Zinc Doping-Induced Lattice Growth Regulation for Enhanced Upconversion Emission in Serum Bilirubin Detection

Upconversion nanoparticles (UCNPs) hold significant potential in the detection of disease biomarkers in serum due to their ability to avoid fluorescence background interference. The design of upconversion probes with a high emission intensity is particularly critical for enhancing the accuracy and sensitivity of visual detection. Herein, we achieved highly efficient luminescent upconversion nanocrystals by enhancing the internal energy transfer efficiency of the nanoparticles through zinc-ion doping, which induced a lattice growth transformation. The nanocrystals can greatly enhance the fluorescence emission intensity while keeping the fluorescence color unchanged. Additionally, a 980 nm near-infrared excited upconversion visual sensing platform was constructed for serum bilirubin detection. By a combination of UCNPs with sulfosalicylic acid (SSA) and iron ions to form an efficient upconversion nanoprobe, fluorescence and colorimetric gradient changes can be observed in the presence of bilirubin. This enables highly sensitive colorimetric and fluorescence detection of bilirubin, with a detection limit as low as 21.4 nM in fluorescence mode. Clinical serum sample tests indicate that the sensor possesses excellent selectivity and anti-interference capability, accurately detecting bilirubin in complex biological matrices. This study exhibits strong upconversion luminescence (UCL) emission and demonstrates the potential for early diagnosis of diseases through high-sensitivity biomarker detection.