Polydimethylsiloxane (PDMS) elastomers are extensively used for soft lithographic replication of microstructures in microfluidic and micro-engineering applications. Elastomeric microstructures are commonly required to fulfil an explicit mechanical role and accordingly their mechanical properties can critically affect device performance. The mechanical properties of elastomers are known to vary with both curing and operational temperatures. However, even for the elastomer most commonly employed in microfluidic applications, Sylgard 184, only a very limited range of data exists regarding the variation in mechanical properties of bulk PDMS with curing temperature. We report an investigation of the variation in the mechanical properties of bulk Sylgard 184 with curing temperature, over the range 25 °C to 200 °C. PDMS samples for tensile and compressive testing were fabricated according to ASTM standards. Data obtained indicates variation in mechanical properties due to curing temperature for Young's modulus of 1.32–2.97 MPa, ultimate tensile strength of 3.51–7.65 MPa, compressive modulus of 117.8–186.9 MPa and ultimate compressive strength of 28.4–51.7 GPa in a range up to 40% strain and hardness of 44–54 ShA.

Accepted/In press). Fully integrated digital microfluidics platform for automated immunoassay; a versatile tool for rapid, specific detection of a wide range of pathogens.

We report a Micro Throttle Pump (MTP) which has been shown to pump 5 microm diameter polystyrene beads at a concentration of 4.5 x 10(7) beads ml(-1). This new MTP design is constructed in a straightforward manner and actuated by a single piezoelectric (PZT) element. Maximum flow rates at 800 Hz drive frequency of 132 microl min(-1) with water and 108 microl min(-1) with a bead suspension were obtained. Maximum back-pressures of 6 kPa were observed in both cases. The reported MTP employs specific location of distinct internal microfluid structures cast in a single compliant elastomeric substrate to exploit the opposing directions of flexure of regions of a piezoelectric-glass composite bonded to the elastomer. By this novel means, distinct flexural regions, exhibiting compressive and tensile stresses respectively, allow both the pump's integrated input and output throttles and its pump chamber to be actuated concurrently by a single PZT. To support MTP design we also report the characterisation of an individual throttle's resistance as a function of actuator deflection and discuss the underlying mechanism of the throttling effect.

We report a micro throttle pump (MTP) with enhanced throttling resulting from beneficial deformation of its elastomer substrate. In the MTP reported, this has doubled the effective deflection of the piezo electric (PZT) actuator with a consequent five-fold enhancement of throttling ratio. This mode of throttling has been modelled by finite element method and computational fluid dynamic techniques whose predictions agreed well with experimental data from a throttle test structure; providing typical throttling ratios of 8:1 at low pressures. The improved throttles have been incorporated in a prototype, single PZT, MTP, fabricated with double-depth microfluidics, which pumped both water and a suspension of 5 µm polystyrene beads at a maximum flow rate of 630 µl min−1 and a maximum back-pressure of 30 kPa at a pumping frequency of 1.1 kHz. This represents an approximate five-fold enhancement of both performance metrics compared to our previous single PZT device.

Rapid, selective particle separation and concentration within the bacterial size range (1-3 lm) in clinical or environmental samples promises significant improvements in detection of pathogenic microorganisms in areas including diagnostics and bio-defence. It has been proposed that microfluidic Dean flow-based separation might offer simple, efficient sample clean-up: separation of larger, bioassay contaminants to prepare bioassay targets including spores, viruses and proteins. However, reports are limited to focusing spherical particles with diameters of 5 lm or above. To evaluate Dean flow separation for (1-3 lm) range samples, we employ a 20 lm width and depth, spiral microchannel. We demonstrate focusing, separation and concentration of particles with closely spaced diameters of 2.1 and 3.2 lm, significantly smaller than previously reported as separated in Dean flow devices. The smallest target, represented by 1.0 lm particles, is not focused due to the high pressures associated with focussing particles of this size; however, it is cleaned of 93 % of 3.2 lm and 87 % of 2.1 lm microparticles. Concentration increases approaching 3.5 times, close to the maximum, were obtained for 3.2 lm particles at a flow rate of 10 ll min -1 . Increasing concentration degraded separation, commencing at significantly lower concentrations than previously predicted, particularly for particles on the limit of being focused. It was demonstrated that flow separation specificity can be fine-tuned by adjustment of output pressure differentials, improving separation of closely spaced particle sizes. We conclude that Dean flow separation techniques can be effectively applied to sample clean-up within this significant microorganism size range.