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Dec 2007

Volume 1, Issue 4, Articles (04xxxx)

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Real-time detection, control, and sorting of microfluidic droplets

Xize Niu, Mengying Zhang, Suili Peng, Weijia Wen, and Ping Sheng

Biomicrofluidics 1, 044101 (2007); http://dx.doi.org/10.1063/1.2795392 (12 pages) | Cited 35 times

Online Publication Date: 3 October 2007

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We report the design and implementation of capacitive detection and control of microfluidic droplets in microfluidic devices. Integrated microfluidic chip(s) with detection/control circuit enables us to monitor in situ the individual volume of droplets, ranging from nanoliter to picoliter, velocity and even composition, with an operation frequency of several kilohertz. Through electronic feedback, we are able to easily count, sort, and direct the microfluidic droplets. Potential applications of this approach can be employed in the areas of biomicrofluidic processing, microchemical reactions as well as digital microfluidics.
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47.85.Np Fluidics
47.55.db Drop and bubble formation
47.85.L- Flow control
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)

Dielectrophoretic discrimination of bovine red blood cell starvation age by buffer selection and membrane cross-linking

Jason E. Gordon, Zachary Gagnon, and Hsueh-Chia Chang

Biomicrofluidics 1, 044102 (2007); http://dx.doi.org/10.1063/1.2818767 (5 pages) | Cited 29 times

Online Publication Date: 27 November 2007

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We report an interesting buffer electric relaxation time tuning technique, coupled with a glutaraldehyde cross-linking cell fixation reaction, which allows for sensitive dielectrophoretic analysis and discrimination of bovine red blood cell (bRBC) starvation age. The buffer composition is selected such that two easily accessible dielectrophoretic crossover frequencies (cof) exist. Low concentration glutaraldehyde fixation was observed to produce a threefold decrease in the higher cof with a comparable increase in the lower cof also witnessed. More importantly, increased glutaraldehyde fixation concentration significantly increased the higher cof by a factor found to be sensitive to the bRBC starvation age.
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87.50.C- Static and low-frequency electric and magnetic fields effects
87.16.D- Membranes, bilayers, and vesicles

Targeted cell detection based on microchannel gating

Mehdi Javanmard, AmirAli H. Talasaz, Mohsen Nemat-Gorgani, Fabian Pease, Mostafa Ronaghi, and Ronald W. Davis

Biomicrofluidics 1, 044103 (2007); http://dx.doi.org/10.1063/1.2815760 (10 pages) | Cited 6 times

Online Publication Date: 30 November 2007

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Currently, microbiological techniques such as culture enrichment and various plating techniques are used for detection of pathogens. These expensive and time consuming methods can take several days. Described below is the design, fabrication, and testing of a rapid and inexpensive sensor, involving the use of microelectrodes in a microchannel, which can be used to detect single bacterial cells electrically (label-free format) in real time. As a proof of principle, we have successfully demonstrated real-time detection of target yeast cells by measuring instantaneous changes in ionic impedance. We have also demonstrated the selectivity of our sensors in responding to target cells while remaining irresponsive to nontarget cells. Using this technique, it can be possible to multiplex an array of these sensors onto a chip and probe a complex mixture for various types of bacterial cells.
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87.17.Ee Growth and division

In vitro studies on ultrasmall superparamagnetic iron oxide nanoparticles coated with gummic acid for T2 MRI contrast agent

I. Rabias, H. Pratsinis, G. Drossopoulou, M. Fardis, T. Maris, N. Boukos, N. Tsotakos, D. Kletsas, E. Tsilibary, and G. Papavassiliou

Biomicrofluidics 1, 044104 (2007); http://dx.doi.org/10.1063/1.2821757 (12 pages) | Cited 8 times

Online Publication Date: 30 November 2007

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Ultrasmall superparamagnetic iron oxide nanoparticles coated with gummic acid have been investigated as possible constituents of aqueous ferrofluids for biomedical applications and especially for MRI contrast agent. The structural characteristics and the size of the nanoparticles have been analyzed as well as the magnetic properties. In order to evaluate any possible capabilities as a contrast agent, the relaxation time, T2, of hydrogen protons in the colloidal solutions of nanoparticles have been measured in order to gain information on the relaxation behavior compared to other MRI contrast agents. The in vitro cytotoxicity of the obtained magnetic nanoparticles of iron oxide coated with gummic acid was investigated by two separate methods (MTT and FACS analysis) and by using three different normal and transformed cell lines. Our results showed that the synthesized nanoparticles had no toxic effect on any of the cell lines used.
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87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
87.61.Tg Clinical applications
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