In an optical tweezers system, the force measurement with a resolution less than pico-Newton can
be achieved by precise measurement and analysis of the trapped particle trajectory. Typically, this
single particle tracking technique is realized by a quadrant position sensor which detects the scattering
lights of the trapping laser beam from the trapped particle. However, as the radius of the trapped
particle is larger than the wavelength of the trapped laser, the scattering pattern becomes complicated,
and it limits the tracking region and the signal sensitivity on the trapped particle. To solve this issue,
an extra probing laser with optimized focal offset according to the trapping laser is applied to improve
the flexibility and performance of our particle tracking system for each particle size. A rule of thumb
between the optimized focal offsets and particle size is also concluded from the experimental results
and theoretical simulations.
This paper focuses on developing the platform technology of real- time biomolecular-interaction analysis (BIA) sensor chips. A detection scheme using the electro-optically modulated surface plasmon resonance (SPR) is suggested to advance the sensor features in reducing measurement complexity and time. The SPR method of a BIA sensing system detects slight changes of refractive index due to the biomolecular interaction at the solid-liquid interface. The most sensitive interrogation method among the possible conventional schemes is to measure the SPR angle of the attenuated total reflection. The electro-optical modulation replaces the mechanism of angle measurement not only to increase the speed but also to increase the size. Recent progress of the multilayer SPR provides an effective mean of tailoring the microchip. Several multilayer configurations have been studied in this paper to realize the electro-optical SPR sensing. Especially, the long-range mode of surface plasmon was investigated to achieve the high resolution and high sensitivity detection.
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