Tetraphenylethene-Based Covalent Organic Polymers with Aggregation-Induced Electrochemiluminescence for Highly Sensitive Bacterial Biosensors

Tetraphenylethene (TPE), which usually serves as aggregation-induced emission and aggregation-induced electrochemiluminescence fluorophores, has been widely applied in fabricating fluorescent nanomaterials and biosensors. However, it is still a tremendous challenge to prepare well-controlled TPE aggregates with strong fluorescence (FL) and electrochemiluminescence (ECL). In this study, we constructed a bacterial ECL biosensing platform with high sensitivity based on TPE-based covalent organic polymer (COP) nanoparticles synthesized by a simple Menschutkin reaction strategy to employ bromide group-carrying molecules and 1,1,2,2-tetrakis(4-(pyridine-4-yl)phenyl)ethene as the cross-linking agent and the emissive moiety, respectively. The ECL Escherichia coli biosensor had high sensitivity, a low limit of detection (0.19 CFU mL^–1), a wide linear range (1 × 10²–5 × 10⁶ CFU mL^–1), and good selectivity. The excellent properties of the bacterial biosensor could be attributed to the uniform spherical COP nanoparticles with enhanced FL and ECL signals, the maximal ECL efficiency of which was 8.4-fold higher than that of the typical tris(bipyridine) ruthenium(II) emitter. The FL and ECL intensities of the TPE-based COP nanoparticles could be adjusted by varying bromide group-carrying molecules and thus regulating their energy gap between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) orbitals. The TPE-based COP nanoparticles with strong FL and ECL intensities pave a promising avenue to construct highly sensitive bacterial ECL biosensors for the large-scale screening of disease-causing bacteria.