What if the Sample Pad Does Not Absorb Sample?
- Hydrophobic materials can prevent smooth sample spreading. Add a suitable surfactant to the treatment buffer to improve wetting.
- Excessive or fixed BSA may slow flow. Reassess the BSA level and combine with Tween-20 or similar additives.
- After pretreatment, sample pads should be fully dried and stored under controlled humidity to reduce batch variation.
What if the Conjugate Pad Does Not Release?
- Irregular or aggregated colloidal gold particles may create inactive conjugate. Start by checking gold sol quality and coupling stability.
- Release buffer should balance surfactants, protein protectants and sugars to support conjugate rehydration and reduce glass fiber adsorption.
- Sugar spraying and drying parameters should be stable to avoid electrostatic adsorption and incomplete release.
How to Troubleshoot False Positives, High Background or Sensitivity Loss?
- Check whether gold conjugate blocking is sufficient, antibody concentration is appropriate, and buffer pH/salt levels are suitable.
- For high membrane background, evaluate dispense volume, blocking system, sample matrix interference and chromatography speed together.
- Sensitivity loss is often linked to moisture content, foil pouch sealing, desiccant status and storage temperature; accelerated stability testing is recommended.
Why Does the Strip Turn Purple or Gray During Drying?
- Color change usually indicates colloidal gold aggregation or activity loss. Review drying temperature, humidity and time first.
- Over-drying may damage protein conformation, while insufficient drying affects long-term stability. A repeatable drying window is essential.
- Use pilot-scale matrices to validate temperature and humidity combinations, then confirm with flow, background and stability data.
Safheal summarizes common issues in colloidal gold lateral flow test strip manufacturing, including sample pads, conjugate release, false positives, sensitivity and drying stability.