Engineering of Solvation Entropy by Poly(4-styrenesulfonic acid) Additive in an Aqueous Electrochemical System for Enhanced Low-Grade Heat Harvesting.

The thermally regenerative electrochemical cycle (TREC) is a reliable and efficient approach to converting low-grade heat into electricity. A high temperature coefficient (α) is the key to maximize the energy conversion efficiency of the TREC system. In this study, we present significant improvement of α of a Prussian blue analogue (PBA)-based electrochemical cell by adding poly(4-styrenesulfonic acid) (PSS) to the electrolyte. Raman spectra showed that water-soluble charged polymers strongly affect the ion hydration structure and increase the entropy change (ΔS) during ion intercalation in PBA. A large α of -2.01 mV K-1 and high absolute heat-to-electricity conversion efficiency up to 1.83% was achieved with a TREC cell in the temperature range 10-40 °C. This study provides a fundamental understanding of the origin of α and a facile method to boosting the temperature coefficient for building a highly efficient low-grade heat harvesting system.

Temperature-Dependent Fracture Resistance of Silicon Nanopillars during Electrochemical Lithiation.

During the lithation of silicon anodes, the solid-state diffusion of lithium into LixSi follows the Arrhenius law, the resulting morphology and fracture behavior are determined by the silicon anode operation temperature. Here, we reveal the temperature dependence of the lithiation mechanics of crystalline silicon nanopillars (SiNPs) via microscopic observations of the anisotropic growth and fracture behavior. We fabricated 1D SiNP structures with various orientations (⟨100⟩, ⟨110⟩, and ⟨111⟩) as working electrodes and operated them at temperatures ranging from -20 to 40 °C. The lithiation of crystalline silicon at low temperatures exhibited preferential volume expansion along ⟨110⟩ and decreased fracture resistance. Furthermore, low temperatures caused the catastrophic fracture of amorphous silicon after the second lithiation. Our findings demonstrate the importance of silicon anode temperature control to prevent mechanical fracture during the cycle of lithium-ion batteries in harsh environments (e.g., electric vehicles in winter).

Copper Hexacyanoferrate Thin Film Deposition and Its Application to a New Method for Diffusion Coefficient Measurement.

The use of Prussian blue analogues (PBA) materials in electrochemical energy storage and harvesting has gained much interest, necessitating the further clarification of their electrochemical characteristics. However, there is no well-defined technique for manufacturing PBA-based microelectrochemical devices because the PBA film deposition method has not been well studied. In this study, we developed the following deposition method for growing copper hexacyanoferrate (CuHCFe) thin film: copper thin film is immersed into a potassium hexacyanoferrate solution, following which the redox reaction induces the spontaneous deposition of CuHCFe thin film on the copper thin film. The film grown via this method showed compatibility with conventional photolithography processes, and the micropattern of the CuHCFe thin film was successfully defined by a lift-off process. A microelectrochemical device based on the CuHCFe thin film was fabricated via micropatterning, and the sodium ion diffusivity in CuHCFe was measured. The presented thin film deposition method can deposit PBAs on any surface, including insulating substrates, and it can extend the utilization of PBA thin films to various applications.

Tear-Based Aqueous Batteries for Smart Contact Lenses Enabled by Prussian Blue Analogue Nanocomposites.

Batteries for contact lenses fabricated by conventional methods could cause severe damage to the eyes if broken. Herein, we present flexible aqueous batteries that operate in tears and provide a safe power supply to smart contact lenses. Nanocomposite flexible electrodes of carbon nanotubes and Prussian blue analogue nanoparticles for cathode and anode were embedded in UV-polymerized hydrogel as not only a soft contact lens but also an ion-permeable separator. The battery exhibited a discharging capacity of 155 µAh in an aqueous electrolyte of 0.15 M Na-ions and 0.02 M K-ions, equivalent to the ionic concentration of tears. The power supply was enough to operate a low-power static random-access memory. In addition, we verified the mechanical stability, biocompatibility and compatibility with a contact lens cleaning solution. It could ultimately enable a safe power supply for smart contact lenses without risk of injury due to the leakage or breakage of the battery.

Efficient Low-Grade Heat Harvesting Enabled by Tuning the Hydration Entropy in an Electrochemical System.

Harvesting of low-grade heat (<100 °C) is promising, but its application is hampered by a lack of efficient and low-cost systems. The thermally regenerative electrochemical cycle (TREC) is a potential alternative system with high energy-conversion efficiency. Here, the temperature coefficient (α), which is a key factor in a TREC, is studied by tuning the hydration entropy of the electrochemical reaction. The change of α in copper hexacyanoferrate (CuHCFe) with intercalation of different monovalent cations (Na+ , K+ , Rb+ , and Cs+ ) and a larger α value of -1.004 mV K-1 being found in the Rb+ system are observed. With a view to practical application, a full cell is constructed for low-grade heat harvesting. The resultant ηe is 4.34% when TREC operates between 10 and 50 °C, which further reaches 6.21% when 50% heat recuperation is considered. This efficiency equals to 50% of the Carnot efficiency, which is thought to be the highest ηe reported for low-grade heat harvesting systems. This study provides a fundamental understanding of the mechanisms governing the TREC, and the demonstrated efficient system paves the way for low-grade heat harvesting.

Tunable Photoluminescence across the Visible Spectrum and Photocatalytic Activity of Mixed-Valence Rhenium Oxide Nanoparticles.

Materials exhibiting excitation-wavelength-dependent photoluminescence, PL, are useful in a range of biomedical and optoelectronic applications. This paper describes a nanoparticulate material whose PL is tunable across the entire visible range and is achieved without adjusting particle size, any postsynthetic doping, or surface modification. A straightforward thermal decomposition of rhenium (VII) oxide precursor yields nanoparticles that comprise Re atoms at different oxidation states. Studies of time-resolved emission spectra and DFT calculations both indicate that tunable PL of such mixed-valence particles originates from the presence of multiple emissive states that become "active" at different excitation wavelengths. In addition, the nanoparticles exhibit photocatalytic activity that, under visible-light irradiation, is superior to that of TiO2 nanomaterials.

Graphene and Graphene Analogs toward Optical, Electronic, Spintronic, Green-Chemical, Energy-Material, Sensing, and Medical Applications.

This spotlight discusses intriguing properties and diverse applications of graphene (Gr) and Gr analogs. Gr has brought us two-dimensional (2D) chemistry with its exotic 2D features of density of states. Yet, some of the 2D or 2D-like features can be seen on surfaces and at interfaces of bulk materials. The substrate on Gr and functionalization of Gr (including metal decoration, intercalation, doping, and hybridization) modify the unique 2D features of Gr. Despite abundant literature on physical properties and well-known applications of Gr, spotlight works based on the conceptual understanding of the 2D physical and chemical nature of Gr toward vast-ranging applications are hardly found. Here we focus on applications of Gr, based on conceptual understanding of 2D phenomena toward 2D chemistry. Thus, 2D features, defects, edges, and substrate effects of Gr are discussed first. Then, to pattern Gr electronic circuits, insight into differentiating conducting and nonconducting regions is introduced. By utilizing the unique ballistic electron transport properties and edge spin states of Gr, Gr nanoribbons (GNRs) are exploited for the design of ultrasensitive molecular sensing electronic devices (including molecular fingerprinting) and spintronic devices. The highly stable nature of Gr can be utilized for protection of corrosive metals, moisture-sensitive perovskite solar cells, and highly environment-susceptible topological insulators (TIs). Gr analogs have become new types of 2D materials having novel features such as half-metals, TIs, and nonlinear optical properties. The key insights into the functionalized Gr hybrid materials lead to the applications for not only energy storage and electrochemical catalysis, green chemistry, and electronic/spintronic devices but also biosensing and medical applications. All these topics are discussed here with the focus on conceptual understanding. Further possible applications of Gr, GNRs, and Gr analogs are also addressed in a section on outlook and future challenges.

Lower Electric Field-Driven Magnetic Phase Transition and Perfect Spin Filtering in Graphene Nanoribbons by Edge Functionalization.

Perfect spin filtering is an important issue in spintronics. Although such spin filtering showing giant magnetoresistance was suggested using graphene nanoribbons (GNRs) on both ends of which strong magnetic fields were applied, electric field controlled spin filtering is more interesting due to much easier precise control with much less energy consumption. Here we study the magnetic/nonmagnetic behaviors of zigzag GNRs (zGNRs) under a transverse electric field and by edge functionalization. Employing density functional theory (DFT), we show that the threshold electric field to attain either a half-metallic or nonmagnetic feature is drastically reduced by introducing proper functional groups to the edges of the zGNR. From the current-voltage characteristics of the edge-modified zGNR under an in-plane transverse electric field, we find a remarkable perfect spin filtering feature, which can be utilized for a molecular spintronic device. Alteration of magnetic properties by tuning the transverse electric field would be a promising way to construct magnetic/nonmagnetic switches.

Electron Transport in Graphene Nanoribbon Field-Effect Transistor under Bias and Gate Voltages: Isochemical Potential Approach.

Zigzag graphene nanoribbon (zGNR) of narrow width has a moderate energy gap in its antiferromagnetic ground state. So far, first-principles electron transport calculations have been performed using nonequilibrium Green function (NEGF) method combined with density functional theory (DFT). However, the commonly practiced bottom-gate control has not been studied computationally due to the need to simulate an electron reservoir that fixes the chemical potential of electrons in the zGNR and electrodes. Here, we present the isochemical potential scheme to describe the top/back-gate effect using external potential. Then, we examine the change in electronic state under the modulation of chemical potential and the subsequent electron transport phenomena in zGNR transistor under substantial top-/back-gate and bias voltages. The gate potential can activate the device states resulting in a boosted current. This gate-controlled current-boosting could be utilized for designing novel zGNR field effect transistors (FETs).

DUSP28 links regulation of Mucin 5B and Mucin 16 to migration and survival of AsPC-1 human pancreatic cancer cells.

The prognosis of pancreatic cancer has not improved despite considerable and continuous effort. Dual-specificity phosphatase 28 (DUSP28) is highly expressed in human pancreatic cancers and exerts critical effects. However, knowledge of its function in pancreatic cancers is extremely limited. Here, we demonstrate the peculiar role of DUSP28 in pancreatic cancers. Analysis using the Gene Expression Omnibus public microarray database indicated higher DUSP28, MUC1, MUC4, MUC5B, MUC16 and MUC20 messenger RNA (mRNA) levels in pancreatic cancers compared with normal pancreas tissues. DUSP28 expression in human pancreatic cancer correlated positively with those of MUC1, MUC4, MUC5B, MUC16 and MUC20. In contrast, there were no significant correlations between DUSP28 and mucins in normal pancreas tissues. Decreased DUSP28 expression resulted in down-regulation of MUC5B and MUC16 at both the mRNA and protein levels; furthermore, transfection with small interfering RNA (siRNA) for MUC5B and MUC16 inhibited the migration and survival of AsPC-1 cells. In addition, transfection of siRNA for MUC5B and MUC16 resulted in a significant decrease in phosphorylation of FAK and ERK1/2 compared with transfection with scrambled-siRNA. These results collectively indicate unique links between DUSP28 and MUC5B/MUC16 and their roles in pancreatic cancer; moreover, they strongly support a rationale for targeting DUSP28 to inhibit development of malignant pancreatic cancer.

Violation of DNA neighbor exclusion principle in RNA recognition.

DNA intercalation has been very useful for engineering DNA-based functional materials. It is generally expected that the intercalation phenomenon in RNA would be similar to that in DNA. Here we note that the neighbor-exclusion principle is violated in RNA by naphthalene-based cationic probes, in contrast to the fact that it is usually valid in DNA. All the intercalation structures are responsible for the fluorescence, where small naphthalene moieties are intercalated in between bases via π-π interactions. The structure is aided by hydrogen bonds between the cationic moieties and the ribose-phosphate backbone, which results in specific selectivity for RNA over DNA. This experimentally observed mechanism is supported by computationally reproducing the fluorescence and CD data. MD simulations confirm the unfolding of RNA due to the intercalation of probes. Elucidation of the mechanism of selective sensing for RNA over DNA would be highly beneficial for dynamical observation of RNA which is essential for studying its biological roles.

Quercetin 3-O-glucoside suppresses epidermal growth factor-induced migration by inhibiting EGFR signaling in pancreatic cancer cells.

Pancreatic cancer is one of the most dangerous cancers and is associated with a grave prognosis. Despite increased knowledge of the complex signaling networks responsible for progression of pancreatic cancer, many challenging therapies have fallen short of expectations. In this study, we examined the anti-migratory effect of quercetin 3-O-glucoside in epidermal growth factor-induced cell migration by inhibiting EGF receptor (EGFR) signaling in several human pancreatic cancer cell lines. Treatment with quercetin, quercetin 3-O-glucoside, and quercetin 7-O-glucoside differentially suppressed epidermal growth factor-induced migration activity of human pancreatic cancer cells. In particular, quercetin 3-O-glucoside strongly inhibited the infiltration activity of pancreatic cancer cells in a dose-dependent manner. Furthermore, quercetin 3-O-glucoside exerted the anti-migratory effect even at a relatively low dose compared with other forms of quercetin. The anti-tumor effects of quercetin 3-O-glucoside were mediated by selectively inhibiting the EGFR-mediated FAK, AKT, MEK1/2, and ERK1/2 signaling pathway. Combinatorial treatment with quercetin 3-O-glucoside plus gemcitabine showed the synergistic anti-migratory effect on epidermal growth factor-induced cell migration in human pancreatic cancer cell lines. These results suggest that quercetin 3-O-glucoside has potential for anti-metastatic therapy in human pancreatic cancer.

Graphene edges and beyond: temperature-driven structures and electromagnetic properties.

The atomic configuration of graphene edges significantly influences the various properties of graphene nanostructures, and realistic device fabrication requires precise engineering of graphene edges. However, the imaging and analysis of the intrinsic nature of graphene edges can be illusive due to contamination problems and measurement-induced structural changes to graphene edges. In this issue of ACS Nano, He et al. report an in situ heating experiment in aberration-corrected transmission electron microscopy to elucidate the temperature dependence of graphene edge termination at the atomic scale. They revealed that graphene edges predominantly have zigzag terminations below 400 °C, while above 600 °C, the edges are dominated by armchair and reconstructed zigzag edges. This report brings us one step closer to the true nature of graphene edges. In this Perspective, we outline the present understanding, issues, and future challenges faced in the field of graphene-edge-based nanodevices.

Two dimensional molecular electronics spectroscopy for molecular fingerprinting, DNA sequencing, and cancerous DNA recognition.

Laser-driven molecular spectroscopy of low spatial resolution is widely used, while electronic current-driven molecular spectroscopy of atomic scale resolution has been limited because currents provide only minimal information. However, electron transmission of a graphene nanoribbon on which a molecule is adsorbed shows molecular fingerprints of Fano resonances, i.e., characteristic features of frontier orbitals and conformations of physisorbed molecules. Utilizing these resonance profiles, here we demonstrate two-dimensional molecular electronics spectroscopy (2D MES). The differential conductance with respect to bias and gate voltages not only distinguishes different types of nucleobases for DNA sequencing but also recognizes methylated nucleobases which could be related to cancerous cell growth. This 2D MES could open an exciting field to recognize single molecule signatures at atomic resolution. The advantages of the 2D MES over the one-dimensional (1D) current analysis can be comparable to those of 2D NMR over 1D NMR analysis.

Noncovalent Interactions of DNA Bases with Naphthalene and Graphene.

The complexes of a DNA base bound to graphitic systems are studied. Considering naphthalene as the simplest graphitic system, DNA base-naphthalene complexes are scrutinized at high levels of ab initio theory including coupled cluster theory with singles, doubles, and perturbative triples excitations [CCSD(T)] at the complete basis set (CBS) limit. The stacked configurations are the most stable, where the CCSD(T)/CBS binding energies of guanine, adenine, thymine, and cytosine are 9.31, 8.48, 8.53, 7.30 kcal/mol, respectively. The energy components are investigated using symmetry-adapted perturbation theory based on density functional theory including the dispersion energy. We compared the CCSD(T)/CBS results with several density functional methods applicable to periodic systems. Considering accuracy and availability, the optB86b nonlocal functional and the Tkatchenko-Scheffler functional are used to study the binding energies of nucleobases on graphene. The predicted values are 18-24 kcal/mol, though many-body effects on screening and energy need to be further considered.