Daniel E. Raymond

Microfluidic sorting of mammalian cells by optical force switching.

Microfluidic-based devices have allowed miniaturization and increased parallelism of many common functions in biological assays; however, development of a practical technology for microfluidic-based fluorescence-activated cell sorting has proved challenging. Although a variety of different physical on-chip switch mechanisms have been proposed, none has satisfied simultaneously the requirements of high throughput, purity, and recovery of live, unstressed mammalian cells. Here we show that optical forces can be used for the rapid (2–4 ms), active control of cell routing on a microfluidic chip. Optical switch controls reduce the complexity of the chip and simplify connectivity. Using all-optical switching, we have implemented a fluorescence-activated microfluidic cell sorter and evaluated its performance on live, stably transfected HeLa cells expressing a fused histone–green fluorescent protein. Recovered populations were verified to be both viable and unstressed by evaluation of the transcriptional expression of two genes, HSPA6 and FOS, known indicators of cellular stress.

Numerical modeling of transport and accumulation of DNA on electronically active biochips

Abstract Transport and accumulation of biomolecules, particularly DNA, in active electronic chips are investigated through numerical modeling and experimental verification. Various geometric and design configurations of electronically active DNA chips are considered. Further, we investigate the effect of electric field distribution on practical design of flow cells and chips. Particular attention is focused on the geometric effects on current and electric field distribution which are well captured by a finite element method-based model. We demonstrate that these geometric effects are observed only in buffers of very low conductivity. We also demonstrate that numerical models which do not include the charge transfer mechanism between electrodes and the buffer solution will fail to predict the reduction of these geometric effects with increased buffer conductivity. The review of the technology is based on computer simulation using a finite element-based computational model and experimental results of electric field distribution, DNA transport and accumulation. Comparison of theoretical results for electrophoretic DNA accumulation with those obtained from experiments and a simple analytical model is presented.