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20 Sep 2004

Volume 85, Issue 12, pp. 2157-2437

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Appl. Phys. Lett. 85, 2390 (2004); http://dx.doi.org/10.1063/1.1796520 (3 pages)

Stas Polonsky and Alan Weger
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Heat conduction calorimeter for massively parallel high throughput measurements with picoliter sample volumes

E. B. Chancellor, J. P. Wikswo, F. Baudenbacher, M. Radparvar, and D. Osterman

Appl. Phys. Lett. 85, 2408 (2004); http://dx.doi.org/10.1063/1.1790075 (3 pages) | Cited 10 times

Online Publication Date: 24 September 2004

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We have developed a bulk micromachined calorimeter with a sensitivity of 1.5 nW∕Hz1∕2 and a 1 ms time constant using a thin film thermopile as the sensing element. The thermopile consists of seven titanium and bismuth thermocouples with a total Seebeck coefficient of 574 μV∕K. The device is capable of measuring enthalpies in chemical or biological reactions in volumes as small as a few picoliters. The device can be fabricated and operated in a massively parallel fashion in combination with ink-jet printing technologies in air and at room temperature, making it ideally suited for biological and biochemical experiments.
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07.20.Fw Calorimeters
65.40.G- Other thermodynamical quantities

A magnetic trap for living cells suspended in a paramagnetic buffer

Adam Winkleman, Katherine L. Gudiksen, Declan Ryan, George M. Whitesides, Derek Greenfield, and Mara Prentiss

Appl. Phys. Lett. 85, 2411 (2004); http://dx.doi.org/10.1063/1.1794372 (3 pages) | Cited 41 times

Online Publication Date: 24 September 2004

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This manuscript describes the fabrication and use of a three-dimensional magnetic trap for diamagnetic objects in an aqueous solution of paramagnetic ions; this trap uses permanent magnets. It demonstrates trapping of polystyrene spheres, and of various types of living cells: mouse fibroblast (NIH-3T3), yeast (Saccharomyces cerevisiae), and algae (Chlamydomonas reinhardtii). For a 40 mM solution of gadolinium (III) diethylenetriaminepentaacetic acid (Gd⋅DTPA) in aqueous buffer, the smallest cell (particle) that could be trapped had a radius of ∼2.5 μm. The trapped particle and location of the magnetic trap can be translated in three dimensions by independent manipulation of the permanent magnets. This letter a1so characterizes the biocompatibility of the trapping solution.
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75.50.Mm Magnetic liquids
75.50.Tt Fine-particle systems; nanocrystalline materials
75.20.Ck Nonmetals
87.50.C- Static and low-frequency electric and magnetic fields effects
75.50.Ww Permanent magnets
87.17.Jj Cell locomotion, chemotaxis

Probing collective dynamics of active particles using modulation force spectroscopy

G. V. Soni, G. Ananthakrishna, and G. V. Shivashankar

Appl. Phys. Lett. 85, 2414 (2004); http://dx.doi.org/10.1063/1.1791325 (3 pages) | Cited 6 times

Online Publication Date: 24 September 2004

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In this letter, we report a method of measuring the dynamic viscosity of self-propelled active particles using an intensity-modulated optical tweezer. We have used a 6 μm trapped polystyrene bead suspended in a bath of motile bacterial cells as a probe. The response function amplitude of the oscillatory bead directly measures the dynamics of the spatiotemporal structure of the motile particles. We find that unlike passive systems, the viscosity is defined by distributions of response function amplitudes that represent the long-range active temporal structures. Appropriate Langevin equations are set up that capture all these essential features.
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87.10.-e General theory and mathematical aspects
87.19.rh Fluid transport and rheology
87.18.Ed Cell aggregation
87.18.Hf Spatiotemporal pattern formation in cellular populations
87.80.Cc Optical trapping

Antifungal activity of polymer-based copper nanocomposite coatings

Nicola Cioffi, Luisa Torsi, Nicoletta Ditaranto, Luigia Sabbatini, Pier Giorgio Zambonin, Giuseppina Tantillo, Lina Ghibelli, Maria D’Alessio, Teresa Bleve-Zacheo, and Enrico Traversa

Appl. Phys. Lett. 85, 2417 (2004); http://dx.doi.org/10.1063/1.1794381 (3 pages) | Cited 26 times

Online Publication Date: 24 September 2004

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Eukaryotes, such as fungi, can be harmful pathogen agents, and the control of their bioactivity is critical as humans are eukaryote organisms, too. Here, copper∕polymer nanocomposites are proposed as antifungal spinnable coatings with controlled copper-releasing properties. The tests of the bioactivity show that fungal growth is inhibited on the nanocomposite-coated plates, and the antifungal activity can be modulated by controlling the Cu nanoparticle loading.
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82.35.Np Nanoparticles in polymers
87.15.R- Reactions and kinetics
64.75.-g Phase equilibria
87.17.-d Cell processes
87.85.J- Biomaterials
81.65.-b Surface treatments
87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications

Probing nanosecond protein motions of calmodulin by single-molecule fluorescence anisotropy

Xin Tan, Dehong Hu, Thomas C. Squier, and H. Peter Lu

Appl. Phys. Lett. 85, 2420 (2004); http://dx.doi.org/10.1063/1.1791329 (3 pages) | Cited 9 times

Online Publication Date: 24 September 2004

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We report a single-molecule fluorescence anisotropy study of calmodulin, a regulatory protein for calcium-dependent cell signaling. Calmodulin in this study contains a site-specifically inserted tetra-cysteine motif that reacted with FlAsH, a biarsenic fluorescein derivative that can be rotationally locked to the host protein. A photon time-stamping technique was employed that combined the capability for both subnanosecond time resolution of time-correlated single photon counting and single-molecule time trajectory recording. The study provided direct characterization of the nanosecond motions of calmodulin tethered to a biologically compatible surface under physiological buffer solution. The unique technical approaches are applicable to single-molecule study of protein conformational dynamics and protein–protein interactions at a wide range of time scales and without the signal convolution of probe-dye molecular motions.
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87.16.Yc Regulatory genetic and chemical networks
87.15.M- Spectra of biomolecules

Development of a biosensor based on laser-fabricated polymer microcantilevers

X. Richard Zhang and Xianfan Xu

Appl. Phys. Lett. 85, 2423 (2004); http://dx.doi.org/10.1063/1.1791731 (3 pages) | Cited 16 times

Online Publication Date: 24 September 2004

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We develop high-sensitivity biosensors based on microcantilevers. The polymer microcantilevers are fabricated by fast and cost-effective laser machining processes. Polymer film is selected because it gives better sensitivity of deflection measurements than silicon due to its lower Young’s modulus and also its cost is much lower. We demonstrate using these polymer microcantilevers for biological molecular analysis in a DNA hybridization experiment. It is shown that our biosensor is capable of detecting 12 base oligonucleotide with concentrations as low as 0.01 μM.
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87.14.G- Nucleic acids
87.85.Va Micromachining
81.20.Wk Machining, milling
42.62.-b Laser applications
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