In this issue: Biotechnolgy Journal 2/2011

On‐chip PCR Cao, Kim and Klapperich , Biotechnol. J. 2011, 6, 177–184 Most microfluidic PCR devices are made of two basic designs: stationary PCR and continuous flow PCR (CF‐PCR). Stationary PCR devices work by thermocycling the device reagents together over time, while CF‐PCR devices work by directing reagents through a single‐channel spatial temperature gradient, which reduces the thermal mass of the reagent and shortens the cycling time. For mass production of inexpensive CF‐PCR devices, fabrication via thermoplastic molding is necessary, although the optimal architecture remains to be optimized. In this issue, researchers from Boston University (MA, USA) explore three channel designs, with varying residence time ratios for the three PCR steps. The authors provide a guide to the CF‐PCR chip design and a model for predicting the performance of new CF‐PCR designs prior to actual chip manufacture. These results provide a faster turnaround time for new device and assay designs, and are likely to greatly facilitate industrial applications. Picoliter DNA sequencing Welch , et al., Biotechnol. J. 2011, 6, 165–176 Previous reports demonstrate pyrosequencing on the nanoliter scale. In this issue, authors from Duke University (Durham, NC, USA) explore the benefits, challenges, and logistics of a device three orders of magnitude smaller, i.e. picoliter scale. They employ digital microfluidics providing programmable movement of discrete droplets on the device for fine control of reactions with very low power requirements. The target DNA is bound to paramagnetic beads so that the DNA can be held magnetically in one location; reagents can be added and excess split away without loss of the DNA. In addition, the picoliterscale reaction of luciferase with adenosine triphosphate presenting the detection steps of pyrosequencing is characterized with all necessary alterations for working at this scale. The described device is ideal for high throughput diagnostics, especially when resources are limited. Deep well cell trapping Jang , et al., Biotechnol. J. 2011, 6, 156–164 One of the challenges of conducting cellular studies in microfluidic chips is to achieve uniform cell seeding. In this issue, Ali Khademhosseini and coworkers (Harward Medical School and MIT, Cambridge, MA, USA) describe a microfluidic mechanism that combines microfluidic valves and deep wells for cell localization and storage. Cells are introduced into the wells by an externally controlled flow. Then valves on the chip control the movement of the cells. To show that external flows generate low shear stress regions in deep wells that enable cell seeding, numerical calculations are performed and experimentally verified by comparing the fraction of stored cells as a function of the well depth and input flow rate upon activation of the valves. As expected, upon reintroduction of the flow, the cells in the deep wells do not move while they are washed away in shallow wells. When extended to a large well array, this mechanism can be used for high‐throughput cell studies, e.g. for monitoring of cell functions and differentiation.