NIR-II window absorbing graphene oxide-coated gold nanorods and graphene quantum dot-coupled gold nanorods for photothermal cancer therapy

Abstract: The graphene-based materials have been used as a potential coating material for nanoparticles due to their excellent passivation. Herein, we report for the first time the colloidal stability, photothermal profile, thermal stability, cytotoxicity, and photo-cytotoxicity of graphene quantum dots (GQDs) coupled with the second infrared window (NIR-II) absorbing gold nanorods (AuNRs/GQDs) and compare it to graphene oxide (GO)-coated NIR-II absorbing AuNRs (AuNRs/GO). The composites were achieved by electrostatic interaction of the GO or GQDs with AuNRs. The results revealed that (i) AuNRs/GQDs were more stable in the aqueous phosphate buffer and cell culture media than AuNRs/GO and AuNRs; (ii) GO enhanced the photothermal efficiency of the AuNRs, whereas GQDs reduced it; (iii) GQDs enhanced the photothermal stability of AuNRs than GO; (iv) both AuNRs/GO and AuNRs/GQDs were biocompatible with mouse colon carcinoma (C26) cell lines and malignant fibrous histiocytoma‐like, expressing a fusion of the luciferase and enhanced green fluorescent protein genes (KM-Luc/GFP) cell lines; and (v) photo-cytotoxicity of AuNRs/GO and AuNRs/GQDs conducted against C26 cell lines showed significantly improved cell death compared to laser irradiation alone; however, AuNRs/GO exhibited high photo-toxicity than AuNRs/GQDs. This study shows that AuNRs/GO and AuNRs/GQDs composites possess unique properties to improve AuNRs and be utilised in photothermal applications

Bifurcation analysis of steady natural convection in a tilted cubical cavity with adiabatic sidewalls

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Transition from multiplicity to singularity of steady natural convection in a tilted cubical enclosure

International audienceThe transition from the complex Rayleigh-B´enard convection to the simple heated-from-the-sides configuration in a cubical cavity filled with a Newtonian fluid is numerically studied. The cavity is tilted by an angle θ around its lower horizontal edge and is heated and cooled from two opposite tilted sides. We first analyze the effect of a marginal inclination angle on quasi-Rayleigh-B´enard convection (θ ≈ 0◦), which is a realistic physical approximation to the ideal Rayleigh-B´enard convection.We then yield the critical angles where multiple solutions that were initially found for θ ≈ 0◦ disappear, eventually resulting in the single steady roll solution found in the heated-from-the-sides configuration (θ = 90◦). We confirm the existence of critical angles during the transition θ : 0◦ → 90◦, and we demonstrate that such angles are a consequence of either singularities or collisions of bifurcation points in the Rayleigh-number-θ parameter space.We finally derive the most important critical angles corresponding to any Newtonian fluid of Prandtl number greater than that of air

Measurement of Soret and Fickian diffusion coefficients by orthogonal phase-shifting interferometry and its application to protein aqueous solutions

International audienceWe have developed a method to measure thermodiffusion and Fickian diffusion in transparent binary solutions. The measuring instrument consists of two orthogonally aligned phase-shifting interferometers coupled with a single rotating polarizer. This high-resolution interferometer, initially developed to measure isothermal diffusion coefficients in liquid systems [J. F. Torres, A. Komiya, E. Shoji, J. Okajima, and S. Maruyama, Opt. Lasers Eng. 50, 1287 (2012)], was modified to measure transient concentration profiles in binary solutions subject to a linear temperature gradient. A convectionless thermodiffusion field was created in a binary solution sample that is placed inside a Soret cell. This cell consists of a parallelepiped cavity with a horizontal cross-section area of 10 × 20 mm2, a variable height of 1–2 mm, and transparent lateral walls. The small height of the cell reduces the volume of the sample, shortens the measurement time, and increases the hydrodynamic stability of the system. An additional free diffusion experiment with the same optical apparatus provides the so-called contrast factors that relate the unwrapped phase and concentration gradients, i.e., the measurement technique is independent and robust. The Soret coefficient is determined from the concentration and temperature differences between the upper and lower boundaries measured by the interferometer and thermocouples, respectively. The Fickian diffusion coefficient is obtained by fitting a numerical solution to the experimental concentration profile. The method is validated through the measurement of thermodiffusion in the well-known liquid pairs of ethanol-water (ethanol 39.12 wt.%) and isobutylbenzene-dodecane (50.0 wt.%). The obtained coefficients agree with the literature values within 5.0%. Finally, the developed technique is applied to visualize biomolecular thermophoresis. Two protein aqueous solutions at 3 mg/ml were used as samples: aprotinin (6.5 kDa)-water and lysozyme (14.3 kDa)-water. It was found that the former protein molecules are thermophilic and the latter thermophobic. In contrast to previously reported methods, this technique is suitable for both short time and negative Soret coefficient measurements