Daming Zhou

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.

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.

Improvement of low-field magnetoresistance and Curie temperature in the hole doping of double perovskites Sr2FeMoO6 polycrystals

Polycrystalline Sr2FeMoO6 compounds with most vacancies at normal Fe sites were fabricated through Mo hole doping; its effect is similar to Fe3+ by our estimation. Sharp increase of magnetoconductance at low field was evidence of spin-polarized tunneling between the grains. The room temperature low-field magnetoresistivity at optimal doping x=0.03 is 8.5% in 3000Oe and increases to 11.4% in 1T associated with soft magnetic behaviors; furthermore it exhibits a ferromagnetic Curie temperature of 450K, connected with hole doping effect. The improved magnetoresistivity behavior was related to Curie temperature.

Assessment of physiological responses and growth phases of different microalgae under environmental changes by Raman spectroscopy with chemometrics

The assessment for cell physiology and growth phases of microalgae plays important roles in ecological and environmental fields since it can be used to forecast water eutrophication level worldwidely. Herein, growth phases and environmental conditions of microalgae were assessed by combining resonance Raman mapping spectroscopy with multivariate analysis methods. And, primary Raman characteristic peaks of microalgae were mined with two-dimensional synchronous spectra. Thereafter, algal growth phases and environmental conditions of microalgae were preliminary classified with different tendencies of characteristic Raman peaks by unsupervised principal component analysis (PCA) and support vector machine (SVM) methods. Our results demonstrated that resonance Raman mapping spectroscopy with PCA and SVM classification models can be used to assess algal growth phases and preliminary predict environmental conditions with characteristic Raman spectra of microalgae in water bodies.

Solid-state nanopores fabricated by pulse-controlled dielectric breakdown

This article describes a promising technique to fabricate individual solid-state nanopores directly on dielectric membranes by using adjustable pulses controlled dielectric breakdown in electrolyte. The pulse parameters are adjustable with the running of fabrication process, which is suitable for various thickness and material of the membrane and control precision with sub-nanometer. Moreover, double-stranded DNA translocations through the reliable nanopores fabricated in this manner were successfully demonstrated, exhibiting excellent electrical signals and long DNA translocation times with high signal-to-noise ratio. This economical and timesaving method shows enormous promise for the manufacturing of future nanopore-based technologies and lays the foundation for future research in the field of single molecule detection.

A microfluidic chip for terahertz spectral detection

Fluidic chips as sample storage devices have been widely used to control and analyze traces of solutions by terahertz time domain spectroscopy (THz-TDS). This paper presents a fluidic chip fabricated with ultra-thick micro-fluidic structures utilizing SU-8 photoresist for THz spectral detection. The chip consists of 2 pieces of quartz windows and a photoresist structure serves as liquid cell between the windows. In order to reduce the attenuation of THz energy by the windows and guarantee measurement stability, an infrared quartz with thickness of 1mm is adopted as the windows. For the purpose of improving the signal-to-noise ratio (SNR) in the frequency band between 1.0 THz-1.5 THz, and making the liquid film thickness match the THz optical path, the structure depth is designed to be 50μm. Water absorption coefficient at 0.1THz-1.5THz was detected with this chip. The result indicates that the chip has a good stability for terahertz spectral detection.