In this work, the aggregation-induced emission ligand
1,1,2,2-tetra(4-carboxylbiphenyl)ethylene
(H4TCBPE) was rigidified in the Ti–O network to
form novel electrochemiluminescence (ECL) emitter H4TCBPE-TiO2 nanospheres, which acted as an effective ECL emitter to construct
an “on–off” ECL biosensor for ultrasensitive
detection of malathion (Mal). H4TCBPE-TiO2 exhibited
excellent ECL responses due to the Ti–O network that can restrict
the intramolecular free motions within H4TCBPE and then
reduce the nonradiative relaxation. Moreover, TiO2 can
act as an ECL co-reaction accelerator to promote the generation of
sulfate radical anion (SO4
•–),
which interacts with H4TCBPE 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 H4TCBPE-TiO2-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 H4TCBPE-TiO2 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.