Fluorescent nanomaterials have great promise in bioanalysis and biotechnological applications because of their unique optical properties, high surface-to-volume ratio, and surface-modifiable quality. The development of fluorescent biosensors with high sensitivity, selectivity, and biocompatibility is of critical importance because it offers a direct visualization tool for the detection of biological macromolecules and the monitoring of biological events in living systems. Most of the conventional organic fluorophores, however, suffer from the self-quenching problem at high concentration or in the aggregated state. Such aggregation-cause quenching (ACQ) effect has greatly limited the scope of their bio-applications.

Recently, our group discovered such a system, in which luminoge...[ Read more ]

Fluorescent nanomaterials have great promise in bioanalysis and biotechnological applications because of their unique optical properties, high surface-to-volume ratio, and surface-modifiable quality. The development of fluorescent biosensors with high sensitivity, selectivity, and biocompatibility is of critical importance because it offers a direct visualization tool for the detection of biological macromolecules and the monitoring of biological events in living systems. Most of the conventional organic fluorophores, however, suffer from the self-quenching problem at high concentration or in the aggregated state. Such aggregation-cause quenching (ACQ) effect has greatly limited the scope of their bio-applications.

Recently, our group discovered such a system, in which luminogen aggregation plays a constructive, instead of destructive, role in the light-emitting process. We have termed this abnormal phenomenon as “aggregation-induced emission” (AIE) and identified the restriction of intramolecular rotation as the main cause of the AIE effect. Attracted by the intriguing phenomenon and its fascinating perspectives, we have launched a new program directed towards the development of new AIE materials and exploration of their biological applications.

In this work, a series of water-soluble AIE luminogens are designed and synthesized. Hydrophilic groups such as amino and sulfonate groups are incorporated into the AIE structures to impart them with good water solubility. Being practically non-emissive in water, these AIE luminogens are induced to emit intensely when bound to biomacromolecules, such as heparin, protamine and albumins, through hydrophobic and electrostatic interactions. Such light-up property enables the quantitation and visualization of biomacromolecules in aqueous solution and in electrophoretic gels.

Incorporation of cleavable hydrophilic bioconjugates into AIE luminogens can enhance the specificity of the bioprobes. The bioprobes are nonluminscent in aqueous media due to their good water solubility. The specific cleavage of hydrophilic groups by enzymes or reactive species in cells induces the aggregation of the hydrophobic AIE residues and thus enhances the fluorescence output. In this work, two bioprobes have been developed by using this strategy for monitoring caspases activity and detection of thiol concentration.

A lipophilic AIE luminogen is designed and utilized as fluorescent visualizer for fast intracellular imaging. The fluorophore is practically nonemissive in solution but induced to emit strongly in the aggregated state or when internalized into cells.