Wouter Sparreboom

Principles and applications of nanofluidic transport

The evolution from microfluidic to nanofluidic systems has been accompanied by the emergence of new fluid phenomena and the potential for new nanofluidic devices. This review provides an introduction to the theory of nanofluidic transport, focusing on the various forces that influence the movement of both solvents and solutes through nanochannels, and reviews the applications of nanofluidic devices in separation science and energy conversion.

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.

Rapid sacrificial layer etching for the fabrication of nanochannels with integrated metal electrodes

We present a rapid etch method to surface-micromachine nanochannels with integrated noble metal electrodes using a single metal sacrificial layer. The method is based on the galvanic coupling of a chromium sacrificial layer with gold electrodes, which results in a 10-fold increase in etch rate with respect to conventional single metal etching. The etch process is investigated and characterized by optical and electrochemical measurements, leading to a theoretical explanation of the observed etch rate based on mass transport. Using this explanation we derive some generic design rules for nanochannel fabrication employing sacrificial metal etching.

Rapid microfluidic solid-phase extraction system for hyper-methylated DNA enrichment and epigenetic analysis

Genetic sequence and hyper-methylation profile information from the promoter regions of tumor suppressor genes are important for cancer disease investigation. Since hyper-methylated DNA (hm-DNA) is typically present in ultra-low concentrations in biological samples, such as stool, urine, and saliva, sample enrichment and amplification is typically required before detection. We present a rapid microfluidic solid phase extraction (μSPE) system for the capture and elution of low concentrations of hm-DNA (≤1 ng ml(-1)), based on a protein-DNA capture surface, into small volumes using a passive microfluidic lab-on-a-chip platform. All assay steps have been qualitatively characterized using a real-time surface plasmon resonance (SPR) biosensor, and quantitatively characterized using fluorescence spectroscopy. The hm-DNA capture/elution process requires less than 5 min with an efficiency of 71% using a 25 μl elution volume and 92% efficiency using a 100 μl elution volume.

High yield DNA fragmentation using cyclical hydrodynamic shearing

We report a new DNA fragmentation technique that significantly simplifies conventional hydrodynamic shearing fragmentation by eliminating the need for sample recirculation while maintaining high fragmentation yield and low fragment length variation, and therefore, reduces instrument complexity and cost, increases fragmentation throughput and is well suited for integration in a lab-on-a-chip platform. The new DNA shearing technique is realized in a microfluidic lab on a chip (LOC) consisting of a chain of series-connected constriction channels that are each separated by a long spacer channel with much larger cross-sectional area. A sample injected to the microfluidic structure undergoes multiple acceleration-deceleration cycles at each constriction channel where the fluid induces strain to the DNA molecules necessary to induce the double chain scission fragmentation, which has a similar effect as multiple recirculation cycles. Experimental results show that the new fragmentation technique improves the fragmentation yield of genomic DNA from 10% for single constriction channels up to 90% for multiple series connected constriction channels.

Frequency dependent AC electroosmotic flow in nanochannels

We report frequency-dependent bidirectional AC electroosmotic flow (AC-EOF) in a nanochannel with double layer overlap. This work follows our report in μTas 2008 of unidirectional AC-EOF in nanochannels [1]. Observed is a bidirectional pumping behavior; simulations of the low frequency pumping confirm a direction opposite to that of AC-EOF in microchannels. By this frequency-dependent bidirectional pumping, nanochannel AC-EOF behaves in fundamentally different way than microchannel AC-EOF. Generally, the results are of importance for the understanding of ion and liquid transport in nanoconfinement.

Nanofluidics: Fundamentals and applications

The paper gives a brief overview of nanofluidic theory, with an emphasis on transport processes in nanochannels. It subsequently reports on recent progress in nanofluidic research in the BIOS/Lab-on-a-Chip group, especially DNA electrophoresis in 20-nm high nanoslits, AC electroosmotic flow in nanochannels, and two-phase flow in nano/microfluidic devices.