Alkaline Phosphatase Inhibition by Tween 20

Symptom

Western blot using alkaline phosphatase (AP)-conjugated antibodies shows weak or no colorimetric signal development. The BCIP/NBT or other AP substrates fail to produce expected colored precipitate even with adequate incubation time.

1. 1 Tween 20 present in wash buffers at standard concentrations (0.05-0.1%) inhibits AP enzyme activity
2. 2 Residual Tween 20 on membrane surface interfering with substrate conversion
3. 3 Non-ionic detergent disrupting AP enzyme conformation and catalytic site
4. 4 Incomplete removal of Tween 20 before substrate incubation

1. 1 Do not use Tween 20 in any buffers when working with AP-conjugated antibodies
2. 2 Replace Tween 20 with alternative non-inhibitory detergents (0.05% Triton X-100 may be suitable)
3. 3 Use Tris-buffered saline (TBS) without detergent for all wash steps in AP protocols
4. 4 Perform final washes with AP buffer (100 mM Tris-HCl pH 9.5, 100 mM NaCl, 5 mM MgCl₂) before substrate
5. 5 If Tween 20 was used, perform extensive washing (6-8 × 10 min) with TBS to remove residual detergent

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