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This paper reports on polyimide microfluidic devices fabricated by photolithography and a layer transfer lamination technology. The microchannels are sealed by laminating an uncured polyimide film on a partially cured layer and subsequent imidization. Selected areas of the microchannels were irradiated with heavy ions of several hundred MeV and the generated ion tracks are chemically etched to submicron pores of high aspect ratio. The ion beam parameters and the track etching conditions define density, length, diameter and shape of the pores. Membrane permeability and separation performance is demonstrated in cross-flow filtration experiments. The devices can be used for selective delivery or probing of fluids to biological tissue, e.g. drug delivery or microdialysis. For chip-based devices the filters can be used as a sample pre-treatment unit for filtration or concentration of particles or molecules.

We present a method to measure effective diffusion coefficients of fluorescently labeled molecules inside a nanofluidic system. Molecules with small diffusion coefficients show a larger lateral dispersion than highly diffusive species, which is counterintuitive. We performed measurements with wheat germ agglutinin proteins and obtained an effective diffusion coefficient which is four orders of magnitude lower than its free diffusion coefficient. Our technique which is a direct and relatively simple measurement of the effective diffusion coefficients inside nanochannels of well controlled dimensions could help fundamental studies in membranes and separation sciences.

Electrical measurement is a widely used technique for the characterization of nanofluidic devices. The electrical conductivity of electrolytes is known to be dependent on temperature. However, the similarity of the temperature sensitivity of the electrical conductivity for bulk and nanochannels has not been validated. In this work, we present the results from experimental measurements as well as analytical modeling that show the significant difference between bulk and nanoscale. The temperature sensitivity of the electrical conductance of nanochannel is higher at low ionic concentration where the nanofluidic transport is governed by the electrostatic effects from the wall. Neglecting this effect can result in significant errors for high temperature measurements. Additionally, the temperature sensitivity of the nanochannel conductance allows to measure the enthalpy change of surface reactions at low ionic concentrations.

We developed Al2O3/W heterogeneous nanopore arrays for field effect modulated nanofluidic diodes. They are fabricated by transferring self-organized nanopores of anodic aluminium oxide into a W thin film. The nanopores are ∼20 nm in diameter and 400 nm in length. After mild oxidation, approximately 10 nm WO3 grows on the surface of W, forming a conformal and dense dielectric layer. It allows the application of an electrical field through the surrounding W electrode to modulate the ionic transport across the entire membrane. Our experimental findings have potential applications in high throughput controlled delivery and electrostatic sorting of biomolecules.

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In this work, we report a nanofluidic gating mechanism that uses the thermal effect for modulating the ionic transport inside nanofluidic channels. The control of the ionic transport inside a nanochannel is demonstrated using electrical conductivity. A thermal gate controls the ionic transport more effectively than most of the other gating mechanisms previously described in the scientific literature. Gating in both bulk and overlapping electric double layer regimes can be obtained. The relatively short response time of opening and closing processes makes it a good candidate for manipulating small molecules in micro- and nanoscale devices.

We present a new fabrication method for solid-state nanoporous membranes based on sacrificial template structures made of silicon. The process consists of creating membranes by evaporating thin-films on sacrificial templates which, after their selective removal, opens the nanopores and releases the free-standing membranes. This way it is possible to define the geometry of the pore by design and to build the membrane by stacking thin-films of various materials through evaporation. Such a membrane with controlled porosity, pore geometry, thickness and nano-channel composition provides new opportunities for selective chemical functionalization, gating, electrical sensing or electrical stimulation inside the nanopore.