Grating-coupled interferometry (GCI)
Discover a new approach to biomolecular interaction analysis
The Kinetics Guide | Binding kinetics with the WAVE system. Download now
Download nowDiscover a new approach to biomolecular interaction analysis
Grating-coupled interferometry is a label-free technique for real-time analysis of molecular interactions. It works by measuring miniscule changes in the local refractive index that occur when molecules bind to a sensor surface, enabling researchers to:
GCI is frequently used in drug discovery for fragment screening, hit-to-lead optimization, and to characterize small-molecule or biologic drug candidates.
Grating-coupled interferometry was developed for the WAVEsystem a Creoptix technology.
Building on the principles of classical waveguide interferometry, it achieves label-free analysis with superior resolution in signal and time compared to traditional surface plasmon resonance (SPR).
WAVEsystem is built on patented GCI technology from Creoptix, a Malvern Panalytical brand. It unlocks biophysical analysis breakthroughs with:
WAVEsystem is the most sensitive label-free optical biosensor on the market, enabling a broader range of assays with information-rich kinetics data you can trust, even for weak binding events.
Measure a wide range of sample types, from small molecules to membrane proteins to crude samples.
Say goodbye to trade-offs between measurement confidence and speed with 10x faster kinetic screening.
WAVEsystem’s greater ease of use and streamlined operation reduce downtime to maximize productivity.
Grating-coupled interferometry is an advanced technique that offers superior data quality and resolution compared to other label-free biomolecular interaction analysis techniques, including:
Waveguide interferometry is the underlying measurement principle for GCI. It works by directing light through an optical waveguide, detecting changes in the refractive index above the waveguide surface. This signal is combined with a parallel reference beam to measure phase shifts.
In traditional waveguide interferometry instruments, splitting the measurement and reference light beams requires a complex spatial setup that makes the physical alignment of the instrument sensitive to thermal drift, vibrations, and mechanical noise.
Bio-layer interferometry works by shining white light down a fiber-optic biosensor tip, which reflects off two surfaces: an internal reference layer and an outer layer where molecules bind.
When the target molecules attach to the tip, the layer thickness changes, altering the inference pattern of the reflected light waves. These are then tracked as real-time wavelength shifts.
Surface plasmon resonance analysis works by directing a beam of polarized light through a glass prism onto a thin metal film, usually made of gold, at an angle that causes total internal reflection.
At a specific angle, depending on the refractive index surrounding the metal surface, the energy of the incoming light couples with and excites surface plasmons, which are collective oscillations of free electrons in the gold layer. Because energy is then transferred from the light to the plasmons, it produces a measurable dip in reflected light intensity at that angle.
To use this technique to measure molecular interactions, ligands are attached directly to the gold surface of the sensor chip, while a fluid carrying the analyte flows over the chip. When the analyte binds to the ligand, the local mass and refractive index change, shifting the resonance angle and enabling researchers to calculate binding speed and affinity.
WAVEsystem’s patented grating-coupled interferometry design enhances the intrinsic benefits of waveguide interferometry to exceed the sensitivity levels of surface plasmon resonance.
Like waveguide interferometry, the evanescent field penetrates less deeply into the sample and extends the light-to-sample interaction length for improved signal-to-noise ratios (<0.01 pg/mm2).
The WAVEsystem GCI readout scheme also 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 SPR, regardless of temperature drifts or vibrations, translating to superior resolution in signal and time.
Below is a summary of how GCI, BLI, and SPR compare as biophysical analytical techniques.
| 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. |
Yes
Suitable for fragments, small molecules, peptides, proteins, viruses, cell culture supernatants, serums, cell lysates |
No
Suitable for small molecules, peptides (limited suitability for fragments, viruses, cell culture supernatants, serums, cell lysates) |
No
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. |
Yes
Off-rates up to kd=10 s-1 |
No
Off-rates up to kd=6 s-1 |
No
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. |
Yes
Measurement under flow conditions |
Yes
Measurement under flow conditions |
No
Measurement under diffusion-limited conditions (no microfluidics) |
|
Low system maintenance
Little downtime due to service or unexpected repairs. |
Yes
No-clog microfluidics |
No
Traditional microfluidics |
Yes
No microfluidics |
Like SPR, GCI – the technology used in the Malvern Panalytical WAVEsystem – also measures changes in refractive index at a sensor surface. However, because GCI builds on the principles of waveguide interferometry, its light travels through the entire length of the sample rather than interacting only with a thin region near the surface, as in traditional SPR.
This allows more binding events to contribute to the overall signal, giving GCI an intrinsically higher primary sensitivity for label-free interaction analysis than SPR, especially when paired with an interferometric readout to translate the phase change of the waveguide mode into an intensity pattern.
A further advantage of GCI over SPR is that the evanescent field penetrates less deeply 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 with a reference beam projected in parallel to a screen.
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 built on different measurement principles.
GCI measures phase shifts in an evanescent wave traveling through a waveguide, while BLI tracks wavelength shifts in white light reflected from the tip of a fiber-optic biosensor.
For users, the more important difference is fluidics. GCI uses continuous microfluidic flow to deliver sample to the sensor, while BLI relies on diffusion, with the biosensor tip dipped directly into a static well. That makes GCI better suited to fast kinetics and tight-binding interactions, where a constant supply of fresh sample matters, while BLI's simpler, flow-free setup favors higher throughput for less demanding kinetics.
Hypothetically, the Malvern Panalytical 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 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.
Yes, standard immobilization techniques such as amine-coupling, Ni-NTA capture and streptavidin-biotin capture are also available for the 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 surfaces available can be found on our KYMAchip page.
Yes. Membrane proteins are among the most challenging targets in interaction analysis, as they're typically expressed at low density, often behave as large, heterogeneous complexes, and can involve substantial size mismatches between the ligand and analyte. This combination of properties demands a level of sensitivity that many label-free techniques struggle to deliver.
GCI's sensitivity makes it particularly well suited to these targets. The WAVEsystem resolves kinetics from signals below 1 pg/mm² (1 RU) and supports ligand-to-analyte molecular-weight ratios of up to 1000:1, accommodating the sharp size mismatches common in membrane protein interactions. Low baseline drift (<0.3 pg/mm²/min) and low noise levels (<0.01 pg/mm²) keep weak, low-abundance binding events distinguishable from background, while fast dissociation rates (up to 10 s⁻¹) can still be accurately captured thanks to optimized fluidics, chip design, and high acquisition rates (1, 10, and 40 Hz).
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