Resources · Guide

Surface Chemistry
Explained

The sensor surface determines how your ligand attaches, whether it can be regenerated, and what sample quality you need.

← Back to Resources

Why it matters

Two strategies, very different trade-offs

Every SPR experiment starts with the same decision: how do you get your ligand onto the sensor surface? The answer determines your surface density, ligand orientation, regeneration strategy, and the purity requirements for your sample.

There are two fundamentally different approaches — direct covalent immobilization (you chemically couple the protein to the surface) and capture-based immobilization (the sensor surface holds a capture agent that grabs your tagged protein). Each has clear advantages and specific limitations.

RANDOM ORIENTATION ✓ ? ✕ SENSOR SURFACE (Au) ligand analyte blocked

STRATEGY 01

Direct immobilization

Covalent · EDC/NHS amine coupling

✓No tag or modification required
✓Permanent — survives hundreds of analyte cycles
!Requires purified protein (>80% homogeneous)
~Random orientation — some active sites may be buried
→Use Immobilization Scouting Kit to optimize preconcentration pH

Sensors

Carboxyl CMD AffiCoat

Kits

Amine Kit Amine CMD Kit Immo. Scouting
ORIENTATED CAPTURE ✓ ✓ ✓ CAPTURE LAYER SENSOR SURFACE (Au) capture agent ligand analyte

STRATEGY 02

Capture-based immobilization

Affinity · Tag or antibody interaction

✓Defined, orientated ligand presentation — all sites accessible
✓Strip and reload ligand — consistent RU level every cycle
✓Most pre-coated sensors are ready to use — no coupling step
✓Works with less-pure samples (antibody-capture sensors)
!Requires a tag or modification (His, biotin, Strep, Fc…)

Sensors

Anti-His NTA Protein A Protein G Streptavidin Strep-Tactin XT Anti-AAVX

Kits

NTA Kit SA Kit IgG Capture Kits

Side-by-side comparison

Direct immobilization
Capture-based
Tag required
None
His · Biotin · Strep · Fc…
Sample purity
>80% purified
Works with crude samples
Orientation
Random — some sites buried
Defined — all sites accessible
Surface lifetime
Permanent — very stable
Renewable — strip and reload
Setup
EDC/NHS activation + coupling
Pre-coated sensors ready to use

When to use each strategy

Direct immobilization

Choose covalent coupling when…

  • Your protein has no tag and can't be modified
  • You need a permanent, ultra-stable surface for long multi-day studies
  • Sample purity is high (>80%) and reproducible
  • You want to maximize surface density for low-MW analytes

Capture-based

Choose capture when…

  • Your protein carries a tag (His, biotin, Strep-tag, Fc region…)
  • You want consistent, orientated surface loading every run
  • Your sample is complex or partially purified
  • You need to regenerate the surface and reload fresh ligand

Ready to choose your sensor?

Use the step-by-step selector on the Sensor Guide to get a recommendation based on your specific ligand tag and experiment type — then go straight to the catalog to build your order.

Sensor Selection Guide → Browse Catalog