Polyethylenimine-Mediated Assembly of Dual-Emissive CsPbBr₃@SiO₂@EuW₁₀ Composite Nanospheres for Ratiometric Detection of 2,6-Dipicolinic Acid

<i>Bacillus anthracis</i>, a highly pathogenic bacterium that causes anthrax, poses a bioterrorism threat to both wildlife and human health. Consequently, as a key biomarker for anthrax spores, quantitative and visual detection of 2,6-dipicolinic acid (DPA) is critical for biodefense and public health security. Herein, a dual-emissive CsPbBr₃@SiO₂@EuW₁₀ (CPB@SiO₂@EuW₁₀) composite nanospheres were successfully prepared through the confinement effect of SiO₂ on CsPbBr₃ perovskite quantum dots (PQDs), followed by a polyethylenimine (PEI)-mediated ionic self-assembly (ISA) of EuW₁₀ on the exterior surface of CsPbBr₃@SiO₂. The resultant CPB@SiO₂@EuW₁₀ composite nanospheres exhibit a selective response to DPA with exceptional luminescent stability and good sensitivity. The green-emitting CsPbBr₃ PQDs centered in the composite nanospheres can be quenched by DPA via the inner filter effect (IFE), while the antenna effect of DPA enhances the red fluorescence of Eu³⁺. The contrasting fluorescence response behaviors of CsPbBr₃ and Eu³⁺ centers endow the CPB@SiO₂@EuW₁₀ composite nanospheres with a self-calibrated sensing mechanism for reliable DPA detection. The low detection limit (LOD) is 0.052 μM within a linear range of 10-120 μM. The ratiometric sensing of DPA based on the CPB@SiO₂@EuW₁₀ fluorescent probe also shows a color shift from green to yellow, enabling visual detection and efficient identification of DPA in aqueous solutions.