Electron-hole plasma Fabry-Perot lasing in a Ga-incorporated ZnO microbelt via Ag nanoparticle deposition.

In this work, individual ZnO via Ga-doped (ZnO:Ga) microbelts with excellent crystallinity and smooth facets can enable the realization of lateral microresonator Fabry-Perot (F-P) microlasers, and the F-P lasing action originates from excitonic state. Interestingly, introducing Ag nanoparticles (AgNPs) deposited on the microbelt can increase F-P lasing characteristics containing a lower threshold and enhanced lasing output. Especially for the large size AgNPs (the diameter d is approximately 200 nm), the lasing features also exhibit a significant redshift of each lasing peak and an observable broadening of the spectral line width with an increase of the excitation fluence. And the remarkable lasing characteristics are belonging to the electron-hole plasma (EHP) luminescence. The behavior and dynamics of the stimulated radiation in an AgNPs@ZnO:Ga microbelt are studied, suggesting the Mott-transition from the excitonic state to EHP state that is responsible for the F-P lasing. These features can be attributed to the working mechanism that the hot electrons created by the large size AgNPs through nonradiative decay can fill the conduction band of nearby ZnO:Ga, leading to a downward shift of the conduction band edge. This novel filling influence can facilitate bandgap renormalization and result in EHP emission. The results provide a comprehensive understanding of the transition between excitonic and EHP states in the stimulated emission process. More importantly, it also can provide new scheme to developing high efficiency and ultra-low threshold microlasing diodes.

Electrochemical detection of methyl-paraoxon based on bifunctional cerium oxide nanozyme with catalytic activity and signal amplification effect.

A new electrochemical sensor for organophosphate pesticide (methyl-paraoxon) detection based on bifunctional cerium oxide (CeO2) nanozyme is here reported for the first time. Methyl-paraoxon was degraded into p-nitrophenol by using CeO2 with phosphatase mimicking activity. The CeO2 nanozyme-modified electrode was then synthesized to detect p-nitrophenol. Cyclic voltammetry was applied to investigate the electrochemical behavior of the modified electrode, which indicates that the signal enhancement effect may attribute to the coating of CeO2 nanozyme. The current research also studied and discussed the main parameters affecting the analytical signal, including accumulation potential, accumulation time, and pH. Under the optimum conditions, the present method provided a wider linear range from 0.1 to 100 µmol/L for methyl-paraoxon with a detection limit of 0.06 µmol/L. To validate the proof of concept, the electrochemical sensor was then successfully applied for the determination of methyl-paraoxon in three herb samples, i.e., Coix lacryma-jobi, Adenophora stricta and Semen nelumbinis. Our findings may provide new insights into the application of bifunctional nanozyme in electrochemical detection of organophosphorus pesticide.

Ultra-broadband Bragg concave diffraction grating designs on 220-nm SOI for wavelength demultiplexing.

The appropriate broadband design of a de/multiplexer can significantly increase the channel number and consequently the transmission capacity of a wavelength division multiplexing system. Herein, we present the first ultra-broadband Bragg concave diffraction grating (CDG) on a 220-nm silicon-on-insulator, covering most of the E, S, C, L, and U telecommunication wavebands spanning from 1.425 to 1.675 µm. A wide-band-gap Bragg mirror is employed to facilitate broadband reflection, with a low diffraction order of grating for a sufficient free spectral range. Numerical simulations show that the proposed approaching blazed concave diffraction grating (AB-CDG) for the two-material case exhibits a high integration, simple fabrication process, and promising spectral performance. We fabricate the grating for design verification with a low transmission loss of -0.6 dB and a crosstalk below -33.7 dB for the eight measured wavelength channels covering the spectral range from 1.5 to 1.61 µm that is limited by the bandwidth of the grating coupler. This design can be used for broadband wavelength demultiplexing, frontier astronomical observation, and spectroscopic imaging.

Electrochemical detection of methyl-paraoxon based on bifunctional cerium oxide nanozyme with catalytic activity and signal amplification effect / 药物分析学报

A new electrochemical sensor for organophosphate pesticide(methyl-paraoxon)detection based on bifunctional cerium oxide(CeO2)nanozyme is here reported for the first time.Methyl-paraoxon was degraded into p-nitrophenol by using CeO2 with phosphatase mimicking activity.The CeO2 nanozyme-modified electrode was then synthesized to detect p-nitrophenol.Cyclic voltammetry was applied to investigate the electrochemical behavior of the modified electrode,which indicates that the signal enhancement effect may attribute to the coating of CeO2 nanozyme.The current research also studied and discussed the main parameters affecting the analytical signal,including accumulation potential,accumulation time,and pH.Under the optimum conditions,the present method provided a wider linear range from 0.1 to 100 μmol/L for methyl-paraoxon with a detection limit of 0.06 μmol/L.To validate the proof of concept,the electrochemical sensor was then successfully applied for the determination of methyl-paraoxon in three herb samples,i.e.,Coix lacryma-jobi,Adenophora stricta and Semen nelum-binis.Our findings may provide new insights into the application of bifunctional nanozyme in electro-chemical detection of organophosphorus pesticide.

A target-mediated fuel-initiated molecular machine for high-sensitive fluorescence assay of the ZIKV gene via strand displacement reaction-based signal recovery and cycling amplification.

Zika virus (ZIKV) is a serious threat to human health due to its widespread human arboviral infections, and early diagnosis is one of the keys to preventing infections from spreading, but there is a lack of highly sensitive and specific detection. In this work, a target-mediated fuel-initiated molecular machine was proposed for the high-sensitive fluorescence assay of the ZIKV gene via strand displacement reaction-based signal recovery and cycling amplification. The molecular machine was prepared by modifying AuNP surfaces with specially designed lock-like DNAs (LLDs). The LLDs assembled with a hairpin DNA (H1) and a fluorescent aDNA can be opened under the trigger of the ZIKV gene and the strand displacement reactions are further initiated with the help of the DNA fuel (H2), which results in the release of the aDNAs and ZIKV genes from the AuNPs, causing the recovery of the fluorescence signal and the cyclic amplification of the gene. The target-mediated fuel-initiated molecular machines output an amplified fluorescence signal with the enhancement of 360%, and possess good sensitivity for detecting the ZIKV gene in serum with a linear calibration curve from 100 pM to 1 fM and a low limit of detection of 0.90 fM. The molecular machines can differentiate the ZIKV gene from the single base mismatched DNA obviously and show good recovery of ZIKV gene detection, which demonstrates the good specificity, reproducibility and reliability of the highly sensitive assay for the early detection of the virus.

Study of interfacial random strain fields in core-shell ZnO nanowires by scanning transmission electron microscopy.

Imaging strain fields at the nanoscale is crucial for understanding the physical properties as well as the performance of oxide heterostructures and electronic devices. Based on scanning transmission electron microscopy (STEM) techniques, we successfully imaged the random strain field at the interface of core-shell ZnO nanowires. Combining experimental observations and image simulations, we find that the strain contrast originates from dechanneling of electrons and increased diffuse scattering induced by static atomic displacements. For a thin sample with a random strain field, a positive strain contrast appears in the low-angle annular dark-field (LAADF) image and a negative contrast in the high-angle annular dark-field (HAADF) image, but for a thick sample (> 120 nm), the positive contrast always occurs in both the LAADF and HAADF images. Through the analysis of the relationship between strain contrast and various parameters, we also discuss the optimum experimental condition for imaging random strain fields.

Electrically pumped Fabry-Perot microlasers from single Ga-doped ZnO microbelt based heterostructure diodes.

Semiconducting micro/nanostructures possessing naturally optical waveguiding behaviors and Fabry-Perot (F-P) like resonances are emerging as versatile building blocks for the assembly of photonic and optoelectronic devices, such as photodetectors, light-emitting diodes, lasers and so on. Individual ZnO micro/nanowires with a rectangular cross-section, such as microwires and microbelts possessing naturally smooth facets along both sides for good optical feedback, can be employed as an underlying F-P mode microcavity whilst as the gain medium for light amplification. In this context, electrically pumped F-P mode microlasers comprising a single ZnO:Ga microbelt and p-GaN substrate have been realized. By treating as the precondition, electrically driven exciton-polariton light-emitting behavior was achieved from the heterojunction diodes, which could be ascribed to strong exciton-photon coupling and waveguided nature of the synthesized microbelts. Once the applied bias exceeded the threshold value, an electrically pumped F-P mode lasing behavior could be observed, the lasing peaks centered at 410.5 nm and 450.5 nm respectively, accompanied with a dramatic narrowing of the spectral line-width to be around 1.0 nm emerging on the waveguided emission spectrum. Therefore, the realization of electrically pumped F-P mode lasing using single microbelt based heterojunction diodes opens the door not only to the fabrication of coherent light sources and model systems for waveguided resonators, but also affords a competitive candidate to develop electrically pumped and ultralow threshold polariton lasers.