Measurement of the position-dependent electrophoretic force on DNA in a glass nanocapillary.

The electrophoretic force on a single DNA molecule inside a glass nanocapillary depends on the opening size and varies with the distance along the symmetrical axis of the nanocapillary. Using optical tweezers and DNA-coated beads, we measured the stalling forces and mapped the position-dependent force profiles acting on DNA inside nanocapillaries of different sizes. We showed that the stalling force is higher in nanocapillaries of smaller diameters.

ComEA is essential for the transfer of external DNA into the periplasm in naturally transformable Vibrio cholerae cells.

The DNA uptake of naturally competent bacteria has been attributed to the action of DNA uptake machineries resembling type IV pilus complexes. However, the protein(s) for pulling the DNA across the outer membrane of Gram-negative bacteria remain speculative. Here we show that the competence protein ComEA binds incoming DNA in the periplasm of naturally competent Vibrio cholerae cells thereby promoting DNA uptake, possibly through ratcheting and entropic forces associated with ComEA binding.

DNA translocation through low-noise glass nanopores.

The effect of electron irradiation-induced shrinking on glass nanocapillaries with diameters ranging from 75 to 14 nm was analyzed by measuring the conductance characteristics with and without DNA translocation. We have investigated nanocapillary shrinking with a scanning electron microscope from several perspectives to understand the geometry of the shrunken nanocapillary. On the basis of this observation, the conductance was modeled with respect to the nanocapillary diameter, which allowed reproducing the experimental results.

Lipid-coated nanocapillaries for DNA sensing.

We report a simple and efficient way to accomplish the chemical modification of glass nanopores by means of lipid self-assembly. Lipid coating improves the success rate of these glass nanopores as biosensors to detect λ-DNA.

Voltage-driven transport of ions and DNA through nanocapillaries.

We study the effect of salt concentration on the ionic conductance and translocation of single DNA molecules through nanocapillaries made out of quartz glass. DNA translocation experiments were performed in aqueous solution for concentrations of KCl between 10 mM and 2 M while ion conductance was characterized from 1 mM to 2 M KCl concentration. Here, we develop a model for the conductance of conical nanocapillaries taking into consideration the surface charge of the quartz glass.

Analyzing single DNA molecules by nanopore translocation.

Small holes in membranes or nanocapillaries can be employed to detect single molecules in solution. In fact, the resistive-pulse technique based on nanopores allows for determination of length, charge, and folding state of deoxyribonucleic acid (DNA). Here, we describe the experimental procedures necessary for measuring single DNA molecules in nanocapillaries.

Simple reconstitution of protein pores in nano lipid bilayers.

We developed a new, simple and robust approach for rapid screening of single molecule interactions with protein channels. Our glass nanopipets can be fabricated simply by drawing glass capillaries in a standard pipet puller, in a matter of minutes, and do not require further modification before use. Giant unilamellar vesicles break when in contact with the tip of the glass pipet and form a supported bilayer with typical seal resistances of ∼140 GΩ, which is stable for hours and at applied potentials up to 900 mV.

Measuring single small molecule binding via rupture forces of a split aptamer.

The rupture force of a split (bipartite) aptamer that forms binding pockets for adenosine monophosphate (AMP) was measured by atomic force spectroscopy. Changes in the rupture force were observed in the presence of AMP, while this effect was absent when mutant aptamers or inosine were used. Thus, changes in the rupture force were a direct consequence of specific binding of AMP to the split aptamer.

Detecting DNA folding with nanocapillaries.

We demonstrate for the first time the detection of the folding state of double-stranded DNA in nanocapillaries with the resistive pulse technique. We show that glass capillaries can be pulled into nanocapillaries with diameters down to 45 nm. We study translocation of lambda -DNA which is driven by an electrophoretic force through the nanocapillary.

Wavelength Dependence of Photoinduced Microcantilever Bending in the UV-VIS Range.

Micromechanical devices such as microcantilevers (MC) respond to irradiationwith light by at least two different, photon-mediated processes, which induce MC bendingas a consequence of differential surface stress. The first and slow bending is due to theabsorption of photons, whose energy is transformed into heat and causes bending ofbimetallic microcantilevers due to thermal expansion. The second type of deflection is fastand caused by photons of sufficient energy to promote electrons across the Schottky barrierand thus create charge carriers, resulting in photoinduced stress that causes MC bending.