Bifunctional TiO 2 Nanoflower-Induced H 4 TCBPE Aggregation Enhanced Electrochemiluminescence for an Ultrasensitive Assay of Organophosphorus.

In this work, the aggregation-induced emission ligand 1,1,2,2-tetra(4-carboxylbiphenyl)ethylene (H 4 TCBPE) was rigidified in the Ti-O network to form novel electrochemiluminescence (ECL) emitter H 4 TCBPE-TiO 2 nanospheres, which acted as an effective ECL emitter to construct an "on-off" ECL biosensor for ultrasensitive detection of malathion (Mal). H 4 TCBPE-TiO 2 exhibited excellent ECL responses due to the Ti-O network that can restrict the intramolecular free motions within H 4 TCBPE and then reduce the nonradiative relaxation. Moreover, TiO 2 can act as an ECL co-reaction accelerator to promote the generation of sulfate radical anion (SO 4 •- ), which interacts with H 4 TCBPE in the Ti-O network to produce enhanced ECL response. In the presence of Mal, numerous ligated probes (probe 1 to probe 2, P1-P2) were formed and released by copper-free click nucleic acid ligation reaction, which then hybridized with hairpin probe 1 (H1)-modified H 4 TCBPE-TiO 2 -based electrode surface. The P1-P2 probes can initiate the target-assisted terminal deoxynucleoside transferase (TdTase) extended reaction to produce long tails of deoxyadenine with abundant biotin, which can load numerous streptavidin-functionalized ferrocenedicarboxylic acid polymer (SA-PFc), causing quenching of the ECL signal. Thus, the ultrasensitive ECL biosensor based on H 4 TCBPE-TiO 2 ECL emitter and click chemistry-actuated TdTase amplification strategy presents a desirable range from 0.001 to 100 ng/mL and a detection limit low to 9.9 fg/mL. Overall, this work has paved an avenue for the development of novel ECL emitters, which has opened up new prospects for ECL biosensing.