Abstract As the critical micelle concentration (CMC) is one of the essential parameters of surfactant, the determination of CMC value is of great significance. We explored a facile and novel strategy based on the visible-light-induced oxidase-like activity of fluorescein for determining the CMC value of cationic surfactants. Fluorescein as a visible-light-induced oxidase mimic can catalyze the change of 3,3′,5,5′-tetramethylbenzidine (TMB) from colorless to blue (oxidation state TMB) under visible light illumination. Nevertheless, it was worth noticed that cationic surfactant could significantly inhibit the catalytic activity of fluorescein with a concentration-dependent mode due to the electrostatic interaction between negatively charged fluorescein and cationic surfactant in aqueous solution. With the increased of surfactants concentrations, the absorbance of the oxidation state TMB was decreased. As the concentration of cationic surfactant reached CMC, the catalytic activity of fluorescence was almost inhibited completely. Therefore, this novel and convenient spectrometric method provides a new idea for the determination of CMC value and also broadens the application of small molecule mimic enzymes.

中文翻译：

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基于荧光素的可见光诱导氧化酶活性测定阳离子表面活性剂的临界胶束浓度

摘要 由于临界胶束浓度(CMC)是表面活性剂的重要参数之一，因此CMC值的测定具有重要意义。我们探索了一种基于荧光素可见光诱导的氧化酶样活性的简便而新颖的策略，用于确定阳离子表面活性剂的 CMC 值。荧光素作为可见光诱导的氧化酶模拟物可以在可见光照射下催化 3,3',5,5'-四甲基联苯胺 (TMB) 从无色变为蓝色（氧化态 TMB）。然而，值得注意的是，由于带负电荷的荧光素与水溶液中的阳离子表面活性剂之间的静电相互作用，阳离子表面活性剂可以以浓度依赖的方式显着抑制荧光素的催化活性。随着表面活性剂浓度的增加，氧化态 TMB 的吸光度降低。当阳离子表面活性剂浓度达到CMC时，荧光催化活性几乎完全被抑制。因此，这种新颖方便的光谱方法为CMC值的测定提供了新的思路，也拓宽了小分子模拟酶的应用。