26 September 2014 Photonic detection and characterization of DNA using sapphire microspheres
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J. of Biomedical Optics, 19(9), 097006 (2014). doi:10.1117/1.JBO.19.9.097006
Abstract
A microcavity-based deoxyribonucleic acid (DNA) optical biosensor is demonstrated for the first time using synthetic sapphire for the optical cavity. Transmitted and elastic scattering intensity at 1510 nm are analyzed from a sapphire microsphere (radius 500  μm, refractive index 1.77) on an optical fiber half coupler. The 0.43 nm angular mode spacing of the resonances correlates well with the optical size of the sapphire sphere. Probe DNA consisting of a 36-mer fragment was covalently immobilized on a sapphire microsphere and hybridized with a 29-mer target DNA. Whispering gallery modes (WGMs) were monitored before the sapphire was functionalized with DNA and after it was functionalized with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). The shift in WGMs from the surface modification with DNA was measured and correlated well with the estimated thickness of the add-on DNA layer. It is shown that ssDNA is more uniformly oriented on the sapphire surface than dsDNA. In addition, it is shown that functionalization of the sapphire spherical surface with DNA does not affect the quality factor (Q≈104) of the sapphire microspheres. The use of sapphire is especially interesting because this material is chemically resilient, biocompatible, and widely used for medical implants.
© 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
Mohammed Sharif Murib, Weng-Siang Yeap, Daan Martens, Peter Bienstman, Ward De Ceuninck, Bart van Grinsven, Michael J. Schöning, Luc Michiels, Ken Haenen, Marcel Ameloot, Ali Serpengüzel, Patrick Wagner, "Photonic detection and characterization of DNA using sapphire microspheres," Journal of Biomedical Optics 19(9), 097006 (26 September 2014). http://dx.doi.org/10.1117/1.JBO.19.9.097006
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KEYWORDS
Sapphire

Optical spheres

Molecules

Scattering

Optical biosensors

Photodetectors

Refractive index

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