BSA–tetraphenylethene derivative conjugates with aggregation-induced emission properties: Fluorescent probes for label-free and homogeneous detection of protease and α1-antitrypsin

Herein, BSA-tetraphenylethene derivative conjugates with aggregation-induced emission (AIE) properties were constructed and used as fluorescent probes for label-free detection of protease and α1-antitrypsin. Conjugated AIE probes were formed based on the electrostatic induced assembly between an ammonium cation of quaternized tetraphenylethene salt and carboxyl anion groups of BSA. While water soluble quaternized tetraphenylethene salt showed very low fluorescence in its well-dispersed state, obvious enhancement in the fluorescence of the aggregated tetraphenylethene derivative on the BSA templates was achieved due to the abnormal aggregation-induced emission properties of tetraphenylethene. These BSA-tetraphenylethene derivative conjugates enabled label-free detection of protease. In the presence of trypsin, the BSA templates were enzymatically hydrolyzed and the conjugates decomposed. Therefore the quaternized tetraphenylethene molecules became increasingly isolated from each other. Accordingly, the aggregation to dispersing state change of tetraphenylethene derivative resulted in an obvious decrease in the fluorescence of the conjugates probes and enabled the sensitive and selective detection of trypsin. Furthermore, upon addition of α1-antitrypsin, the enzymatic activity of trypsin was inhibited and the fluorescence was consequently preserved. Sensitive detection of α1-antitrypsin was thus realised. The protein-tetraphenylethene derivative conjugates with aggregation-induced emission properties therefore show great promise for the monitoring of biological processes and cancer diagnostics with simplicity, high sensitivity, and rapid response.