Weak signal: labeling versus recovery
Check target azides, free competitors and dye dissolution, then measure labeling and recovery after purification. If labeling is adequate but signal is weak, inspect the source, filter and working concentration. If labeling is low, investigate the reaction conditions.
High background: carryover and adsorption
Expose a matched no-azide sample to dye and purify it identically. Persistent signal points to carryover or nonspecific adsorption. When comparing working concentrations or washes, keep exposure or gain fixed and check that target signal is retained.
Use matched controls to locate background
Handle and acquire the complete reaction, no-azide sample and no-dye sample consistently. Negative controls help interpret background but do not replace product-composition analysis.
| Control result | Next step |
|---|---|
| Signal without dye | Check autofluorescence, other labels and instrument background |
| Signal persists in purified no-azide sample | Check residual dye or nonspecific adsorption and compare cleanup or washing |
| Signal only in the complete reaction | Assess labeling with product separation, average labeling density and functional testing |