Low temperature bonding of PMMA and COC microfluidic substrates using UV/ozone surface treatment

The use of UV/ozone surface treatments for achieving low temperature bonds between PMMA and COC microfluidic substrates is evaluated. Low temperature bond strengths, approaching those of native polymer substrates bonded above their glass transition temperatures, are demonstrated for both thermoplastics. To evaluate the effects of the UV/O(3) surface treatment on the operation of bonded microfluidic devices, the relationship between UV/O(3) exposure and polymer hydrophilicity and surface chemistry are measured. Post-treatment surface chemistry is evaluated by XPS (X-ray photoelectron spectroscopy) analysis, and the stability of the treated surfaces following solvent exposure is reported. Electroosmotic flow within fabricated microchannels with modified wall surfaces is also characterized. Overall, UV/O(3) treatment is found to enable strong low temperature bonds between thermoplastic microfluidic substrates using a simple, low cost, and high throughput fabrication technology.     

Single molecule measurements within individual membrane-bound ion channels using a polymer-based bilayer lipid membrane chip

The measurement of single poly(ethylene glycol) (PEG) molecules interacting with individual bilayer lipid membrane-bound ion channels is presented. Measurements were performed within a polymer microfluidic system including an open-well bilayer lipid membrane formation site, integrated Ag/AgCl reference electrodes for on-chip electrical measurements, and multiple microchannels for independent ion channel and analyte delivery. Details of chip fabrication, bilayer membrane formation, and alpha-hemolysin ion channel incorporation are discussed, and measurements of interactions between the membrane-bound ion channels and single PEG molecules are presented.     

Tiling R 5 by Crosses

An n-dimensional cross comprises 2n+1 unit cubes: the center cube and reflections in all its faces. It is well known that there is a tiling of R ⁿ by crosses for all n. AlBdaiwi and the first author proved that if 2n+1 is not a prime then there are $2^{\aleph_{0}}$ non-congruent regular (= face-to-face) tilings of R ⁿ by crosses, while there is a unique tiling of R ⁿ by crosses for n=2,3. They conjectured that this is always the case if 2n+1 is a prime. To support the conjecture we prove in this paper that also for R ⁵ there is a unique regular, and no non-regular, tiling by crosses. So there is a unique tiling of R ³ by crosses, there are $2^{\aleph_{0}}$ tilings of R ⁴, but for R ⁵ there is again only one tiling by crosses. We guess that this result goes against our intuition that suggests ‘the higher the dimension of the space, the more freedom we get’.