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10 Sep 2007

Volume 91, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 91, 112501 (2007); http://dx.doi.org/10.1063/1.2780107 (3 pages)

Y. Liu, S. Gliga, R. Hertel, and C. M. Schneider
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Fiber-optic coupler based refractive index sensor and its application to biosensing

Hidehisa Tazawa, Tomohiko Kanie, and Makoto Katayama

Appl. Phys. Lett. 91, 113901 (2007); http://dx.doi.org/10.1063/1.2783278 (3 pages) | Cited 15 times

Online Publication Date: 10 September 2007

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A simple and highly sensitive biosensor based on a fiber-optic coupler is developed. The change of refractive index due to biomolecular interaction on the surface of the coupler can be detected as the change of the transmission power. The sensitivity of the sensor is evaluated to be a noise level equivalent to a refractive index variation of 4×10−6. The binding of streptavidin is detected to be concentration dependent over a range of 0.5–2 μg/ml, by immobilizing biotin on the coupler surface via aminosilan treatment. This sensor allows the construction of a low-cost, portable, and label-free biosensing system.
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42.81.Pa Sensors, gyros
42.81.Qb Fiber waveguides, couplers, and arrays
87.80.-y Biophysical techniques (research methods)
07.60.Vg Fiber-optic instruments

Separation of long DNA molecules through cleavage of hydrogen bonds under a stretching force

Lizeng Gao, Jiamin Wu, Di Gao, and Jianzhong Wu

Appl. Phys. Lett. 91, 113902 (2007); http://dx.doi.org/10.1063/1.2784967 (3 pages) | Cited 5 times

Online Publication Date: 10 September 2007

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The authors report that long DNA molecules of different lengths can be separated under a stretching force by cleaving hydrogen bonds that tether one end of the DNA to a substrate. This separation method can be implemented with a simple direct current electric field, does not require separation matrices, and, in principle, has no upper limit on the length of the DNA that can be efficiently separated. Here, they demonstrate efficient separation of lambda DNA (48 502 base pairs) from human genomic DNA (>100 000 base pairs) using this method.
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87.14.G- Nucleic acids
87.15.B- Structure of biomolecules

Phase interrogation of localized surface plasmon resonance biosensors based on electro-optic modulation

Tzyy-Jiann Wang and Chih-Wei Hsieh

Appl. Phys. Lett. 91, 113903 (2007); http://dx.doi.org/10.1063/1.2783213 (3 pages) | Cited 4 times

Online Publication Date: 11 September 2007

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A resolution-tunable localized surface plasmon resonance (LSPR) biosensor employing electro-optically modulated phase interrogation is presented. This biosensor modulates the analyte-dependent LSPR phase characteristic through electro-optic effect by varying the wave vector of lightwave for exciting surface plasmon. The induced LSPR phase change is measured by the collinear heterodyne technique and its relation with the applied voltage is utilized to determine the analyte concentration. Experimental results show that the regression slope of the phase-voltage relation decreases with the analyte concentration and the detection sensitivity can be increased by widening the waveguide width and using thinner gold film beneath gold nanoparticles. Detection resolution of this LSPR biosensor can be enhanced by increasing the applied voltage to enlarge the induced phase change. The presented LSPR biosensor employing phase interrogation has the features of resolution tunability, fast modulation speed, high modulation stability, and noise reduction.
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87.80.-y Biophysical techniques (research methods)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.Hp Optical processors, correlators, and modulators
42.82.Et Waveguides, couplers, and arrays

Two dimensional simulation on immunoassay for a biosensor with applying electrothermal effect

Chih-Kai Yang, Jeng-Shian Chang, Sheng D. Chao, and Kuang-Chong Wu

Appl. Phys. Lett. 91, 113904 (2007); http://dx.doi.org/10.1063/1.2784941 (3 pages) | Cited 3 times

Online Publication Date: 12 September 2007

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For diffusion-limited proteins, the diffusion boundary layer on the reacting surface hinders the binding reaction. The authors performed finite-element simulations of the electrothermal effect on the reaction kinetics of C-reactive protein (CRP)–anti-CRP. The induced vortices stir the flow and enhance the transport rate of analytes. They attribute the enhancement to the reduction of the thickness of diffusion boundary layer. Significant interference patterns of the votices are observed by varying the position of the reacting surface. These patterns are utilized to optimize the enhancement factor, yielding 5.166 and 3.744 times for association and dissociation, respectively, under voltage (15 Vrms) and frequency (100 kHz).
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68.35.Fx Diffusion; interface formation
82.30.Nr Association, addition, insertion, cluster formation
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
87.14.E- Proteins
82.20.-w Chemical kinetics and dynamics
82.37.Np Single molecule reaction kinetics, dissociation, etc.
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