Tetraphenylethene-Based Covalent Organic Polymers\nwith Aggregation-Induced Electrochemiluminescence for Highly Sensitive\nBacterial Biosensors

Tetraphenylethene\n(TPE), which usually serves as aggregation-induced\nemission and aggregation-induced electrochemiluminescence fluorophores,\nhas been widely applied in fabricating fluorescent nanomaterials and\nbiosensors. However, it is still a tremendous challenge to prepare\nwell-controlled TPE aggregates with strong fluorescence (FL) and electrochemiluminescence\n(ECL). In this study, we constructed a bacterial ECL biosensing platform\nwith high sensitivity based on TPE-based covalent organic polymer\n(COP) nanoparticles synthesized by a simple Menschutkin reaction strategy\nto employ bromide group-carrying molecules and 1,1,2,2-tetrakis(4-(pyridine-4-yl)phenyl)ethene\nas the cross-linking agent and the emissive moiety, respectively.\nThe ECL Escherichia coli biosensor\nhad high sensitivity, a low limit of detection (0.19 CFU mL<sup>–1</sup>), a wide linear range (1 × 10<sup>2</sup>–5 × 10<sup>6</sup> CFU mL<sup>–1</sup>), and good selectivity. The excellent\nproperties of the bacterial biosensor could be attributed to the uniform\nspherical COP nanoparticles with enhanced FL and ECL signals, the\nmaximal ECL efficiency of which was 8.4-fold higher than that of the\ntypical tris(bipyridine) ruthenium(II) emitter. The FL and ECL intensities\nof the TPE-based COP nanoparticles could be adjusted by varying bromide\ngroup-carrying molecules and thus regulating their energy gap between\nhighest occupied molecular orbital (HOMO) and lowest unoccupied molecular\norbital (LUMO) orbitals. The TPE-based COP nanoparticles with strong\nFL and ECL intensities pave a promising avenue to construct highly\nsensitive bacterial ECL biosensors for the large-scale screening of\ndisease-causing bacteria.