Banner image for CovalX epitope mapping services showing a 3D molecular surface model of an antibody-antigen interaction de novo sequencing

Epitope Mapping Service CovalX provides epitope mapping services using XL-MS and HDX-MS to characterize antibody binding sites and protein-protein interactions at the peptide level.

Affinity: BLI & SPR

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CovalX offers two complementary label-free interaction platforms, Surface Plasmon Resonance (SPR) and Bio-Layer Interferometry (BLI), covering both high-accuracy kinetic characterization and fast candidate screening on the same molecule, alongside its mass spectrometry-based characterization portfolio.

Binding Kinetics in Biotherapeutic Development

Real-time, label-free binding data supports lead selection from early discovery through comparability assessment. Kinetic and affinity profiles generated by SPR and BLI serve as functional fingerprints for ranking candidates, grouping antibodies by epitope, and comparing production batches, process changes, or innovator and biosimilar pairs. This data feeds directly into the biological activity and comparability sections of IND, BLA, and biosimilar dossiers, complementing the structural and mass spectrometry based characterization generated elsewhere in the portfolio, and is referenced in ICH Q5E comparability packages accepted by both FDA and EMA.

Techniques

Surface plasmon resonance sensor chip with gold film, immobilized ligand and analyte

Resonance (SPR) Detection Principle Surface plasmon resonance directs polarized light through a prism onto a gold-coated sensor chip. Binding of the analyte to the immobilized ligand modifies the local refractive index and shifts the resonance angle measured at the detector. The resulting sensorgram yields association and dissociation rate constants and equilibrium dissociation constants without labeling.

Surface Plasmon Resonance (SPR)

SPR tracks binding in real time by measuring refractive index changes as one partner flows across a sensor chip on which the other is immobilized. The technique provides high accuracy at low sample consumption, with an affinity range spanning femtomolar to millimolar binding, and supports drug discovery, lead optimization, membrane target characterization, and comparability studies. [Learn more about SPR analysis.]

Biolayer interferometry biosensor tip with immobilized ligand capturing analyte in solution

Biolayer Interferometry (BLI) Detection Principle Biolayer interferometry measures the interference pattern generated by white light reflected at two surfaces of the biosensor: the immobilized biolayer and an internal reference layer. Analyte binding to the ligand increases the optical thickness of the biolayer and shifts the interference spectrum, producing label-free, real-time association and dissociation profiles for kinetic and affinity determination.

Bio-Layer Interferometry (BLI)

BLI tracks binding at the tip of a fiber optic biosensor dipped directly into the sample, with no microfluidics involved. The open, dip-and-read format tolerates crude or viscous samples and supports high-throughput screening of large candidate panels, hybridoma clones, and epitope binning, ahead of higher-accuracy kinetic confirmation. [Learn more about BLI analysis. ServicePage coming soon!]

Choosing between SPR and BLI

Throughput needs.

BLI runs in a 96 or 384-well format with multiple channels working in parallel. If the project involves screening many candidates (antibody panels, clone selection), BLI is usually faster.

Sensitivity requirements.

SPR detects smaller molecules and weaker affinities more reliably. For fragment screening, small-molecule binding, or low-affinity interactions, SPR is the stronger choice.

Sample consumption.

BLI requires larger sample volumes since it isn’t fluidic. If material is limited (early-stage antibody discovery, low-yield expression), SPR consumes less analyte per run.

Matrix tolerance.

BLI tolerates crude samples like cell culture supernatant without extensive purification. SPR is more sensitive to non-specific binding from complex matrices and generally needs cleaner samples.

Kinetic precision.

SPR gives more accurate kon/koff values and is the standard for regulatory submissions requiring precise affinity data (KD, ka, kd). BLI kinetics are reliable for ranking and screening but show more variability at the extremes of the affinity range.

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Not sure whether SPR or BLI best fits your project?

Contact us and we’ll assess your sample and objectives.

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One CRO, Coordinated Data

Affinity and kinetic analysis at CovalX is integrated with the broader characterization portfolio. Candidates ranked by SPR or BLI can move directly to HDX-MS or XL-MS high-resolution epitope mapping of the binding interface, on the same sample submission, and every SPR project begins with intact protein QC by High-Mass MALDI MS.

Running these analyses through a single CRO reduces sample handling steps, keeps molecular context consistent across techniques, and consolidates reporting into a single deliverable.