Partial collapse of DNA tetrahedron for miRNA assay with duplex-specific nuclease-assisted amplification.

We establish a facile electrochemical approach for detecting miRNA. Programmable DNA tetrahedron is designed using thiol groups for electrode modification, the amino group for the localization of electrochemical species and a hairpin structure that responds to target miRNA. In addition, duplex-specific nuclease-assisted amplification helps improve the sensitivity of this biosensor. The target-initiated partial collapse of the DNA tetrahedron event integrates recognition, electrode immobilization, signal recruitment and amplification. By measuring the sharp silver stripping peak, the highly sensitive detection of miRNA is achieved, which also performs satisfactorily challenging biological samples. This method is featured with simple operation, high sensitivity and practical utility, exhibiting great application potential in clinical diagnosis.

Wavelength tuning robustness optimization for a high-temperature single-mode VCSEL used in chip-scale atomic sensing systems.

In this paper, the wavelength current tuning characteristics of high-temperature-operation single-mode vertical-cavity surface-emitting lasers (VCSELs) for chip-scale atomic sensing systems are studied. Excellent wavelength current tuning robustness is helpful to improve the stability of atomic sensing systems. By optimizing the size of the oxide aperture combined with surface relief mode control technology, the single-mode VCSEL with an 8 µm oxide aperture can achieve 2.02 mW output power at 355 K, and the wavelength current tuning coefficient is ∼0.25nm/mA. This excellent wavelength current tuning robustness results from the low active current density and device heat generation due to the optimized oxide aperture size.

Construction of fluorescence logic gates responding to telomerase and miRNA based on DNA-templated silver nanoclusters and the hybridization chain reaction.

In this study, we have developed novel fluorescence logic gates for simultaneous analysis of telomerase activity and miRNA. An imperfectly complementary duplex is assembled which can be destroyed by telomerase catalyzed extension or miRNA mediated strand displacement. The released single-stranded DNA further initiates the subsequent hybridization chain reaction. The output response of the OR gate originates from fuel strand-templated silver nanoclusters (AgNCs). On the other hand, a three-way junction is constructed for the AND gate, which can be destroyed in the presence of miRNA and telomerase. The finally released DNA is also applied to trigger the hybridization chain reaction for the generation of a fluorescence response. The constructed logic gates are sensitive and reliable in the analysis of telomerase and miRNA for potential practical applications.

Simulation and experimental research of a high-order Bragg grating semiconductor laser.

In this paper, the influence of the epitaxial structure on distributed Bragg reflector (DBR) grating characteristics is studied by simulation analysis. Comparative analysis shows that the symmetrical epitaxial structure can achieve a lower threshold current and, thus, a higher power. Based on the simulated structure, a DBR laser based on a symmetric epitaxial structure was fabricated, and a single longitudinal mode laser output at ∼1060nm was obtained. The maximum power was 104.5 mW, and the side mode suppression ratio (SMSR) is 43 dB.

High-order DBR semiconductor lasers: effect of grating parameters on grating performance.

In this paper, a high-order distributed Bragg reflector (DBR) semiconductor laser operating at 1064 nm is demonstrated based on simulation analysis. To get optimal Bragg grating characteristics, four parameters of the Bragg grating were analyzed in detail. Forty-nine-order Bragg gratings were designed with a reflectivity of 6% and a FWHM of 3 nm, which can realize mode selection while lasing. The Bragg gratings were designed to maximize the use of light. Transmission of the rear laser facet is theoretically 0. This simulation result provides a simple and efficient DBR semiconductor laser scheme without cavity surface coating.

High-order DBR semiconductor lasers: effect of grating parameters on grating performance: publisher's note.

This publisher's note amends the author listing in Appl. Opt.59, 8789 (2020)APOPAI0003-693510.1364/AO.402699.

High-power vertical external-cavity surface-emitting laser emitting switchable wavelengths.

In this paper we reported on the optically pumped VECSELs with switchable lasing wavelengths. The two lasing wavelengths of λ ≈ 954 nm and 1003 nm are generated at different pumping powers from the same gain chip. The thermal rollover of output power is observed twice, and the first rollover on the power curve indicates the switch of lasing wavelength. During the operation of our VECSEL, the increase of pumping power changes the temperature within the gain chip, and thus the gain spectrum is tuned to the one of two modes, which is defined by the dips on the reflectivity spectrum. The maximum output power of each wavelength exceeds 2.2 W at -5 °C. The dual-wavelength emission at λ ≈954 nm and 1003 nm is also demonstrated, and the output power of the dual-wavelength emission reached nearly 2 W.

Electrochemical detection of T4 polynucleotide kinase based on target-assisted ligation reaction coupled with silver nanoparticles.

Phosphorylation of DNA is a critical event for normal cell processes such as DNA replication, DNA repair and DNA recombination. It is important to develop accurate and convenient approach for the detection of kinase and inhibition. In this work, we have described a novel sensing strategy for T4 polynucleotide kinase. A single-stranded DNA probe is firstly immobilized on the surface of the electrode. After phosphorylated by target kinase, it could be ligated with amino group labeled DNA probe by certain hybridization. Denaturation process is then proceeded to release unligated DNA probes, which may help reduce the background signal. The remained amino groups could be used to adsorb silver nanoparticles (AgNPs) as electrochemical species for the quantification of T4 polynucleotide kinase. This biosensor shows high sensitivity and selectivity. It may also be used for the screening kinase inhibitors. Therefore, it shows great potential utility in biological process investigation, drug discovery and clinical diagnosis.

[Optimization of broad-band flat-field holographic concave grating without astigmatism].

The desirable imaging locations of the flat-field holographic concave gratings should be in a plane. And the object can be imaged perfectly by the grating when the tangential focal curve and sagittal focal curve both superpose the intersection of the image plane and dispersion plane. But actually, the defocus can not be eliminated over the entire wavelength range, while the astigmatism vanishes when the grating parameters satisfy some conditions. An optimization method for broad-band flat-field holographic concave gratings with absolute astigmatism correction was proposed. The ray tracing software ZEMAX was used for investigating the imaging properties of the grating. And we made a comparison between spectral performance of gratings designed by this new method and that by conventional method, respectively. The results indicated that the spectral performance of gratings designed by using the absolute astigmatism correction method can be as good as gratings designed with the conventional method. And the focusing performance in the sagittal direction is much better, so that the S/N ratio can be greatly improved.

[Effect of curvature radius error on the flat-field holographic concave grating resolution and its compensation].

The spectral resolution of the spectrometer will be seriously deteriorated by radius error which is inevitable in the flat-field holographic concave grating fabrication. In order to give theoretical guidance to the design and assembly of the spectrometers, the geometric ray-tracing method was used to calculate and analyze the variation of the spectral image width with different radius error. It was discovered that in a wide range of the radius error, the position of the tangential focal curve moves forward or backward as the radius changes, while the shape of the tangential focal curve remains almost unchanged. As is shown through the calculation, the radius error can be compensated by adjustment of the detector's position or entrance slit distance. The simulation results indicate that with proper modification of the using structure, the grating can have a spectral resolution as good as the designed results.

High-power vertical-cavity surface-emitting laser with an optimized p-contact diameter.

A 980 nm bottom-emitting vertical-cavity surface-emitting laser (VCSEL) with a p-contact diameter is reported to achieve high power and good beam quality. A numerical simulation is conducted on the current spreading in a VCSEL with oxidation between the active region and the p-type distributed Bragg reflector. It is found that, for a particular oxide aperture diameter, somewhat homogeneous current distribution can be achieved for a VCSEL with an optimized p-contact diameter. The far-field divergence angle from a 600 microm diameter VCSEL is suppressed from 30 degrees to 15 degrees, and no strong sidelobe is observed in the far-field pattern by using the optimized p-contact diameter. There is a slight rise in threshold and optical output power that is due to the p-contact optimization. By improving the device packaging method, the maximum optical output power of the device is 2.01 W.

Design and characterization of a nonuniform linear vertical-cavity surface-emitting laser array with a Gaussian far-field distribution.

A 980 nm bottom-emitting vertical-cavity surface-emitting laser array with a nonuniform linear arrangement is reported to realize emission with a Gaussian far-field distribution. This array is composed of five symmetrically arranged elements of 200 microm, 150 microm, and 100 microm diameter, with center spacing of 300 microm and 250 microm, respectively. An output power of 880 mW with a high power density of 1 kW/cm2 is obtained. The divergence angle is below 20 degrees in the range of operating current from 0 A to 6 A. The theoretical simulation of the near-field and the far-field distribution is in good agreement with the experimental result. The comparison between this nonuniform linear array, the single device, and the conventional two-dimensional array is carried out to demonstrate the good performance of the linear array.