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22 Mar 2004

Volume 84, Issue 12, pp. 2013-2211

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 2100 (2004); http://dx.doi.org/10.1063/1.1688997 (3 pages)

P. Sutter, E. Sutter, and T. R. Ohno
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Molecular-scale biophotodiode consisting of a green fluorescent protein/cytochrome c self-assembled heterolayer

Jeong-Woo Choi and Masamichi Fujihira

Appl. Phys. Lett. 84, 2187 (2004); http://dx.doi.org/10.1063/1.1655689 (3 pages) | Cited 22 times

Online Publication Date: 16 March 2004

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A molecular photodiode that consists of a protein heterolayer is investigated at the molecular scale for construction of a bioelectronic device. Cytochrome c and green fluorescent protein (GFP) were used as an electron acceptor and a sensitizer in the molecular layer by mimicking photosynthesis. A self-assembled monolayer of thiol-modified cytochrome c was formed on Au-coated glass, and then GFP was adsorbed onto the cytochrome c surface by electrostatic attraction. Photoinduced current was generated and the photoswitching property was observed by repeated step illumination. The rectifying property by scanning tunneling spectroscopy based current–voltage characteristics was achieved in the protein heterolayer. Thus, the proposed heterolayer functioned as a biomolecular photodiode with photocurrent generation and the rectifying property. © 2004 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.65.+h Molecular electronic devices
87.14.E- Proteins
87.15.M- Spectra of biomolecules
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
68.43.Mn Adsorption kinetics
72.40.+w Photoconduction and photovoltaic effects
87.64.Dz Scanning tunneling and atomic force microscopy

Simulation of terahertz pulse propagation in biological systems

E. Pickwell, B. E. Cole, A. J. Fitzgerald, V. P. Wallace, and M. Pepper

Appl. Phys. Lett. 84, 2190 (2004); http://dx.doi.org/10.1063/1.1688448 (3 pages) | Cited 30 times

Online Publication Date: 16 March 2004

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Studies in terahertz (THz) imaging have revealed a significant difference between skin cancer (basal cell carcinoma) and healthy tissue. Since water has strong absorptions at THz frequencies and tumor affects the water content of tissue, a likely contrast mechanism is variation in water content. Modeling the propagation of a THz pulse through water is the first step toward understanding the origin of contrast in terahertz pulsed images of skin cancer. In this letter, we develop a finite-difference-time-domain simulation to model the propagation of a THz pulse and incorporate double Debye theory to model the behavior of water subject to THz radiation. Furthermore, we apply this model to skin. © 2004 American Institute of Physics.
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87.85.Lf Tissue engineering
87.15.A- Theory, modeling, and computer simulation
87.50.S- Radiofrequency/microwave fields effects

Topologic mixing on a microfluidic chip

Hao Chen and Jens-Christian Meiners

Appl. Phys. Lett. 84, 2193 (2004); http://dx.doi.org/10.1063/1.1686895 (3 pages) | Cited 64 times

Online Publication Date: 16 March 2004

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Mixing two liquids on a microfluidic chip is notoriously hard because the small dimensions and velocities on the chip effectively prevent turbulence. We present a topological mixing scheme that exploits the laminarity of the flow to repeatedly fold the flow and exponentially increase the concentration gradients to obtain fast and efficient mixing by diffusion. It is based on helical flow channels with opposite chiralities that split, rotate, and recombine the fluid stream in a topology reminiscent of a series of Möbius bands. This geometry is realized in a simple six-stage, two-layer elastomer structure with a footprint of 400 μm×300 μm per stage that mixes two solutions efficiently at Reynolds numbers between 0.1 and 2. This represents more than an order of magnitude reduction in the size of microfluidic mixers that can be manufactured in standard multilayer soft lithography techniques. © 2004 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.40.Hp Lithography, masks and pattern transfer
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