With an ultrafast time-resolved photoluminescence system utilizing a Kerr gate, the time-resolved photoluminescence of core and shell constituents within CdSe/CdS dot-in-rod heterostructures is studied as a function of heterostructure size. Measurements performed at low excitation fluence generating, on average, less than one exciton per nanorod, reveal photoluminescence from direct recombination of carriers in the CdS heterostructure rod with lifetime generally increasing from 0.4 ps to 1.3 ps as the rod length increases. Decay of the CdS rod photoluminescence is accompanied by an increase in emission from the CdSe core on comparable time scales, also trending towards larger values as the rod length increases. The observed kinetics can be explained without invoking a non-radiative trapping mechanism. We also present alloying as a mechanism for enhancing electron confinement and reducing fluorescence lifetime at nanosecond time scales.

Two species of monodisperse nanocrystals (NCs) can self-assemble into a variety of complex 2D and 3D periodic structures, or binary NC superlattice (BNSL) films, based on the relative number and size of the NCs. BNSL films offer great promise for both fundamental scientific studies and optoelectronic applications; however, the utility of as-assembled structures has been limited by the insulating ligands that originate from the synthesis of NCs. Here we report the application of an in situ ligand exchange strategy at a liquid−air interface to replace the long synthesis ligands with short ligands while preserving the long-range order of BNSL films. This approach is demonstrated for BNSL structures consisting of PbSe NCs of different size combinations and ligands of interest for photovoltaic devices, infrared detectors, and light-emitting diodes. To confirm enhanced coupling introduced by ligand exchange, we show ultrafast (∼1 ps) directional carrier transfer across the type-I heterojunction formed by NCs of different sizes within ligand-exchanged BNSL films. This approach shows the potential promise of functional BNSL films, where the local and long-range energy landscape and electronic coupling can be adjusted by tuning NC composition, size, and interparticle spacing.

Annular dark-field scanning transmission electron microscopy (ADF-STEM) is employed to provide a statistical description of faceting, core location, stacking faults, and polar self-assembly behavior of CdSe/CdS dot-in-rod heterostructures. Applied to dot-in-rod and rod-in-rod heterostructures, STEM enables statistical measurements of core locations that show that the position of the CdSe core lies at ≈45% of the length of the sample, slightly closer to the blunt (001) facet of the CdS nanorod shell. A study of stacking faults reveals a substantially enhanced probability near the epitaxial interface of the core and shell, suggesting the role of epitaxial strain in the formation of defects. Structural analysis is extended to liquid-crystalline monolayers of nanorods, and the role of dipolar interactions within lamellae is analyzed using one-dimensional pair-distribution analysis of polarity, showing that the nanorods have a random dipole alignment.

Biofilms act as a reservoir of infection, and periodically release cells in vicinity that are capable of developing new biofilm colonies and disseminate infection. Many chronic bacterial infections are serious that are associated with biofilms and have high morbidity and mortality, partly due to their higher resistance to antimicrobial agents, and partly due to lack of strong biocides which can efficiently treat and inhibit biofilm formation. We recently demonstrated that nonequilibrium non-thermal dielectric-barrier discharge plasma (Plasma) can also be applied to control pathogens via applying treated-liquids, and these liquids acquire broad-spectrum antimicrobial properties. In present studies we demonstrated a range of plasma-activated simple chemical solutions which significantly inhibited biofilm formation by multidrug-resistant bacterial pathogens. Plasma-activated methionine solution exhibited strong inhibitory activity against the biofilms of carbapenem-resistant Acinetobacter baumannii, methicillin-resistant Staphylococcus aureus, metallo-β-lactamase (NDM1)-positive Klebsiella pneumoniae, and Enterococcus faecalis, and prevented the formation of biofilms by about 70% as compared to untreated controls in single exposure. In addition to inhibition of biofilm formation, a complete inactivation of biofilm-embedded bacterial cells was observed in less than 30 minute's exposure to candidate plasma-activated methionine solution. These findings suggest that plasma-activated solutions have a potential to prevent biofilm formation, and as biofilm inhibitor.

Single particle tracking is used to investigate the effect of nanoparticle shape anisotropy on dynamics. The mean squared displacements of poly­(ethylene glycol) (PEG)-functionalized quantum dot (QD) and quantum rod (QR) probes of similar diameters are examined during the gelation of a tetra-poly­(ethylene glycol) (tetra-PEG) hydrogel. At early times prior to the gel time (t gel), QDs exhibit greater mobility than their QR counterparts. However, as gelation proceeds, QRs exhibit increased dynamics compared to QDs, suggesting enhanced rod dynamics in increasingly confined networks. Potential mechanisms are discussed, including the influence of rotational dynamics and the increased parallel diffusion of rods in confined systems. This study provides insights into developing nanoparticle probes of different shape anisotropy, with particular importance for their use in drug delivery and other biomedical applications.