Articles by Philip C. Samson in JoVE
Window on a Microworld: Simple Microfluidic Systems for Studying Microbial Transport in Porous Media Dmitry A. Markov1,2, Philip C. Samson1, David K. Schaffer1, Adit Dhummakupt1, John P. Wikswo1,2,3,4, Leslie M. Shor5,6 1Vanderbilt Institute for Integrative Biosystems Research and Education, Vanderbilt University, 2Department of Biomedical Engineering, Vanderbilt University, 3Department of Molecular Physiology and Biophysics, Vanderbilt University, 4Department of Physics and Astronomy, Vanderbilt University, 5Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, 6Center for Environmental Sciences and Engineering, University of Connecticut Microfluidic devices can be used to visualize complex natural processes in real time and at the appropriate physical scales. We have developed a simple microfluidic device that mimics key features of natural porous media for studying growth and transport of bacteria in the subsurface.
Other articles by Philip C. Samson on PubMed
Tape Underlayment Rotary-node (TURN) Valves for Simple On-chip Microfluidic Flow Control Biomedical Microdevices. Feb, 2010 | Pubmed ID: 19859812 We describe a simple and reliable fabrication method for producing multiple, manually activated microfluidic control valves in polydimethylsiloxane (PDMS) devices. These screwdriver-actuated valves reside directly on the microfluidic chip and can provide both simple on/off operation as well as graded control of fluid flow. The fabrication procedure can be easily implemented in any soft lithography lab and requires only two specialized tools-a hot-glue gun and a machined brass mold. To facilitate use in multi-valve fluidic systems, the mold is designed to produce a linear tape that contains a series of plastic rotary nodes with small stainless steel machine screws that form individual valves which can be easily separated for applications when only single valves are required. The tape and its valves are placed on the surface of a partially cured thin PDMS microchannel device while the PDMS is still on the soft-lithographic master, with the master providing alignment marks for the tape. The tape is permanently affixed to the microchannel device by pouring an over-layer of PDMS, to form a full-thickness device with the tape as an enclosed underlayment. The advantages of these Tape Underlayment Rotary-Node (TURN) valves include parallel fabrication of multiple valves, low risk of damaging a microfluidic device during valve installation, high torque, elimination of stripped threads, the capabilities of TURN hydraulic actuators, and facile customization of TURN molds. We have utilized these valves to control microfluidic flow, to control the onset of molecular diffusion, and to manipulate channel connectivity. Practical applications of TURN valves include control of loading and chemokine release in chemotaxis assay devices, flow in microfluidic bioreactors, and channel connectivity in microfluidic devices intended to study competition and predator/prey relationships among microbes.
Open Access Microfluidic Device for the Study of Cell Migration During Chemotaxis Integrative Biology : Quantitative Biosciences from Nano to Macro. Nov, 2010 | Pubmed ID: 20949221 Cells sense and interpret chemical gradients, and respond by localized responses that lead to directed migration. An open microfluidic device (OMD) was developed to provide quantitative information on both the gradient and morphological changes that occurred as cells crawled through various microfabricated channels. This device overcame problems that many current devices have been plagued with, such as complicated cell loading, media evaporation and channel blockage by air bubbles. We used a micropipette to set up stable gradients formed by passive diffusion and thus avoided confounding cellular responses produced by shear forces. Two versions of the OMD are reported here: one device that has channels with widths of 6, 8, 10 and 12 Î¼m, while the other has two large 100 Î¼m channels to minimize cellular interaction with lateral walls. These experiments compared the migration rates and qualitative behavior of Dictyostelium discoideum cells responding to measurable cAMP and folic acid gradients in small and large channels. We report on the influence that polarity has on a cell's ability to migrate when confined in a channel. Polarized cells that migrated to cAMP were significantly faster than the unpolarized cells that crawled toward folic acid. Unpolarized cells in wide channels often strayed off course, yet migrated faster than unpolarized cells in confined channels. Cells in channels farthest from the micropipette migrated through the channels at rates similar to cells in channels with higher concentrations, suggesting that cell speed was independent of mean concentration. Lastly, it was found that the polarized cells could easily change migration direction even when only the leading edge of the cell was exposed to a lateral gradient.
Single-nanocrystal Spectroscopy of White-light-emitting CdSe Nanocrystals The Journal of Physical Chemistry. A. Apr, 2011 | Pubmed ID: 21338163 We report the observation of broad-spectrum fluorescence from single CdSe nanocrystals. Individual semiconductor nanocrystals typically have a narrower emission spectrum than that of an ensemble. However, our experiments show that the ensemble white-light emission observed in ultrasmall CdSe nanocrystals is the result of many single CdSe nanocrystals, each emitting over the entire visible spectrum. These results indicate that each white-light-emitting CdSe nanocrystal contains all the trap states that give rise to the observed white-light emission.