To come up to the demand for extremely sensitive biosensors for parallel real-time bioanalyses, we present several
configurations of label-free biosensors on Silicon-on-Insulator (SOI) optical chips. We discuss results on microring
resonators with a non-fouling polymer coating, increased sensitivity with slotted wire resonators and the design
and fabrication of an integrated surface plasmon resonance interferometer. The high refractive index contrast
of SOI offers submicron-size features with high quality for dense integration, high sensitivity and detection with
very low analyte volumes. The fabrication method, 193nm deep-UV lithography, allows for mass production of
cheap disposable biochips.
We present several nanophotonic biosensors on silicon-on-insulator: ring resonator based devices, slotted ring
resonators to increase the interaction between light and the sample, and finally devices based on nanoplasmonic
interferometers.
Label-free biosensors for protein detection try to overcome the stability and reliability problems of commercialized
systems relying on the detection of labeled molecules. We propose a micron sized integrated Silicon-on-Insulator
optical biosensor based on a microring cavity that enables real time and sensitive measurements of protein dynamics,
fast sample preparation and multiparameter detection for extremely low analyte quantities. Fabrication with Deep UV
lithography for standard CMOS processing allows for cheap mass production and integration with electronic functions
for complete lab-on-chip devices. The SOI material system offers a high refractive index contrast suitable for the
fabrication of submicron sized optical cavities of very high quality. The shift of resonance wavelength that occurs when
the dielectric surroundings of such a cavity is changed, is used for sensing. We demonstrate a SOI optical microring
resonator with radius 5 micron capable of detecting bulk refractive index changes of 10-4. Modification of the
semiconductor surface, allowing for immobilization of biomolecules, is characterized by X-ray Photoelectron
Spectroscopy, ellipsometry, Scanning Contact Angle and Atomic Force Microscopy. We use the avidin/biotin high
affinity couple to demonstrate good repeatability and the detection of protein concentrations down to 50 ng/ml. Negative
control using low interaction protein couples shows low responses, proving the realization of real specific binding.
Integration with a microfluidic setup will allow for more precise monitoring of the interaction dynamics, while lining up
the microrings in arrays will allow for cheap high throughput label-free multiparameter analyses.
Silicon-on-Insulator (SOI) is a very interesting material system for highly integrated photonic circuits. The high
refractive index contrast allows photonic waveguides and waveguide components with submicron dimensions
to guide, bend and control light on a very small scale so that various functions can be integrated on a chip.
Moreover, SOI offers a flexible platform for integration with surface plasmon based components which in turn
allows for even higher levels of miniaturization. Key property of both waveguide types is the mode distribution
of the guided modes: a high portion of the light is concentrated outside of the core material, thus making them
suitable for sensitive detection of environmental changes.
We illustrate chemical and label-free molecular biosensing with SOI microring resonator components. In
these microring resonator sensors, the shift of the resonance wavelength is measured. A ring of radius 5 micron
is capable of detecting specific biomolecular interaction between the high affinity protein couple avidin/biotin
down to a few ng/ml avidin concentration. We describe the integration of surface plasmon waveguides with SOI
waveguides and discuss the principle of a highly sensitive and compact surface plasmon interferometric sensor
suitable for biosensing. The device is two orders of magnitude smaller than current integrated SPR sensors, and
has a highly customizable behavior. We obtain a theoretical limit of detection of 10-6 RIU for a component of
length 10 microns. We address material issues and transduction principles for these types of sensors.
Besides in chemical sensors, the SOI microring resonators can also be used in physical sensors. We demonstrate
a strain sensor in which the shift of the resonance wavelength is caused by mechanical strain. We have
experimentally characterized the strain sensors by performing a bending test
We will present recent progress in several devices based on silicon-on-insulator nanophotonics using deep-UV lithography. We will report on high efficiency grating couplers, ultra-compact arrayed waveguide gratings and ring-resonator based biosensors.
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