparation of AuNPs and their use for development of different diagnostic platforms.