Janus nanoparticles for contrast enhancement of T1-T2 dual mode magnetic resonance imaging.

The accuracy of magnetic resonance imaging (MRI) scanning can be improved using a multifunctional nanosystem having T1-T2 dual contrast enhancement. Specifically, the combination of both T1 and T2 effects in a single system helps in acquiring cross validated information during dual mode MRI and reduces the required dose. In this study, polyethylene glycol (PEG) stabilized MnFe2O4@MnO Janus nanoparticles were developed as novel dual-mode MR imaging agents. MnO contributed to T1 contrast whereas MnFe2O4 enabled T2 contrast. The PEG molecules afforded solubility and stability to the contrast agent in water, making it acceptable for biomedical purposes. The biocompatibility of the developed nanosystem was confirmed by cell viability studies. The r2/r1 ratio remained at a suitable value, justifying the applicability of the contrast agent for dual mode MRI. Finally, the efficiency of the agent for T1-T2 contrast enhancement was confirmed through in vitro and ex vivo MRI experiments.

Phase engineering of seamless heterophase homojunctions with co-existing 3R and 2H phases in WS2 monolayers.

Self-organized semiconductor-semiconductor heterostructures (3R-2H) that coexist in atomically thin 2D monolayers forming homojunctions are of great importance for next-generation nanoelectronics and optoelectronics applications. Herein, we investigated the defect controlled growth of heterogeneous electronic structure within a single domain of monolayer WS2 to enable in-plane homojunctions consisting of alternate 2H semiconducting and 3R semiconducting phases of WS2. X-ray photoelectron, Raman, and photoluminescence spectroscopy along with fluorescence and Kelvin probe force microscopy imaging confirm the formation of homojunctions, enabling a direct correlation between chemical heterogeneity and electronic heterostructure in the atomically thin WS2 monolayer. Quantitative analysis of phase fractions shows 59% stable 2H phase and 41% metastable 3R phase estimated over WS2 flakes of different sizes. Time-resolved fluorescence lifetime imaging confirms distinct contrast between 2H and 3R phases with two distinct lifetimes of 3.2 ns and 1.1 ns, respectively. Kelvin probe force microscopy imaging revealed an abrupt change in the contact potential difference with a depletion width of ∼2.5 µm, capturing a difference in work function of ∼40 meV across the homojunction. Further, the thermal stability of coexisting phases and their temperature dependent optical behavior show a distinct difference among 2H and 3R phases. The investigated aspects of the controlled in plane growth of coexisting phases with seamless homojunctions, their properties, and their thermal stability will enable the development of nanoscale devices that are free from issues of lattice mismatch and grain boundaries.

Solution-processed poly(3,4-ethylenedioxythiophene) thin films as transparent conductors: effect of p-toluenesulfonic acid in dimethyl sulfoxide.

Conductivity enhancement of thin transparent films based on poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) by a solution-processed route involving mixture of an organic acid and organic solvent is reported. The combined effect of p-toluenesulfonic acid and dimethyl sulfoxide on spin-coated films of PEDOT-PSS on glass substrates, prepared from its commercially available aqueous dispersion, was found to increase the conductivity of the PEDOT-PSS film to ∼3500 S·cm(-1) with a high transparency of at least 94%. Apart from conductivity and transparency measurements, the films were characterized by Raman, infrared, and X-ray photoelectron spectroscopy along with atomic force microscopy and secondary ion mass spectrometry. Combined results showed that the conductivity enhancement was due to doping, rearrangement of PEDOT particles owing to phase separation, and removal of PSS matrix throughout the depth of the film. The temperature dependence of the resistance for the treated films was found to be in accordance with one-dimensional variable range hopping, showing that treatment is effective in reducing energy barrier for interchain and interdomain charge hopping. Moreover, the treatment was found to be compatible with flexible poly(ethylene terephthalate) (PET) substrates as well. Apart from being potential candidates to replace inorganic transparent conducting oxide materials, the films exhibited stand-alone catalytic activity toward I(-)/I3(-) redox couple as well and successfully replaced platinum and fluorinated tin oxide as counter electrode in dye-sensitized solar cells.