Poor Detection of Small Molecular Weight Proteins (Western Blot Immunodetection)

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Accepted Answer

Proteins below 15-20 kDa show weak or absent signal while larger proteins are detected normally. Small protein bands appear diffuse or masked. Common causes: 1) Large blocking molecules (e.g., BSA at 66 kDa) sterically masking small protein epitopes 2) Excessive surfactant (Tween-20, Triton X-100) concentration stripping small proteins from membrane 3) Prolonged incubation times causing small proteins to wash off membrane 4) Small proteins transferring through membrane during electroblotting Solutions: 1) Use low molecular weight blocking agents such as casein, polyvinylpyrrolidone (PVP), or protein-free blockers instead of BSA or milk 2) Minimize surfactant concentration (reduce Tween-20 to <0.05% or eliminate Triton X-100) 3) Reduce antibody and wash incubation times; use gentle agitation 4) Use membrane with smaller pore size (0.2 µm PVDF instead of 0.45 µm) for proteins <20 kDa; reduce transfer time and voltage