Gold nanoparticle design for RNA compaction.

RNA-based therapeutics hold a great promise in treating a variety of diseases. However, double-stranded RNAs (dsRNAs) are inherently unstable, highly charged, and stiff macromolecules that require a delivery vehicle. Cationic ligand functionalized gold nanoparticles (AuNPs) are able to compact nucleic acids and assist in RNA delivery. Here, we use large-scale all-atom molecular dynamics simulations to show that correlations between ligand length, metal core size, and ligand excess free volume control the ability of nanoparticles to bend dsRNA far below its persistence length. The analysis of ammonium binding sites showed that longer ligands that bind deep within the major groove did not cause bending. By limiting ligand length and, thus, excess free volume, we have designed nanoparticles with controlled internal binding to RNA's major groove. NPs that are able to induce RNA bending cause a periodic variation in RNA's major groove width. Density functional theory studies on smaller models support large-scale simulations. Our results are expected to have significant implications in packaging of nucleic acids for their applications in nanotechnology and gene delivery.

Tuning Microbial Activity via Programmatic Alteration of Cell/Substrate Interfaces.

A wide portfolio of advanced programmable materials and structures has been developed for biological applications in the last two decades. Particularly, due to their unique properties, semiconducting materials have been utilized in areas of biocomputing, implantable electronics, and healthcare. As a new concept of such programmable material design, biointerfaces based on inorganic semiconducting materials as substrates introduce unconventional paths for bioinformatics and biosensing. In particular, understanding how the properties of a substrate can alter microbial biofilm behavior enables researchers to better characterize and thus create programmable biointerfaces with necessary characteristics on demand. Herein, the current status of advanced microorganism-inorganic biointerfaces is summarized along with types of responses that can be observed in such hybrid systems. This work identifies promising inorganic material types along with target microorganisms that will be critical for future research on programmable biointerfacial structures.

Behavior of E. coli with Variable Surface Morphology Changes on Charged Semiconductor Interfaces.

Bacterial behavior is often controlled by structural and composition elements of their cell wall. Using genetic mutant strains that change specific aspects of their surface structure, we modified bacterial behavior in response to semiconductor surfaces. We monitored the adhesion, membrane potential, and catalase activity of the Gram-negative bacterium Escherichia coli (E. coli) that were mutant for genes encoding components of their surface architecture, specifically flagella, fimbriae, curli, and components of the lipopolysaccharide membrane, while on gallium nitride (GaN) surfaces with different surface potentials. The bacteria and the semiconductor surface properties were recorded prior to the biofilm studies. The data from the materials and bioassays characterization supports the notion that alteration of the surface structure of the E. coli bacterium resulted in changes to bacterium behavior on the GaN medium. Loss of specific surface structure on the E. coli bacterium reduced its sensitivity to the semiconductor interfaces, while other mutations increase bacterial adhesion when compared to the wild-type control E. coli bacteria. These results demonstrate that bacterial behavior and responses to GaN semiconductor materials can be controlled genetically and can be utilized to tune the fate of living bacteria on GaN surfaces.

Characterization of Pseudomonas aeruginosa Films on Different Inorganic Surfaces before and after UV Light Exposure.

The changes of the surface properties of Au, GaN, and SiO x after UV light irradiation were used to actively influence the process of formation of Pseudomonas aeruginosa films. The interfacial properties of the substrates were characterized by X-ray photoelectron spectroscopy and atomic force microscopy. The changes in the P. aeruginosa film properties were accessed by analyzing adhesion force maps and quantifying the intracellular Ca2+ concentration. The collected analysis indicates that the alteration of the inorganic materials' surface chemistry can lead to differences in biofilm formation and variable response from P. aeruginosa cells.