Fluorescent bioprobe is an essential tool for bioscience, biotechnological and clinical research. The utilization of fluorescent probes enables direct visualization of the bio-events, real time monitoring of the microenvironmental changes in biological systems, and selectively tagging of a molecule/cell of interest. Most of the conventional organic fluorescent dyes are emissive in dilute solutions. Their fluorescence, however, is weakened or even quenched upon aggregation or when heavily labeled in a biomacromolecule. This so called “aggregation caused quenching” (ACQ) effect greatly limits their application.

In 2001, a new class of fluorophores with an opposite property has been discovered. These fluorophores are non-emissive when molecularly dissolved but are induced to emit...[ Read more ]

Fluorescent bioprobe is an essential tool for bioscience, biotechnological and clinical research. The utilization of fluorescent probes enables direct visualization of the bio-events, real time monitoring of the microenvironmental changes in biological systems, and selectively tagging of a molecule/cell of interest. Most of the conventional organic fluorescent dyes are emissive in dilute solutions. Their fluorescence, however, is weakened or even quenched upon aggregation or when heavily labeled in a biomacromolecule. This so called “aggregation caused quenching” (ACQ) effect greatly limits their application.

In 2001, a new class of fluorophores with an opposite property has been discovered. These fluorophores are non-emissive when molecularly dissolved but are induced to emit extensively by aggregate formation. This phenomenon is named “aggregation-induced emission” (AIE). Attracted by its intriguing phenomenon and its promising perspectives, a program focused on the development of novel AIE probes and exploration of their application in biotechnology has been launched.

For biotechnological applications, fluorescent dyes with intense emission in long wavelength region are extremely attractive owing to their capability of overcoming the interferences of autofluorescence of the biological systems. To afford red emitting AIE molecules, we have incorporated the traditional red emitter cyanine dyes into the AIE unit. The resultant AIE active hemicyanine dyes are successfully generated. These dyes display strong red emission with large Stokes shift. They are pH sensitive, switching their emission color from red to blue with the increase of pH. Because of this intriguing property, they are also utilized for intracellular pH mapping. Live/dead cell discrimination is achieved by using the silole based hemicyanine dyes. The lifetime signal of these dyes indicates the viscosity of the environment. We thus take the first step in sensing viscosity in the intracellular microenvironment by fluorescent lifetime imaging of cells stained with AIE dyes. Moreover, these dyes can also be used as chemical sensors, showing selectivity towards homocysteine over cysteine, glutathione and other amino acids in in vitro test.

Last but not least, the AIE labeled biopolymer are highly emissive once aggregated. We prepare a biocompatible, highly fluorescent chitosan by labeling the polymer with a large number of AIE dyes. The resultant bioconjugates can be used for long-term cell tracking by tracing the cells for up to 15 passages, which is unachievable by other commercial dyes.