Grating-Coupled Interferometry

Grating-Coupled Interferometry

Engineered around a proprietary Grating-Coupled Interferometry (GCI) technology to deliver improved data quality from label-free biomolecular interaction analysis, the Creoptix™ WAVEsystem builds on Waveguide Interferometry to achieve superior resolution in signal and time compared to traditional Surface Plasmon Resonance. This allows researchers to quickly and accurately measure kinetic rates, determine affinity constants, and monitor the concentrations of even low abundance interacting analytes in crude samples such as biofluids. With unrivalled flexibility and high sensitivity, the Creoptix™ WAVEsystem brings label-free analysis to a whole new world of applications, revolutionizing the study of biomolecular interactions.

How we see light

Our patented Grating-Coupled Interferometry design leverages and enhances the intrinsic benefits of Waveguide Interferometry to exceed the sensitivity levels of Surface Plasmon Resonance. Like Waveguide Interferometry, the evanescent field penetrates less deep into the sample and extends the light-to-sample interaction length for improved signal-to-noise ratios (<0.01 pg/mm2). However, our GCI readout scheme has the advantage that the interferogram is created in the time-domain and within the waveguide, instead of being projected onto a CCD camera. Measuring refractive index changes on the sensor surface as time-dependent phase-shift signals therefore provides a more robust readout compared to classical Waveguide Interferometry or Surface Plasmon Resonance, regardless of temperature drifts or vibrations, translating to superior resolution in signal and time.

Surface Plasmon Resonance

Surface Plasmon Resonance is a label-free, optical biosensing technology that measures changes in refractive index close to a sensor surface. Traditional Surface Plasmon Resonance sensors consist of an electrically conducting metal film (gold) upon which the ligand of interest is immobilized. When polarized light at a defined angle (the incidence angle) hits the metal film, it excites collective oscillations of free electrons (surface plasmons), with an electromagnetic field extending beyond the metal surface. This so-called evanescent wave is used to probe the refractive index near to the sensor surface. When the immobilized ligand binds an analyte in solution, this local refractive index increases in direct proportion to the number of molecules bound to the sensor, making the refractive index shift equivalent to a change in mass. Reading out the refractive index shift by monitoring the incidence angle change allows researchers to use Surface Plasmon Resonance to determine the concentrations of interacting analytes (affinity) or to study real-time binding kinetics (association and dissociation rates) without the need to use labels.

SPR CX weblandscape

Surface Plasmon Resonance

Molecular interactions are detected as changes in refractive index within an evanescent field (orange) of the surface plasmon shown as energy dips at specific incidence angle.

Waveguide Interferometry

Like Surface Plasmon Resonance, Waveguide Interferometry also measures changes in refractive index at a sensor surface. However, in contrast to traditional Surface Plasmon Resonance, the light in Waveguide Interferometry can travel through the entire length of the sample. This allows more binding events to contribute to the overall signal, giving Waveguide Interferometry an intrinsically higher primary sensitivity for label-free interaction analysis, especially when paired with an interferometric readout to translate the phase change of the waveguide mode into an intensity pattern. A further advantage of Waveguide Interferometry over Surface Plasmon Resonance is that the evanescent field penetrates less deep into the sample, minimizing the disturbance caused by bulk refractive index changes and increasing the signal-to-noise ratio.

WI CX weblandscape

Waveguide Interferometry

Molecular interactions are detected as changes in refractive index within an evanescent field (orange) causing a phase shift of the beam in the waveguide and hence an interference to a reference beam projected in parallel to a screen.

Grating-Coupled Interferometry – a proprietary technology from Creoptix

Interpretation of Waveguide Interferometry data relies on accurate alignment of the reference beam and the measurement beam. However, during classical Waveguide Interferometry, perfect alignment is extremely challenging and sensitive to environmental effects such as temperature shifts or mechanical distortions or vibrations. With our proprietary Grating-Coupled Interferometry technology, we have developed a solution to eliminate the alignment issues common to classical waveguide set-ups, thereby offering the first robust implementation of Waveguide Interferometry on the market.

GCI CX weblandscape

Grating-Coupled Interferometry

In Grating-Coupled Interferometry (GCI) the reference beam is also coupled into the waveguide. Consequently, interference happens within the waveguide and a high-resolution, time-dependent and robust phase shift signal is created.

A further benefit of the Creoptix™ WAVEsystem is that it offers a crude-sample robustness normally only achieved with plate-based assays. This is attributable to clog-free microfluidics, making the Creoptix™ WAVEsystem ideal for label-free biomolecular interaction analysis in complex biofluids such as serum, plasma or cerebrospinal fluid (CSF), all of which are important to pharmacokinetic evaluations. By facilitating greater flexibility in the choice of sample material, the Creoptix™ WAVEsystem allows researchers to more accurately determine binding kinetics in physiologically relevant samples for better prediction of drug efficacy.

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