Elewout Hallynck

Photonic crystal biosensor based on angular spectrum analysis

The need for cost effective and reliable biosensors in e.g. medical applications is an ever growing and everlasting one. Not only do we strive to increase sensitivity and detection limit of such sensors; ease of fabrication or implementation are equally important. In this work, we propose a novel, photonic crystal based biosensor that is able to operate at a single frequency, contrary to resonance based sensors. In a certain frequency range, guided photonic crystal modes can couple to free space modes resulting in a Lorentzian shape in the angular spectrum. This Lorentzian can shift due to refractive index changes and simulations have shown sensitivities of 65 degrees per refractive index unit and more.

Integrated Optical Pressure Sensors in Silicon-on-Insulator

An optical pressure sensor can be useful in many applications where electronics fall short (e.g., explosive environments). We have fabricated and characterized compact, integrated optical pressure sensors on a silicon-on-insulator platform using ring resonators and Mach-Zehnder interferometers. The silicon substrate is locally etched using KOH to produce very thin membranes of 3.28 μm. Measurements have shown that spectral features in our devices can shift up to 370 pm going from 0 to 80 kPa.

Reaction tubes: A new platform for silicon nanophotonic ring resonator sensors

Label-free biosensing with silicon nanophotonic ring resonator sensors has proven to be an excellent sensing technique for achieving high throughput and high sensitivity, comparing favorably with other labeled and label-free sensing techniques. However, as in any biosensing platform, silicon nanophotonic ring resonator sensors require a fluidic component that allows the continuous delivery of the sample to the sensor surface. This is the big disadvantage of this platform since this type of microfluidic system is very much removed from the daily practice in, e.g., hospital labs, which still relies to a large degree on platforms like 96-well microtiter plates or reaction tubes. To address this major drawback, we propose the combination of a simple and lab-compatible reaction tube platform, with label-free nanophotonic biosensors with a special microfluidic system imbedded into the same chip, where the flow is through the chip rather than over the chip as in more traditional approaches. This shows that label-free nanophotonic ring resonators can be also used in the user-friendly platform like reaction tubes or well microtiter plates, conserving their excellent performance.

Silicon photonics biosensing: different packaging platforms and applications

We present two different platforms integrating silicon photonic biosensors. One is based on integration with reaction tubes to be compatible with traditional lab approaches. The other uses through-chip fluidics in order to achieve better mixing of the analyte.

Ring resonator based SOI biosensors

In this paper, two recent advances in silicon ring resonator biosensors are presented. First, we address the problem that due to the high index contrast, small deviations from perfect symmetry lift the degeneracy of the normal resonator mode. This severely deteriorates the quality of the output signal. To address this, we discuss an integrated interferometric approach to give access to the unsplit, high-quality normal modes of the microring resonator. Second, we demonstrate how digital microfluidics can be used for effective fluid delivery to nanophotonic microring resonator sensors fully constructed in SOI.

Digital Microfluidics With Pressure-Based Actuation

One of the key issues in biosensors is the time it takes for biomolecules in a solution to reach and bind to the sensor surface (particularly in low-concentration analytes). We present a novel flow scheme without microfluidic channels for label-free biosensors to decrease the delivery time of biomolecules. Through designing the biosensor in such a way that it becomes a membrane with holes, we can apply a droplet on it and push or pull it through the membrane by means of a pressure difference. Contrary to traditional microfluidics for, e.g., flow cells where the analyte flows over the sensor, the flow is now directed through the sensor. We have implemented this scheme in silicon-on-insulator biosensors and have demonstrated in a first proof-of-principle experiment, an improvement in delivery time of at least a factor of three.

Silicon nanophotonic ring resonator sensors integrated in reaction tubes

Enzyme-linked immunosorbent assays (ELISA) are the most popular immunoassay techniques performed every day in hospitals and laboratories and they are used as a diagnostic tool in medicine and plant pathology, as well as a qualitycontrol check in various industries. However, complex labeling techniques are required to be able to perform the assay and non-specific binding and endpoint timing are difficult to optimize. These issues could be solved by label-free techniques such as silicon nanophotonic microring resonator sensors, but this platform requires complex microfluidics, which is very much removed from the daily practice in e.g. hospital labs, which still relies to a large degree on platforms like 96-well microtiter plates or reaction tubes. To address these issues, here, we propose the combination of a simple and compatible reaction tube platform with label free silicon-on-insulator (SOI) photonic biosensors, where the flow is through the sensor chip as opposed to over the chip as in more conventional approaches. This device allows real time detection and analysis. Its great flexibility and small footprint make it ideal for an easy handling in any laboratory.

Reaction tubes as a platform for silicon nanophotonic ring resonator biosensors

We propose the combination of a simple reaction tube platform with label free SOI photonic biosensors. The device allows for the excellent performance of ring resonator sensors in a user-friendly platform to be used in labs and hospitals.

Photonic crystal biosensor in spatial fourier domain

We propose a photonic crystal biosensor, operating at a single wavelength, based on analysis of resonant guided modes in the spatial Fourier domain. Sensitivities of 65 degrees per RIU and more have been simulated.