What is the extinction coefficient of TMB of wavelength 654nm?

Answer 1

TMB is the most sensitive chromogenic substrate for detection of horseradish peroxidase (HRP)-labeled probes. In the presence of HRP and hydrogen peroxide (H2O2), TMB is oxidized first to a blue, cation free radical having an absorption maximum at 653 nm (ε = 3.9 x 104 M-1cm-1). Upon further reaction with HRP/H2O2, or addition of acid, the radical is converted to a terminal oxidation product, a yellow diimine that absorbs light at 450 nm (ε = 5.9 x 104 M-1cm-1). Increased sensitivity (2 - 4 fold) is afforded by the yellow diimine, as its molar extinction coefficient is greater than that of the blue radical. search.cosmobio.co.jp/cosmo_search_p/search_gate2/docs/CBC_/613544.20050405.pdf

Answer 2

The extinction coefficient of TMB (3,3',5,5'-tetramethylbenzidine) at a wavelength of 654 nm is typically around 39,000 M^(-1)cm^(-1). This value may vary depending on the specific conditions and purity of the TMB sample being used.