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In the study, a hydroxypropyl guar gum (HPG) gel was prepared using modified nano-TiO2 particles as a crosslinking agent. Firstly, nano-TiO2 particles were prepared using the sol–gel method. Nano-TiO2 particles were spherical and densely distributed; the effective particle size was 29.0 nm, and particle size distribution was uniform. Then, the modified nano-TiO2 particles were synthesized by modifying nano-TiO2 with polyhydroxy carboxylate. The microstructure of nano-TiO2 and modified nano-TiO2 crosslinked HPG gel were investigated. The layered distribution and crosslinked network of the modified nano-TiO2 gel were denser than that of nano-TiO2 crosslinked HPG gel. The modified nano-TiO2 crosslinked HPG gel shows stable viscoelasticity at 60 ℃. Compared with nano-TiO2 crosslinked HPG gel, it has better temperature resistance and shear resistance, and can adapt to formation fracturing at 140 ℃, indicating that this gel may have potential application in fracturing. [ABSTRACT FROM AUTHOR]

In the study, hydroxypropyl guar gum (HPG) gel is prepared by using Nano-ZrO2 particles as the cross-linking agent. The Nan-ZrO2 particles are prepared by using oil-water interface method. The physical properties such as morphology, particle size, and crystal structure of the Nano-ZrO2 particles are analyzed by SEM, particle size analyzer, FT-IR, and XRD, respectively. The results show that the Nano-ZrO2 particles are spherical particles with a little agglomeration; these spherical particles have a tetragonal structure and higher crystallinity, and the mean diameter of the first-level grain is 24 nm. The rheological properties including shear stress, complex modulus, elasticity modulus (G′), and viscosity modulus (G′′) of the Nano-ZrO2 cross-linked HPG gel are investigated. The results show that the Nano-ZrO2 cross-linked HPG gel is a pseudo-plastic non-Newtonian fluid with higher elastic modulus (G′ > G′′) and lower tanδ (tanδ < 1, the ratio of viscous and elastic modulus), which indicate that the Nano-ZrO2 cross-linked HPG gel may have potential application in fracturing. [ABSTRACT FROM AUTHOR]

Herein, a novel bimodal ratiometric probe for sensitive and selective detection of biothiols (including glutathione (GSH), cysteine (Cys) and homocysteine (Hcys)) was constructed, which was based on the redox reaction between manganese dioxide nanoflakes (MnO 2 NFs) and rhodamine (RhB) and biothiols. When MnO 2 NFs was added into RhB solution, RhB was oxidized to a series of derivatives, accompanying with the colorimetric color changing from purple to light pink and fluorescence changing from red to green. In the presence of GSH, Cys or Hcys, they could reduce MnO 2 NFs to Mn 2+ , thereby preventing the following oxidization of RhB and the corresponding color and fluorescence changes. The absorption intensity ratio and fluorescence intensity ratio showed good linear relationships with the concentrations of biothiols. The colorimetric detection limits for GSH, Cys and Hcys were 0.057 μM, 0.140 μM and 0.087 μM, respectively. And the fluorescence detection limits were 0.177 μM, 0.282 μM and 0.161 μM. More importantly, this probe was successfully applied to monitor the concentration of GSH/Cys/Hcys in human serum samples, with satisfactory recovery. Thus, this MnO 2 NFs-RhB platform can potentially be a candidate for the detection of biothiols., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)