Water-soluble near-infrared fluorescent probes enhanced by ionic co-assembly of a four-armed amphiphile with SDBS: Toward application in cell imaging

Near-infrared (NIR) organic fluorescent probes have attracted great deal of attention for application in cell imaging, where the probes demand good water solubility, strong emission and good cytocompatibility. In this study, a conjugate of anthraquinone and tetraphenylethylene is introduced into an amphiphile (denoted by BTPEAQ-10) with four pyridinium terminated aliphatic chains. The assemblies of BTPEAQ-10 show an NIR emission peaked at 670 nm. Ionic co-assembly with sodium dodecyl benzene sulfonate leads to drastic enhancement of the fluorescent emission to 30-fold. Controlling experiments on different surfactants and anionic groups show that both the hydrophilic group and the alkyl chain play critical role to the emission enhancement. Both the assemblies and co-assemblies have good water solubility and cytocompatibility, and were applied in cell imaging. The co-assemblies showed much better contrast of cell imaging due to the higher emission property.