Electrochemical aptasensor based on carboxylated graphene oxide modified carbon paste electrode for strontium ultrasensitive detection

Determination of strontium ions (Sr²⁺) is crucial with regard to human health and environmental protection. In this work, an electrochemical aptasensor was designed using carboxylated graphene oxide (CGO)-modified carbon paste electrode (CGO/CPE) for ultrasensitive determination of Sr²⁺ ions. The electrochemical determination was accomplished with employing the constructed G-quadruplex (G4) aptamer at the surface of aptasensor in presence of carmoisine (CA) as an electrochemical label. Moreover, NH₂-functionalized aptamer was immobilized onto CGO/CPE via carboxylic group. Hence, differential pulse voltammetry was applied for detection of any possible signal changes of CA on the aptasensor surface. The reduction peak currents of CA in the absence and presence of Sr²⁺ in solution were different and this difference was linearly dependent to the concentration of Sr²⁺ in solution. The analytical results revealed that our novel aptasensor showed two appropriate linear ranges (0.1-8.0 pM and 3.0-20.0 nM) versus to Sr²⁺ ion concentrations with the limit of detection of 0.06 pM (S/N = 3). Excellent stability, selectivity and reproducibility were achieved with this new electrochemical aptasensor. Additionally, the aptasensor showed good achievements in analysis of Sr²⁺ in aqueous and urine real samples, which making this proposed method a promising candidate for electrochemical detection of Sr²⁺ in real samples.

Insights into the trace Sr2+ impact on the gel properties and spatial structure of mutton myofibrillar proteins

Myofibrillar proteins (MPs) and the quality of meat strongly depend on the properties of MP gels, which in turn depend on several parameters that include the thermal history and the concentration of metal ions. Strontium element (Sr) widely exists in mineral water and is found as strontium ions (Sr²⁺), which is an essential trace element for humans. This study investigated the effects of trace Sr²⁺ on the structure-function relationship of mutton MPs, as well as their gels with water. Trace concentrations of Sr²⁺ were found to significantly alter the conformation of the MPs. An increase in Sr²⁺ concentration was associated with a reduction in the tightness and strength of the gel and a significant increase in its water-holding capacity As compared to the untreated control sample, the solubility, particle size, and the magnitude of the Zeta potential of the gels increased by 13.03 %, 12.62 %, and 19.73 %, respectively, whereas the water retention capacity and the gel strength increased by 23.13 % and 21.90 %, at a Sr²⁺ concentration of 5.0 mg/L. Molecular docking predicted an increase in ionic bonds and disulfide bonds because Sr²⁺ had a strong interaction with hydrophilic amino acids and acidic amino acids. The analysis of molecular forces further verified the significant facilitation of interactions between MP molecules with the induction of Sr²⁺. As compare to the untreated control group, the ionic and disulfide bonds increased by 141.17 % and 66.94 %, when treated with 5.0 mg/L Sr²⁺. These changes were likely due to the enhancement of protein-protein interactions caused by Sr²⁺, which could induce MP molecules to properly unfold and aggregate in gel formation. The results could provide a basis for improving the texture and the quality of meat and meat products.

Bioactive strontium ions/ginsenoside Rg1-incorporated biodegradable silk fibroin-gelatin scaffold promoted challenging osteoporotic bone regeneration

Autogenous healing of osteoporotic fractures is challenging, as the regenerative capacity of bone tissues is impaired by estrogen reduction and existed pro-inflammatory cytokines. In this study, a biofunctional ginsenoside Rg1 and strontium-containing mineral (SrHPO₄, SrP)-incorporated biodegradable silk fibroin-gelatin (SG) scaffold (Rg1/SrP/SG) was developed to stimulate the osteoporotic bone repair. The incorporation of 15 wt% SrP significantly enhanced the mechanical strength, stimulated the osteogenic differentiation of mouse bone marrow mesenchymal stem cells, and suppressed the osteoclastogenesis of RAW264.7 in a concentration-related manner. The loading of Rg1 in SG and 15SrP/SG scaffolds obviously promoted the angiogenesis of human umbilical vein endothelial cells via activating the expression of vascular endothelial growth factor and basic fibroblast growth factor genes and proteins. The bioactive strontium ions (Sr²⁺) and Rg1 released from the scaffolds together mediated lipopolysaccharide-treated macrophages polarizing into M2 type. They downregulated the expression of inflammatory-related genes (interleukin (IL)-1β, tumor necrosis factor α, and IL-6) and stimulated the expression of genes related to anti-inflammation (Arginase and IL-10) as well as bone repair (BMP-2 and PDGF-BB) in the macrophages. The in vivo results also displayed that SrP and Rg1 significantly promoted the bone repair effect of SG scaffolds in osteoporotic critical-sized calvarial defects. Besides, the degradation rate of the scaffolds was close to the bone regeneration rate. Therefore, the simultaneous addition of SrP and Rg1 is a promising way for facilitating the osteoporotic bone repair activity of SG scaffolds via promoting the osteogenesis and angiogenesis, as well as inhibiting the osteoclastogenesis and inflammation.

Potentiality of living Bacillus pumilus SWU7-1 in biosorption of strontium radionuclide

Bacillus pumilus SWU7-1 was isolated from strontium ion (Sr(II))-uncontaminated soil, its biosorption potential was evaluated, and the effect of γ-ray radiation treatment on its biosorption was discussed. Domesticated under Sr(II) stress promoted the biosorption ability of B. pumilus to Sr(II), and the biosorption efficiency increased from 46.09% to 94.69%. At a lower initial concentration, the living bacteria had the ability to resist the biosorption of Sr(II). The optimal initial concentration range was 54-130 mg/L. The biosorption profile was better matched by Langmuir than Freundlich model, showing that the biosorption process of Sr(II) by the experimental strain was closer to the surface adsorption. According to Langmuir model, the maximum biosorption capacity of B. pumilus on Sr (II) was 299.4 mg/g. During the bacterial growth in the biosorption process, the changes in biosorption capacity and efficiency can be divided into two phases, and a pseudo-second-order model is followed in each phase. There was no significant difference in the biosorption efficiency of bacteria with different culture time after γ-ray radiation, and all of them were above 90%, which showed that B. pumilus had significant radiation resistance under experimental conditions. This study emphasized the potential application of B. pumilus in the treatment of radioactive Sr(II) pollution by biosorption.

Nickel-metal-organic framework nanobelt based composite membranes for efficient Sr2+ removal from aqueous solution

The sorption removal of radionuclides Sr²⁺ using a freestanding functional membrane is an interesting and significant research area in the remediation of radioactive wastes. Herein, a novel self-assembled membrane consisting of metal-organic framework (MOF) nanobelts and graphene oxides (GOs) are synthesized through a simple and facile filtration method. The membrane possesses a unique interwove morphology as evidenced from SEM images. Batch experiments suggest that the GO/Ni-MOF composite membrane could remove Sr²⁺ ions from aqueous solutions and the Sr²⁺ adsorption capacity and efficiency of the GO/Ni-MOF composite membrane is relevant to the MOF content in the composite. Thus, the dominant interaction mechanism was interface or surface complexation, electrostatic interaction as well as ion substitution. The maximum effective sorption of Sr²⁺ over GO/Ni-MOF membrane is 32.99% with 2 mg composite membrane containing a high content of Ni-MOF at 299 K in 100 mg/L Sr²⁺ aqueous solution. The FT-IR and XPS results suggest that the synergistic effect between GO and Ni-MOF is determinant in the sorption Sr²⁺ process. The GO/Ni-MOF composite membrane is demonstrated to have the advantages of efficient removal of Sr²⁺, low cost and simple synthesis route, which is promising in the elimination of radionuclide contamination.

Synergistic interface behavior of strontium adsorption using mixed microorganisms

The proper handling of low-level radioactive waste is crucial to promote the sustainable development of nuclear power. Research into the mechanism for interactions between bacterium and radionuclides is the starting point for achieving successful remediation of radionuclides with microorganisms. Using Sr(II) as a simulation radionuclide and the mixed microorganisms of Saccharomyces cerevisiae and Bacillus subtilis as the biological adsorbent, this study investigates behavior at the interface between Sr(II) and the microorganisms as well as the mechanisms governing that behavior. The results show that the optimal ratio of mixed microorganisms is S. cerevisiae 2.0 g L^-1 to B. subtilis 0.05 g L^-1, and the optimal pH is about 6.3. Sr(II) biosorption onto the mixed microorganisms is spontaneous and endothermic in nature. The kinetics and the equilibrium isotherm data of the biosorption process can be described with pseudo-second-order equation and the Langmuir isotherm equation, respectively. The key interaction between the biological adsorbent and Sr(II) involves shared electronic pairs arising from chemical reactions via bond complexation or electronic exchange, and spectral and energy spectrum analysis show that functional groups (e.g., hydroxyl, carboxyl, amino, amide) at the interface between the radionuclide and the mixed microorganisms are the main active sites of the interface reactions.

Invention of Hollow Zirconium Tungesto-Vanadate at Nanotube Morphological Structure for Radionuclides and Heavy Metal Pollutants Decontamination from Aqueous Solutions

Zirconium tungesto-vanadate cation exchange material was successfully architectured at open ended nanotubes morphological structure in the presence of polyvinyl alcohol as a stabilizing agent using microwave route. The ion exchange capacity (IEC) of the material was recorded as 4.8 meq/g of about 640 m(2)/g for a specific surface area. The x-ray diffraction pattern of the material implies its crystallinity. Both scanning and transmission electron microscopes identified the average aspect ratio of the architectured nanotubes as 6.5 and its hollow structure. The material posed 96.4 % cadmium ion decontamination within 90 min compared with 84 % strontium decontamination at the same time.