## 3 Application of AIEgens in the Detection of Pesticide Residues in Fluorescence Sensors
### Detection of Pesticides by Porous Organic Polymer Sensors Based on AIEgens  
Integrating AIEgens with porous organic polymers boosts sensitivity, selectivity, multifunctionality, stability, and reusability in pesticide detection. This approach utilizes the combined effects of AIE and various mechanisms to achieve effective sensing and detection. For example, in 2020, [PERSON] et al. synthesized three fluorescent porous organic polymers containing N-benzylcarbazole groups PAN-C (A17-1), PAN-C-Br (A17-2), and PAN-C-OCH\({}_{3}\) (A17-3) through a one-step polymerization reaction for the identification and detection of six pesticides in water (Figure 17a,b) [83]. The carbazole moiety in these polymers is electron-rich due to the conjugation between the benzene ring and the nitrogen atom, while the pesticides are electron-deficient due to the presence of electron-withdrawing groups such as phosphorothiates, nitro groups, and electronegative fluorine and chlorine atoms. This results in a higher LUMO energy for the polymers compared to the pesticides, allowing for excited-state electron transfer from the LUMO orbitals of the polymer to the pesticide molecules, which leads to fluorescence quenching. Additionally, A17-1-coated sensing test strips were used for pesticide detection, demonstrating a rapid color change within 1-2 s upon contact with the pesticide solution, indicating a fast fluorescent response (Figure 17c). The paper could be easily regenerated by rinsing with ethanol, with the bright cyan color and fluorescence intensity remaining stable after 12 cycles, showcasing excellent reusability (Figure 17d). Inspired by the above-mentioned work, in 2022, [PERSON] et al. synthesized two micro/mesoporous fluorescent polymers, JY1 (denoted as A18-1) and JY2 (denoted as A18-2), which feature AIE-active chromophores for visual detection of pesticides (Figure 18a) [84]. These probes are capable of detecting four pesticides: imidacloprid (IDP), trifumizole (TFZ), lambda-cyhalothrin (LCT), and cyfluthrin (CFT). The detection mechanism relies on a donor-excited PET process. Under UV light, electrons in the ground state of the chromophore are excited to the LUMO orbitals. In this excited state, the electrons can transfer to the LUMO orbitals of the pesticide molecules, leading to fluorescence quenching (Figure 18b). By introducing AIEgens into porous fluorescent polymers, the high sensitivity and anti-interference ability for pesticide detection could be achieved. Moreover, A18-1 has been developed into a portable fluorescent detection plate, enabling convenient and reusable on-site monitoring and early warning of pesticide residues (Figure 18c). This advancement offers significant potential for practical applications in pesticide detection. In the same year, [PERSON] et al. also synthesized two AIE-active fluorescent porous polymers, PAN-TPE-1 (A19-1) and PAN-TPE-2 (A19-2) (Figure 19a,b), and investigated their chemical sensing properties for five pesticides: IDP, acetamiprid (AMP), TFZ, indoxacarb (IXC), and LCT [85]. They evaluated the fluorescence spectra of A19-1 and A19-2 in aqueous solutions with varying pesticide concentrations and quantitatively assessed their sensitivity using the fluorescence quenching Stern-Volmer coefficient (K\({}_{\text{SV}}\)) and LOD. They also conducted interference experiments to test the ability of the polymers to detect pesticides in complex environments. A19-1 exhibited impressive K\({}_{\text{SV}}\) and LOD values of 53,745 M\({}^{-1}\) and 28 ppb for IDP, respectively, which are significantly higher than those reported for other porous materials and exceed those for the other four pesticides by factors of 3 to 10 [93]. Additionally, A19-1 and A19-2 were prepared into a fluorescence detection plate for visualization and practical detection experiments, as shown in Figure 19c. This study highlights the strong pesticide recognition ability of these probes and demonstrates the promising potential of AIE-activated porous polymers for pesticide detection.