3,3,5,5-Tetramethylbenzidine dihydrochloride, 1 g

Stock solutions (All solutions are stable for at least 1 year at 4 °C):
0.5 g NBT in 10 ml 70 % dimethylformamide;
0.5 g BCIP (p-toluidine salt) in 10 ml 100 % dimethylformamide.
Incubation buffer for alkaline phosphatase:
100 mM NaCl, 5 mM MgCl₂,100 mM Tris (pH 9.5).
Fresh substrate solution: 66 μl NBT stock solution + 10 ml incubation buffer, mix well, add 33 μl BCIP stock solution. Use within 1 hour.
Blot development: Approx. 10 ml substrate solution per 15 x 15 cm² membrane surface. Develop at room temperature until bands become visible (approx. 30 mins).
Reaction stop: Rinse with PBS/20 mM EDTA.

Dissolve 1 mg TMB in 0.1 ml dimethylsulfoxide (Art. No. 4720); add 9.9 ml of a 0.1 M sodium acetate solution (pH 6.0) (Powder: Art. No. 6779), filter and add H₂O₂ (Art. No. 8070) (final concentration 0.01 %).

Always prepare freshly!

Incubation 10-30 mins at room temperature (approx. 50 μl per microtitre well; finally add 50 μl 1 M H₂SO₄, Art. No. X873, per well).
Photometric quantitation at 450 nm.

Reference: Bos E.S. et al. (1981) J. Immunoassay 2, (3/4), 187.