Antibody or Reagent Loss of Activity from Improper Storage (ELISA (Signal Problems))

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Progressive signal loss over time using the same reagents. Previously working protocols suddenly fail. Positive controls that worked before now show reduced or no signal. Common causes: 1) Multiple freeze-thaw cycles degrade antibody structure and reduce binding affinity 2) Fluorophore-conjugated antibodies exposed to light undergo photobleaching and signal loss 3) Storage temperature higher than recommended accelerates protein denaturation 4) Repeated use of antibodies from same aliquot reduces effective concentration through adsorption and degradation 5) Enzyme conjugates lose activity when stored improperly or past expiration date Solutions: 1) Aliquot antibodies and reagents into single-use volumes immediately upon receipt; avoid repeated freeze-thaw (maximum 3-5 cycles) 2) Store fluorophore-conjugated antibodies in dark at 4°C; wrap vials in aluminum foil to prevent light exposure 3) Follow datasheet storage instructions precisely: typically -20°C or -80°C for long-term, 4°C for working solutions 4) Use fresh aliquots of primary and secondary antibodies for each new experiment 5) Run positive controls with known working reagents to identify degraded components; discard and replace if activity is lost