2D Colloidal Crystals with Anisotropic Impurities.

We report a study of 2D colloidal crystals with anisotropic ellipsoid impurities using video microscopy. It is found that at low impurity densities, the impurity particles behave like floating disorder with which the quasi-long-range orientational order survives and the elasticity of the system is actually enhanced. There is a critical impurity density above which the 2D crystal loses the quasi-long-range orientational order.

2D isotropic-nematic transition in colloidal suspensions of ellipsoids.

Liquid crystals are important condensed matter systems for technological applications, as well as for fundamental studies. An important unresolved issue is the nature of the phase transition in a two-dimensional (2D) liquid crystal system. In contrast to numerous computational studies reported in the last few decades, there have been no convincing experiments to verify these numerical results.

Dynamical processes of interstitial diffusion in a two-dimensional colloidal crystal.

In two-dimensional (2D) solids, point defects, i.e., vacancies and interstitials, are bound states of topological defects of edge dislocations and disclinations.

Rapid fabrication of solid-state nanopores with high reproducibility over a large area using a helium ion microscope.

The fabrication of solid-state nanopores in an insulating membrane has attracted much attention for biomolecule analysis such as DNA sequencing and detection in recent years. For practical applications and device integration, the challenges include precise size control for sub 10 nm nanopores, excellent repeatability and rapid fabrication over a large area to reduce the cost for mass production. A helium ion beam could provide an effective fabrication approach to produce such solid-state nanopores.

On the distribution of DNA translocation times in solid-state nanopores: an analysis using Schrödinger's first-passage-time theory.

In this short paper, a correction is made to the recently proposed solution of Li and Talaga to a 1D biased diffusion model for linear DNA translocation, and a new analysis will be given to their data. It was pointed out by us recently that this 1D linear translocation model is equivalent to the one that was considered by Schrödinger for the Ehrenhaft–Millikan measurements on electron charge. Here, we apply Schrödinger’s first-passage-time distribution formula to the data set in Li and Talaga.

Detection of DNA hybridizations using solid-state nanopores.

We report an experimental study of using DNA translocation through solid-state nanopores to detect the sequential arrangement of two double-stranded 12-mer hybridization segments on a single-stranded DNA molecule. The sample DNA is a trimer molecule formed by hybridizing three single-stranded oligonucleotides. A polystyrene bead is attached to the end of the trimer DNA, providing a mechanism in slowing down the translocation and suppressing the thermal diffusion, thereby allowing the detection of short features of DNA by standard patch-clamp electronics.

Reverse DNA translocation through a solid-state nanopore by magnetic tweezers.

Voltage-driven DNA translocation through nanopores has attracted wide interest for many potential applications in molecular biology and biotechnology. However, it is intrinsically difficult to control the DNA motion in standard DNA translocation processes in which a strong electric field is required in drawing DNA into the pore, but it also leads to uncontrollable fast DNA translocation. Here we explore a new type of DNA translocation.

The potential and challenges of nanopore sequencing.

A nanopore-based device provides single-molecule detection and analytical capabilities that are achieved by electrophoretically driving molecules in solution through a nano-scale pore. The nanopore provides a highly confined space within which single nucleic acid polymers can be analyzed at high throughput by one of a variety of means, and the perfect processivity that can be enforced in a narrow pore ensures that the native order of the nucleobases in a polynucleotide is reflected in the sequence of signals that is detected. Kilobase length polymers (single-stranded genomic DNA or RNA) or small molecules (e.

Statics and dynamics of 2D colloidal crystals in a random pinning potential.

We report the first experimental study of a model system of a two-dimensional colloidal crystal in a random pinning potential. The colloidal crystal consists of monodispersed charged polystyrene microspheres suspended in deionized aqueous media and confined near a rough charged surface. It is found that the static orientational correlation function g6(r) decays exponentially for intermediate and strong pinning, in agreement with theories.

Lithography-free formation of nanopores in plastic membranes using laser heating.

Synthetic nanopores are a new class of single-molecule sensors capable of electronically detecting, counting, and characterizing biomolecules. There have been studies of nanopore formation in solid-state materials. This paper reports a novel lithography-free method of nanopore formation in plastic membranes fluidized using laser heating.