RSC Advances

Cheon, Dongkeun; Son, Myungwoo; Ham, Moon-Ho; Lee, Woong

doi: 10.1039/c6ra21726epmid: N/A

The resistive switching behaviour of amorphous ZnO (a-ZnO) sandwiched between Ga-doped ZnO (GZO) transparent conductive oxide and Al electrode is reported. Transparent GZO films were deposited on polymer substrates as bottom electrodes using pulsed DC magnetron sputtering at 100 °C, on which a-ZnO films were deposited by RF magnetron sputtering at room temperature. The layered structure prepared in this manner was semi-transparent to visible light and its current–voltage hysteresis was representative of a bipolar resistive switching behaviour. The observation of such a resistive switching behaviour was attributed to the employment of a-ZnO as a dielectric layer and the use of Al and GZO as electrodes, which enabled the formation of Schottky barrier only at the a-ZnO/GZO interface. The conduction through the dielectric layer during the high resistance state was due to the Schottky emission as deduced from the consideration of band structures and the fitting of the current–voltage relations to the various conduction models. Switching to the low resistance state was attributed to the filament formation due to the migration of oxygen vacancies during the set process. In control experiments where crystalline ZnO was used as the dielectric layer, resistive switching behaviour was not observed.

Duarte-Guevara, Carlos; Swaminathan, Vikhram V.; Reddy, Bobby; Huang, Jui-Cheng; Liu, Yi-Shao; Bashir, Rashid

doi: 10.1039/c6ra19685cpmid: N/A

The use of field effect transistors (FETs) as the transduction element for the detection of DNA amplification reactions will enable portable and inexpensive nucleic acid analysis. Transistors used as biological sensors, or BioFETs, minimize the cost and size of detection platforms by leveraging fabrication methods already well developed for electronics. Here, we report a dual-gate BioFET (DG-BioFET) array platform with 1024×1024 sensors that is used for on-chip electrical detection of loop-mediated isothermal amplification (LAMP) reactions that target food borne bacterial pathogens. The DG-BioFETs of our 7 × 7 mm2 array are able to electrically detect pH changes that are triggered by nucleotide incorporation during LAMP elongation. Multiple 250 nL reactions can be simultaneously electrically monitored in our array that is divided in 30 micro-chambers with gold-coated anisotropically etched silicon wells that act both as reference electrode and confinement element. Our characterization results show that the gold-biased DG-BioFETs have a sensitivity of 32 mV pH−1 (equivalent to 2 μA pH−1) and an average resolution of 0.5 pH units. This sensitivity is high enough to detect the pH changes triggered by the amplification reaction, but to maximize our signal-to-noise ratio and improve our quantitative conclusions we use a group of data analysis techniques that are available in our high-density platform that monitors each reaction with ∼3500 independent BioFETs. We use redundancy techniques to minimize the overall standard deviation of our measurements, the Grubbs test to eliminate measurements outside the expected normal distribution, and reference micro-chambers to subtract the common noise. With these techniques we are capable of reducing the P value, of a t-test comparing positive and negative readings, from a typical 0.17 to 0.03. The platform that we present along with the analysis techniques that we developed allow the on-chip electrical detection and identification of E. coli O157 and S. typhi with parallel LAMP assays targeting eae and invA genes. The LAMP reactions are highly specific, without false positives, and our titration assays demonstrate a limit of detection of 23 CFU per reaction on chip.

Manshad, Soheila; Sazegar, Mohammad Reza; Mohd. Nawawi, Mohd. Ghazali; Hassan, Hashim bin

doi: 10.1039/c6ra22104apmid: N/A

Polyetherimide (PEI) flat-sheet membranes (PM) as a nanohybrid membrane were fabricated through dry-thermal (PMDT) and thermal treatment (PMTT) methods using graphene oxide (GO) as a nanofiller. Characterization of PM membranes was carried out using Fourier transform infrared (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The PMDT membrane cross-section showed a sponge-like structure resulting in higher permeability and lower separation factor. The SEM image (cross-section) of the PMTT membrane showed a dense structure with higher separation factor and lower permeation flux than those of the PMDT membrane. Incorporation of GO into the PEI matrix significantly reduced the contact angle surface hydrophobicity of the membranes. The nanohybrid membrane exhibited an exceptional pervaporation performance at a concentration of 95 wt% n-butanol. The permeation flux of PMDT and PMTT membranes were 1100.26 and 642.69 kg m−2 h−1 and their separation factors were 89.39 and 96.96, respectively. The GO incorporation and novel fabrication techniques resulted in excellent separation performance.

Yang, Yuhong; Qi, Xueyu; Liu, Ruiling; He, Qian; Yang, Chunhao

doi: 10.1039/c6ra21776apmid: N/A

A one-pot transition-metal-free, base-mediated synthesis of a novel series of functionalized thieno[2,3-c]coumarins via a cascade reaction from chromones has been developed. This cascade reaction involves a Michael addition–Knoevenagel condensation–intramolecular cyclization. This transformation proceeds under mild conditions and gives various thieno[2,3-c]coumarins in good-to-excellent yields. The methodology is tolerant of a wide range of functional groups and applicable to library synthesis.

Upama, Mushfika Baishakhi; Wright, Matthew; Puthen-Veettil, Binesh; Elumalai, Naveen Kumar; Mahmud, Md Arafat; Wang, Dian; Chan, Kah Howe; Xu, Cheng; Haque, Faiazul; Uddin, Ashraf

doi: 10.1039/c6ra23288dpmid: N/A

The efficiency of organic photovoltaic devices continues to increase; however, their limited stability is currently a barrier to the commercial prospects of the technology. Burn-in photo degradation, caused by continuous illumination under a light source, can cause a significant reduction in device performance. Our aim was to investigate this degradation pathway for the high-efficiency polymer PTB7, which was compared to the well-studied P3HT:PC71BM material system. In this study, we compared the burn-in aging profile for organic solar cells containing either P3HT or PTB7 as the donor polymer. This showed that PTB7:PC71BM solar cells exhibit a severe initial reduction in performance, due mainly to reduced short circuit current density (Jsc), during the 5 hour test period. P3HT:PC71BM cells were relatively stable during this test. Photothermal deflection spectroscopy (PDS), which provides sensitive measurement of sub bandgap absorption, was employed to discover the underlying mechanism causing this discrepancy. In PTB7-based devices, a significant increase in sub bandgap absorption was observed after illumination, which was attributed to the formation of sub bandgap trap states. This mechanism was identified as a contributing factor to the severe burn-in for PTB7-based organic solar cells. No such increase was observed for P3HT:PC71BM films.

Zhang, Di; Wenya, Liu; Chen, Keke; Cheng, Junye; Zhao, Yufen; Ye, Yong

doi: 10.1039/c6ra24667bpmid: N/A

A new rosamine-based fluorescent probe (RosCHO) for bisulfite was obtained by one pot reaction of p-phthalaldehyde and 3-(diethylamino)phenol, which showed excellent selectivity, high sensitivity and a rapid response toward bisulfite in aqueous solution. Upon the addition of HSO3−, the aldehyde moiety in probe RosCHO formed a hydrogen sulfite-dependent adduct product, leading to fluorescence enhancement due to the different ICT process. The detection limit for bisulfite was as low as 7 × 10−8 M, and fluorescence imaging of bisulfite in MCF-7 cells demonstrated its value to practical application in biological systems.

Long, Yuan; Li, Mingfei; Qu, Huixia; Xing, Zheyu; Wei, Chaoliang; Zhan, Jingjing

doi: 10.1039/c6ra23888bpmid: N/A

Magnetic carbon submicron spheres possessing good sorption abilities and easy collection are of interest in environmental engineering including oil spill cleanup. Here we describe a facile one-step process for the preparation of spherical submicron carbon–γ-Fe2O3 composites with controllable magnetic susceptibility and strong adsorption capability. Based on an aerosol-assisted technology, common precursors including sucrose, iron sulfate and a tiny amount of concentrated sulfuric acid were distributed and confined to numerous aerosol droplets, where the concurrence of sucrose carbonization and phase transition in iron species rapidly led to the formation of spherical carbon–γ-Fe2O3 composites. Meanwhile, magnetic saturation (Ms) values and the surface properties of the obtained composites could be controlled by simply adjusting the heating temperature, and the highest Ms at 44.83 emu g−1 is much greater than those of samples obtained using other common methods. In the application of oil spill cleanup including diesel, gasoline and crude oil, these magnetic carbon submicron spheres exhibit high adsorption ability, easy separation and good recyclability. Such a simple technology may serve as a generalizable process to synthesize other types of magnetic composites such as titanium dioxide, silica and aluminum dioxide for broad applications.

Wang, Zhi-Qiang; Xu, Kun; Zhang, Xu; Li, Ting; Zheng, Shao-Long; Yu, Lin-Tao; Mao, Wu-Tao; Chen, Chang-Zhong; Wang, Li-Ya

doi: 10.1039/c6ra23244bpmid: N/A

Herein we report a copper-mediated intramolecular aerobic oxidative cyclization of alkynes and sulfonylcrotonates. This method provides simple, efficient and easy to operate access to a variety of highly functionalized naphthyl ketones with excellent functional group tolerance.

Wang, Jinzuan; Yang, Jun; Huang, Tao; Yin, Wenyan

doi: 10.1039/c6ra21281fpmid: N/A

Self-assembled manganese cobalt oxide (Mn0.5Co2.5O4) nanofibers sandwiched in graphene sheets (Mn0.5Co2.5O4@G) are successfully synthesized by a hydrothermal treatment and annealing process. Owning to the unique sandwich-like structures, rich active sites, and boosted electrical conductivity, Mn0.5Co2.5O4@G composite demonstrates superior electrochemical performance for potential supercapacitors. In a three-electrode system, it exhibits excellent cycling stability with a specific capacitance retention of 93.8% after 10 000 cycles at a current density of 10 A g−1, and achieves specific capacitances of 617 and 434 F g−1 at the ultrahigh current densities of 30 and 40 A g−1, respectively. For an asymmetric supercapacitor of Mn0.5Co2.5O4@G//AC, high energy densities of 36.8 and 13.6 W h kg−1 are also achieved at power densities of 147.3 and 3755.8 W kg−1, respectively. It is believed that the synthesized Mn0.5Co2.5O4@G composite can be a promising electrode material for high-performance supercapacitors, and the present synthetic strategy can be further extended for designing many other functional composites with desirable nanostructures and performance.

Hu, Gaofei; Xu, Tiantian; Chen, Xiaoqing; James, Tony D.; Xu, Suying

doi: 10.1039/c6ra22737fpmid: N/A

The development of low-cost and biocompatible inorganic photothermal nanoagents with broadband sunlight absorption and high photothermal conversion efficiency as broad spectrum fungicides is highly desirable for the large scale antibacterial treatment especially in the wild, because of their highly efficient anti-bacteria ability via solar irradiation. Here, we present a facile strategy for the synthesis of Cu7S4 nanorods (NRs) with broadband light absorption (300–3300 nm) and high photothermal conversion efficiency (57.8%, 808 nm), and the use of these NRs as broad spectrum fungicides for efficient disinfection using natural sunlight as light source. In the presence of Cu7S4 NRs, with natural sunlight irradiation (70 mW cm−2), both Gram-positive (S. aureus) and Gram-negative (E. coli) bacterium strains (2 mL, 106 mL−1) were completely killed in 10 min. These results suggest that our Cu7S4 NRs are effective and broad spectrum photothermal anti-bacterial agents regardless of drug resistance, that are particularly suitable for anti-bacteria activity in the wild using solar irradiation where artificial light sources are not available. Due to their strong near infrared (NIR) absorption, these biocompatible and low-cost Cu7S4 NRs may also serve as promising agents for photothermal therapy of tumors, disinfection in clinics, food sterilization and environmental treatment.