Intracellular pH homeostasis is essential for the survival and function of biological cells. Negatively charged molecular probes, such as pyranine (HPTS), tend to exhibit poor salt tolerance and unsatisfactory cell permeability, limiting their widespread use in intracellular assays. Herein, we explored a charge neutralization strategy using multicharged cationic nanocarriers for an efficient and stable assembly with the pH-sensitive HPTS. Through immobilization and neutralization with poly-(allylamine hydrochloride)-stabilized red-emitting gold nanoclusters (PAH-AuNCs), the resulting nanoprobes (HPTS-PAH-AuNCs) offered improved salt tolerance, satisfactory cell permeability, and dual-emission properties. The fluorescence ratio exhibited a linear response over the pH range of 3.0−9.0. Moreover, the proposed HPTS-PAH-AuNCs were successfully applied to determine and visualize lysosomal pH variations in living cells, which indicated great potential for biosensing and bioimaging applications in living systems. Benefiting from the charge neutralization strategy, various types of probes can be expected to achieve broader analytical applications.
The structural phase of micelles plays an important role in controlling the micellar performance. Despite the great developments of some advanced characterization techniques, it remains challenging to achieve fast and sensitive determination of micellar transitions in solution. Herein, a novel indicator system for micellar transitions was developed based on the micelle-mediated peroxyoxalate chemiluminescence that showed a sensitive response toward the changes of micellar morphologies. A peroxyoxalate derivative and a fluorophore were first coassembled into the hydrophobic cavities of micelles of the typical cationic surfactant cetyltrimethylammonium bromide (CTAB). A strong and rapidly falling chemiluminescence response was exhibited in spherical micelles as a result of the loose arrangement of CTAB molecules. By contrast, rodlike or wormlike micelles transformed from spherical micelles could induce a compact arrangement of CTAB molecules, leading to a weak chemiluminescence emission with a slow decay rate. The practicability and universality of the chemiluminescent indicator were demonstrated by determining the micellar transitions in a variety of surfactant solutions (ionic, nonionic, and polymeric). These findings open attractive perspectives for the practice of chemiluminescence technique in micelle characterization.
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