ULVAC AFFINIX Q — QCM Molecular Interaction Analysis
The ULVAC AFFINIX Q series are quartz crystal microbalance (QCM) instruments for real-time, label-free measurement of molecular binding kinetics in liquid. Applications include drug-target interaction screening, antibody characterisation, biosensor development, protein-lipid interaction studies, and polymer film characterisation. The instrument measures resonant frequency shift (proportional to bound mass) and energy dissipation (layer viscoelasticity) simultaneously.
Part Numbers
Operating Principle
A piezoelectric quartz crystal oscillates at approximately 27 MHz. Molecular binding to the functionalised sensor surface adds mass, reducing the resonant frequency. The Sauerbrey equation: Δf = −C·Δm (C ≈ 0.183 Hz·cm²/ng for 27 MHz crystals). Sub-nanogram sensitivity per unit area. The simultaneously measured dissipation factor D distinguishes rigid films (low D, Sauerbrey model valid) from soft or hydrated layers (high D, Voigt viscoelastic model required).
Sensor Handling and Surface Preparation
- Handle sensors by the edge only — fingerprints or particles on the active gold surface degrade sensitivity and are difficult to remove
- Store unused sensors in original packaging, dry, at room temperature, away from light
- Clean gold surface before functionalisation: UV/ozone treatment 10–15 min, or rinse with ethanol → deionised water → nitrogen dry
- Functionalise with SAM (e.g. 11-MUA or thiol derivative) before covalent ligand coupling, or use streptavidin-biotin system for biotinylated ligands
- Equilibrate sensor in running buffer for at least 20 minutes before starting assay to obtain stable baseline
Commissioning and First-Run Procedure
- Install sensor crystal into measurement cell — verify o-ring seats evenly around the electrode
- Prime fluidic lines with running buffer before connecting to cell — all air bubbles must be eliminated
- Fill measurement cell with running buffer (typically PBS pH 7.4 or assay-specific buffer)
- Set temperature controller to assay temperature and allow 20–30 minutes for thermal equilibration
- Verify baseline frequency drift is below 1 Hz/min before proceeding
- Perform reference buffer injection to confirm baseline stability and check for buffer mismatch artefacts
- Begin assay: inject analyte at required concentration and flow rate per experimental protocol
Fault Diagnosis
| Symptom | Cause | Action |
|---|---|---|
| Noisy or jumping baseline | Air bubble trapped in measurement cell | Prime fluidics; gently tap cell; check connections for leaks |
| Drift above 2 Hz/min | Temperature not equilibrated | Wait longer; check thermostat setpoint and confirm water bath circulation |
| No frequency shift on analyte injection | Ligand not coupled to surface; analyte inactive | Verify surface chemistry protocol; check analyte activity and concentration |
| Frequency spike at injection start | Buffer mismatch between sample and running buffer | Prepare sample in running buffer; match ionic strength and pH exactly |
| High dissipation, small frequency shift | Soft hydrated binding layer (polymer, vesicle, or cell) | Normal behaviour — apply Voigt viscoelastic model for mass calculation |
| Poor regeneration between cycles | High-affinity or irreversible binding | Optimise regeneration buffer (pH, salt concentration); consider single-use sensors |
| No crystal frequency signal | Crystal cracked, contaminated, or incorrectly seated | Inspect crystal; replace if cracked; clean flow cell and reinstall |
Preventive Maintenance
- Replace o-rings in measurement cell every 50 measurement cycles or on first sign of leak
- Flush all fluidic lines with deionised water after each measurement day
- Flush with 0.1% SDS solution weekly to remove protein residue from tubing
- If instrument is not used for more than one week: flush with deionised water, nitrogen-dry the flow cell, and store dry
- Inspect Luer connectors and tubing for cracks or kinking every 3 months
Training and Application Support
Training is available for ULVAC AFFINIX Q users on: experimental design for kinetics measurement, surface functionalisation protocols, data analysis using Sauerbrey and Voigt models, assay optimisation for specific molecular pairs, and troubleshooting. Contact mail@ulvacheliot.com with instrument model (AFFINIX Q4 or Q8), assay type, and a brief description of support required.
Service Enquiry
For sensor crystals, o-ring replacement kits, flow cell components, and service visits: email mail@ulvacheliot.com. Please provide: instrument model, serial number, and a description of items required or fault observed.