SPECTROSCOPY, IMAGING, OTHER TECHNIQUES |
Detection of protein orientation on silica microsphere surface using TE/TM whispering gallery modes
Mayumi Noto 1, David Keng 1, Iwao Teraoka 1* and Stephen Arnold 1
1 Polytechnic University
* To whom correspondence should be addressed. E-mail: teraoka{at}poly.edu.
Submitted on December 15, 2006
Revised on January 31, 2007
Accepted on 15 February 2007
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Abstract |
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The state of adsorbed protein molecules can be examined by comparing the shifts in a narrow-line resonance wavelength of transverse electric (TE) and transverse magnetic (TM) whispering gallery modes (WGM) when the molecules adsorb onto a transparent microsphere that houses WGM. In adsorption of bovine serum albumin (BSA) onto an aminopropyl-modified silica microsphere, the TM-to-TE shift ratio indicated highly anisotropic polarizability of BSA in the direction normal to the surface, most likely ascribed to anchoring of the heart-shaped protein molecule by one of its tips. The polarization-dependent resonance shift was confirmed when the surrounding refractive index was uniformly changed by adding salt, which would simulate adsorption of large objects.
Key Words:
adsorption, biosensor, protein orientation, silica surface, whispering gallery modes
