PDMS Microstructures Research Articles

Instant oxidation of closed microchannels

A new method for instant oxidation of closed, bonded microchannels is presented and evaluated. By placing the tip-formed electrode of a corona plasma equipment in the reservoir of a PDMS microstructure, the plasma spark can spread into the microchannel and oxidize the inner PDMS channel walls. By applying this process, the non-specific adsorption of hydrophobic affinity analytes is markedly decreased, here evaluated with the fluorescent dye Rhodamine B and standard protein BSA. The results show that the surface adsorption in plasma-treated channels is reduced significantly, e.g. the amount of BSA adsorbed at 35 mm distance from the reservoir is only 35% of the amount of BSA adsorbed in non-treated channels. The surface shows very low adsorption during the first 200 min after oxidation, and has recovered (90%) its hydrophobicity first after 24 h. This method of instant surface oxidation has in our group been widely used to simplify microfluidic studies of microstructure prototypes, since the need of other more complicated surface modifications to lower analyte adsorption is eliminated.

Stability-Enhanced Pixel Isolation Method for Flexible Liquid Crystal Displays

We proposed a new method of enhancing the stability of a liquid crystal (LC) mode for flexible display applications. In the device, LC molecules are isolated in pixels where LCs are surrounded by a microstructure produced by a stamping method with a durable elastomer such as poly(dimethylsiloxane) (PDMS). Two substrates are tightly attached by a solidified polymer layer produced by anisotropic phase separation from LC/polymer composites. The electrooptic characteristics of our sample are comparable to those of a normal sample without a PDMS microstructure. This method can be applicable to the fabrication of large plastic LCDs using a roll-to-roll process.

A Method for Precision Patterning of Silicone Elastomer and Its Applications

This paper presents a general microfabrication method for precision patterning of thin-film poly(dimethylsiloxane) (PDMS). The method enables PDMS microstructures with controlled lateral dimensions and thickness on a silicon or glass substrate. Two applications based on this new method are discussed. First, a scanning probe microscopy (SPM) probe with PDMS tip is developed and used for scanning probe contact printing (SPCP). Second, this paper demonstrates surface micromachined membranes with integrated silicone gaskets.

Poly(dimethylsiloxane) microchip: microchannel with integrated open electrospray tip.

A polymer microchip with an open tip for electrospray mass spectrometry is presented. The tip consists of a groove with parallel walls where a droplet can form at the end surface. A lid covers the whole chip except at the microchannel tip, which is left open. Poly(dimethylsiloxane) (PDMS) microchips were cast using a nickel mould which in turn was replicated from a dry etched silicon wafer. Tips with microchannel widths of around 50 microm could easily be replicated. Since the tip had no cover, the assembly of microchip and cover was simplified. A total ion current variation of 5% during 300 s was achieved for a 1 microM myoglobin solution. The non-complex design of the cover makes it suitable for versatile tests of chip prototypes. The nickel mould was found to be useful for PDMS microstructure fabrication. Also, such a robust mould allows casting electrospray tips in more rigid thermoset materials.

Elastomer-glass micropump employing active throttles.

We report a reciprocating microfluidic pump, the Micro Throttle Pump (MTP), constructed in a relatively uncomplicated manner from glass and microstructured poly(dimethylsiloxane)(PDMS). Unconventionally, the MTP employs throttling of fluid flow as distinct from fully-closing valve structures. Accordingly, this technique offers the prospect of solid-phase suspension tolerance. The reported MTP employs piezoelectrically (PZT) actuated deformation of flow constrictions (throttles) fabricated from PDMS at the two ports of a central, PZT actuated pump chamber. By appropriate time-sequencing of the individual PZTs' actuation, pumping can be induced in either direction. PDMS' elasticity further facilitates throttle operation by virtue of allowing significant PZT flexure that is substantially independent of the underlying PDMS microstructure. In contrast, in a rigid substrate such as silicon, deformation is constrained to where underlying microstructured cavities exist and this restricts design options. We describe the construction and performance of a prototype MTP capable of pumping 300 microl min(-1) or alternatively generating a back-pressure of 5.5 kPa. Preliminary modelling of MTP operation is also presented.

Microfluidic devices fabricated in poly(dimethylsiloxane) for biological studies.

This review describes microfluidic systems in poly(dimethylsiloxane) (PDMS) for biological studies. Properties of PDMS that make it a suitable platform for miniaturized biological studies, techniques for fabricating PDMS microstructures, and methods for controlling fluid flow in microchannels are discussed. Biological procedures that have been miniaturized into PDMS-based microdevices include immunoassays, separation of proteins and DNA, sorting and manipulation of cells, studies of cells in microchannels exposed to laminar flows of fluids, and large-scale, combinatorial screening. The review emphasizes the advantages of miniaturization for biological analysis, such as efficiency of the device and special insights into cell biology.

Rapid prototyping of glass and PDMS microstructures for micro total analytical systems and micro chemical reactors by microfabrication in the general laboratory

A method is presented that permits the microfabrication of glass chips for micro total analytical systems and micro chemical reactors in the general laboratory. The method does not require any specialist facilities, and for the first time provides a reliable and reproducible method for fabricating such devices without access to a clean room. The predictability of the process is achieved by utilising commercially available starting materials.