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The adsorption of calf thymus DNA to 45 Å nanoparticles of Cd(II)-rich CdS has been examined by photoluminescence spectroscopy as a function of temperature. The resulting van't Hoff plot suggests that the driving force for adsorption is entropy, and the enthalpic contribution to DNA−surface binding is slightly unfavorable. A likely source of the increase in entropy upon binding is release of solvent and/or counterions from the interface, analogous to what has been observed for nonspecific protein−DNA interactions. Reverse salt titrations suggest that counterion release is a substantial component of the nanoparticle−DNA interaction.

We have examined the adsorption of different DNA sequences to mercaptoethanol-capped CdS quantum dots, ∼40 Å diameter, as a minimalist model for nonspecific protein−DNA interactions, and compared these results to what we have previously found for Cd2+-surface-rich dots of the same size (Mahtab, R.; Rogers, J. P.; Murphy, C. J. J. Am. Chem. Soc. 1995, 117, 9099). We find that neutralization of the surface leads to no detectable binding, based on our luminescence assay, for “straight” and A-tract oligonucleotides, while a crystallographically “kinked” sequence does still bind, but by a factor of 4 less than that observed for a divalent metal ion-rich surface. The binding constants for both surfaces are within the range of nonspecific protein−DNA interactions. The kinetics of binding are also monitored and are compared to nonspecific protein−DNA interactions for large DNA fragments. Issues of biopolymer static bending vs flexibility are also addressed with fluorescence resonance energy transfer experiments.

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BackgroundDeposits of aggregated amyloid-β protein (Aβ) are a pathological hallmark of Alzheimer’s disease (AD). Thus, one therapeutic strategy is to eliminate these deposits by halting Aβ aggregation. While a variety of possible aggregation inhibitors have been explored, only nanoparticles (NPs) exhibit promise at low substoichiometric ratios. With tunable size, shape, and surface properties, NPs present an ideal platform for rationally designed Aβ aggregation inhibitors. In this study, we characterized the inhibitory capabilities of gold nanospheres exhibiting different surface coatings and diameters.ResultsBoth NP diameter and surface chemistry were found to modulate the extent of aggregation, while NP electric charge influenced aggregate morphology. Notably, 8 nm and 18 nm poly(acrylic acid)-coated NPs abrogated Aβ aggregation at a substoichiometric ratio of 1:2,000,000. Theoretical calculations suggest that this low stoichiometry could arise from altered solution conditions near the NP surface. Specifically, local solution pH and charge density are congruent with conditions that influence aggregation.ConclusionsThese findings demonstrate the potential of surface-coated gold nanospheres to serve as tunable therapeutic agents for the inhibition of Aβ aggregation. Insights gained into the physiochemical properties of effective NP inhibitors will inform future rational design of effective NP-based therapeutics for AD.Electronic supplementary materialThe online version of this article (doi:10.1186/s13036-017-0047-6) contains supplementary material, which is available to authorized users.