> ## Documentation Index
> Fetch the complete documentation index at: https://docs.adaptyvbio.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Binding

> Measure whether and how strongly your proteins bind their targets

## Two ways to run binding

### Binding screening (2 concentrations)

* **What it is:** Fast triage using two target concentrations to sort variants by binding strength.
* **When to use:** Early discovery and library down‑selection.
* **Output:** Strong / Medium / Weak / Non‑binder classification with ranked responses.

### Affinity characterization (4+ concentrations)

* **What it is:** Multi‑concentration series (typically 5–7) with global fitting for precise KD, kon, and koff.
* **Why this works:** Multiple concentrations across orders of magnitude constrain the fit, separating association (kon) and dissociation (koff). This yields reliable KD across a wider range (≈0.1 nM to 10 µM) than single‑point reads.
* **When to use:** Lead optimization, benchmarking, and mechanism studies.
* **Output:** KD, kon, koff with confidence intervals and fit diagnostics.

<CardGroup cols={2}>
  <Card title="Expression" icon="dna" href="/docs/experiment-types/expression">
    Confirm expression and yield before binding.
  </Card>

  <Card title="Thermostability" icon="temperature-high" href="/docs/experiment-types/thermostability">
    Use Tm to pick robust variants.
  </Card>
</CardGroup>

## Choose the right depth

* **Screening**: Maximize throughput and minimize cost to find winners.
* **Characterization**: Quantify kinetics to pick and improve the best.

## Related pages

* [Expression](/docs/experiment-types/expression)
* [Thermostability](/docs/experiment-types/thermostability)
* [Enzyme Activity](/docs/experiment-types/enzyme-activity)
* [Binding Data Package](/docs/experiment-setup/binding-data-package)
* [BLI technology overview](/wiki/technologies/BLI)
* [SPR technology overview](/wiki/technologies/SPR)

## FAQs

<AccordionGroup>
  <Accordion title="Why don't I always get KD values for my proteins?">
    Our assay loads your constructs onto sensors and measures association/dissociation against a target analyte. If expression is None/Low, signal-to-noise may be insufficient for precise KD. Stronger expression yields cleaner fits.
  </Accordion>

  <Accordion title="What KD range can you quantify?">
    Typically \~0.1 nM to 10 µM. At the extremes (very tight/weak) accuracy drops; we can adjust concentrations and contact times to bias for tight or weak interactions as needed.
  </Accordion>

  <Accordion title="What do binding labels mean?">
    True: clear binder above controls. False: expresses but at/below control signals. Unknown: no/low expression or marginal signals. Strength buckets: Strong (sub 50 nM), Medium (50 nM–1 µM), Weak (>1 µM).
  </Accordion>

  <Accordion title="How are curves fitted?">
    We record time and wavelength shift at 5 Hz and fit 1:1 models; when multiple concentrations are run, we use global fitting across the series.
  </Accordion>

  <Accordion title="Why do screening KDs differ from full characterization?">
    Screening uses 1–2 concentrations to triage binders; uncertainty is higher than multi‑concentration characterization designed for precise KD, kon, koff.
  </Accordion>

  <Accordion title="Do you support specificity and cross‑reactivity tests?">
    Yes. We can run cross‑reactivity and polyspecificity panels (e.g., BVP, BSA/HSA); full‑serum profiling is in development.
  </Accordion>

  <Accordion title="How do you handle non‑specific binding (NSB)?">
    We screen new targets for NSB and adjust buffers or suppliers. High NSB can lead to negative‑shift curves after reference subtraction.
  </Accordion>

  <Accordion title="What about unusual or bi‑phasic curves?">
    May indicate multi‑step mechanisms or conformational change. Relative rankings remain useful; precise kinetics may require expanded concentration series.
  </Accordion>

  <Accordion title="Do you offer competition/inhibition assays?">
    Yes. We run neutralization/inhibition and competition formats (IC50, epitope access) on request.
  </Accordion>
</AccordionGroup>

<Callout>
  Ready to set up a binding experiment? Visit <a href="https://start.adaptyvbio.com/binding" target="_blank" rel="noreferrer">start.adaptyvbio.com/binding</a>.
</Callout>