Biomedical subjects

Robert Riehn

Publications and source records attributed to Robert Riehn.

7 recordsLinked to original sources

PubMed2006

Wetting micro- and nanofluidic devices using supercritical water.

We describe a method for wetting micro- and nanofluidic devices with water or any other pure liquid. The process is performed by enclosing the fluidic device in a liquid-filled cell, heating the cell to a temperature above the critical point of the liquid, and subsequent cooling of the cell to room temperature. Because the process liquid is essentially a gas during wetting, arbitrary shapes can be wetted. We demonstrate wetting of micro- and nanostructures in a fused-silica device with only a single inlet. The process is low-cost, fast, safe, and very reliable.

Microfluidic Analytical Techniques↗

PubMed2006

In vivo and scanning electron microscopy imaging of up-converting nanophosphors in Caenorhabditis elegans.

We show here that upconversion phosphors can be imaged both by infrared excitation and in a scanning electron microscope. We have synthesized and characterized for this work up-converting phosphor nanoparticles nonaggregated nanocrystals of size range 50-200 nm. We have investigated the optical properties of 50-200 nm nanoparticles and found a square dependence of the emitted visible fluorescence on the infrared excitation and verified that under electron excitation similar narrow band emission spectra can be obtained as is seen with IR upconversion. The viability of the nanoparticles for biological imaging was confirmed by imaging the digestive system of the nematode worm Caenorhabditis elegans, and we have confirmed using energy-dispersive X-ray analysis that the up-conversion nanoparticles can be identified in a scanning electron microscope at high spatial resolution.

Animals↗

PubMed2006

A nanofluidic railroad switch for DNA.

We present a metamaterial consisting of a two-dimensional, asymmetric lattice of crossed nanochannels in fused silica, with channel diameters of 80 nm to 140 nm. When DNA is introduced, it is stretched and linearized. We show that the asymmetry in channel dimensions gives rise to a preferred direction for DNA orientation and a preferred direction for transport under dc electrophoresis. Interestingly, the preferred axis of orientation and transport can be switched by 90 degrees through application of an ac voltage. We explain the results in terms of an energy landscape for polyelectrolytes that consists of entropic and dielectrophoretic contributions and whose strength and sign can be tuned by changing the ac field strength.

DNA↗

PubMed2005

Restriction mapping in nanofluidic devices.

We have performed restriction mapping of DNA molecules using restriction endonucleases in nanochannels with diameters of 100-200 nm. The location of the restriction reaction within the device is controlled by electrophoresis and diffusion of Mg2+ and EDTA. We have successfully used the restriction enzymes SmaI, SacI, and PacI, and have been able to measure the positions of restriction sites with a precision of approximately 1.5 kbp in 1 min using single DNA molecules.

DNA↗

PubMed2005

Statics and dynamics of single DNA molecules confined in nanochannels.

The successful design of nanofluidic devices for the manipulation of biopolymers requires an understanding of how the predictions of soft condensed matter physics scale with device dimensions. Here we present measurements of DNA extended in nanochannels and show that below a critical width roughly twice the persistence length there is a crossover in the polymer physics.

Bacteriophage lambda↗

PubMed2004

From the Cover: The dynamics of genomic-length DNA molecules in 100-nm channels.

We show that genomic-length DNA molecules imaged in nanochannels have an extension along the channel that scales linearly with the contour length of the polymer, in agreement with the scaling arguments developed by de Gennes for self-avoiding confined polymers. This fundamental relationship allows us to measure directly the contour length of single DNA molecules confined in the channels, and the statistical analysis of the dynamics of the polymer in the nanochannel allows us to compute the SD of the mean of the extension. This statistical analysis allows us to measure the extension of lambda DNA multimers with a 130-nm SD in 1 min.

DNA↗

PubMed2004

Fabrication of conjugated polymers nanostructures via direct near-field optical lithography.

We report our investigations into the fabrication of nanostructures of poly(p-phenylene vinylene) via direct scanning near-field lithography of its soluble precursor. Our technique is based on the spatially selective inhibition of the precursor solubility by exposure to the ultraviolet optical field present at the apex of commercially available, Au-coated near-field probes with aperture diameters between 40 and 80 nm (+/-5 nm). After development in methanol and thermal conversion under vacuum we obtain features with a minimum dimension of 160 nm. We analyse our results via tapping-mode atomic force microscopy, and find a clear phase contrast between the core and the centre of the lithographed features, corroborating the hypothesis that hard, fully insolubilised regions are surrounded by a gel-like phase, which we estimate of the order of 110-130 nm for the smallest features, by comparing our experiments with simulations carried out using a Bethe-Bouwkamp model. Use of such model also allows us to discuss the influence of probe size, tip-sample distance, and film thickness on the resolution of the lithographic process. We demonstrate the use of the technique for the direct writing of two-dimensional periodic structures with intentional defects and a periodicity relevant to applications in the visible range.

Journal Article↗