Covalent functionalization of reduced graphene oxide with porphyrin by means of diazonium chemistry for nonlinear optical performance

Reduced graphene oxide (RGO)-porphyrin (TPP) nanohybrids (RGO-TPP 1 and RGO-TPP 2) were prepared by two synthetic routes that involve functionalization of the RGO using diazonium salts. The microscopic structures, morphology, photophysical properties and nonlinear optical performance of the resultant RGO-TPP nanohybrids were investigated. The covalent bonding of the porphyrin-functionalized-RGO nanohybrid materials was confirmed by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and thermogravimetric analysis. Attachment of the porphyrin units to the surface of the RGO by diazotization significantly improves the solubility and ease of processing of these RGO-based nanohybrid materials. Ultraviolet/visible absorption and steady-state fluorescence studies indicate considerable π-π interactions and effective photo-induced electron and/or energy transfer between the porphyrin moieties and the extended π-system of RGO. The nonlinear optical properties of RGO-TPP 1 and RGO-TPP 2 were investigated by open-aperture Z-scan measurements at 532 nm with both 4 ns and 21 ps laser pulses, the results showing that the chemical nanohybrids exhibit improved nonlinear optical properties compared to those of the benchmark material C60, and the constituent RGO or porphyrins.Financial support from the National Natural Science Foundation of China (51432006, 50925207, 51172100), the Ministry of Science and Technology of China for the International Science Linkages Program (2011DFG52970), the Ministry of Education of China for the Changjiang Innovation Research Team (IRT14R23), the Ministry of Education and the State Administration of Foreign Experts Affairs for the 111 Project (B13025), and 100 Talents Program of CAS are gratefully acknowledged. M.G.H., C.Z. and M.P.C. thank the Australian Research Council (ARC) for support

Digital microfluidics for automated hanging drop cell spheroid culture.

Cell spheroids are multicellular aggregates, grown in vitro, that mimic the three-dimensional morphology of physiological tissues. Although there are numerous benefits to using spheroids in cell-based assays, the adoption of spheroids in routine biomedical research has been limited, in part, by the tedious workflow associated with spheroid formation and analysis. Here we describe a digital microfluidic platform that has been developed to automate liquid-handling protocols for the formation, maintenance, and analysis of multicellular spheroids in hanging drop culture. We show that droplets of liquid can be added to and extracted from through-holes, or "wells," and fabricated in the bottom plate of a digital microfluidic device, enabling the formation and assaying of hanging drops. Using this digital microfluidic platform, spheroids of mouse mesenchymal stem cells were formed and maintained in situ for 72 h, exhibiting good viability (>90%) and size uniformity (% coefficient of variation <10% intraexperiment, <20% interexperiment). A proof-of-principle drug screen was performed on human colorectal adenocarcinoma spheroids to demonstrate the ability to recapitulate physiologically relevant phenomena such as insulin-induced drug resistance. With automatable and flexible liquid handling, and a wide range of in situ sample preparation and analysis capabilities, the digital microfluidic platform provides a viable tool for automating cell spheroid culture and analysis

Digital microfluidics for automated hanging drop cell spheroid culture.

Cell spheroids are multicellular aggregates, grown in vitro, that mimic the three-dimensional morphology of physiological tissues. Although there are numerous benefits to using spheroids in cell-based assays, the adoption of spheroids in routine biomedical research has been limited, in part, by the tedious workflow associated with spheroid formation and analysis. Here we describe a digital microfluidic platform that has been developed to automate liquid-handling protocols for the formation, maintenance, and analysis of multicellular spheroids in hanging drop culture. We show that droplets of liquid can be added to and extracted from through-holes, or "wells," and fabricated in the bottom plate of a digital microfluidic device, enabling the formation and assaying of hanging drops. Using this digital microfluidic platform, spheroids of mouse mesenchymal stem cells were formed and maintained in situ for 72 h, exhibiting good viability (>90%) and size uniformity (% coefficient of variation <10% intraexperiment, <20% interexperiment). A proof-of-principle drug screen was performed on human colorectal adenocarcinoma spheroids to demonstrate the ability to recapitulate physiologically relevant phenomena such as insulin-induced drug resistance. With automatable and flexible liquid handling, and a wide range of in situ sample preparation and analysis capabilities, the digital microfluidic platform provides a viable tool for automating cell spheroid culture and analysis

Facile hydrothermal synthesis and optical limiting properties of TiO2-reduced graphene oxide nanocomposites

TiO2/recluced graphene oxide (RGO) nanocomposites Gx (RGO titania nanocomposite, x grams tetrabutyl titanate per 0.03 g RGO, x = 0.25, 0.50, 1.00) were prepared by a hydrothermal method: graphene oxide was reduced to RGO in a 2:1 water:ethanol mixture in the presence of varying quantities of tetrabutyl titanate, which deposited as TiO2 on the RGO sheets. The nanocomposites were characterized by a combination of Fourier transform infrared spectroscopy, diffuse reflectance ultraviolet-visible spectroscopy, photoluminescence spectroscopy, Raman spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy studies. The nanocomposite G0.25 exhibits enhanced nonlinear optical properties compared to its individual components, which is ascribed to a combination of mechanisms. The role of defects and electron/energy transfer in the optical limiting performance of G0.25 was clarified with the help of Raman and photoluminescence spectroscopies. Intensity-dependent switching between reverse saturable absorption and saturable absorption behavior was observed with the G0.50 nanocomposite. (C) 2015 Elsevier Ltd. All rights reserved

Functionalization of reduced graphene oxide with axially-coordinated metal-porphyrins: facile syntheses and temporally-dependent nonlinear optical properties

Reduced graphene oxide-tin porphyrin (RGO-SnTPP) nanohybrids with good dispersibility have been prepared by two covalent functionalization approaches. The microscopic structure and morphology of the RGO-SnTPP nanohybrids were characterized by various spectroscopic techniques including Fourier transform infrared spectroscopy, Raman spectroscopy, transmission electron microscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy. Ground-state absorption and steady-state fluorescence studies indicate considerable π–π interactions and effective photo-induced electron and/or energy transfer from the porphyrin moieties to the RGO. Their nonlinear optical properties were investigated using the Z-scan technique at 532 nm with both picosecond and nanosecond laser pulses. The RGO-SnTPP hybrids were found to exhibit large nonlinear optical responses due to a combination of mechanisms, while significant differences in their nonlinear optical responses were observed, highlighting the influence on photophysical properties of the degree of functionalization and the synthetic approach employed.Financial support from the National Natural Science Foundation of China (51432006, 50925207, 51172100), the Ministry of Science and Technology of China for the International Science Linkages Program (2011DFG52970), the Ministry of Education of China for the Changjiang Innovation Research Team (IRT13R24), the Ministry of Education and the State Administration of Foreign Experts Affairs for the 111 Project (B13025), 100 Talents Program of CAS, and Jiangsu Innovation Research Team are gratefully acknowledged. M. G. H., M. P. C., and C. Z. thank the Australian Research Council (ARC) for support

Multi-walled carbon nanotubes covalently functionalized by axially coordinated metal-porphyrins: Facile syntheses and temporally dependent optical performance

Axially coordinated metal-porphyrin-functionalized multi-walled carbon nanotube (MWCNT) nanohybrids were prepared via two different synthetic approaches (a one-pot 1,3-dipolar cycloaddition reaction and a stepwise approach that involved 1,3-dipolar cycloaddition followed by nucleophilic substitution), and characterized through spectroscopic techniques. Attachment of the tin porphyrins to the surface of the MWCNTs significantly improves their solubility and ease of processing. These axially coordinated (5,10,15,20-tetraphenylporphyrinato)tin(IV) (SnTPP)-MWCNTs exhibit significant fluorescence quenching. The third-order nonlinear optical properties of the resultant nanohybrids were studied by using the Z-scan technique at 532 nm with both nanosecond and picosecond laser pulses. The results show that the nanohybrids exhibit significant reverse saturable absorption or saturable absorption when nanosecond or picosecond pulses, respectively, are employed. Improvement in the nanosecond regime nonlinear absorption is observed on proceeding to the nanohybrids and is ascribed to a combination of the outstanding properties of MWCNTs and the chemically attached metal-porphyrins.Financial support from the National Natural Science Foundation of China (Nos. 51432006, 50925207, and 51172100), the Ministry of Science and Technology of China for the International Science Linkages Program (No. 2011DFG52970), the Ministry of Education of China for the Changjiang Innovation Research Team (No. IRT14R23), the Ministry of Education and the State Administration of Foreign Experts Affairs for the 111 Project (No. B13025), 100 Talents Program of CAS, and Jiangsu Innovation Research Team are gratefully acknowledged. M. G. H., M. P. C., and C. Z. thank the Australian Research Council (ARC) for support