Abstract The present study compared the photothermal anticancer activity of near-infrared (NIR)-excited graphene nanoparticles and carbon nanotubes (CNT). Despite lower NIR-absorbing capacity, ...suspension of polyvinylpyrrolidone-coated graphene sheets exposed to NIR radiation (808 nm, 2 W/cm2 ) generated more heat than DNA or sodium dodecylbenzenesulfonate-solubilized single-wall CNT under the same conditions. Accordingly, graphene nanoparticles performed significantly better than CNT in inducing photothermal death of U251 human glioma cells in vitro. The superior photothermal sensitivity of graphene sheets could be largely explained by their better dispersivity, which has been supported by a simple calculation taking into account thermodynamic, optical and geometrical properties of the two type of carbon nanoparticles. The mechanisms of graphene-mediated photothermal killing of cancer cells apparently involved oxidative stress and mitochondrial membrane depolarization resulting in mixed apoptotic and necrotic cell death characterized by caspase activation/DNA fragmentation and cell membrane damage, respectively.
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•A new approximation to McCumber-Sturge relation has been introduced.•Bandshift of luminescence peaks is modelled without polylogarithmic functions.•Approximation allows for the ...extraction of the Debye temperature and coupling parameter.•The approximation works better at lower temperatures than Walsh and Di Bartolo approximation.
Temperature-induced bandshift of luminescence peaks is frequently described with McCumber-Sturge relation which is difficult for fitting or practical applications due to its mathematical complexity. Here for the first time, we give its exact solution in terms of polylogarithms, and an excellent approximation that is better at lower temperatures than the approximation by Walsh and Di Bartolo (WB). The novel approximation is analytically compared with that of WB, clearly giving the preferred temperature and Debye temperature ranges for each approximation. Three additional approximations are given, each with lowered complexity, until the equivalent quadratic form of Magomedov’s approximation is reached. All approximations are compared for their complexity vs applicable temperature range.
Eu(III)-doped GdVO4 nanocrystals were prepared by precipitation of the Gd(III) and (Eu(III) citrate complexes, with fractions of Eu(III) ranging from 5 to 100mol%. Their red fluorescence is strongly ...quenched by H2O2, and this finding forms the basis for a fluorometric assay for H2O2 with a limit of detection as low as 1.6μM. The probe was further employed to design a highly sensitive enzymatic assay for glucose.
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•Synthesis of fluorescent nanocrystals (NCs) of type GdVO4 and doped with varying fractions of Eu(III) ions.•The NCs are shown to be viable fluorescent probes for hydrogen peroxide.•The NCs can be used as probes for sensing glucose via the hydrogen peroxide produced by enzymatic action of glucose oxidase.•Detection limits are as low as 1.6μM for H2O2 and 2.1μM for glucose.
The authors describe the preparation of Eu3+-doped GdVO4 nanocrystals (NCs) by precipitation of the Gd3+(Eu3+)-citrate complex which was then converted to the respective vanadate by dialysis. The fractions of Eu3+ ranged from 5 to 100mol%. The NCs were characterized by XRD, TEM, ICP-OES and dynamic light scattering which revealed that they possess superior colloidal stability in aqueous solutions in that no precipitation can be observed even after several months. The NCs display red and largely red-shifted fluorescence (peaking at 618nm) on photoexcitation at around 300nm. Fluorescence is strongly quenched by hydrogen peroxide. It is also shown that the fraction of doping with Eu3+ strongly affects quenchability. Most efficient quenching by H2O2 is observed if the NCs are doped with 50% of Eu3+. The findings were exploited to develop a fluorometric assay for H2O2 that works in the 5 to 250μM concentration range, with a limit of detection as low as 1.6μM (at a signal-to-noise ratio of 3). The probe was further employed to design a highly sensitive enzymatic assay for glucose via measurement of the quantity of H2O2 formed as a result of the catalytic action of glucose oxidase.
Abstract Synthesis of new antibacterial agents is becoming increasingly important in light of the emerging antibiotic resistance. In the present study we report that electrochemically produced ...graphene quantum dots (GQD), a new class of carbon nanoparticles, generate reactive oxygen species when photoexcited (470 nm, 1 W), and kill two strains of pathogenic bacteria, methicillin-resistant Staphylococcus aureus and Escherichia coli . Bacterial killing was demonstrated by the reduction in number of bacterial colonies in a standard plate count method, the increase in propidium iodide uptake confirming the cell membrane damage, as well as by morphological defects visualized by atomic force microscopy. The induction of oxidative stress in bacteria exposed to photoexcited GQD was confirmed by staining with a redox-sensitive fluorochrome dihydrorhodamine 123. Neither GQD nor light exposure alone were able to cause oxidative stress and reduce the viability of bacteria. Importantly, mouse spleen cells were markedly less sensitive in the same experimental conditions, thus indicating a fairly selective antibacterial photodynamic action of GQD.
In order to compare spectroscopic properties between nanosized and that in single crystal form of YPO4:Pr3+, temperature-dependence of the red emission from 3P0 → 3H4 and 1D2 → 3H4 transitions of ...YPO4:0.1 at. % Pr3+ nanopowders has been investigated in details. The emission spectra of the sample in size of 20 nm, under selective excitation at 3P2, measured at different temperatures, T = 10, 100, 200 and 300 K have been recorded. The variation of emission intensity of each 3P0 → 3H4 and 1D2 → 3H4 against temperature has been investigated. Several spectral lines constitute 1D2 → 3H4 emission, assigned to transitions between 1D2 and 3H4 Stark levels are observed with no noticeable shifts between them and those observed at the single crystal. It is found that 1D2 → 3H4 emission intensity dominates that of 3P0 → 3H4 transition, pointing out the high efficiency of the multiphonon relaxation (MPR) process from 3P0 to 1D2. Fitting the temperature dependence of 3P0 → 3H4 emission intensity permits to estimate the phonons and their energies involved in non-radiatively transition between 3P0 and 1D2 levels, which are found different from single crystal. Also, fitting the multiphonon relaxation (MPR) rates against temperature, extracted from the measured 1D2 lifetime gives information that seven phonons can be involved to bridge the gap between 1D2 and 1G4. Furthermore, the possibility to use the YPO4: 0.1 at. % Pr3+ in the nano-thermometry application in temperature range T = 10–300 K was investigated.
•Temperature-dependence of the red emission YPO4:Pr3+ nanophosphor has been studied.•The phonons and their energies involved between 3P0 and 1D2 are different from single crystal.•Seven high energy phonons are involved to can bridge the gap between 1D2 and 1G4 by MPR process.•The possibility to use the YPO4: Pr3+ in the nano-thermometry application was investigated.
Luminescence thermometry on europium doped TiO2 films, prepared by the plasma electrolytic oxidation, was investigated by the Luminescence Intensity Ratio method. The performance of the material for ...temperature sensing was tested from room temperature to 260 °C. The theoretical fit of the emission intensity ratio of Eu3+5D1→7F1 and 5D0→7F2 transitions revealed the energy difference between 5D1 and 5D0 levels of 1777 cm−1. Temperature sensitivity was calculated on the entire temperature range, with maximum value of 3.43 %K−1 at 293 K. The relationship between Judd-Ofelt and thermometric parameters was demonstrated, and further utilized for the calculation of the radiative transition probability, dipole strength and radiative lifetime of the 5D1→7F1 transition.
•The performance of the TiO2:Eu3+ for temperature sensing has been investigated.•TiO2:Eu3+ was prepared by the plasma electrolytic oxidation method.•High sensitivity was obtained by the Luminescence Intensity Ratio method.•The complete Judd-Ofelt analysis has been carried out.•Judd-Ofelt and thermometry together yield a new calculation method.
•Fluorescence of Eu3+ doped TiO2 nanoparticles can be used for temperature sensing.•Temperature sensing can be realized from both emission spectra and emission decays.•Relative sensitivity of ...2.43%K−1 and resolution better than 1K are found.
Luminescence temperature sensing with Eu3+ doped TiO2 nanoparticles was tested over a temperature range of 307–533K. Anatase Eu3+:TiO2 nanoparticles of 10–20nm in diameter are prepared using the hydrolytic sol–gel route. In photoluminescence emission spectra of Eu3+:TiO2 nanoparticles two distinct spectral regions are observed: the high energy spectral region associated with the trap emission of the TiO2 host, and the low energy spectral region with well resolved emission peaks of the Eu3+ ions. The ratio between Eu3+ emission and TiO2 trap emission, and the Eu3+ emission decay shows strong temperature dependence, and are tested for temperature sensing. It is found that relative sensor sensitivity ranges from 0.17 to 2.43%K−1 and is among the highest recorded for inorganic nanosensors. Temperature resolution is better than 1K over a wide temperature range and reaches 0.33K for decay measurements and 0.46K for the fluorescence intensity ratio measurements at about 400K.
Herein, Eu3+ doped Gd2Ti2O7 nanoparticles were tested for application in ratiometric luminescence thermometry. It is shown that two combinations of emissions: one that uses two emissions of Eu3+ ions ...and one that uses one emission of Eu3+ ions and trap emission of Gd2Ti2O7 provide thermometry over the 303–423K temperature range with relative sensitivities between 0.14%K−1 and 0.95%K−1. Thermometry based on two Eu3+ emissions from 5D0 to 5D1 levels has a higher relative sensitivity, but lower absolute sensitivity than thermometry based on one Eu3+ emission and trap emission of Gd2Ti2O7. The tested material is prepared by Pechini-type polymerized complex route and is composed of agglomerated nanoparticles of ~30–50nm in size with pure-phase cubic structure (space group Fd-3m) as evidenced from electron microscopy and X-ray diffraction measurements.
•Eu3+ doped Gd2Ti2O7 nanoparticles can serve as probes for luminescence thermometry.•Gd2Ti2O7 trap emission is an excellent internal standard for luminescence thermometry.•Temperature is measured over 303–423K range with sensitivity ranging 0.14–0.95%K−1.
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