Abstract

Label-Free Silicon-on-Insulator "Lab on a chip" Optical Biosensors based on Interferometers

Najla Najeeb, PhD student, University of Nottingham

We demonstrate Lab-on-a-Chip immunosensors based on interferometer technology capable of label-free, real time, parallel detection and identification of multiple analytes with extremely high sensitivity. Two types of interferometers are reported. Both are based on Silicon-on-Insulator (SOI) material to allow sub-micron featured densely packed devices using established fabrication technology. The first sensor consists of Mach-Zehnder interferometers (MZIs) fabricated with silicon photonic wires. The high index contrast core-cladding photonic wires supporting a TM mode can be designed to have extremely high sensitivity for low analyte volumes. A method of selective surface functionalisation by salinisation was developed to attach albumin to the silicon photonic wires. The antibody then binds to the albumin. The second sensor is a label-free self-aligned plasmonic interferometer. The interfering plasmonic modes are excited on either side of a thin gold layer embedded into a silicon photonic wire. Only the mode on the upper surface interacts with the analyte. The resonant wavelength is thus sensitive to the analyte index. In both scenarios the sensors maybe excited in parallel using a 1xN MMI input coupler (where N=20) enabling parallel detection of multiple species.