Jan William van Nieuwkasteele

Field-Dependent DNA Mobility in 20 nm High Nanoslits.

The transport behavior of lambda-DNA (48 kbp) in fused silica nanoslits is investigated upon application of electrical fields of different strengths. The slit dimensions are 20 nm in height, 3 microm in width, and 500 microm in length. With fields of 30 kV/m or below, the molecules move fluently through the slits, while at higher electrical fields, the DNA molecules move intermittently, resulting in a strongly reduced mobility. We propose that the behavior can be explained by mechanical and/or field-induced dielectrophoretic DNA trapping due to the surface roughness in the nanoslits. The observation of preferential pathways and trapping sites of the lambda-DNA molecules through the nanoslits supports this hypothesis and indicates that the classical viscous friction models to explain the DNA movement in nanoslits needs to be modified to include these effects. Preliminary experiments with the smaller XbaI-digested litmus-DNA (2.8 kbp) show that the behavior is size-dependent, suggesting that the high field electrophoresis in nanoslits can be used for DNA separation.

Electrokinetic DNA transport in 20nm-high nanoslits: Evidence for movement through a wall-adsorbed polymer nanogel

The electrokinetic transport behavior of λ‐DNA (48 kbp) in 20 nm‐high fused‐silica nanoslits in the presence of short‐chain PVP is investigated. Mobility and video data show a number of phenomena that are typical of DNA transport through gels or polymer solutions, thus indicative of rigid migration obstacles in the DNA pathway. Calculations show that a several nanometer thin layer of wall‐adsorbed PVP (‘nano‐gel’) can provide such a rigid obstacle matrix to the DNA. Such ultrathin wall‐adsorbed polymer layers represent a new type of matrix for electrokinetic DNA separation.

In situ surface-enhanced raman spectroelectrochemical analysis system with a hemin modified nanostructured gold surface

An integrated surface-enhanced Raman scattering (SERS) spectroelectrochemical (SEC) analysis system is presented that combines a small volume microfluidic sample chamber (<100 μL) with a compact three-electrode configuration for in situ surface-enhanced Raman spectroelectrochemistry. The SEC system includes a nanostructured Au surface that serves dual roles as the electrochemical working electrode (WE) and SERS substrate, a microfabricated Pt counter electrode (CE), and an external Ag/AgCl reference electrode (RE). The nanostructured Au WE enables highly sensitive in situ SERS spectroscopy through large and reproducible SERS enhancements, which eliminates the need for resonant wavelength matching of the laser excitation source with the electronic absorption of the target molecule. The new SEC analysis system has the merits of wide applicability to target molecules, small sample volume, and a low detection limit. We demonstrate in situ SERS spectroelectrochemistry measurements of the metalloporphyrin hemin showing shifts of the iron oxidation marker band ν4 with the nanostructured Au working electrode under precise potential control.

Spatial Site-Patterning of Wettability in a Microcapillary Tube

Substrate functionalization is of great importance in successfully manipulating flows and liquid interfaces in microdevices. Herein, we propose an alternative approach for spatial patterning of wettability in a microcapillary tube. The method combines a photolithography process with self-assembled monolayer formation. The modified microcapillaries show very sharp boundaries between the alternating hydrophilic/hydrophobic segments with an achieved smallest domain dimension down to 60 μm inside a 580 μm inner diameter capillary. Our two-step method allows us to pattern multiple types of functional groups in an enclosed channel. Such structures are promising regarding the manipulation of segmented flows inside capillaries.

Design of turbulent tangential micro-mixers that mix liquids on the nanosecond time scale

Unravelling (bio)chemical reaction mechanisms and macromolecular folding pathways on the (sub)microsecond time scale is limited by the time resolution of kinetic instruments for mixing reactants and observation of the progress of the reaction. To improve the mixing time resolution, turbulent four- and two-jet tangential micro-mixers were designed and characterized for their mixing and (unwanted) premixing performances employing acid-base reactions monitored by a pH-sensitive fluorescent dye. The mixing performances of the micro-mixers were determined after the mixing chamber in a free-flowing jet. The premixing behavior in the vortex chamber was assessed in an optically transparent glass-silicon replica of a previously well-characterized stainless-steel four-jet tangential micro-mixer. At the highest flow rates, complete mixing was achieved in 160ns with only approximately 9% premixing of the reactants. The mixing time of 160ns is at least 50 times shorter than estimated for other fast mixing devices. Key aspects to the design of ultrafast turbulent micro-mixers are discussed. The integration of these micro-mixers with an optical flow cell would enable the study of the very onset of chemical reactions in general and of enzyme catalytic reactions in particular.

Nanosensing platforms: physics, technology, and applications

Novel nanotextured Au surfaces are presented with periodically self-aligned nanopyramid structures with precisely defined pitch that are closely packed with 2 nm separation gaps over large areas and form high-density (~1 km cm-2) arrays of hot-spot scattering sites ideally suited for surface-enhanced Raman scattering (SERS) and Raman spectroscopy. Average Raman enhancement factors from physically adsorbed rhodamine 6G on patterned Au surfaces resulted in EF~106. The Raman average EF has been characterized over large areas using benzenethiol monolayers chemisorbed on the Au nanopyramid surfaces. From the 1074 cm-1 ring mode of BT on surfaces with 200 nm pitch the EF=(0.8±0.04)×106, and for surfaces with 500 nm pitch the EF=(0.32±0.01)×107 from over 99% of the imaged area. Maximum EF>108 have been measured in both cases.