Molybdenum sulfide-reduced graphene oxide p-n heterojunction nanosheets with anchored oxygen generating manganese dioxide nanoparticles for enhanced photodynamic therapy.

In an unprecedented approach, p-n heterojunction nanosheets comprising ∼5 nm thick p-type MoS2 nanoplates integrated onto n-type nitrogen doped reduced graphene oxide (n-rGO) have been employed for photodynamic therapy (PDT). When near infrared (NIR) light with 980 nm wavelength was irradiated on this nanocomposite, effective electron-hole separation was obtained across the heterojunction. The nanosheets were modified with lipoic acid functionalized poly(ethylene glycol) to provide better biocompatibility and colloidal stability in physiological solution. The surface decorated 3-5 nm MnO2 nanoparticles (NPs) triggered the disproportionation of intracellular H2O2 which improved generation of reactive oxygen species (ROS) for enhanced PDT cancer therapy, studied in vitro. The role of N-doping in rGO and the effect of immobilization of MnO2 NPs were systematically investigated by control experiments. Our smartly designed p-MoS2/n-rGO-MnO2-PEG nanosheets outperform conventional PDT agents by overcoming limitations such as low absorption band, unfavourable bioavailability and limitations in tissue oxygenation.

Phenomenal Ultraviolet Photoresponsivity and Detectivity of Graphene Dots Immobilized on Zinc Oxide Nanorods.

A combination of dimensionally reduced graphene quantum dots (GQDs) having edge effects and the vertically aligned ZnO nanorods shows highly selective visible-blind ultraviolet (UV) sensing. The GQD immobilized ZnO nanorod heterostructure shows remarkable responsivity of ∼6.62 × 104 A/W and detectivity of ∼1.78 × 1015 Jones under 365 nm (10 µW) incident light and 2 V bias potential with high stability of at least 5 cycles, fast response time of 2.14 s, and recovery time of 0.91 s. The grain boundary assisted electron transport across GQDs was calculated from the normalized absorption below bandgap. The highest UV responsivity and detectivity were found to be proportional to the lowest trap state density at the grain boundaries (Qt) and minimum grain boundary potential (Eb). For the best GQD, Qt and Eb were found to be ∼4 × 1013 cm-2 and 0.4 meV, respectively. The phenomenal performance of ZnO-GQD heterostructure is attributed to the efficient immobilization of GQDs on ZnO nanorods and the idea of employing GQDs as photosensitizers than solely as electron transporting medium. The efficiency of GQDs is superior to carbon quantum dots (CQDs) containing minimal graphitic domains, and graphene oxide (GO) or reduced graphene oxide (rGO) having larger dimensions preventing their immobilization on ZnO nanorods.

High Pressure Experimental Studies on CuO: Indication of Re-entrant Multiferroicity at Room Temperature.

We have carried out detailed experimental investigations on polycrystalline CuO using dielectric constant, dc resistance, Raman spectroscopy and X-ray diffraction measurements at high pressures. Observation of anomalous changes both in dielectric constant and dielectric loss in the pressure range 3.7-4.4 GPa and reversal of piezoelectric current with reversal of poling field direction indicate to a change in ferroelectric order in CuO at high pressures. A sudden jump in Raman integrated intensity of Ag mode at 3.4 GPa and observation of Curie-Weiss type behaviour in dielectric constant below 3.7 GPa lends credibility to above ferroelectric transition. A slope change in the linear behaviour of the Ag mode and a minimum in the FWHM of the same indicate indirectly to a change in magnetic ordering. Since all the previous studies show a strong spin-lattice interaction in CuO, observed change in ferroic behaviour at high pressures can be related to a reentrant multiferroic ordering in the range 3.4 to 4.4 GPa, much earlier than predicted by theoretical studies. We argue that enhancement of spin frustration due to anisotropic compression that leads to change in internal lattice strain brings the multiferroic ordering to room temperature at high pressures.