FIDA (Flow-Induced Dispersion Analysis) technology provides multiple simultaneous readouts in a single experiment. Thanks to its foundation in absolute hydrodynamic radius measurement, FIDA delivers robust and publication-ready data that go beyond traditional biophysical techniques. Below you will find an overview of each readout and what it means for research and drug discovery.

Molecular Size

Molecular size refers to the absolute hydrodynamic radius of a molecule in solution. Unlike molecular weight, which is a calculated value, hydrodynamic radius directly reflects how a molecule behaves in its native environment. This measurement allows researchers to study conformational changes, oligomerization, and protein–ligand interactions with precision. Read more here.

Binding Affinity

Binding affinity is the strength of the interaction between two molecules at equilibrium, expressed by the dissociation constant (Kd). It reflects the balance between association and dissociation rates. Low Kd values indicate strong binding, while high Kd values correspond to weaker interactions. Read more about it here.

Binding Kinetics

Binding kinetics describe the rates at which molecules associate and dissociate. The association rate constant (Kon) quantifies how quickly two molecules form a complex, while the dissociation rate constant (Koff) describes how quickly the complex falls apart. Together, these values provide mechanistic insight into molecular recognition and complex stability. As of our knowledge FIDA is the only technology capable of measuring kinetics in solution (without surface immobilization). Read more here.

Sample Viscosity

Viscosity is a measure of ''how easily a sample flows.'' In biophysics is the measure of a fluid’s internal resistance to flow, caused by the friction between its molecules. In biological samples, viscosity reflects how molecular interactions, crowding, or the presence of large biomolecules (such as proteins, nucleic acids, or polymers) influence solution dynamics. High viscosity can affect diffusion rates, molecular mobility, and binding kinetics, making it a critical parameter in protein formulation, cell biology, and biophysical assays.Monitoring viscosity is important for formulation studies, protein stability, and understanding how excipients affect biomolecules. With FIDA, viscosity can be tracked directly in small volumes, making it useful for both research and quality control. Read more here

Aggregation

Aggregation is the process by which individual molecules associate into larger assemblies, ranging from small oligomers to insoluble fibrils. Aggregation can be reversible or irreversible and is often driven by hydrophobic interactions, misfolding, or environmental stress. It directly impacts protein stability, therapeutic safety, and disease mechanisms. With FIDA you can study protein stability, amyloid fibrils, biomolecular condensates, read more here.

Sample Stickiness

Stickiness refers to nonspecific attractive interactions between biomolecules or between biomolecules and surfaces. It can result from electrostatic forces, hydrophobic patches, or exposed domains prone to aggregation. In practice, stickiness affects solubility, stability, and assay reliability. Measuring stickiness helps identify problematic formulations or unstable proteins. FIDA quantifies stickiness in-solution, helping identify potential risks early in the research pipeline. Explore more about stickiness and how to handle it in out knowldege base. Or read more about the readout on our website.

Quantification

Quantification in biophysics refers to determining the absolute concentration of a molecule in solution. Unlike relative methods, absolute quantification does not rely on calibration curves but instead derives concentration from fundamental physical parameters, such as diffusion and hydrodynamic radius. Read more about quantification measurement. Or see application example.

Sample Loss

Sample loss occurs when part of the material is degraded, aggregated, or otherwise unavailable during measurement. FIDA automatically reports on sample loss for every assay, offering an additional layer of experimental control and insights into sample integrity. Read more here.

Polydispersity Index

Polydispersity index (PDI) is a measure of the width of a molecular size distribution in a sample. In protein science, it reflects heterogeneity, indicating whether the sample consists of uniform molecules or contains size variants such as aggregates or oligomers. Read more about it here.

Labelling Quality (free label)

In FIDA, labelling quality is determined by directly detecting any free label present in the sample that has not been conjugated to the protein. The presence of free label indicates suboptimal labeling, which can compromise experimental accuracy and data interpretation. By reporting free label content automatically, FIDA provides researchers with assurance of sample integrity before further analysis. Read more here or here.

PDB Correlator

The PDB correlator links experimentally determined hydrodynamic radius values to structural models deposited in the Protein Data Bank (PDB). By comparing measured Rh with theoretical values derived from atomic coordinates, researchers can validate structural states, detect conformational changes, and confirm folding models. Read more on our website or in this application note.

Why Multiple Readouts Matter

By combining these 11 readouts in a single, in-solution assay, FIDA reduces complexity, saves precious sample material, and accelerates decision-making. This versatility is possible only because FIDA is based on absolute hydrodynamic radius measurement, giving researchers reliable, multiparametric data from one experiment.

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