Orion Scott

DNA analysis using an integrated microchip for multiplex PCR amplification and electrophoresis for reference samples.

A system that automatically performs the PCR amplification and microchip electrophoretic (ME) separation for rapid forensic short tandem repeat (STR) forensic profiling in a single disposable plastic chip is demonstrated. The microchip subassays were optimized to deliver results comparable to conventional benchtop methods. The microchip process was accomplished in sub-90 min compared with >2.5 h for the conventional approach. An infrared laser with a noncontact temperature sensing system was optimized for a 45 min PCR compared with the conventional 90 min amplification time. The separation conditions were optimized using LPA-co-dihexylacrylamide block copolymers specifically designed for microchip separations to achieve accurate DNA size calling in an effective length of 7 cm in a plastic microchip. This effective separation length is less than half of other reports for integrated STR analysis and allows a compact, inexpensive microchip design. This separation quality was maintained when integrated with microchip PCR. Thirty samples were analyzed conventionally and then compared with data generated by the microfluidic chip system. The microfluidic system allele calling was 100% concordant with the conventional process. This study also investigated allelic ladder consistency over time. The PCR-ME genetic profiles were analyzed using binning palettes generated from two sets of allelic ladders run three and six months apart. Using these binning palettes, no allele calling errors were detected in the 30 samples demonstrating that a microfluidic platform can be highly consistent over long periods of time.

Fracture of nanoscale copper films on elastomer substrates

This letter describes the evolution of crack spacing in copper films (bonded to elastomer substrates) as a function of applied strain. Tension tests were conducted on cast poly(dimethylsiloxane) substrates coated with sputtered copper films with 200–600 nm thickness. Optical microscopy was used to measure the spacings between parallel cracks (normal to the tension direction) at various levels of applied strain in the range of 0.01%–10%. The measured relationships between applied strain and crack spacing are predicted by micromechanical models of behavior between cracks; the experiments indicate Gc∼400–600 J/m2 with an implied defect spacing of ∼100–600 μm. These values are consistent with the theoretical work that is dissipated during necking instabilities during plastic deformation.This letter describes the evolution of crack spacing in copper films (bonded to elastomer substrates) as a function of applied strain. Tension tests were conducted on cast poly(dimethylsiloxane) substrates coated with sputtered copper films with 200–600 nm thickness. Optical microscopy was used to measure the spacings between parallel cracks (normal to the tension direction) at various levels of applied strain in the range of 0.01%–10%. The measured relationships between applied strain and crack spacing are predicted by micromechanical models of behavior between cracks; the experiments indicate Gc∼400–600 J/m2 with an implied defect spacing of ∼100–600 μm. These values are consistent with the theoretical work that is dissipated during necking instabilities during plastic deformation.

Elastomer membrane actuators utilizing ultrathin metal electrodes

We prepare a thin (~100 μm) silicone-based elastomer membrane and sputter ultra-thin copper electrodes (16-192 nm) onto each side of the film. Voltages of varying magnitude (1-8 kV) are applied to the electrodes causing an electrostatic pressure to develop which then compresses the elastomer in the through thickness direction. The edges of the membrane are constrained against in-plane expansion, forcing the membrane to deform out of plane. The in-plane strains developed by applying an electric field are characterized by measuring the stiffness of the membrane via indentation at different applied voltages. Closed-form solutions for membrane deflection are used with the experimental measurements to determine the relationship between the modulus of the cracked electrode/elastomer multi-layer and the electrically induced in-plane strain. Analytical models predicting the relationship between electrode crack spacing, layer properties, and effective modulus of the multi-layer are presented. Building on the knowledge gained from the membrane experiments, uni- axial tension specimens of an electrode/elastomer multi-layer are tested and preliminary results discussed.