Katrien De Vos

Silicon-on-Insulator microring resonator for sensitive and label-free biosensing.

Label-free biosensors attempt to overcome the stability and reliability problems of biosensors relying on the detection of labeled molecules. We propose a label-free biosensor based on microring cavities in Silicon-on-Insulator (SOI) that fits in an area below 10x10mum(2). The resonance wavelength shift that occurs when the surroundings of a cavity is changed, is used for sensing. While theoretically the performance for bulk refractive index changes is moderate (10(-5)), this device performs outstanding in terms of absolute molecular mass sensing (theoretical sensitivity of 1fg molecular mass) thanks to its extremely small dimensions. We use the avidin/biotin high affinity couple to demonstrate good repeatability and detection of protein concentrations down to 10ng/ml. Fabrication with Deep UV lithography allows for cheap mass production and integration with electronic functions for complete lab-on-chip devices.

SOI optical microring resonator with poly(ethylene glycol) polymer brush for label-free biosensor applications

Label-free monitoring of biomolecular interactions has become of key importance for the emerging proteomics field. Monitoring real time interaction kinetics and high throughput screening of complex samples is of major importance for a variety of applications. We previously reported the use of Silicon-on-Insulator photonics microring resonators for cheap disposable biosensors on chip. Silicon photonics is a platform for micro- and nanoscale integrated devices that can be fabricated at extremely low cost, with standard CMOS processing facilities. Incorporation of a hydrophilic heterobifunctional polymer coating on the silicon chips largely improved the systems response to non-specific binding. We report the chemical coating procedure, the chemical surface characterization and optical measurements for both specific and non-specific interactions. Two heterobifunctional polymer coatings were investigated, alpha-sulfanyl-omega-carboxy-poly(ethylene glycol) and monoprotected diamino-poly(ethylene glycol). Homogenous coatings with thicknesses of 2.3 and 2.5 nm were obtained, corresponding to a surface loading of 99 pm/cm(2) carboxy- and 97 pm/cm(2) aminogroups, respectively. The polymer coated sensor with covalently bound biotin receptor molecules showed very low response to Bovine Serum Albumin (BSA) up to 1 mg/ml in contrast to a high response to avidin with much lower concentrations (2, 10, 87.5 and 175 microg/ml). By extrapolation the detection limit is about 10 ng/ml or 0.37 fg avidin mass. Comparison with the values reported for standard silanization confirms the polymer coating does not deteriorate the systems limit of detection. This makes the optical biosensor chip suitable to be integrated in a microflow system for commercial label-free biosensors and for lab-on-a-chip applications.

Optical biosensor based on silicon-on-insulator microring cavities for specific protein binding detection

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.

Effect of device density on the uniformity of silicon nano-photonic waveguide devices

We report wavelength selective device nonuniformity of 1 nm over a 200 mm SOI wafer using CMOS fabrication technology. We also report correlation between device density and nonuniformity.

Biosensors in silicon on insulator

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.

Si based waveguide and surface plasmon sensors

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

Label-free biosensors on silicon-on-insulator optical chips

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.

High Index-Contrast Silicon-On-Insulator Nanophotonics

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

SOI Microring Resonator Sensor Integrated on a Fiber Facet

The application of optical fiber technology for sensing has undergone tremendous growth over the last years. Its use for imaging hard-to-reach locations and its property to conduct light to a remote convenient location make of it a suitable tool for in vivo sensing applications, such as endoscopy. Here, we present an optical fiber probe sensor for label-free biosensing based on SOI ring resonators. We describe the operating principle of the device, the technology used to integrate a Silicon-on-insulator (SOI) chip on a fiber facet and discuss some experimental results.