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.

Flocculation is a key purification step in cell-based processes for the food and pharmaceutical industry where the removal of cells and cellular debris is aided by adding flocculating agents. However, finding the best suited flocculating agent and optimal conditions to achieve rapid and effective flocculation is a nontrivial task. In conventional analytical systems, turbulent mixing creates a dynamic equilibrium between floc growth and breakage, constraining the determination of floc formation rates. Furthermore, these systems typically rely on end-point measurements only. We have successfully developed for the first time a microfluidic system for the study of flocculation under well controlled conditions. In our microfluidic device (μFLOC), floc sizes and growth rates were monitored in real time using high-speed imaging and computational image analysis. The on-line and in situ detection allowed quantification of floc sizes and their growth kinetics. This eliminated the issues of sample handling, sample dispersion, and end-point measurements.We demonstrated the power of this approach by quantifying the growth rates of floc formation under forty different growth conditions by varying industrially relevant flocculating agents (pDADMAC, PEI, PEG), their concentration and dosage. Growth rates between 12.2 μm s −1 for a strongly cationic flocculant (pDADMAC) and 0.6 μm s −1 for a non-ionic flocculant (PEG) were observed, demonstrating the potential to rank flocculating conditions in a quantitative way. We have therefore created a screening tool to efficiently compare flocculating agents and rapidly find the best flocculating condition, which will significantly accelerate early bioprocess development.

We have previously reported that microthrottle pumps (MTPs) display the capacity to pump solid phase suspensions such as polystyrene beads which prove challenging to most microfluidic pumps. In this paper we report employing a linear microthrottle pump (LMTP) to pump whole, undiluted, anticoagulated, human venous blood at 200 μl min(-1) with minimal erythrocyte lysis and no observed pump blockage. LMTPs are particularly well suited to particle suspension transport by virtue of their relatively unimpeded internal flow-path. Micropumping of whole blood represents a rigorous real-world test of cell suspension transport given blood's high cell content by volume and erythrocytes' relative fragility. A modification of the standard Drabkin method and its validation to spectrophotometrically quantify low levels of erythrocyte lysis by hemoglobin release is also reported. Erythrocyte lysis rates resulting from transport via LMTP are determined to be below one cell in 500 at a pumping rate of 102 μl min(-1).

The development of microfluidic devices is an iterative process that involves series of improvements, which can be costly and time consuming. We present a packaging system which makes use of an accessible rapid prototyping method, and facilitates the rapid and reliable implementation of polymeric microfluidic device designs. The packaging system uses a modular design and is based on an adhesive-free connection of a reusable and stiff polymeric interface plate with a disposable, soft microfluidic chip under compression. We characterised the system by numerically and experimentally studying the effect of compression and key dimensions on burst pressure and flow rate. All parts are fabricated with readily available low-cost materials and micro-milling technology. The presented approach is both facilitating and systematising the fabrication of devices with different degrees of complexity; keeping assembly and interconnection simple and straightforward. Furthermore, minimising the time between a design and a finished working prototype yields rapid verification of microfluidic design concepts and testing of assays. Several chip designs were fabricated, then growth of stem cells and hydrodynamic vertical flow focusing in a microfluidic device were realised using our approach. Our approach minimises the need for re-development and re-testing of interface components; reducing cost and time requirements.