Nano

Nucleic acids detection has significant meanings in disease diagnosis, monitoring of environment and so on. However, only trace concentration of nucleic acids exists in specimen. Ultrasensitive nucleic acids detection is required based on the strategies of signal amplification. Currently, DNA nanotechnologies are employed to amplify the detecting signal, mainly including DNA hybridization-based sensors and DNA circuits-based sensors. DNA circuits-based sensors have higher sensitive than that of DNA hybridization-based sensors, which attract the attention of researchers. With this view, we present an overview of DNA circuits-based amplification strategies for nucleic acids detection with fluorescent sensors and electrochemical sensors, respectively. It mainly contains duplex specific nuclease (DSN)-based DNA circuits and strand displace reaction (SDR)-based DNA circuits, which enable nucleic acids to trigger DNA circuits without consumption. The strategies can multiply the increase of the signal of nucleic acids with simple operation. Meanwhile, this review discusses the current challenges and future outlook of DNA circuits in sensors. We envision that our review provides implications to promote the development of DNA circuits-based biosensors for nucleic acids detection.

Oil phase CuInSe₂ quantum dots (CISe QDs) were synthesized via a hot-injection method, exhibiting a near-infrared (NIR) emission wavelength of 710nm with poor fluorescence intensity. Therefore, we address this challenge by introducing two strategies: doping and ligand exchange. First, Zn was used as a dopant to improve the fluorescent properties of CISe QDs synthesized by the same method. The PL peak position of the resulting Zn–CuInSe (ZnCISe) QDs could be tuned from 600nm to 662nm, and the PL intensity of the QDs was greatly improved. Except that, this Zn doping strategy can help to improve the fluorescence lifetime and reduce defects, leading to increased quantum yield. Next, the aqueous phase transfer of ZnCISe QDs was achieved through an efficient ligand exchange strategy using glutathione (GSH) as the bifunctional ligand. Mercaptoacetic acid (MPA) was also used as an essential additive for GSH ligand exchange. With this method, we obtained high-quality hydrophilic ZnCISe QDs with particle sizes less than 3nm and good monodispersity. In addition, DLS measurements showed a unimodal peak shape of the hydrated ZnCISe QDs in ultrapure water with particle sizes ranging from 7nm to 40nm. Finally, the cytotoxicity studies revealed that the viabilities of the cells incubated with ZnCISe QDs from 1$\mu$g/mL to 18$\mu$g/mL remained at levels greater than 90%, which indicates that QDs with good biocompatibility are promising fluorescent probes.

Carbon materials are widely used as anodes of supercapacitors due to the long cycling stability, but the low capacitance results in low energy density of the supercapacitor device in aqueous solution, greatly limiting the application field of the supercapacitor. Here, the spiral low-crystalline Ni(OH)₂ supported on self-standing layered film structure of N-doped graphene/carbon nanotubes film (NCF) is reported. The prepared flexible film electrode of low-crystalline Ni(OH)₂/NCF is functioned as cathode directly, presenting high gravimetric capacitance (GC) and areal capacitance of 2130Fg${}^{-1}$ (2Ag${}^{-1}$) and 2.88Fcm${}^{-2}$ (1Ag${}^{-1}$). Also, this self-standing electrode film shows ultra-long cycle life, retaining 111.4% of initial capacitance after 30 000 circles at large current densities (20Ag${}^{-1}$) and almost 0% fade before 10 000 circles. Moreover, Ni(OH)₂/NCF and activated polyaniline derived carbon (APDC) have been assembled into an asymmetric supercapacitor, exhibiting a high gravimetric energy density of 60Whkg${}^{-1}$ at 800Wkg${}^{-1}$, suggesting that the obtained electrode has a good prospect application in long cycling stability with high energy density of supercapacitor devices.

A facial method is demonstrated here for the controllable fabrication of nano-NbN with three-dimensional cotton like structure. It is composed of two-step synthesis strategy and uses ammonia as nitrogen source. The prepared NbN has three-dimensional cotton like structure formed by nanoparticles with a size of around 20nm. It is found that the temperature of nitriding has a great influence on the size of crystal grain. 800^∘C is the most appropriate temperature to form this special structure of nano-NbN. As a catalyst for oxygen reduction reaction, nano-NbN is discovered to have a significant property, which is much better than that of niobium nitride prepared from oxide precursor without any treatment. Inspired by this strategy, the electrocatalytic performance of transition metal nitrides in nanoscale can be better studied.

As an important amino acid in the body, L-histidine participates in various physiological processes. Therefore, it is of great necessity to establish a rapid and effective method for L-histidine sensing, especially in blood and urine. In this work, a fluorescence sensor for detection of L-histidine was successfully developed using Cu-MOFs/Fe${}^{3+}$ sensor. Cu-MOFs with blue emission served as the identification unit and signal source, and Fe${}^{3+}$ played the role of “quencher” in this system. Fe${}^{3+}$ induced the fluorescence quenching of Cu-MOFs to form Cu-MOFs/Fe${}^{3+}$ sensor due to the effect of photoinduced electron transfer (PET). After the addition of L-histidine, Fe${}^{3+}$ was captured by L-histidine to form L-histidine-Fe${}^{3+}$ complex, which inhibited the PET effect from Cu-MOFs to Fe${}^{3+}$, resulting in the fluorescence recovery of Cu-MOFs. With such a design, L-histidine detection was realized with a wide linear range from 1$\mu$M to 190$\mu$M. The limit of detection (LOD) was calculated as low as 0.156$\mu$M. In addition, successful detection of L-histidine in blood serum with high selectivity and sensitivity indicated the real applications and potential diagnostic value of Cu-MOFs/Fe${}^{3+}$ system.

Electrocatalytic reduction of CO₂ into carbon-containing chemical product is greatly desired for mitigating the air pollution and energy crisis. However, there is great challenge to design highly active and stable electrocatalyst for the CO₂ reduction reaction (CO₂RR). Here, we develop a facile strategy of graphitic carbon nitride nanosheets-immobilized single-atom Zn (ZnSA–CN–G) to control the mitigation of electrocatalytic CO₂RR. The as-synthesized ZnSA–CN–G nanosheets not only possess abundant single-atom Zn as active sites, but also show unique architectures with high surface area and high electrical conductivity. Consequently, the ZnSA–CN–G nanosheets exhibit high electrocatalytic selectivity for CO₂RR, including a high Faradaic efficiency value of 87.1% for the production of CO at $-$0.5V versus RHE. Moreover, such simple approach can be further applied to synthesize a variety of other single-atom catalysts.

This study investigated the effects of annealing temperature on the structure evolution and antifungal performance of TiO₂/Fe₃O₄ nanocomposites. The TiO₂/Fe₃O₄ nanocomposites were fabricated through a combination of sonochemical and coprecipitation routes. The TiO₂ structure evolved from an amorphous phase to a crystalline anatase phase starting at an annealing temperature of $450^{\circ }$C while Fe₃O₄ evolved to $\gamma$-Fe₂O₃ and $\alpha$-Fe₂O₃ starting at an annealing temperature of $600^{\circ }$C. The increases in the crystallite sizes and lattice parameters were also identified because of the increase in the annealing temperature. The TiO₂/Fe₃O₄ nanocomposites tended to agglomerate due to van der Waals forces. The molecular structural dynamics of TiO₂/Fe₃O₄ nanocomposites were also studied by infrared spectroscopy within the wavenumber range of 400–4000cm${}^{-1}$. The antifungal activity of TiO₂/Fe₃O₄ nanocomposites was better than those of individual TiO₂ and Fe₃O₄. These results showed that structure evolution plays an essential role in the antifungal performance of TiO₂/Fe₃O₄ nanocomposites.

The development of heterojunction composites with core–shell structure could effectively facilitate the separation of carriers. In this work, a novel In₂O₃-SnS₂ (IOS) core–shell heterojunction photocatalyst was successfully synthesized for the efficient photocatalytic reduction of hexavalent chromium (Cr(VI)), namely, the In₂O₃ nanorods were obtained through successive hydrothermal and carbonization process using urea and glucose as template. Then, SnS₂ nanosheets were successfully in situ coated onto In₂O₃ nanorods. The spectroscopic characterization and photo-electrochemistry test indicated that the IOS core–shell heterojunction could effectively accelerate the separation and transport of carriers and suppress the recombination of carriers. The photocatalytic performance of IOS was evaluated by photocatalytic reduction Cr(VI). The results showed that IOS-4 samples almost completely removed Cr(VI) (20 mg/L), within 90 min under visible light, which was superior to pure In₂O₃ and SnS₂. Furthermore, IOS samples also possess excellent stability, the removal efficiency was still maintained at 90% after five cycles. This work provided a reliable method for designing core–shell heterojunctions for the photocatalytic removal of Cr(VI) under visible light.

In this paper, we prepared a fluorescent sensor based on carbon quantum dots (CDs) and molecularly imprinted technology (MIT) that was successfully synthesized and applied to the detection of aspirin (Asp) residues in biological and pharmaceutical samples. The molecularly imprinted fluorescence sensor had the high sensitivity of quantum dots and the high selectivity of molecularly imprinted polymers (MIPs). Nitrogen-doped carbon quantum dots (N-CDs) with high fluorescence intensity were prepared and then was coated with silicon by the reverse microemulsion method. Finally, 3-aminopropyltriethoxysilane (APTES) was used as the functional monomer and Asp as the template molecule, molecularly imprinted layers were formed around the N-CDs. Under the best experimental conditions, the detection limit of the sensor was 0.198mgL${}^{-1}$. Between 0.9–9.0mgL${}^{-1}$, this fluorescence sensor had a good linear relationship with the concentration of Asp. To test the practicability of the sensor, we used this fluorescent sensor to detect Asp in human urine and saliva. Satisfied recovery rate between 101.1–105.1% and 102.1–106.0% were obtained, respectively.

Core/shell structured Ni/Fe₃O₄ composites with grain sizes of 200–800 nm were synthesized by using a hydrothermal method. The phase structure, morphology, magnetic and electromagnetic absorption properties of the as-prepared samples were characterized by various analysis techniques. Experimental results revealed that spinel Fe₃O₄ was in situ deposition on the surface of Ni spheres through electrostatic interactions. Moreover, the Ni/Fe₃O₄ mass ratios had a significant influence on the electromagnetic absorption performances. When the mass ratio of Ni/Fe₃O₄ was 1:1, the composites reached an outstanding reflection loss (RL) of $-$48.06dB at 12.96GHz with a thin thickness of 1.8mm. Meanwhile, the effective absorption bandwidth was 5.36GHz (10.72–16.08GHz), covering the X and Ku bands. The enhanced electromagnetic absorption performance of core/shell structured Ni/Fe₃O₄ composites as compared to pure Ni, may be attributed to the multiple interfacial polarization, magnetic exchange coupling resonance and optimal impedance matching. Consequently, core/shell structured Ni/Fe₃O₄ composites would be promising candidates for a wider range of electromagnetic absorption applications.

This paper presents a systematic investigation of high-temperature transport characteristics of a single nanowire Gallium Nitride nanowire field-effect transistor (GaN-NWFET) ranging from room temperature to as high as $350^{\circ }$C for the first time. The GaN-NWFET demonstrated a very good on/off current ratio ($I_{\mathrm{\text{on}}}∕I_{\mathrm{\text{off}}})$ of $3\times 10^3$ for the p-side and $2.5\times 10^3$ for the n-side at room temperature and considerably well at high temperatures. In fact, the device exhibited an on/off current ratio of $5.5\times 10^2$ and a transconductance value of $0.96\mu$S for the p-side at $350^{\circ }$C indicating a good gating effect even at high temperatures. Additionally, the device exhibited very high mobilities with the hole mobility of $3.26\times 10^3$cm²/V. s and electron mobility of $3.14\times 10^3$ cm²/V. s at room temperature. Furthermore, the device showed very high transconductance values of $0.92\mu$S and $20.3\mu$S at the temperatures of $25^{\circ }$C and $250^{\circ }$C, respectively. As a consequence, the GaN-NWFET devices could find much use not only in high-power, but also in low-power transistor applications beyond the ambient temperature $\mathrm{\text{range}}(>300^{\circ }$C) of silicon and silicon-on-insulator technologies for electronic and photonic circuits.

Hierarchical core–shell architectures with multi-walled carbon nanotubes as core and MnO₂ sheets shaped in an array mode as shell (MWCNTs@MnO₂) were successfully synthesized via a simple wet chemical method. X-ray diffraction patterns and X-ray photoelectron spectroscopy analysis revealed that the composites were successfully prepared. Morphological characterizations were made by scanning electron microscopy and transmission electron microscopy. Vector network analyzer was employed to investigate the electromagnetic parameters of the composites. A possible attenuation mechanism was discussed, and the high-performance microwave absorption properties were attributed to the porous microstructure, polarization effect, dielectric loss and the synergistic action between MWCNTs and $\delta$-MnO₂. A minimum reflection loss (RL) of $-$50.6dB was achieved at a thickness of 1.4mm, and an effective absorption bandwidth ($\mathrm{\text{RL}}<-10$dB) covered 4.2GHz (from 13.8GHz to 18GHz) at a thickness of 1.3mm. Therefore, these results suggested that the MWCNTs@$\delta$-MnO₂ composites can be an excellent candidate for microwave absorption materials.

In this work, a series of three dimensions nanoporous Pd/M_xO_y ($\mathrm{\text{M}}=\mathrm{\text{Zr}}$, Ti, Co, Ni) composites are directly prepared by a simple dealloying method, their electrocatalytic performances are investigated. The structure analysis results show that the pores size of the composites is distinctly reduced, and their specific surface area is obviously increased compared with the nanoporous Pd when adding M_xO_y. As an anode catalyst, these three-dimensional (3D) nanoporous Pd/M_xO_y composites exhibit remarkable electrocatalytic performance (activity and stability) than that of the nanoporous Pd for ethanol electrooxidation, the order of the performance is as follows: Pd/NiO $>$ Pd/Co₂O₃ s $>$ Pd/TiO₂ s $>$ Pd/ZrO${}_2>$ Pd. Among the composites, the nanoporous Pd/NiO composite shows the best performance, which is approximately 3.6 times that of the single nanoporous Pd. The performance improvement of the composites for the ethanol oxidation is attributed to the structure optimization, interfacial electronic effect and dual functional mechanism between Pd and M_xO_y.