Cuifeng Ying

3D nanopore shape control by current-stimulus dielectric breakdown

We propose a simple and cost-effect method, current-stimulus dielectric breakdown, to manipulate the 3D shapes of the nanochannels in 20-nm-thick SiNx membranes. Besides the precise control of nanopore size, the cone orientation can be determined by the pulse polarity. The cone angle of nanopores can be systematically tuned by simply changing the stimulus pulse waveform, allowing the gradual shape control from conical to obconical. After they are formed, the cone angle of these nanopores can be further tuned in a certain range by adjusting the widening pulse. Such size and 3D shape controllable abiotic nanopores can construct a constriction in the nanochannel and hence produce a sub-nm “sensing zone” to suit any desired bio-sensing or precise DNA sequencing. Using these conical nanopores, 20-nt ssDNA composed of homopolymers (poly(dA)20, poly(dC)20, and poly(dT)20) can be clearly differentiated by their ionic current signals.

Precise fabrication of a 5 nm graphene nanopore with a helium ion microscope for biomolecule detection

We report a scalable method to fabricate high-quality graphene nanopores for biomolecule detection using a helium ion microscope (HIM). HIM milling shows promising capabilities for precisely controlling the size and shape, and may allow for the potential production of nanopores at wafer scale. Nanopores could be fabricated at different sizes ranging from 5 to 30 nm in diameter in few minutes. Compared with the current solid-state nanopore fabrication techniques, e.g. transmission electron microscopy, HIM is fast. Furthermore, we investigated the exposure-time dependence of graphene nanopore formation: the rate of pore expansion did not follow a simple linear relationship with exposure time, but a fast expansion rate at short exposure time and a slow rate at long exposure time. In addition, we performed biomolecule detection with our patterned graphene nanopore. The ionic current signals induced by 20-base single-stranded DNA homopolymers could be used as a basis for homopolymer differentiation. However, the charge interaction of homopolymer chains with graphene nanopores, and the conformations of homopolymer chains need to be further considered to improve the accuracy of discrimination.

A simplified hollow-core microstructured optical fibre laser with microring resonators and strong radial emission

A simplified hollow-core microstructured optical fibre (SHMOF) laser with microring resonators and strong radial emission is demonstrated. We propose that a submicron thickness silica ring embedded in the SHMOF can act as a microring resonator, with the advantages of being both compact and solid. Furthermore, the microfluidics can be easily controlled with a side pumping scheme. We also obtained a highly stable and tunable laser. The attractive possibility of developing microfluidic dye lasers within single SHMOFs presents opportunities for integrated optics applications and biomedical analysis.

Enhanced reverse saturable absorption and optical limiting properties in a protonated water-soluble porphyrin

Nonlinear optical properties of water-soluble porphyrin 5,10,15,20-Tetrakis (1-methyl-4-pyridinio) porphyrin tetra (p-toluenesulfonate) (TMPyP), protonated TMPyP (), TMPyP film with the gelatin matrix (TMPyP/Gelatin) were investigated by the open-aperture Z-scan technique in the nanosecond regime. Results show that exhibits a larger ratio of excited state absorption cross-section to that of the ground state and enhanced reverse saturable absorption properties compared with TMPyP and TMPyP/Gelatin. also shows the superior optical limiting performance, even better than the benchmark material C60 and the multi-walled carbon nanotubes (MWNTs) dispersion.

Band-edge lasing in Rh6G-doped dichromated gelatin at different excitations

One-dimensional photonic crystal band-edge lasing at different excitations was studied experimentally by altering the excitation angle. We considered almost every condition including in-band, out-of-band and near the band edge while keeping the density of states unchanged. Holographic rhodamin 6G-doped dichromated gelatin was used for creating low-threshold photonic band-edge lasing (PBEL). Lasing actions excited near the high-energy and low-energy band edges were observed simultaneously, and their full widths at half maximum were different. The results show that the PBEL intensity and pump efficiency are sensitive to the excitation angle, enhanced obviously at the excitation near the band edge and suppressed distinctly in the band which agreed well with the theoretical prediction. We also demonstrated for the first time that active matters exist not only in the air voids but also in the high-index regions of the gelatin.

Monitoring tetracycline through a solid-state nanopore sensor

Antibiotics as emerging environmental contaminants, are widely used in both human and veterinary medicines. A solid-state nanopore sensing method is reported in this article to detect Tetracycline, which is based on Tet-off and Tet-on systems. rtTA (reverse tetracycline-controlled trans-activator) and TRE (Tetracycline Responsive Element) could bind each other under the action of Tetracycline to form one complex. When the complex passes through nanopores with 8 ~ 9 nanometers in diameter, we could detect the concentrations of Tet from 2 ng/mL to 2000 ng/mL. According to the Logistic model, we could define three growth zones of Tetracycline for rtTA and TRE. The slow growth zone is 0–39.5 ng/mL. The rapid growth zone is 39.5−529.7 ng/mL. The saturated zone is > 529.7 ng/mL. Compared to the previous methods, the nanopore sensor could detect and quantify these different kinds of molecule at the single-molecule level.

Rectifcation of Ion Current Determined by the Nanopore Geometry: Experiments and Modelling*

We provide a way to precisely control the geometry of a SiN x nanopore by adjusting the applied electric pulse. The pore is generated by applying the current pulse across a SiN x membrane, which is immersed in potassium chloride solution. We can generate single conical and cylindrical pores with different electric pulses. A theoretical model based on the Poisson and Nernst—Planck equations is employed to simulate the ion transport properties in the channel. In turn, we can analyze pore geometries by fitting the experimental current-voltage (I–V) curves. For the conical pores with a pore size of 0.5–2nm in diameter, the slope angles are around −2.5° to −10°. Moreover, the pore orifice can be enlarged slightly by additional repeating pulses. The conic pore lumen becomes close to a cylindrical channel, resulting in a symmetry I–V transport under positive and negative biases. A qualitative understanding of these effects will help us to prepare useful solid-nanopores as demanded.

Fabrication of multiple nanopores in a SiN x membrane via controlled breakdown

This paper reports a controlled breakdown (CBD) method to fabricate multiple nanopores in a silicon nitride (SiNx) membrane with control over both nanopore count and nanopore diameter. Despite the stochastic process of the breakdown, we found that the nanopores created via CBD, tend to be of the same diameter. We propose a membrane resistance model to explain and control the multiple nanopores forming in the membrane. We prove that the membrane resistance can reflect the number of nanopores in the membrane and that the diameter of the nanopores is controlled by the exposure time and strength of the electric field. This controllable multiple nanopore formation via CBD avoids the utilization of complicated instruments and time-intensive manufacturing. We anticipate CBD has the potential to become a nanopore fabrication technique which, integrated into an optical setup, could be used as a high-throughput and multichannel characterization technique.

Hyperspectral imaging using the single-pixel Fourier transform technique

Hyperspectral imaging technology is playing an increasingly important role in the fields of food analysis, medicine and biotechnology. To improve the speed of operation and increase the light throughput in a compact equipment structure, a Fourier transform hyperspectral imaging system based on a single-pixel technique is proposed in this study. Compared with current imaging spectrometry approaches, the proposed system has a wider spectral range (400–1100 nm), a better spectral resolution (1 nm) and requires fewer measurement data (a sample rate of 6.25%). The performance of this system was verified by its application to the non-destructive testing of potatoes.

Miniband lasing in a 1D dual-periodic photonic crystal

In this letter, we demonstrate miniband lasing in a 1D dual-periodic photonic crystal (PC). The lasing efficiency is dramatically enhanced by about eight times and meanwhile the threshold is decreased to about 1/6 of that of the band-edge lasing in a single-periodic PC. This high optical conversion efficiency can be attributed to the extremely flat dispersion and large mode volume of the miniband induced by dual-periodicity. Numerical studies are presented to explain the mechanism of the spontaneous emission enhancement induced by the miniband, which are in good accord with our experiments. This finding may provide potential applications to low-threshold lasers and the semiconductor laser community.