Polyaromatic Profluorescent Nitroxide Probes with Enhanced Photostability.

Novel profluorescent mono- and bis-isoindoline nitroxides linked to napthalimide and perylene diimide structural cores are described. These nitroxide-fluorophore probes display strongly suppressed fluorescence in comparison to their corresponding non-radical diamagnetic methoxyamine derivatives. The perylene-based probe possessing two isoindoline systems tethered through ethynyl linkages was shown to be the most photostable in solution, demonstrating significantly enhanced longevity over the 9,10-bis(phenylethynyl)anthracene fluorophore used in previous profluorescent nitroxide probes.

Two-photon fluorescence microscopy imaging of cellular oxidative stress using profluorescent nitroxides.

A range of varying chromophore nitroxide free radicals and their nonradical methoxyamine analogues were synthesized and their linear photophysical properties examined. The presence of the proximate free radical masks the chromophore's usual fluorescence emission, and these species are described as profluorescent. Two nitroxides incorporating anthracene and fluorescein chromophores (compounds 7 and 19, respectively) exhibited two-photon absorption (2PA) cross sections of approximately 400 G.M. when excited at wavelengths greater than 800 nm. Both of these profluorescent nitroxides demonstrated low cytotoxicity toward Chinese hamster ovary (CHO) cells. Imaging colocalization experiments with the commercially available CellROX Deep Red oxidative stress monitor demonstrated good cellular uptake of the nitroxide probes. Sensitivity of the nitroxide probes to H(2)O(2)-induced damage was also demonstrated by both one- and two-photon fluorescence microscopy. These profluorescent nitroxide probes are potentially powerful tools for imaging oxidative stress in biological systems, and they essentially "light up" in the presence of certain species generated from oxidative stress. The high ratio of the fluorescence quantum yield between the profluorescent nitroxide species and their nonradical adducts provides the sensitivity required for measuring a range of cellular redox environments. Furthermore, their reasonable 2PA cross sections provide for the option of using two-photon fluorescence microscopy, which circumvents commonly encountered disadvantages associated with one-photon imaging such as photobleaching and poor tissue penetration.

Interfacial piezoelectric polarization locking in printable Ti3C2Tx MXene-fluoropolymer composites.

Piezoelectric fluoropolymers convert mechanical energy to electricity and are ideal for sustainably providing power to electronic devices. To convert mechanical energy, a net polarization must be induced in the fluoropolymer, which is currently achieved via an energy-intensive electrical poling process. Eliminating this process will enable the low-energy production of efficient energy harvesters. Here, by combining molecular dynamics simulations, piezoresponse force microscopy, and electrodynamic measurements, we reveal a hitherto unseen polarization locking phenomena of poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) perpendicular to the basal plane of two-dimensional (2D) Ti3C2Tx MXene nanosheets. This polarization locking, driven by strong electrostatic interactions enabled exceptional energy harvesting performance, with a measured piezoelectric charge coefficient, d33, of -52.0 picocoulombs per newton, significantly higher than electrically poled PVDF-TrFE (approximately -38 picocoulombs per newton). This study provides a new fundamental and low-energy input mechanism of poling fluoropolymers, which enables new levels of performance in electromechanical technologies.

Synergic bactericidal effects of reduced graphene oxide and silver nanoparticles against Gram-positive and Gram-negative bacteria.

Reduced graphene oxide (rGO) is a promising antibacterial material, the efficacy of which can be further enhanced by the addition of silver nanoparticles (nAg). In this study, the mechanisms of antibacterial activity of rGO-nAg nanocomposite against several important human pathogenic multi-drug resistant bacteria, namely Gram-positive coccal Staphylococcus aureus and Gram-negative rod-shaped Escherichia coli and Proteus mirabilis are investigated. At the same concentration (100 µg/ml), rGO-nAg nanocomposite was significantly more effective against all three pathogens than either rGO or nAg. The nanocomposite was equally active against P. mirabilis and S. aureus as systemic antibiotic nitrofurantoin, and significantly more effective against E. coli. Importantly, the inhibition was much faster in the case of rGO-nAg nanocomposite compared to nitrofurantoin, attributed to the synergistic effects of rGO-nAg mediated contact killing and oxidative stress. This study may provide new insights for the better understanding of antibacterial actions of rGO-nAg nanocomposite and for the better designing of graphene-based antibiotics or other biomedical applications.