Density Functional Theory Study of Nonvolatile Electrical Control of Half-Metallicity in Multiferroic RuCl₂/Al₂S₃ Heterostructures: Implications for Spin Memory Devices

To overcome the volatility and high-power dissipation in conventional control approaches in spin-dependent devices, such as spin memory devices, there is an urgent need to realize nonvolatile all-electric spin manipulation in two-dimensional van der Waals (vdW) ferromagnetic (FM) semiconductors. Herein, we investigate the electronic and transport features of the multiferroic heterostructure (HS) RuCl2/Al2S3 built by coupling the ferrovalley semiconductor RuCl2 monolayer with the ferroelectric (FE) Al2S3 monolayer by employing first-principles density functional theory plus nonequilibrium Green’s function transport theory. It is shown that the nonvolatile and reversible switching between the FM semiconductor and half-metallicity can be realized in the RuCl2/Al2S3 HS by electrically controlling the FE polarization states of the Al2S3 sublayer. Moreover, the large out-of-plane magnetic anisotropy and Curie temperature near room temperature of RuCl2 can also survive in the vdW RuCl2/Al2S3 HS, which is of practical importance. Notably, the FE sublayer Al2S3 still retains its original semiconducting nature in different polarization states, which is beneficial to realize the polarization switching via an applied electric field. Furthermore, an all-electric controlled valve effect with an ultrahigh on/off ratio and pure spin-polarized current in the on state is confirmed in conceptual two-probe devices based on the RuCl2/Al2S3 HS. These findings shed light on the potential applications of the all-electrically controlled vdW multiferroic HS RuCl2/Al2S3 in compact and highly efficient information processing and data storage

Interaction Between Optically-Generated Charge-Transfer States and Magnetized Charge-Transfer States toward Magneto-Electric Coupling

This article reports the magneto-dielectric studies on the coupling between optically generated CT states and magnetized CT states based on thin-film devices with the architecture of ITO/TPD:BBOT/TPD/Co/Al. The magnetized CT states are generated at the Co/TPD interface, generating a magneto-dielectric response with a broad, non-Lorentzian line-shape. The optically generated CT states are formed at the TPD:BBOT interfaces in the heterojunction under photoexcitation, leading to a magneto-dielectric signal with a narrow, Lorentzian line-shape. We find that combining the optically generated CT states and magnetized CT states yields a new magneto-dielectric signal with distinctive line-shape and amplitude in the ITO/TPD:BBOT/TPD/Co/Al device. The magneto-dielectric analysis indicates that there exists a coupling between optically generated CT states and magnetized CT states through the interactions between the magnetic Co/TPD interface and the optically excited TPD:BBOT heterojunction. Furthermore, we show that the coupling between optically generated CT states and magnetized CT states experiences Coulomb interactions and spin–orbital interaction by changing (i) the density of optically generated CT states and (ii) the separation distance between optically generated CT states and magnetized CT states. Clearly, this coupling provides a new approach to mutually tune magnetic and electronic properties through thin-film engineering by combining magnetic and organic materials

Spin Radical Enhanced Magnetocapacitance Effect in Intermolecular Excited States

This article reports the magnetocapacitance effect (MFC) based on both pristine polymer MEH-PPV and its composite system doped with spin radicals (6R-BDTSCSB). We observed that a photoexcitation leads to a significant positive MFC in the pristine MEH-PPV. Moreover, we found that a low doping of spin radicals in polymer MEH-PPV causes a significant change on the MFC signal: an amplitude increase and a line-shape narrowing under light illumination at room temperature. However, no MFC signal was observed under dark conditions in either the pristine MEH-PPV or the radical-doped MEH-PPV. Furthermore, the magnitude increase and line-shape narrowing caused by the doped spin radicals are very similar to the phenomena induced by increasing the photoexcitation intensity. Our studies suggest that the MFC is essentially originated from the intermolecular excited states, namely, intermolecular electron–hole pairs, generated by a photoexcitation in the MEH-PPV. More importantly, by comparing the effects of spin radicals and electrically polar molecules on the MFC magnitude and line shape, we concluded that the doped spin radicals can have the spin interaction with intermolecular excited states and consequently affect the internal spin-exchange interaction within intermolecular excited states in the development of MFC. Clearly, our experimental results indicate that dispersing spin radicals forms a convenient method to enhance the magnetocapacitance effect in organic semiconducting materials

The sensitivity analysis of BiLC Rho GTPase biosensors to GEFs and GAPs.

<p>(A) The results of optical imaging among different upstream regulatory proteins. The luminescent signals were normalized using cotransfection of renilla luciferase plasmid (pRL-tk) and represented by the ratio of luminescent intensity of firefly luciferase (FL) at 600 nm to that of renilla luciferase (RL) at 500 nm. The final results were normalized by the luminescence ratio of the control vehicles, which were designated with “1”. Data is reported as the fold increase in luminescence ratio (FL/RL) relative to control. Error bars denote standard deviations. Asterisks (*) denotes samples that show a difference from the control vector with statistical significance by analysis of variance (ANONA) (<i>p</i>≤0.01). The data shown was obtained by three separate experiments performed with quadruplicate culture wells. The results highly accord with the well-known experimental data, indicating that the BiLC biosensors can response to the upstream regulatory molecules. And this ability of BiLC GTPase sensors can be used to examine the substrate selectivity of GEFs and GAPs and quantify their catalytic activities in intact living cells. (B and C) The western blots carried out in parallel to demonstrate protein expression among different GEFs and GAPs. The figure only shows the results of the CDC42 biosensors as a representative.</p

The application of BiLC strategy to image the three main members of Rho GTPases.

<p>(A) The results of optical imaging of three kinds of BiLC RhoGTPase biosensors. The relative luminescence was calculated by the ratio of luminescent intensity of firefly luciferase (FL) at 600 nm to that of renilla luciferase (RL) at 500 nm (n = 4, representative of 4 independent experiments). Error bars denote standard deviations. Asterisks (*) denotes samples that show a difference from the nonspecific complementation (the non-interactive GTPase-effector pairs or the effector loop mutants) with statistical significance by analysis of variance (ANOVA) (<i>p</i>≤0.01). This result indicates that the nonspecific complementation does not impede the correct interpretation of effective interactions induced by GTPase activation. WYJH (#) denotes samples that show a difference from the wild-type biosensor with statistical significance by ANOVA (<i>p</i>≤0.01). This result indicates that the BiLC sensors possess the discriminatory power among different GTPase activity states. (B) The results of coimmunoprecipitation. The results show that the expressions of the BiLC biosensors had no significant discrimination among different alleles of Rho biosensor, but the intensities of the PPIs displayed obvious diversities, which were in accordance with the results obtained by our optical imaging. (C) In vivo optical CCD imaging of BiLC Rho GTPase biosensors. The pseudotumors in living mice were generated by engrafting with transiently transfected 293 cells. The pRL-tk plasmid was cotransfected and RL activity was detected to normalize the planted cell number. 24 h after implantation, the mice were imaged using IVIS spectrum. A significant discrimination of luciferase activity was detected among different alleles of Rho GTPase. (I: the dominant active mutants; II: the wild-type Rho GTPases; III: the effector-loop mutants; IV: the dominant negative mutants).</p

Optimizing the appropriate configuration (or domain arrangement) for BiLC Rho GTPase biosensor.

<p>(A) The optical results of eight different configurations. Relative luciferase activities were detected in living 293 cells cotransfected with the different configurations of N- and C-terminal FL fragments with interacting proteins CDC42 and WASP constructed with different orientations. Correct configuration is very critical to achieving efficient reconstruction of luciferase activity with PCA strategy. In each configuration, luciferase activity was compared among CDC42 WT, G12V, T17N and F37A mutants, which represent different levels of CDC42 activity and different degrees of the interaction. WT, G12V, T17N and F37A indicate wild type, constitutively active mutant, dominant negative mutant and effector mutant, respectively. The results were normalized using cotransfection of RL and represented by the ratio of luminescent intensity of FL at 600 nm to that of RL at 500 nm. The data shown are representative of three separate experiments performed with quadruplicate culture wells. The results show that the combinations containing Nfluc416-WASP/CDC42-Cfluc398 and Nfluc416-WASP/Cfluc398-CDC42 produced a greater level of luminescent signal and wider dynamic rang for different levels of CDC42 activity. (B) The western blots carried out in parallel to demonstrate the protein expression among CDC42 WT, G12V, T17N and F37A biosensors. This figure only shows the results of Nfluc416-WASP/Cfluc398-CDC42 as representative.</p

Optimizing appropriate dissection site of firefly luciferase for BiLC Rho GTPase biosensor.

<p>(A) The optical imaging results among different split-sites of firefly luciferase. Relative luciferase activities were detected in living 293 cells cotransfected with the five different combinations of split firefly luciferase fragments (Nfluc416-WASP/Cfluc398-CDC42, Nfluc416-WASP/Cfluc417-CDC42, Nfluc437-WASP/Cfluc438-CDC42, Nfluc398-WASP/Cfluc384-CDC42, Nfluc445-WASP/Cfluc446-CDC42), respectively. In each luciferase fragments combination, luciferase activity was compared among CDC42 WT, G12V, and F37A mutants. WT, G12V, and F37A indicate wild type, the constitutively active mutant, and the effector-loop mutant, respectively. The results were normalized using cotransfection of renilla luciferase plasmid (pRL-tk) and represented by the ratio of luminescent intensity of firefly luciferase (FL) at 600 nm to that of renilla luciferase (RL) at 500 nm (FL/RL). The data shown are representative of four separate experiments performed with quadruplicate culture wells. The result shows that the combination (Nfluc416/Cfluc398) had the widest dynamic range and the highest luciferase activity restoration. (B) The western blots carried out in parallel to demonstrate the protein expression among CDC42 WT, G12V, and F37A biosensors. This figure only shows the results of Nfluc416-WASP/CDC42-Cfluc398 as representative.</p

The sensitivity analysis of BiLC Rho GTPase sensors to extracellular ligands.

<p>(A) The temporal response of BiLC Rho GTPase sensors stimulated by extracellular ligands. After being serum-starved in serum-free DMEM medium for 6 h, mouse fibroblast NIH3T3 cells were detected the luminescent signals by adding D-luciferin until the intensities became steady, then stimulated with insulin (2 mg/mL), lysophosphatidic acid (40 ng/mL) and bradykinin (100 ng/mL), which are the known activator of Rac1, RhoA and Cdc42 respectively, and then immediately acquired the sequence image (1-min exposure; emission filter, open; f-stop, 1; binning, 8; field of view, 15 cm) for 30 min using IVIS spectrum. The data shown were obtained by three separate experiments performed with quadruplicate culture wells. The result shows that not only the activation signals of Rho GTPases from upstream pathways but also the subsequent decrease following the hydrolysis of GTP can be displayed and quantified by the BiLC-based biosensors. And the optical results (left) accord with that of ‘pull-down’ in our previous work (right). (B) The responses of BiLC Rho GTPase sensors to different concentration of extracellular ligands. The cells were stimulated with different concentrations of the stimulators and the luciferase activity was acquired after 3 min by IVIS spectrum (1-min exposure; emission filter, open; f-stop, 1; binning, 8; field of view, 15 cm). The data shown was obtained by three separate experiments performed with quadruplicate culture wells. The optical results (upper) were in accordance with that of our previous ‘pull-down’ (under).</p

The schematic diagrams of the constructs and the mechanism for BiLC-based Rho GTPase biosensors.

<p>(A) The graphic schemes of the constructs used in process of optimizing the appropriate dissection sites of firefly luciferase. For the construct of CDC42-Cfluc, CDC42 (AA 1–176) was used and the carboxy-terminal region of CDC42 (AA171–191) was added to the downstream of the fusion protein, making sure the correct localization to the plasma membrane and the regulation of GDIs. (B) The graphic schemes of the constructs used in process of optimizing the appropriate orientation of the reporter fragments (FN and FC) and the interacting proteins (WASP and CDC42). If CDC42 was fused to the N-terminal of the reporter fragment, CDC42 (AA 1–176) was used and the carboxy-terminal region of CDC42 (AA 171–191) was added downstream of the reporter fragment. (C) The schematic diagram of the optimal configuration and the mechanism for BiLC-based Rho GTPase biosensors. We use the optimal configuration as representative to describe the mechanism of the biosensors. In this strategy, two non-functional luciferase fragments are respectively fused, in fame and with a short flexible linker (G₂S)_2∼4 or (G₄S)_1∼2, to Rho GTPase and the GBD of the specific effector. Once Rho GTPase is activated by upstream stimulating factors, the two luciferase fragments (luc1 and luc2) are brought into close proximity by the active Rho GTPase binding to the GBD of the effector, leading to the restoration of luciferase activity and photon production in presence of the substrate.</p

Smac Therapeutic Peptide Nanoparticles Inducing Apoptosis of Cancer Cells for Combination Chemotherapy with Doxorubicin

Smac-conjugated nanoparticle (Smac-NP) was designed to induce the apoptosis of cancer cells and as a drug carrier for combination therapy. It contained three parts, a SmacN7 peptide which could induce apoptosis of cancer cells by interacting with XIAPs, the cell penetrating domain rich in arginine, and four hydrophobic tails for self-assembled Smac-NP. We demonstrated that Smac-NPs exerted an antitumor effect in breast cancer cell MDA-MB-231 and nonsmall lung cancer (NSCLC) cell H460, which efficiently inhibited cancer cells proliferation without influencing normal liver cell lines LO2. Smac-NPs also significantly induced apoptosis of MDA-MB-231 and H460 cells through activating pro-caspase-3, down-regulating the expression of antiapoptotic protein Bcl-2 and up-regulating the pro-apoptotic protein Bax. Furthermore, Smac-NPs could be explored as a drug delivery system to load hydrophobic drug such as DOX for combination therapy. The DOX-loaded nanoparticles (DOX-Smac-NPs) exhibited higher cellular uptake efficiency and antitumor effect. Our work provided a new insight into therapeutic peptides integrated with drug simultaneously in one system for cancer combination treatment