The conformation of thiol-linked oligonucleotides on the surface of Au nanoparticles was controlled by treatment with 6-mercapto-1-hexanol (MCH). MCH displaces noncovalent base adsorption to the surface, changing the oligo conformation on the Au surface. By controlling MCH concentration and reaction time, a change in effective size (D eff) of the Au−DNA conjugates and improved hybridization ability was observed, suggesting a reduced nonspecific adsorption of the oligo to the Au.

We report a systematic study of the base-dependent behavior of oligonucleotides linked to Au NP surfaces. Ten 15mer sequences were designed to investigate the effect of oligonucleotide sequence and high-affinity nucleotide location relative to the nanoparticle surface. The nucleotide position was varied within the sequence to be proximal, midway, or distal to the 5′ thiol. High-affinity motifs of adenine, guanine, and cytosine were placed in polythymine sequences, with a homobase oligonucleotide of thymine as a control sequence. Oligonucleotide reactivity toward the NPs and the extent of hybridization of the conjugates varied with sequence. Chemical treatment of the NP surface to remove nonspecific adsorption removed sequence-dependent effects on the hybridization. The behavior of the conjugates can be explained by nonspecific adsorption, where A-and C-containing oligonucleotides have a higher affinity for the NP surface.

We evaluate Ferguson analysis as a method for simultaneously measuring the size and zeta-potential of gold nanoparticle-DNA (Au NP-DNA) conjugates. This approach is highly suitable when the particle size is <20 nm and biomolecular conformation results in a nonspherical or nonlinear conjugate, causing conventional dynamic light scattering and zeta-potential measurements to be unable to achieve consistent results. We show the applicability of the method by varying the size of gold nanoparticles (5–20 nm) and the loading of methoxypolyethylene glycol/DNA on particle surface and buffer concentrations. Due to the low ionic mobility of tris-borate-EDTA buffer (TBE) and relatively high zeta-potential of Au NP-DNA, Henry’s solutions with higher order correction terms are necessary for obtaining the zeta-potential from the measured free mobility and size.

Summary Nanotechnology has held great promise for revolutionizing biology. The biological behavior of nanomaterials depends primarily on how they interface to biomolecules and their surroundings. Unfortunately, interface issues like non-specific adsorption are still the biggest obstacles to the success of nanobiotechnology and nanomedicine, and have held back widespread practical use of nanotechnology in biology. Not only does the biological interface of nanoparticles needs to be understood and controlled, but nanoparticles must be treated as biological entities rather than inorganic ones. Furthermore, one can adopt an engineering perspective of the nanoparticle-biological interface, realizing that it has unique, exploitable properties.

Gold nanoparticle (AuNP)-DNA conjugates can enhance in vitro translation of a protein.Enhancement occurs via a combination of non-specific adsorption of translation-related molecules and the ribosome to the AuNP-DNA and specific binding to the mRNA of interest. AuNP-DNA conjugates enhanced protein production of fluorescent proteins (mCherry, eGFP) in retic lysate mixes by 65-100%. Gel electrophoresis was used to probe non-specific adsorption of the AuNP-DNA conjugates to the translation machinery. It was determined that non-specific adsorption is critical for enhancement, and if it was eliminated, expression enhancement did not occur. The interaction of the mRNA with the DNA on the AuNP surface influenced the amount of enhancement, and was probed by expression in the presence of RNase H. These results suggest that higher translation enhancement occurs when the DNA on the AuNP forms an incomplete duplex with the mRNA. Tuning the balance between non-specific adsorption and specific binding of the AuNP-DNA conjugates could result in the translation enhancement of a specific gene in a mixture. Keywordsnanoparticle-DNA conjugates; non-specific adsorption; in vitro translation; selective enhancement; antisense; DNA-mRNA hybridization; nanoparticle-mPEG Due to their unique properties, nanoparticles (NPs) are attractive for numerous biological and therapeutic applications. [1][2][3][4][5][6][7][8][9][10] One of the biggest barriers for utilizing NPs is non-specific adsorption, where biomolecules non-covalently adsorb to NPs, obscuring biological function and leading to denaturation and undesirable effects. [11][12][13][14] Unfortunately, non-specific adsorption is complex, where an enormous number of non-covalent bonds between biomolecules and NP surfaces or ligands can form. Non-specific adsorption is difficult to not only prevent but also directly probe, and thus remains poorly understood. [15][16] Despite the fact that gold NPs (AuNPs) have versatile surface chemistry, efforts to simply eliminate nonspecific adsorption via surface modification 17 with inert molecules [18][19] have met limited success. [20][21][22][23] Consequently, non-specific adsorption is a major hindrance for nanobiotechnology.SUPPORTING INFORMATION. Nanoparticle sizing, effects of fluorescence quenching, and free mPEG on expression, and additional experiments exploring the effect of RNase H is included in the Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org. Here we adopt a different perspective of non-specific adsorption and demonstrate that it is ideal for enhancing the efficiency of a biological reaction, in vitro translation. Translation, the synthesis of a protein encoded in mRNA, is complex and involves the ribosome, mRNA, and hundreds of other species. 24 It can potentially be enhanced by recruiting and coordinating translation machinery and mRNA. [25][26] Because AuNP-DNA conjugates are approximately the same size as proteins, they can act as artificial scaffolds to bring p...

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The effective hydrodynamic size and free mobility of particles of varying aspect ratio were evaluated by Ferguson analysis of gel electrophoresis. The ligand layer thickness was estimated from the difference between the effective size and the size of the metal core from TEM imaging. The zeta potential of the particles was calculated from the Ferguson analysis result by applying conventional electrophoresis theories for spheres and cylinders. The results show that Henry's solution for spherical particles can be used to obtain the zeta potential of cylindrical particles without requiring the use of TEM for size analysis.

Present work experimentally characterizes the optical property of blended plasmonic nanofuids based on gold nanorod (AuNR) with different aspect ratios. The existence of localized surface plasmon resonance was verified from measured extinction coefficient of three AuNR solutions, and spectral tunability of AuNR nanofluid was successfully demonstrated in the visible and near-infrared spectral region. The representative aspect ratio and volume fraction of each sample were then calculated from the relation between extinction coefficient and extinction efficiency, which leads to the design of a blended plasmonic nanofluid having broad-band absorption characteristic in the visible and near-infrared spectral region. The results obtained from this study will facilitate the development of a novel volumetric solar thermal collectors using plasmonic nanofluids.