Amphiphiles, i.e., compounds with both hydrophilic and hydrophobic parts, only form micelles at concentrations above a certain threshold, called the critical micelle concentration (CMC). Measuring the CMC accurately can be challenging. Fluorometry, for example, is a simple and sensitive method, but suffers from interference due to fluctuation in background fluorescence. The accuracy of CMC determination could potentially be improved by using fluorophores with negligible background fluorescence.

Weili Zhao, Wei Wu, Fudan University and Tongji University School of Medicine, both Shanghai, China, and colleagues have synthesized a series of aza-BODIPY-based fluorophores. A distinctive feature of these fluorophores is absolute aggregation-caused quenching, or aACQ, in an aqueous environment due to spontaneous aggregation. The strength of aACQ-based fluorometry lies in the near-zero background at an amphiphile concentration below the CMC, and therefore, negligible interference.

Using aACQ fluorophores in place of conventional fluorophores, the CMCs of different surfactants and amphiphilic copolymers were measured with improved accuracy and high sensitivity. The researchers believe this method might be an improvement over the use of conventional fluorophores for the measurement of CMCs.

• Accurate and sensitive probing of onset of micellization based on absolute aggregation‐caused quenching effect,
  Haisheng He, Chang Liu, Jiang Ming, Yongjiu Lv, Jianping Qi, Yi Lu, Xiaochun Dong, Weili Zhao, Wei Wu,
  Aggregate 2022.
  https://doi.org/10.1002/agt2.163