A high efficiency label-free photonic biosensor based on vertically stacked ring resonators

• Published in: The European physical journal. ST, Special topics Special topics, 2014-09, Vol.223 (10), p.2009-2021
• Main Authors: Campanella, C. E., Campanella, C. M., De Leonardis, F., Passaro, V. M. N.
• Format: Article
• Language: English
• Subjects: Atomic; Classical and Continuum Physics; Condensed Matter Physics; Materials Science; Measurement Science and Instrumentation; Molecular; Optical and Plasma Physics; Physics; Physics and Astronomy; Regular Article; Taking Detection to the Limit: Biosensing with Optical Microcavities
• ISSN: 1951-6355; 1951-6401
• DOI: 10.1140/epjst/e2014-02244-5

In this paper we propose an optical biosensor based on two vertically stacked Silicon on Insulator (SOI) micro-ring resonators interacting with a microfluidic ring channel. This device behaves as a resonant optical coupler and it is very sensitive to the variation of the coupling coefficient between the two vertically stacked ring resonators. A ring microfluidic channel is proposed in the coupling region between the two vertically stacked ring resonators. The inner walls of the channel are funzionalized in order to the trap a specific biological species. Assuming a biotin-streptavidin system, the straptividin trapping gives rise to a change of the biological thickness of about 3 nm. This thickness increase of the deposited layer leads to a consequent change in the coupling strength between the two rings. These theoretical predictions have been validated by using both 3D Finite-Difference Time-Domain (FDTD) and 3D full-vectorial Finite Element Method (FEM) approaches. Moreover, by appropriately choosing the design parameters of the micro-resonant structure, we evaluate a sensitivity of the spectral response to the streptavidin adlayer variation of about 20% nm −1 for TE polarization and 34% nm −1 for TM polarization, which represents an important achievement to obtain selective SOI bio-sensors with ultra-high resolution.