Chitosan‑stabilized protein capsules for sustained and reliable chemiluminescent detection of hydrogen peroxide

Chemiluminescence (CL) quantification of hydrogen peroxide (H₂O₂) by conventional flash‑type systems is hindered by the short emission window, which compromises the accuracy and reproducibility. Here we report a chitosan‑stabilized CL capsule (LHB@CS) platform for sustained and reliable detection of H₂O₂. The capsules are prepared via a one‑pot ultrasonication‑assisted method, in which luminol and hemin are co‑encapsulated within the oil phase and chitosan (CS) is adsorbed as a colloidal stabilizer. Upon addition of H₂O₂, H₂O₂ diffuses into the oil phase and triggers the hemin-catalyzed CL reaction, producing a sustained emission for about 200 s with approximately 85% of the peak intensity retained at 30 s. This intense and sustained CL behavior arises from confined luminol oxidation and restricted H₂O₂ diffusion within the capsule structure. The CS coating prevents macroscopic phase separation of the capsules over 48 h and LHB@CS capsules show easy redispersion for sampling even after 15-day storage with over 90% retained CL signal. The capsule‑based sensing platform achieves sensitive H₂O₂ quantification with a detection limit of 0.04 μM, and shows satisfactory recoveries (99.86-104.38%) in spiked human serum and drinking water. This work demonstrates that chitosan coating on protein capsules improves colloidal stability without compromising the CL performance, providing a simple and practical strategy for capsule-based H₂O₂ sensing applications.