SPR vs BLI: Which Biosensor Technique is Right for You?
Surface Plasmon Resonance and Bio-Layer Interferometry are the two dominant label-free biosensor technologies for measuring binding kinetics. This guide breaks down the key differences to help you choose — or use both.
Analyze Your Data →How Each Technology Works
🟡 Surface Plasmon Resonance (SPR)
SPR measures changes in the refractive index near a thin gold film on a glass sensor chip. When polarized light hits the gold surface at a specific angle, surface plasmons are excited. Binding of molecules to the surface changes the local refractive index, shifting the resonance angle.
The response is measured in resonance units (RU), where 1 RU ≈ 1 pg/mm² of bound mass. SPR uses a microfluidic system to deliver analyte over the immobilized ligand, creating a continuous-flow environment that closely mimics solution-phase behavior.
Key instruments: Biacore T200, Biacore 8K+, Biacore S200, Carterra LSA, Bruker Sierra, Nicoya Alto
🟢 Bio-Layer Interferometry (BLI)
BLI measures the interference pattern of white light reflected from two surfaces: the internal reference layer and the biolayer at the tip of a fiber-optic biosensor. When molecules bind to the biosensor tip, the optical thickness increases, causing a shift in the interference pattern.
The response is measured in nanometers (nm) of wavelength shift. BLI uses a dip-and-read format — biosensor tips are dipped into microplate wells containing samples. This eliminates the need for microfluidics and makes the system inherently robust to matrix effects.
Key instruments: Sartorius Octet RED96e, Octet R8, Octet R2, Octet K2, Gator Prime
Side-by-Side Comparison
| Parameter | SPR | BLI |
|---|---|---|
| Detection Principle | Refractive index change at gold surface | Optical thickness change at biosensor tip |
| Sample Delivery | Continuous flow (microfluidics) | Dip-and-read (no fluidics) |
| Throughput | Low–Medium (serial or 8-channel) | Medium–High (8, 16, or 96 channels) |
| Sample Consumption | Low (µL-scale, but continuous flow) | Moderate (200 µL wells, but recoverable) |
| Sensitivity | Very high (~0.1 pg/mm² surface mass) | High (~0.1 nm wavelength shift) |
| Small Molecule Detection | Excellent (high sensitivity per unit mass) | Limited (requires high density or amplification) |
| Crude Sample Tolerance | Limited (requires clean samples) | Excellent (dip-and-read minimizes matrix effects) |
| Instrument Cost | $$$ – $$$$ | $$ – $$$ |
| Consumable Cost | Moderate (sensor chips reusable 50–100×) | Moderate (biosensor tips, single-use) |
| Ease of Use | Moderate (fluidics maintenance required) | Easy (no fluidics, minimal maintenance) |
| Mass Transport Effects | Flow-rate dependent, well-characterized | Shaking-speed dependent, less predictable |
When to Choose SPR vs BLI
Choose SPR When…
- ✓You need to characterize small molecules (<500 Da) where BLI lacks sensitivity
- ✓You require the highest kinetic accuracy for regulatory submissions
- ✓You are measuring very fast kinetics (ka > 10⁶ M⁻¹s⁻¹) where controlled flow rates help
- ✓You need concentration analysis (CFCA) alongside kinetics
- ✓Your application requires thermodynamic analysis with precise temperature control
Choose BLI When…
- ✓You need high throughput — screening hundreds of clones or conditions
- ✓You are working with crude samples like cell culture supernatants
- ✓You want minimal maintenance — no fluidics to prime or degas
- ✓You are performing epitope binning with many antibody pairs
- ✓Your lab has limited biosensor experience — BLI has a shorter learning curve
Can You Compare Data Between Platforms?
Yes — kinetics are kinetics. The fundamental binding parameters (ka, kd, KD) describe the molecular interaction itself, not the detection method. A well-designed experiment on SPR and BLI should yield comparable rate constants for the same interaction.
That said, there are practical considerations. Mass transport limitations differ between flow-based (SPR) and dip-and-read (BLI) systems. Immobilization strategies vary — SPR typically uses amine coupling or capture on CM5/CM7 chips, while BLI uses pre-coated biosensor tips (SA, AHC, AR2G, etc.). These differences can introduce systematic offsets if experiments are not properly controlled.
The key to cross-platform comparison is proper experimental design: matched surface densities, appropriate analyte concentrations, and careful reference subtraction. When these are done correctly, published studies consistently show agreement within 2–3× for rate constants and often within 30% for KD values.
KinetiHub makes cross-platform comparison straightforward by providing a unified analysis environment. Upload your Biacore and Octet data side by side, fit with the same kinetic models, and compare parameters directly — no format conversion or software switching needed.
KinetiHub: Instrument-Agnostic Analysis
Multi-Format Import
Upload data from Biacore (tab-delimited txt), Octet (.frd), and other platforms. KinetiHub handles the parsing so you don't have to.
Unified Fitting Engine
Same kinetic models, same fitting algorithms, same quality metrics — regardless of whether your data came from SPR or BLI.
Cross-Platform Comparison
Compare kinetic parameters from different instruments in one place. Ideal for method transfer validation and multi-site studies.
Learn more about each platform's data analysis workflow:
Frequently Asked Questions
Is SPR more sensitive than BLI?
In general, yes. SPR can detect smaller mass changes and is better suited for small molecule characterization. The refractive index–based detection is inherently more sensitive than the optical thickness measurement used by BLI. However, for typical protein–protein interactions (antibodies, receptors, enzymes), both technologies provide excellent sensitivity. The practical sensitivity difference matters most for fragments and compounds below ~200 Da.
Can I compare SPR and BLI results?
Absolutely. The kinetic rate constants (ka and kd) and equilibrium dissociation constant (KD) describe the intrinsic properties of the molecular interaction. When experiments are well-designed on both platforms, the results should agree within experimental error. KinetiHub allows you to upload and analyze data from both SPR and BLI instruments, making it straightforward to compare results across platforms. See our Academy for guidance on experimental design.
Which is better for antibody characterization?
It depends on the stage of your workflow. During early discovery and screening, BLI excels due to its high throughput and tolerance for crude samples — you can dip directly into hybridoma supernatants without purification. For detailed kinetic characterization of lead candidates, SPR is often preferred because of its superior sensitivity and well-established regulatory acceptance (FDA/EMA submissions commonly reference Biacore data). Many antibody development programs use both: BLI for screening and ranking, SPR for definitive kinetic characterization.
What about GCI (Grating-Coupled Interferometry)?
GCI is a newer label-free technique offered by Creoptix (now Malvern Panalytical) that combines the flow-based sample delivery of SPR with interferometric detection. It offers excellent sensitivity and very fast injection switching, which can be advantageous for complex kinetic models. KinetiHub can analyze GCI data exported as CSV — learn more on our Academy pages.
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