The fabrication of electrospun composite polyurethane fibers capable of dual-action antibacterial dendrimer release is reported. Generation 4 (G4) poly(amidoamine) dendrimers were functionalized with octyl alkyl chain or quaternary ammonium (QA) moieties followed by modification of the resulting secondary amines with N-diazeniumdiolate nitric oxide (NO) donors to produce dual-action antibacterial dendrimers. Control and NO-releasing dendrimers were doped into polyurethane solutions prior to electrospinning of the polymer to yield well-defined dendrimer-doped composite polyurethane fibers. The fiber mats were semi-porous (≥30% porosity) and exhibited high water uptake (>100% relative to fiber mass). Dendrimer-and NOrelease characteristics (rates and totals) were dependent on the dendrimer modification and polyurethane composition, with total dendrimer-and NO-release amounts ranging from 10 -80 μg/mg and 0.027 -0.072 μmol NO/mg, respectively. The antibacterial action of the fibers was evaluated against Gram-negative and Gram-positive bacterial strains. Nitric oxide-releasing fibers demonstrated broad-spectrum bactericidal action at short (2 h) and long (24 h) timescales.

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The fluorescence intensity emitted by nitrogen-vacancy (NV) centers in diamond nanoparticles can be readily modulated by the application of a magnetic field using a small electromagnet. By acquiring interleaved images acquired in the presence and absence of the magnetic field and performing digital subtraction, the fluorescence intensity of the NV nanodiamond can be isolated from scattering and autofluorescence even when these backgrounds are changing monotonically during the experiments. This approach has the potential to enable the robust identification of nanodiamonds in organisms and other complex environments. Yet, the practical application of magnetic modulation imaging to realistic systems requires the use of quantitative analysis methods based on signal-to-noise considerations. Here, we describe the use of magnetic modulation to analyze the uptake of diamond nanoparticles from an aqueous environment into Caenorhabditis elegans, used here as a model system for identification and quantification of nanodiamonds in complex matrices. Based on the observed signal-tonoise ratio of sets of digitally subtracted images, we show that nanodiamonds can be identified on an individual pixel basis with a >99.95% confidence. To determine whether surface functionalization of the nanodiamond significantly impacted uptake, we used this approach to analyze the presence of nanodiamonds in C. elegans that had been exposed to these functionalized nanodiamonds in the water column, with uptake likely occurring by ingestion. In each case, the images show a significant nanoparticle uptake. However, differences in uptake between the three ligands were not outside of the experimental error, indicating that additional factors beyond the surface charge are important factors controlling uptake. Analysis of the number of pixels above the threshold in individual C. elegans organisms revealed distributions that deviate significantly from a Poisson distribution, suggesting that uptake of nanoparticles may not be a statistically independent event. The results presented here demonstrate that magnetic modulation combined with quantitative analysis of the resulting images can be used to robustly characterize nanoparticle uptake into organisms.

Metal oxide nanoparticles have many useful applications in environmental studies, as tracking agents in life sciences, and in nutrient delivery for nano-enhanced agriculture. A key challenge in controlling the behavior of metal oxide nanoparticles in aqueous media is that molecular ligands are unstable with respect to hydrolytic cleavage from the surfaces. This instability limits the practical application of metal oxide nanoparticles in aqueous media. We have developed a method for producing nanometer-thin carbon shells on the surface of Al 2 O 3 , Cr 3+ :Al 2 O 3 (nanoruby), ZnO, and Fe 3 O 4 (magnetite) metal oxides that provides a scaffold for subsequent covalent chemical functionalization. Fluorescence measurements using carbonized Cr 3+ :Al 2 O 3 (nanoruby) confirm that these thin carbon coatings have relatively little impact on the optical properties, allowing bright emission with less than 50% decrease in fluorescence intensity compared to an identical nanoruby without carbon coating. We demonstrate the utility for functionalization by modifying C-coated Al 2 O 3 with molecular ligands bearing positive and negative charges. This approach provides a pathway for functionalization of a broad range of metal oxide nanoparticles with molecular ligands that can confer specific molecular properties to the nanoparticle surfaces in aqueous media while taking advantage of the high strength and stability of C−C interfacial bonds between surface ligands and the carbon shell.

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