Nanofluidics

Jan Eijkel is Associate Professor in microfluidics and nanofluidics in the BIOS/Lab on a Chip group (MESA+ Institute for Nanotechnology, University of Twente, The Netherlands). He studied pharmacy (University of Amsterdam) and theology (University of Utrecht) and obtained a Ph.D. in biosensor research at the University of Twente. His research interests include physical and colloid chemistry, electrochemistry, microseparation methods, and microplasma physics and applications. Geen abstract beschikbaa

Contactless angle detection using permalloy

An overview is given of measurements on angle detectors. The detectors consist of a pair of planar-Hall elements opposite to a rotatable magnet. The measurements are performed on a number of planar-Hall elements of different shape and size, and show good agreement with a previously described theoretical mode. To increase the accuracy of the angle detector, three modifications of the original concept of the planar-Hall elements are treated: a ring-shaped element having increased output voltage; an optimized configuration of a pair of planar-Hall elements and a permanent magnet, to cancel out the effects of magnetic anisotropy in the permalloy on the accuracy of the angle detector; and an annealing step at 500 degrees C applied to the permalloy to create a magnetically isotropic film. The results of measurements on planar-Hall elements as suggested in modifications are presented and show good agreement with theory

Detection of protein concentrations using a pH-step titration method

A stimulus-response method based on the application of a pH step is proposed for the detection of protein immobilized in a membrane on top of an ion-sensitive field-effect transistor (ISFET). The ISFET response to a step-wise change in pH, applied at the interface between the membrane and the surrounding solution, depends on the concentration of protein immobilized in the membrane because proton-dissociation reactions of the protein cause a delayed diffusion of protons and hydroxyl ions through the membrane. Our theoretical description shows that the delay in ISFET response is linearly related to the concentration of protein immobilized in the membrane. Experiments performed with lysozyme as a model protein show the feasibility of this detection principle

ISFET responses on a stepwise change in electrolyte concentration at constant pH

Responses on a stepwise increase of the electrolyte concentration of bare ISFETs can interfere with responses of an ISFET with an affinity membrane deposited on the gate. In this paper the responses of bare ISFETs are studied. Results of experiments and simulations are presented and the mechanism is explained

A novel description of ISFET sensitivity with the buffer capacity and double-layer capacitance as key parameters

The pH sensitivity of ISFETs arises from interactions of protons with ISFET gate surface sites. This sensitivity is described by a new simpler model with the intrinsic buffer capacity and the differential capacitance as key parameters. The obtained expression is independent of the models used for the chemical surface equilibria and the charge profile in the solution. The general expression for the sensitivity is elaborated using the site-binding theory and the Gouy-Chapman-Stern theory. The relatively high sensitivity of Ta2O5 ISFETs is explained using this elaborated theory. It is shown that the electrolyte concentration has almost no influence on the sensitivity of Ta2O5 ISFETs

Transport in nanofluidic systems: a review of theory and applications

In this paper transport through nanochannels is assessed, both of liquids and of dissolved molecules or ions. First, we review principles of transport at the nanoscale, which will involve the identification of important length scales where transitions in behavior occur. We also present several important consequences that a high surface-to-volume ratio has for transport. We review liquid slip, chemical equilibria between solution and wall molecules, molecular adsorption to the channel walls and wall surface roughness. We also identify recent developments and trends in the field of nanofluidics, mention key differences with microfluidic transport and review applications. Novel opportunities are emphasized, made possible by the unique behavior of liquids at the nanoscale

Do Firms Sell Forward for Strategic Reasons? An Application to the Wholesale Market for Natural Gas

Building on a model of the interaction of risk-averse firms that compete in forward and spot markets, we develop an empirical strategy to test whether oligopolistic firms use forward contracts for strategic motives, for risk-hedging, or for both. An increase in the number of players weakens the incentives to sell forward for risk-hedging reasons. However, if strategic motives are also relevant, then an increase in the number of players strengthens the incentives to sell forward. This difference provides the analyst with a way to identify whether strategic considerations are important at motivating firms to sell forward. Using data from the Dutch wholesale market for natural gas where we observe the number of players, spot and forward sales, and churn rates, we find evidence that strategic reasons play an important role at explaining the observed firms’ (inverse) hedge ratios. In addition, the data lend support to the existence of a learning effect by wholesalers.market power, risk-hedging, forward contracts, spot market, over-the-counter trade, market transparency, churn rates