GCI vs Waveguide Interferometry and SPR
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, the Creoptix 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.
GCI vs BLI vs SPR: technology comparison
|Grating-Coupled Interferometry (GCI)
|Surface Plasmon Resonance (SPR)
|Biolayer Interferometry (BLI)
|Broadest application range
Suitable for a variety of molecules ranging from low to high molecular weights, purified or crude.
Suitable for Fragments, Small Molecules, Peptides, Proteins, Viruses, Cell Culture Supernatants, Serums, Cell lysates
Suitable for Small Molecules, Peptides (limited suitability for Fragments, Viruses, Cell Culture Supernatants, Serums, Cell lysates)
Suitable for Cell Culture Supernatants, Serums, Cell lysates (limited suitability for Peptides, Proteins, Viruses)
|Measure weakest binders
Ability to measure kinetics with fast off-rates thanks to fast fluidics and high acquisition rates.
Off-rates up to kd=10 s-1
Off-rates up to kd=1 s-1
Off-rates up to kd=0.1 s-1
|Measure tightest binders
Ability to accurately measure kinetics even for tight binders and fast on-rates.
Measurement under flow conditions
Measurement under flow conditions
Measurement under diffusion-limited conditions (no microfluidics)
|Low system maintenance
Little downtime due to service or unexpected repairs.
Frequently asked questions
- Advantages of Waveguide Interferometry over Surface Plasmon Resonance
- 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.
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.
- How is Grating-Coupled Interferometry (GCI) different from Bio-Layer Interferometry (BLI)?
- Although both Grating-Coupled Interferometry (GCI) and Bio-Layer Interferometry (BLI) work by using interference to measure refractive index changes on a thin layer above the surface of the sensor, they are two completely different technologies. GCI, the technology used in the Creoptix WAVEsystem, measures the effect of refractive index changes on an evanescent wave generated by the light passing through the waveguide in the sensor. These refractive index changes affect the phase of the light traveling through the waveguide, and interference with a reference light beam (hence interferometry) is needed to measure the phase change reliably and precisely. In contrast, BLI analyzes the interference pattern of white light reflected from two surfaces: a layer of protein immobilized on the biosensor tip, and an internal reference layer. Any change in the number of molecules bound to the biosensor tip can cause a shift in the interference pattern that may be measured in real-time as an increase in optical thickness at the biosensor tip; this results in a wavelength shift in the interference pattern.
- Can Grating-Coupled Interferometry (GCI) detect conformational changes?
- Hypothetically, the Creoptix WAVEsystem can detect conformational changes, provided those conformational changes make sufficient contribution to a change in the refractive index. The WAVEcontrol software also supports suitable interaction models which account for conformational changes. Despite this, conformational changes are difficult to infer purely based on either Creoptix WAVE kinetic data or SPR data. This is because conformational changes are seldom a one-step process, meaning models that would perfectly fit the kinetic data would be far too complicated to be fully trusted. Additionally, conformational changes might generate unexpected responses (e.g. negative curves) due to the surface reorganization, which could prove extremely difficult to analyze and quantify consistently. We recommend performing orthogonal validation of any suspected conformational changes and ensuring that kinetic analysis is as simple as possible, for instance by analyzing kinetic differences between functional mutants.
- Are the ligand capture and immobilization techniques used for SPR/BLI also suitable for GCI?
- Yes, standard immobilization techniques such as amine-coupling, Ni-NTA capture and streptavidin-biotin capture are also available for the Creoptix WAVEsystem on polycarboxylate surfaces; dextran surfaces can be supplied on request. Additionally, there is a wide range of other immobilization methods, including lipidic interactions or Protein A/G capture. An overview of the available surfaces (WAVEchips®) can be found here.